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Showing 1 - 36 of 36 Journals sorted alphabetically
Acta Meteorologica Sinica     Hybrid Journal   (Followers: 3)
Advances in Atmospheric Sciences     Hybrid Journal   (Followers: 26)
Advances in Climate Change Research     Open Access   (Followers: 1)
Advances in Meteorology     Open Access   (Followers: 13)
Aeolian Research     Hybrid Journal   (Followers: 5)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 10)
American Journal of Climate Change     Open Access   (Followers: 9)
Atmósfera     Open Access   (Followers: 1)
Atmosphere     Open Access   (Followers: 15)
Atmosphere-Ocean     Full-text available via subscription   (Followers: 11)
Atmospheric Chemistry and Physics (ACP)     Open Access   (Followers: 17)
Atmospheric Chemistry and Physics Discussions (ACPD)     Open Access   (Followers: 6)
Atmospheric Research     Hybrid Journal   (Followers: 33)
Atmospheric Science Letters     Open Access   (Followers: 21)
Boundary-Layer Meteorology     Hybrid Journal   (Followers: 15)
Bulletin of the American Meteorological Society     Open Access   (Followers: 26)
Carbon Balance and Management     Open Access   (Followers: 5)
Change and Adaptation in Socio-Ecological Systems     Open Access   (Followers: 1)
Climate     Open Access   (Followers: 2)
Climate Change Economics     Hybrid Journal   (Followers: 10)
Climate Change Responses     Open Access  
Climate Dynamics     Hybrid Journal   (Followers: 20)
Climate law     Hybrid Journal   (Followers: 4)
Climate of the Past (CP)     Open Access   (Followers: 4)
Climate of the Past Discussions (CPD)     Open Access   (Followers: 1)
Climate Policy     Hybrid Journal   (Followers: 28)
Climate Research     Hybrid Journal   (Followers: 4)
Climate Risk Management     Open Access  
Climate Services     Open Access  
Climate Summary of South Africa     Full-text available via subscription  
Climatic Change     Hybrid Journal   (Followers: 43)
Current Climate Change Reports     Hybrid Journal  
Developments in Atmospheric Science     Full-text available via subscription   (Followers: 9)
Dynamics and Statistics of the Climate System     Open Access  
Dynamics of Atmospheres and Oceans     Hybrid Journal   (Followers: 9)
Earth Perspectives - Transdisciplinarity Enabled     Open Access  
Energy & Environment     Full-text available via subscription   (Followers: 15)
Environmental and Climate Technologies     Open Access   (Followers: 3)
Global Meteorology     Open Access   (Followers: 3)
International Journal of Atmospheric Sciences     Open Access   (Followers: 8)
International Journal of Biometeorology     Hybrid Journal   (Followers: 1)
International Journal of Climate Change Strategies and Management     Hybrid Journal   (Followers: 9)
International Journal of Climatology     Hybrid Journal   (Followers: 20)
International Journal of Image and Data Fusion     Hybrid Journal   (Followers: 1)
Journal of Applied Meteorology and Climatology     Full-text available via subscription   (Followers: 17)
Journal of Atmospheric and Oceanic Technology     Full-text available via subscription   (Followers: 19)
Journal of Atmospheric and Solar-Terrestrial Physics     Hybrid Journal   (Followers: 33)
Journal of Atmospheric Chemistry     Hybrid Journal   (Followers: 6)
Journal of Climate     Full-text available via subscription   (Followers: 31)
Journal of Climatology     Open Access   (Followers: 1)
Journal of Hydrology and Meteorology     Open Access   (Followers: 6)
Journal of Hydrometeorology     Full-text available via subscription   (Followers: 4)
Journal of Integrative Environmental Sciences     Hybrid Journal   (Followers: 4)
Journal of Meteorology and Climate Science     Full-text available via subscription   (Followers: 5)
Journal of Space Weather and Space Climate     Open Access   (Followers: 8)
Journal of the Atmospheric Sciences     Full-text available via subscription   (Followers: 43)
Journal of Weather Modification     Full-text available via subscription   (Followers: 1)
Large Marine Ecosystems     Full-text available via subscription  
Mathematics of Climate and Weather Forecasting     Open Access   (Followers: 2)
Mediterranean Marine Science     Open Access  
Meteorologica     Open Access  
Meteorological Applications     Hybrid Journal   (Followers: 3)
Meteorologische Zeitschrift     Full-text available via subscription   (Followers: 2)
Meteorology and Atmospheric Physics     Hybrid Journal   (Followers: 13)
Mètode Science Studies Journal : Annual Review     Open Access  
Monthly Notices of the Royal Astronomical Society     Hybrid Journal   (Followers: 4)
Monthly Notices of the Royal Astronomical Society Letters     Hybrid Journal   (Followers: 4)
Monthly Weather Review     Full-text available via subscription   (Followers: 21)
Nature Climate Change     Full-text available via subscription   (Followers: 48)
Nature Reports Climate Change     Full-text available via subscription   (Followers: 22)
Open Journal of Modern Hydrology     Open Access   (Followers: 3)
Revista Brasileira de Meteorologia     Open Access   (Followers: 1)
Revista Iberoamericana de Bioeconomía y Cambio Climático     Open Access  
Russian Meteorology and Hydrology     Hybrid Journal   (Followers: 2)
Space Weather     Full-text available via subscription   (Followers: 7)
Studia Geophysica et Geodaetica     Hybrid Journal   (Followers: 1)
Tellus A     Open Access   (Followers: 9)
Tellus B     Open Access   (Followers: 8)
The Cryosphere (TC)     Open Access   (Followers: 3)
The Cryosphere Discussions (TCD)     Open Access   (Followers: 2)
The Quarterly Journal of the Royal Meteorological Society     Hybrid Journal   (Followers: 18)
Theoretical and Applied Climatology     Hybrid Journal   (Followers: 4)
Weather     Hybrid Journal   (Followers: 10)
Weather and Climate Extremes     Open Access   (Followers: 5)
Weather and Forecasting     Full-text available via subscription   (Followers: 9)
Weatherwise     Hybrid Journal   (Followers: 1)
气候与环境研究     Full-text available via subscription   (Followers: 1)
Journal Cover Journal of Atmospheric and Solar-Terrestrial Physics
  [SJR: 1.045]   [H-I: 61]   [33 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1364-6826
   Published by Elsevier Homepage  [2970 journals]
  • Comparison of Artificial Intelligence Methods and Empirical Equations to
           Estimate Daily Solar Radiation
    • Abstract: Publication date: Available online 15 June 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Saeid Mehdizadeh, Javad Behmanesh, Keivan Khalili
      In the present research, three artificial intelligence methods including Gene Expression Programming (GEP), Artificial Neural Networks (ANN) and Adaptive Neuro-Fuzzy Inference System (ANFIS) as well as, 48 empirical equations (10, 12 and 26 equations were temperature-based, sunshine-based and meteorological parameters-based, respectively) were used to estimate daily solar radiation in Kerman, Iran in the period of 1992 to 2009. To develop the GEP, ANN and ANFIS models, depending on the used empirical equations, various combinations of minimum air temperature, maximum air temperature, mean air temperature, extraterrestrial radiation, actual sunshine duration, maximum possible sunshine duration, sunshine duration ratio, relative humidity and precipitation were considered as inputs in the mentioned intelligence methods. To compare the accuracy of empirical equations and intelligence models, root mean square error (RMSE), mean absolute error (MAE), mean absolute relative error (MARE) and determination coefficient (R2) indices were used. The results showed that in general, sunshine-based and meteorological parameters-based scenarios in ANN and ANFIS models presented high accuracy than mentioned empirical equations. Moreover, the most accurate method in the studied region was ANN11 scenario with five inputs. The values of RMSE, MAE, MARE and R2 indices for the mentioned model were 1.850MJ m-2 day-1, 1.184MJ m-2 day-1, 9.58 % and 0.935, respectively.

      PubDate: 2016-06-18T18:18:09Z
  • Comparison of the dynamical response of low latitude middle atmosphere to
           the major stratospheric warming events in the northern and southern
    • Abstract: Publication date: Available online 16 June 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): G.J. Bhagavathiammal, S. Sathishkumar, S. Sridharan, S. Gurubaran
      This study presents comparison of low-latitude dynamical responses to boreal 2008/09 and austral 2002 winter Major Stratospheric Warming (MSW) events, as both events are of vortex split type. During these winters, planetary wave (PW) variability and changes in low-latitude circulation are examined using European Center for Medium Range Weather Forecasting (ECMWF) reanalysis (ERA)-interim data sets and mesospheric wind data acquired by the MF radars at Tirunelveli (8.7°N) and Rarotonga (22°S). Eliassen-Palm diagnostic is used to provide an evidence for the lateral PW energy propagation from high to low-latitudes during both the MSW events. The PW flux reaches much lower latitudes during the boreal event than during the austral event. The low-latitude westward winds at stratospheric heights are stronger (weaker) during the boreal (austral) MSW. Weak (strong) PW wave activity at low latitude mesospheric heights during boreal (austral) MSW indicates the influence of low-latitude stratospheric westward winds on the vertical propagation of PW to low-latitude mesosphere.

      PubDate: 2016-06-18T18:18:09Z
  • Comparison of IRI-2012 with JASON-1 TEC and incoherent scatter radar
           observations during the 2008–2009 solar minimum period
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146
      Author(s): Eun-Young Ji, Geonhwa Jee, Changsup Lee
      The 2008–2009 solar minimum period was unprecedentedly deep and extended. We compare the IRI-2012 with global TEC data from JASON-1 satellite and with electron density profiles observed from incoherent scatter radars (ISRs) at middle and high latitudes for this solar minimum period. Global daily mean TECs are calculated from JASON-1 TECs to compare with the corresponding IRI TECs during the 2008–2009 period. It is found that IRI underestimates the global daily mean TEC by about 20–50%. The comparison of global TEC maps further reveals that IRI overall underestimates TEC for the whole globe except for the low-latitude region around the equatorial anomaly, regardless of season. The underestimation is particularly strong in the nighttime winter hemisphere where the ionosphere seems to almost disappear in IRI. In the daytime equatorial region, however, the overestimation of IRI is mainly due to the misrepresentation of the equatorial anomaly in IRI. Further comparison with ISR electron density profiles confirms the significant underestimation of IRI at night in the winter hemisphere.

      PubDate: 2016-06-14T15:29:10Z
  • Statistical analysis of electric field parameters for negative lightning
           in Malaysia
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146
      Author(s): Chin-Leong Wooi, Zulkurnain Abdul-Malek, Noor-Azlinda Ahmad, Ali I. El Gayar
      This paper presents a comparative study on the electric field and its derivative parameters of negative lightning in Malaysia and other regions. This study is the first in Malaysia where the parameters of negative electric field and its derivative are thoroughly analyzed. 104 negative lightning flashes containing 277 negative return strokes occurring within 10–100km from the measuring station and recorded during monsoon period in the state of Johor, Malaysia had been analyzed. It was found that 73% of the recorded flashes are multiple strokes with an average multiplicity of 2.6 strokes per flash. For first return strokes, the arithmetic mean (AM) of initial peak electric field and the AM of initial peak electric field derivative are 21.8V/m and 11.3V/m/µs, respectively. The initial peaks of electric field and its derivative for first return strokes are larger than those for the subsequent return strokes. Comparison of overall results with those obtained earlier in Sri Lanka, Germany, Sweden, Japan, Florida indicates that several electric field and its derivative parameters are affected by propagation media and geographical region. Similarity of results with other countries having the same climatic condition is also observed.

      PubDate: 2016-06-14T15:29:10Z
  • Thermodynamic and dynamic structure of atmosphere over the east coast of
           Peninsular Malaysia during the passage of a cold surge
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146
      Author(s): Azizan Abu Samah, C.A. Babu, Hamza Varikoden, P.R. Jayakrishnan, Ooi See Hai
      An intense field observation was carried out for a better understanding of cold surge features over Peninsular Malaysia during the winter monsoon season. The study utilizes vertical profiles of temperature, humidity and wind at high vertical and temporal resolution over Kota Bharu, situated in the east coast of Peninsular Malaysia. LCL were elevated during the passage of the cold surge as the relative humidity values decreased during the passage of cold surge. Level of Free Convection were below 800hPa and equilibrium levels were close to the LFC in most of the cases. Convective available potential energy and convection inhibition energy values were small during most of the observations. Absence of local heating and instability mechanism are responsible for the peculiar thermodynamic structure during the passage of the cold surge. The wind in the lower atmosphere became northeasterly and was strong during the entire cold surge period. A slight increase in temperature near the surface and a drop in temperature just above the surface were marked by the passage of the cold surge. A remarkable increase in specific humidity was observed between 970 and 900hPa during the cold surge period. Further, synoptic scale features were analyzed to identify the mechanism responsible for heavy rainfall. Low level convergence, upper level divergence and cyclonic vorticity prevailed over the region during the heavy rainfall event. Dynamic structure of the atmosphere as part of the organized convection associated with the winter monsoon was responsible for the vertical lifting and subsequent rainfall.

      PubDate: 2016-06-14T15:29:10Z
  • Ionospheric response under the influence of the solar eclipse occurred on
           20 March 2015: Importance of autoscaled data and their assimilation for
           obtaining a reliable modeling of the ionosphere
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146
      Author(s): M. Pietrella, M. Pezzopane, A. Settimi
      This paper wants to highlight how the availability of measurements autoscaled at some reference ionospheric stations, and their assimilation by ionospheric models, was of crucial importance in determining, during the solar eclipse conditions occurred on 20 March 2015, a reliable representation of the ionosphere. Even though the solar eclipse falls in the recovery phase of the St. Patrick geomagnetic storm started on 17 March 2015, its influence on the ionospheric plasma seems undeniable. The reference ionospheric stations considered here are those of Rome (41°.8’ N, 12°.5’ E), and Gibilmanna (37°.9’ N, 14°.0’ E), Italy. Specifically, in a time interval including that of the eclipse, the electron density profiles autoscaled by the Automatic Real-Time Ionogram Scaler with True-height (ARTIST) system at San Vito (40°.6′ N, 17°.8′ E), Italy, which are here considered as the truth profiles, were compared with both the electron density profiles calculated by the IRI-SIRMUP-Profiles (ISP) model, after assimilating data recorded at Rome and Gibilmanna, and the electron density profiles provided by the IRI-CCIR model. The ISP and IRI-CCIR performances were then evaluated in terms of the root mean square errors made on the whole electron density profiles. The three-dimensional (3-D) electron density mappings of the ionosphere provided by ISP and IRI-CCIR models were also considered as the ionospheric environment by the ray tracing software tool IONORT to calculate quasi-vertical synthesized ionograms over the short radio link San Vito – Brindisi (40°.4′ N, 17°.6′ E), Italy. The corresponding synthesized values of foF2 and fxF2, obtained by IONORT-ISP and IONORT-(IRI-CCIR) procedures, were compared with those autoscaled by ARTIST from the vertical ionograms recorded at the truth site of San Vito. Some examples of IONORT-ISP and IONORT-(IRI-CCIR) synthesized ionograms are shown and discussed. Finally, comparisons in terms of foF2 deduced by long-term prediction and nowcasting maps are also shown. The results achieved in this work demonstrate how the assimilation of autoscaled data into the ionospheric models turned out to be valuable in providing a better representation of the ionospheric electron density under very unusual conditions.

      PubDate: 2016-06-14T15:29:10Z
  • Regional trends of aerosol optical depth and their impact on cloud
           properties over Southern India using MODIS data
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146
      Author(s): K. Rama Gopal, K. Raja Obul Reddy, G. Balakrishnaiah, S.MD. Arafath, N. Siva Kumar Reddy, T. Chakradhar Rao, T. Lokeswara Reddy, R. Ramakrishna Reddy
      Remote sensing of global aerosols has constituted a great scientific interest in a variety of applications related to global warming and climatic change. In the present study we investigate the spatial and temporal variations of aerosol optical properties and its impact on various properties of clouds over Southern India for the last ten years (2005–2014) by using Moderate Resolution Imaging Spectroradiometer (MODIS) data retrieved from the onboard Terra and Aqua satellites. The spatial distributions of annual mean lowest Aerosol Optical Depth (AOD) value is observed in Bangalore (BLR) (0.22±0.04) and the highest AOD value is noted in Visakhapatnam (VSK) (0.39±0.05). Similarly high Fine Mode Fraction (FMF) is noticed over VSK and Thiruvananthapuram (TVM), while lower values are observed in Anantapur (ATP), Hyderabad (HYD), Pune (PUNE) and BLR. From the results, a negative correlation was found between AOD and Cloud Top Temperature (CTT), Cloud Top Pressure (CTP) where as, a positive correlation was observed between AOD and Cloud Fraction (CF), Water Vapor (WV) over the selected regions. Monthly average AOD and FMF are plotted for analysis of the trends of aerosol loading in a long-term scale and both values showed statistically significant enhancing trend over all regions as derived from the MODIS measurements. Further, the annual variation of spatial correlation between MODIS and MISR (Multi - Angle Imaging Spectro Radiometer) AOD has been analyzed and the correlation coefficients are found to be higher in two of the regions VSK and PUNE (>0.8), and considerably lower for TVM (<0.7).

      PubDate: 2016-06-14T15:29:10Z
  • Empirical model of the main ionospheric trough for the nighttime winter
    • Abstract: Publication date: Available online 20 May 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): A.T. Karpachev, M.V. Klimenko, V.V. Klimenko, L.V. Pustovalova
      For the first time we developed an empirical model of the main ionospheric trough, MIT, for quiet (Kp=2) nighttime (18:00–06:00 LT) winter conditions in the Northern and Southern hemispheres for all levels of solar activity. The model consists of two parts: 1) the MIT position model in terms of geographical latitude and longitude; 2) the MIT shape model in terms of the latitudinal-longitudinal foF2 variations in the range of 45–75°N latitudes in the Northern hemisphere and of 40–80°S in the Southern hemisphere. Thus, an empirical model of the quiet nighttime subauroral ionosphere has been developed. To construct this model the Interkosmos-19 and CHAMP satellites data have been used. The in-situ N e measurements at the CHAMP heights were transformed to the electron density at F2 layer peak height (i.e. to N m F2 and then to foF2). In the frame of the model the diurnal and longitudinal variations in the MIT minimum position were revealed and studied in detail. Also the longitudinal and latitudinal variations in foF2 in the MIT region were investigated. Accuracy of the model was tested according to the ground-based ionospheric stations data. It is shown that the constructed model much more adequately reproduces the variations in the winter nighttime subauroral ionospheric structure, including the MIT position and shape variations, than the International Reference Ionosphere model (IRI-2012). The online version of the MIT model is available on the IZMIRAN website: for free using and more detailed testing.

      PubDate: 2016-06-14T15:29:10Z
  • Improvement of global ionospheric VTEC maps using the IRI 2012 ionospheric
           empirical model
    • Abstract: Publication date: Available online 1 June 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Cheng Wang, Chuang Shi, Hongping Zhang, Lei Fan
      In this study, vertical total electron content values derived from an ionospheric empirical model (IRI 2012) are applied to global ionospheric modeling. Firstly, a comparison of VTEC maps between IRI 2012 and IGS GIMs during the year 2014 is investigated. The comparison shows that IRI 2012 is capable of representing the TEC at middle and high latitudes. Furthermore, IRI 2012 is applied to provide priori VTEC values as virtual measurements for global ionospheric modeling during the year 2014. The results show that the new approach not only eliminates the non-physical negative VTEC values but also improves the accuracy of VTEC maps. The VTEC RMS maps are improved by 3.67%, 2.95% and 22.16% in the Northern Band, Middle Band and Southern Band of the global ionosphere, respectively. This work also investigates the consistency between VTEC maps from different solutions, IGS final products and GIMs of Ionosphere Associate Analysis Centers (IAACs). The comparisons suggest that there is a slightly better consistency between the improved VTEC maps and the IGS final products. The consistencies of the VTEC maps are improved by 4.58%, 2.76% and 4.77% in the Northern Band, Middle Band and Southern Band, respectively. The annual mean values of the root mean square (RMS) of the differences between the improved VTEC maps and GIMs of IAACs are approximately 4~6 TECU. The results indicate that the new VTEC maps using the IRI 2012 model have better agreement with the IGS final GIMs.

      PubDate: 2016-06-14T15:29:10Z
  • Estimation of nighttime dip-equatorial E-region current density using
           measurements and models
    • Abstract: Publication date: Available online 7 June 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Kuldeep Pandey, R. Sekar, B.G. Anandarao, S.P. Gupta, D. Chakrabarty
      The existence of the possible ionospheric current during nighttime over low-equatorial latitudes is one of the unresolved issues in ionospheric physics and geomagnetism. A detailed investigation is carried out to estimate the same over Indian longitudes using in situ measurements from Thumba ( 8.5 ° N , 76.9 ° E ), empirical plasma drift model (Fejer et al., 2008) and equatorial electrojet model developed by Anandarao (1976). This investigation reveals that the nighttime E-region current densities vary from ∼ 0.3 to ∼ 0.7A/km2 during pre-midnight to early morning hours on geomagnetically quiet conditions. The nighttime current densities over the dip equator are estimated using three different methods (discussed in methodology section) and are found to be consistent with one another within the uncertainty limits. Altitude structures in the E-region current densities are also noticed which are shown to be associated with altitudinal structures in the electron densities. The horizontal component of the magnetic field induced by these nighttime ionospheric currents is estimated to vary between ∼ 2 and ∼ 6nT during geomagnetically quiet periods. This investigation confirms the existence of nighttime ionospheric current and opens up a possibility of estimating base line value for geomagnetic field fluctuations as observed by ground-based magnetometer.

      PubDate: 2016-06-14T15:29:10Z
  • A small mission concept to the sun-earth Lagrangian L5 point for
           innovative solar, heliospheric and space weather science
    • Abstract: Publication date: Available online 8 June 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): B. Lavraud, Y. Liu, K. Segura, J. He, G. Qin, M. Temmer, J.-C. Vial, M. Xiong, J.A. Davies, A.P. Rouillard, R. Pinto, F. Auchère, R.A. Harrison, C. Eyles, W. Gan, P. Lamy, L. Xia, J.P. Eastwood, L. Kong, J. Wang, R.F. Wimmer-Schweingruber, S. Zhang, Q. Zong, J. Soucek, J. An, L. Prech, A. Zhang, P. Rochus, V. Bothmer, M. Janvier, M. Maksimovic, C.P. Escoubet, E.K.J. Kilpua, J. Tappin, R. Vainio, S. Poedts, M.W. Dunlop, N. Savani, N. Gopalswamy, S.D. Bale, G. Li, T. Howard, C. DeForest, D. Webb, N. Lugaz, S.A. Fuselier, K. Dalmasse, J. Tallineau, D. Vranken, J.G. Fernández
      We present a concept for a small mission to the Sun-Earth Lagrangian L5 point for innovative solar, heliospheric and space weather science. The proposed INvestigation of Solar-Terrestrial Activity aNd Transients (INSTANT) mission is designed to identify how solar coronal magnetic fields drive eruptions, mass transport and particle acceleration that impact the Earth and the heliosphere. INSTANT is the first mission designed to (1) obtain measurements of coronal magnetic fields from space and (2) determine coronal mass ejection (CME) kinematics with unparalleled accuracy. Thanks to innovative instrumentation at a vantage point that provides the most suitable perspective view of the Sun-Earth system, INSTANT would uniquely track the whole chain of fundamental processes driving space weather at Earth. We present the science requirements, payload and mission profile that fulfill ambitious science objectives within small mission programmatic boundary conditions.

      PubDate: 2016-06-14T15:29:10Z
  • IFC-Ed. board
    • Abstract: Publication date: July 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 145

      PubDate: 2016-06-14T15:29:10Z
  • Evaluation of the impact of atmospheric ozone and aerosols on the
           horizontal global/diffuse UV Index at Livorno (Italy)
    • Abstract: Publication date: Available online 14 June 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Daniele Scaglione, Danilo Giulietti, Marco Morelli
      A study was conducted at Livorno (Italy) to evaluate the impact of atmospheric aerosols and ozone on the solar UV radiation and its diffuse component at ground in clear sky conditions. Solar UV radiation has been quantified in terms of UV Index (UVI), following the ISO 17166:1999/CIE S007/E-1998 international standard. UVI has been calculated by exploiting the libRadtran radiative transfer modelling software as a function of both the Aerosols Optical Depth (AOD) and the Total Ozone Column (TOC). In particular AOD and TOC values have been remotely sensed by the Ozone Monitoring Instrument (OMI) on board the NASA's EOS (Earth Observing System) satellites constellation. An experimental confirmation was also obtained by exploiting global UVI ground-based measurements from the 26/9/14 to 12/8/15 and diffuse UVI ground-based measurements from the 17/5/15 to 12/8/15. For every considered value of Solar Zenith Angle (SZA) and atmospheric condition, estimates and measurements confirm that the diffuse component contributes for more than 50% on the global UV radiation. Therefore an exposure of human skin also to diffuse solar UV radiation can be potentially harmful for health and need to be accurately monitored, e.g. by exploiting innovative applications such as a mobile app with a satellite-based UV dosimeter that has been developed. Global and diffuse UVI variations due to the atmosphere are primarily caused by the TOC variations (typically cyclic): the maximum TOC variation detected by OMI in the area under study leads to a corresponding variation in global and diffuse UVI of about 50%. Aerosols in the area concerned, mainly of maritime nature, have instead weaker effects causing a maximum variation of the global and diffuse UVI respectively of 9% and 35% with an SZA of 20° and respectively of 13% and 10% with an SZA of 60°.

      PubDate: 2016-06-14T15:29:10Z
  • Thermosphere variation at different altitudes over the northern polar cap
           during magnetic storms
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146
      Author(s): Yanshi Huang, Qian Wu, Cheryl Y. Huang, Yi-Jiun Su
      In this study, we report observations and simulation results of heated neutrals at various altitudes inside the polar cap during two magnetic storms in January 2005. The Poynting flux measurements from the Defense Meteorological Satellite Program (DMSP) satellites show enhanced energy input in the polar cap during the storm main phase, which is underestimated in the TIE-GCM simulation. Neutral temperature measurements at 250km from the ground-based Fabry-Perot Interferometer (FPI) at Resolute Bay are presented, along with the neutral density observations at 360km and 470km from Challenging Minisatellite Payload (CHAMP) and the Gravity Recovery and Climate Experiment (GRACE) satellites, respectively. These data have been analyzed to demonstrate the altitudinal dependence of neutral response to the storm energy input. By comparing the TIE-GCM simulation results and the observations, we demonstrate that Poynting fluxes as well as the thermosphere response were underestimated in the model. The simulated neutral temperature at Resolute Bay increases by approximately 260° and 280°K for the two events, respectively, much lower than the observed temperature enhancements of 750° and 900°K. Neutral density enhancements with more than 30% increase over the background density were also observed at polar latitudes, with no clear distinction between the auroral zone and polar cap. All measurements indicate enhancements at high latitudes poleward of 80° magnetic latitude (MLAT) implying that substantial heating can occur within the polar cap during storms.

      PubDate: 2016-06-14T15:29:10Z
  • Auroral boundary movement rates during substorm onsets and their
           correspondence to solar wind and the AL index
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146
      Author(s): Tushar Andriyas
      A statistical analysis of the equatorward and poleward auroral boundary movement during substorm onsets, the related solar wind activity, GOES 8 and 10 magnetic field, and the westward auroral electrojet (AL) index is undertaken, during the years 2000–2002. Auroral boundary data were obtained from the British Antarctic Survey (BAS). These boundaries were derived using auroral images from the IMAGE satellite. The timing of the onsets was derived from the Frey et al. (2004) database. Data were also classified based on the peak AL around the onset and the onset latitude, in order to analyze the differences, if any, in the rates of movement. It was found that the absolute ratio of the rate of movement of the mean poleward and equatorward boundaries was slower than the rate of mean movement around the midnight sector. The stronger the onset (in terms of the peak AL around the onset) was, the faster the rate of movement for both the boundaries. This implies that the stronger the AL signature around the onset, the weaker the magnetic field was prior to the onset and the faster it increased after the onset at GOES 8 and 10 locations. The stronger the AL signature, the thicker the latitudinal width of the aurora was, prior to the onset and higher was the increase in the width after the onset, due to large poleward and average equatorward expansion. Magnetotail field line stretching and relaxation rates as measured by GOES were also found to lie in the same order of magnitude. It is therefore concluded that the rates of latitudinal descent prior to a substorm onset and ascent after the onset, of the mean auroral boundaries, corresponds to the rate at which the tail field lines stretch and relax before and after the onset, respectively.

      PubDate: 2016-06-14T15:29:10Z
  • Polar cap arcs: Sun-aligned or cusp-aligned?
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146
      Author(s): Y. Zhang, L.J. Paxton, Qinghe Zhang, Zanyang Xing
      Polar cap arcs are often called sun-aligned arcs. Satellite observations reveal that polar cap arcs join together at the cusp and are actually cusp aligned. Strong ionospheric plasma velocity shears, thus field aligned currents, were associated with polar arcs and they were likely caused by Kelvin–Helmholtz waves around the low-latitude magnetopause under a northward IMF Bz . The magnetic field lines around the magnetopause join together in the cusp region so are the field aligned currents and particle precipitation. This explains why polar arcs are cusp aligned.

      PubDate: 2016-06-14T15:29:10Z
  • Estimation of global solar radiation using an artificial neural network
           based on an interpolation technique in southeast China
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146
      Author(s): Ling Zou, Lunche Wang, Aiwen Lin, Hongji Zhu, Yuling Peng, Zhenzhen Zhao
      Solar radiation plays important roles in energy application, vegetation growth and climate change. Empirical relations and machine-learning methods have been widely used to estimate global solar radiation (GSR) in recent years. An artificial neural network (ANN) based on spatial interpolation is developed to estimate GSR in southeast China. The improved Bristow–Campbell (IBC) model and the improved Ångström–Prescott (IA–P) model are compared with the ANN model to explore the best model in solar radiation modeling. Daily meteorological parameters, such as sunshine duration hours, mean temperature, maximum temperature, minimum temperature, relative humidity, precipitation, air pressure, water vapor pressure, and wind speed, along with station-measured GSR and a daily surface GSR dataset over China obtained from the Data Assimilation and Modeling Center for Tibetan Multi-spheres (DAM), are used to predict GSR and to validate the models in this work. The ANN model with the network of 9-17-1 provides better accuracy than the two improved empirical models in GSR estimation. The root-mean-square error (RMSE), mean bias error (MBE), and determination coefficient (R 2) are 2.65MJm−2, −0.94MJm−2, and 0.68 in the IA−P model; 2.19MJm−2, 1.11MJm−2, and 0.83 in the IBC model; 1.34MJm−2, −0.11MJm−2, and 0.91 in the ANN model, respectively. The regional monthly mean GSR in the measured dataset, DAM dataset, and ANN model is analyzed. The RMSE (RMSE %) is 1.07MJm−2 (8.91%) and the MBE (MBE %) is −0.62MJm−2 (−5.21%) between the measured and ANN-estimated GSR. The statistical errors of RMSE (RMSE %) are 0.91MJm−2 (7.28%) and those of MBE (MBE %) are −0.15MJm−2 (−1.20%) between DAM and ANN-modeled GSR. The correlation coefficients and R2 are larger than 0.95. The regional mean GSR is 12.58MJm−2. The lowest GSR is observed in the northwest area, and it increases from northwest to southeast. The annual mean GSR decreases by 0.02MJm−2 decade−1 over the entire southeast China. The GSR in 52 stations experiences a decreasing trend, and 21% of the stations are significant at the 95% level.

      PubDate: 2016-06-14T15:29:10Z
  • The strength and hemispheric asymmetry of Equatorial Ionization Anomaly
           during two geomagnetic storms in 2013 from Global Ionosphere Map and SAMI2
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146
      Author(s): Weihua Luo, Zhengping Zhu, Jiaping Lan
      The variations of the strength and the hemispheric asymmetry of EIA were studied by Global Ionosphere Map (GIM) and SAMI2 during two geomagnetic storm periods in March and June 2013. Compared with the 30-days median TEC, the TEC at the two crests of EIA had small variations while the TEC at the trough had a more remarkable variation for the two storms after the SSC. The TEC difference between the two EIA peaks had an increase or decrease several hours after the SSC, the asymmetry between the two crests of EIA represented by the defined asymmetry index has no obvious variations except several hours after the SSC, and EIA strength represented by the Crest-to-Trough Ratio (CTR) had a remarkable increase one day after the SSC day for March storm and decrease several hours after the SSC for June storm. The variations last several hours, with more than 40% variations compared with the value during the quiet period. The EIA peaks were also found to move toward the equator after the SSC during the two storms. The simulation from SAMI2 and HWM07 also shows that EIA crests would move toward the equator during storm time and EIA strength would decrease, which suggests that the disturbed neutral wind and disturbed electric field may be important factors affecting the EIA during the storm periods.

      PubDate: 2016-06-14T15:29:10Z
  • Quantitative and qualitative assessment of diurnal variability in
           tropospheric humidity using SAPHIR on-board Megha-Tropiques
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146
      Author(s): K.N. Uma, Siddarth Shankar Das
      The global diurnal variability of relative humidity (RH) from August 2012 to May 2014 is discussed for the first time using ‘Sounder for Atmospheric Profiling of Humidity in the Inter-tropical Regions (SAPHIR)’, a microwave humidity sounder onboard Megha-Tropiques (MT). It is superior to other microwave satellite humidity sounders in terms of its higher repetitive cycle in the tropics owing to its low-inclination orbit and the availability of six dedicated humidity sounding channels. The six layers obtained are 1000–850, 850–700, 700–550, 550–400, 400–250 and 250–100hPa. Three hourly data over a month has been combined using equivalent day analysis to attain a composite profile of complete diurnal cycle in each grid (2.5°×2.5°). A distinct diurnal variation is obtained over the continental and the oceanic regions at all the layers. The magnitude in the lower tropospheric humidity (LTH), middle tropospheric humidity (MTH) and the upper tropospheric humidity (UTH) show a large variability over the continental regions compared to that over oceans. The monthly variability of the diurnal variation over the years has also been discussed by segregating into five different continental and four different oceanic regions. Afternoon peaks dominate in the LTH over the land and the desert regions. The MTH is found to vary between the evening and the early morning hours over different geographical regions and not as consistent as that of the LTH. The UTH maximum magnitude is generally observed during the early morning hours, over the continents. Interestingly, the Oceanic regions are found to have a dominant magnitude in the afternoon hours similar to that of the continents in the LTH, evening maximum in the MTH and the early morning maximum in the UTH. The underlying mechanisms involved in the variability of humidity over different regions are also discussed. The study reveals the complexity involved in the understanding the diurnal variability over the continents and open oceans.

      PubDate: 2016-06-14T15:29:10Z
  • Bottom-side profile parameters (B0, B1) characteristics over the brazilian
           equatorial and low latitudes and their comparison with different options
           in the IRI-2012 model during the 24th solar minimum (2010-2011)
    • Abstract: Publication date: Available online 12 May 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): K. Venkatesh, P.R. Fagundes
      The present study reports the characteristics of the bottom-side profile thickness (B0) and shape (B1) parameters from ionosonde and IRI-2012 model over the Brazilian sector. The ionosonde data from an equatorial station Fortaleza and a low latitude station Cachoera Paulista during a two year period from 2010 to 2011 are considered in this study. Simultaneous comparison is made on the performance of three different options ‘Gul-1987’, ‘Bil-2000’ and the ‘ABT-2009’ for bottom-side profile estimation in the latest available IRI-2012. The diurnal and seasonal characteristics of the B0 and B1 from ionosonde measurements are studied and compared with those from the IRI-2012 model using the three different options. It is seen that the Gul-1987 method shows better predictions of the observed B0 at the equatorial and low latitudes values when compared with the other options. The latest option ‘ABT-2009’ has shown improved predictions in the estimation of B1 compared with those from the other methods particularly during the night-time hours. A comparison on the seasonal characteristics of the day maximum values of B0 between observations and the three different options in IRI-2012 reveals that the Gul-1987 method shows better predictions of the seasonal variations in B0 while ABT-2009 method shows better predictions of seasonal variations in B1. Further, an insight into the percentage of deviations in the estimation of B0 and B1 reveals that the models overestimate the B0 during night-time and underestimate the B0 (at equator) during day-time while they underestimate the B1 during night-time hours at both locations. Also, the variations in the bottom-side total electron content are studied using the three different methods in the IRI-2012 model and compared with those derived from the ionosonde observations.

      PubDate: 2016-05-15T15:15:42Z
  • An ionospheric assimilation model along a meridian plane
    • Abstract: Publication date: Available online 7 May 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Huijun Le, Libo Liu, Zhipeng Ren, Lianhuan Hu, Yiding Chen, Weixing Wan
      In this paper, we developed a two-dimensional ionospheric assimilation model that assimilates the observations of peak electron density of F2-layer (NmF2) and the peak height of F2-layer (hmF2) derived from five ionosonde stations along the 120°E meridian, using three-dimensional variation techniques (3DVAR) based on a physics-based ionosphere theoretical model. The assimilation system can well produce the assimilated results along the 120°E meridian plane by using the data of NmF2 and hmF2 at five ionosonde stations from Mohe (52.0°N) to Sanya (18.3°N). The root mean square error (RMSE) between the analysis results of the assimilation model and the ionosonde observations is much lower than that between the results from international reference ionosphere (IRI) and the ionosonde observations. In addition, we carried out the assimilation test by taking the IRI results as the observations to check the assimilated results in the regions without observations. The assimilated result in the southern hemisphere (RMSE=0.29) is much worse than that in the northern hemisphere (RMSE=0.10) because no observations in the southern hemisphere were used. If the data derived from the four ionosonde stations in Australia are used, the assimilated result in the southern hemisphere would be much more accurate. In addition to NmF2 and hmF2, the assimilation model can also adjust the total electron content (TEC). The RMSE between the TEC after assimilation and the observed GPS TEC is much lower than that between the TEC from the IRI model and the observed GPS TEC.

      PubDate: 2016-05-09T20:52:04Z
  • Rain rate intensity model for communication link design for indian region
    • Abstract: Publication date: Available online 7 May 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Aravind. Kilaru, Sarat K Kotamraju, Nicholas Avlonitis, K.Ch. Sri Kavya
      A study on rain statistical parameters such as one minute rain intensity, possible number of minute occurrences with respective percentage of time in a year has been evaluated for the purpose of communication link design at Ka, Q, V bands as well as at Free-Space Optical communication links (FSO). To understand possible outage period of a communication links due to rainfall and to investigate rainfall pattern, Automatic Weather Station (AWS) rainfall data is analysed due its ample presence across India. The climates of the examined AWS regions vary from desert to cold climate, heavy rainfall to variable rainfall regions, cyclone effective regions, mountain and coastal regions. In this way a complete and unbiased picture of the rainfall statistics for Indian region is evaluated. The analysed AWS data gives insight into yearly accumulated rainfall, maximum hourly accumulated rainfall, mean hourly accumulated rainfall, number of rainy days and number of rainy hours from 668 AWS locations. Using probability density function the one minute rainfall measurements at KL University is integrated with AWS measurements for estimating number of rain occurrences in terms of one minute rain intensity for annual rainfall accumulated between 100 mm to 5000mm to give an insight into possible one minute accumulation pattern in an hour for comprehensive analysis of rainfall influence on a communication link for design engineers. So that low availability communications links at higher frequencies can be transformed into a reliable and economically feasible communication links for implementing High Throughput Services (HTS).

      PubDate: 2016-05-09T20:52:04Z
  • Substorm probabilities are best predicted from solar wind speed
    • Abstract: Publication date: Available online 6 May 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): P.T. Newell, K. Liou, J.W. Gjerloev, T. Sotirelis, S. Wing, E.J. Mitchell
      Most measures of magnetospheric activity – including auroral power (AP), magnetotail stretching, and ring current intensity – are best predicted by solar wind-magnetosphere coupling functions which approximate the frontside magnetopause merging rate. However radiation belt fluxes are best predicted by a simpler function, namely the solar wind speed, v. Since most theories of how these high energy electrons arise are associated with repeated rapid dipolarizations such as associated with substorms, this apparent discrepancy could be reconciled under the hypothesis that the frequency of substorms tracks v rather than the merging rate – despite the necessity of magnetotail flux loading prior to substorms. Here we investigate this conjecture about v and substorm probability. Specifically, a continuous list of substorm onsets compiled from SuperMAG covering January 1, 1997 through December 31, 2007 are studied. The continuity of SuperMAG data and near continuity of solar wind measurements minimize selection bias. In fact v is a much better predictor of onset probability than is the overall merging rate, with substorm odds rising sharply with v. Some loading by merging is necessary, and frontside merging does increase substorm probability, but nearly as strongly as does v taken alone. Likewise, the effects of dynamic pressure, p, are smaller than simply v taken by itself. Changes in the solar wind matter, albeit modestly. For a given level of v (or B z ), a change in v (or B z ) will increase the odds of a substorm for at least 2h following the change. A decrease in driving elevates substorm probabilities to a greater extent than does an increase, partially supporting external triggering. Yet current v is the best single predictor of subsequently observing a substorm. These results explain why geomagnetically quiet years and active years are better characterized by low or high v (respectively) than by the distribution of merging estimators. It appears that the flow of energy through the magnetosphere is determined by frontside merging, but the burstiness of energy dissipation depends primarily on v.

      PubDate: 2016-05-09T20:52:04Z
  • Characteristics of the most intense lightning storm ever recorded at the
           CN tower
    • Abstract: Publication date: Available online 7 May 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): A.M. Hussein, S. Kazazi, M. Anwar, M. Yusouf, P. Liatos
      Lightning strikes to the CN Tower have been optically observed since 1978. In 1990, five independent systems started to operate to simultaneously record parameters of lightning strikes to the tower, including the time derivative of the current, the associated electric and magnetic fields, and the channel optical characteristics. On August 24, 2011, during an unusually severe lightning storm, video records showed that the CN Tower was struck with 52 lightning flashes within 84 minutes and 6.9 seconds. Thus, this storm produced, on average, a flash to the tower every 99 seconds. However, the CN Tower lightning current derivative measurement system only recorded 32 flashes, which were perfectly time-matched with 32 of the 52 video-recorded flashes. It is found that the current derivative measurement system recorded every video-recorded flash that contained at least one return stroke. Based on the analysis of video records, it is noted that each of the storm's 52 flashes contains an initial-stage current, proving that all flashes were upward initiated. This unique CN Tower storm – the most intense ever recorded at the tower – is here thoroughly analyzed, based on video and current records. The inter-flash time within the storm is found to vary between 10.6 s and 274 s, with an overall average of 98 s. It is also found that the inter-flash time between successive non-return-stroke flashes is on average 64% longer than that for successive flashes containing return strokes. Statistical analysis of video and current data clearly reveals that the time duration of flashes containing initial-stage currents and return strokes is on average 27% longer than that of flashes that only have initial-stage currents. Furthermore, it is important to note that the time duration of the initial-stage current in flashes containing no return strokes is on average 76% longer than that in flashes containing return strokes. Therefore, it is possible to conclude that if the time duration of the initial-stage current in a flash is long enough, resulting in large charge transfer, then there is less probability of having return strokes following it. The 32 current-recorded flashes contain a total of 156 return strokes, with an average multiplicity of 4.875. It is worth mentioning that during one decade, 1992-2001, the CN Tower current derivative measurement system only recorded 478 return strokes, demonstrating that the number of return strokes recorded at the tower within about 84 minutes is close to one third of those recorded at the tower during one decade. This finding clearly shows the great value and rarity of the presented extensive lightning current derivative data. Only one of the 32 current-recorded flashes is proved to be positive with a single return stroke. Based on current records, out of a total of 124 inter-stroke time intervals, 94% are found to be within 200ms, with an overall inter-stroke time average of 68.1ms. The maximum inter-stroke time recorded during this storm is 726.3ms, the longest ever recorded at the CN Tower.

      PubDate: 2016-05-09T20:52:04Z
  • Atmospheric ionization induced by precipitating electrons: Comparison of
           CRAC:EPII model with a parametrization model
    • Abstract: Publication date: Available online 7 May 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): A.A. Artamonov, A.L. Mishev, I.G. Usoskin
      Results of a comparison of a new model CRAC:EPII (Cosmic Ray Atmospheric Cascade: Electron Precipitation Induced Ionization) with a commonly used parametric model of atmospheric ionization is presented. The CRAC:EPII is based on a Monte Carlo simulation of precipitating electrons propagation and interaction with matter in the Earth's atmosphere. It explicitly considers energy deposit: ionization, pair production, Compton scattering, generation of Bremsstrahlung high energy photons, photo-ionization and annihilation of positrons, multiple scattering as physical processes accordingly. Propagation of precipitating electrons and their interactions with air is simulated with the GEANT4 simulation tool PLANETOCOSMICS code using NRLMSISE00 atmospheric model. Ionization yields are computed and compared with a parametrization model for different energies of incident precipitating energetic electrons, using simulated fluxes of mono-energetic particles. A good agreement between the two models is achieved in the mesosphere but the contribution of Bremsstrahlung in the stratosphere, which is not accounted for in the parametric models, is found significant. As an example, we calculated profiles of the ion production rates in the middle and upper atmosphere (below 100km) on the basis of balloon-born measured spectra of precipitating electrons for 30-Oct-2002 and 07-Jan-2004.

      PubDate: 2016-05-09T20:52:04Z
  • Equatorward evolution of auroras from the poleward auroral boundary
    • Abstract: Publication date: Available online 29 April 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): O. Saka, K. Hayashi, M.F. Thomsen
      An all-sky imager installed at the midnight sector in Dawson City (66.0° in geomagnetic latitude) recorded the equatorward evolution of auroras from the auroral poleward boundary. The auroras evolved as shear layers expanding southeastward with velocities of 1 to 4km/s, referred to as N-S auroras, and occurred during the transient intensification of the convection electric fields in the nighttime magnetosphere, as inferred from an electron spectrogram at geosynchronous altitudes. A continuous increase in the inclination angle of the field lines and magnetic field perturbations associated with propagating ionospheric loop currents were observed in the auroral zone during the N-S auroras. Simultaneously, Pc4 pulsations were observed at low latitudes from night to day sectors. We conclude the following: (1) the N-S auroras are an auroral manifestation of the earthward drift of plasma sheet electrons in the equatorial plane associated with transient and localized convection electric fields; (2) the Pc4 pulsations are produced in the magnetosphere by plasma sheet ions in the plasmasphere. The localized convection fields produce a vortical motion of plasmas in the equatorial plane, which may initiate the N-S auroras and ionospheric loop currents in the auroral zone.

      PubDate: 2016-05-04T20:27:09Z
  • Features of Positive Ground Flashes Observed in Kathmandu Nepal
    • Abstract: Publication date: Available online 1 May 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Pitri Bhakta Adhikari, Shriram Sharma, Kedarnath Baral
      Lightning vertical electric fields pertinent to the subtropical thunderstorms occuring over the rugged terrain have been measured and recorded at a hilly station Kathmandu, Nepal. In the present work, waveforms of the positive ground flashes have been selected from all the records and were analyzed. To the best of our knowledge, this is the first time that fine structure of electric field signature pertinent to the positive return stroke; have been analyzed and presented from Nepal. One hundred and thirty three (133) of the total of four hundred twenty-five (425) flashes were selected from seven thunderstorm days and analyzed. Of the data recorded for seven days, 133 flashes (31.3%) were positive flashes and 276 flashes (64.9%) were cloud flashes. Majority of the positive ground flashes were found to be single stroke ones, whereas, the average number of strokes per flash is found to be 1.1 with a maximum value of 4. Majority of the positive ground flashes were found either lacking the initial breakdown process and the leader stage or these processes could not be detected. The return strokes are found to be succeded by large incloud activity in the continuing current portion of the flash. The average zero-crossing time of the positive return strokes was found to be 60.45µs with a range of 447.81µs and the average rise time was found to be 9.44µs with a range of 42.56µs.

      PubDate: 2016-05-04T20:27:09Z
  • Validation of NeQuick 2 model over the kenyan region through data
           ingestion and the model application in ionospheric studies
    • Abstract: Publication date: Available online 26 April 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): O. J Olwendo, C Cesaroni
      NeQuick 2 is an ionospheric electron density model which provides electron density for a given location. Its output depends on solar activity expressed by 12-month running average sunspot number (R12) or solar radio flux (F10.7). To improve the model capabilities to reproduce electron density, data ingestion techniques have been implemented which replace the standard solar activity indices input with effective parameters that allow adapting a model to a certain data sets. In regions like the Sub-Saharan Africa where few observational data were available until recently, the performance of the ingested model needs some validation. This study investigates the performance of NeQuick 2 in the Kenya region, a low latitude region by assisting the model with total electron content measurement from a single GNSS station. These measurements are used to calculate effective ionization level parameters, which enable the difference between the measured and modelled TEC over the station to be less or equal to 0.5 TECU. The results show that by using computed effective parameters values as inputs in nearby stations, the model performance is greatly improved for both the low and moderate solar activity. This work has also demonstrated the capability of the model to describe spatial distribution of the total electron content in the low- latitude ionosphere.

      PubDate: 2016-05-04T20:27:09Z
  • Large ice particles associated with small ice water content observed by
           AIM CIPS imagery of polar mesospheric clouds: Evidence for microphysical
           coupling with small-scale dynamics
    • Abstract: Publication date: Available online 2 May 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): D. Rusch, G. Thomas, A. Merkel, J. Olivero, A. Chandran, J. Lumpe, J. Carstans, C. Randall, S. Bailey, J. Russell
      Observations by the Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of Ice in the Mesosphere (AIM) satellite have demonstrated the existence of Polar Mesospheric Cloud (PMC) regions populated by particles whose mean sizes range between 60 and 100nm (radii of equivalent volume spheres). It is known from numerous satellite experiments that typical mean PMC particle sizes are of the order of 40–50nm. Determination of particle size by CIPS is accomplished by measuring the scattering of solar radiation at various scattering angles at a spatial resolution of 25km2. In this size range we find a robust anti-correlation between mean particle size and albedo. These very-large particle-low-ice (VLP-LI) clouds occur over spatially coherent areas. The surprising result is that VLP-LI are frequently present either in the troughs of gravity wave-like features or at the edges of PMC voids. We postulate that an association with gravity waves exists in the low-temperature summertime mesopause region, and illustrate the mechanism by a gravity wave simulation through use of the 2D Community Aerosol and Radiation Model for Atmospheres (CARMA). The model results are consistent with a VLP-LI population in the cold troughs of monochromatic gravity waves. In addition, we find such events in Whole Earth Community Climate Model/CARMA simulations, suggesting the possible importance of sporadic downward winds in heating the upper cloud regions. This newly-discovered association enhances our understanding of the interaction of ice microphysics with dynamical processes in the upper mesosphere.

      PubDate: 2016-05-04T20:27:09Z
  • Impacts of Air–Sea Exchange Coefficients on Snowfall Events over the
           Korean Peninsula
    • Abstract: Publication date: Available online 2 May 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Jung-Yoon Kang, Young Cheol Kwon
      Snowfall over the Korean Peninsula is mainly associated with air mass transformation by the fluxes across the air–sea interface during cold-air outbreaks over the warm Yellow Sea. The heat and momentum exchange coefficients in the surface flux parameterization are key parameters of flux calculations across the air–sea interface. This study investigates the effects of the air–sea exchange coefficients on the simulations of snowfall events over the Korean Peninsula using the Weather Research and Forecasting (WRF) model. Two snowfall cases are selected for this study. One is a heavy snowfall event that took place on January 4, 2010, and the other is a light snowfall event that occurred on December 23–24, 2011. Several sensitivity tests are carried out with increased and decreased heat and momentum exchange coefficients. The domain-averaged precipitation is increased (decreased) with increased (decreased) heat exchange coefficient because the increased (decreased) surface heat flux leads to more (less) moist conditions in the low level of the atmosphere. On the other hand, the domain-averaged precipitation is decreased (increased) with increased (decreased) momentum exchange coefficient because the increased (decreased) momentum coefficient causes reduction (increase) of wind speed and heat flux. The variation of precipitation in the heat exchange coefficient experiments is much larger than that in the momentum exchange coefficient experiments because the change of heat flux has a more direct impact on moisture flux and snowfall amount, while the change of momentum flux has a rather indirect impact via wind speed changes. The low-pressure system is intensified and moves toward North when the heat exchange coefficient is increased because warming and moistening of the lower atmosphere contributes to destabilize the air mass, resulting in the change of precipitation pattern over the Korean Peninsula in the heat exchange coefficient experiments.

      PubDate: 2016-05-04T20:27:09Z
  • IFC-Ed. board
    • Abstract: Publication date: June 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 143–144

      PubDate: 2016-05-04T20:27:09Z
  • Identifying the occurrence of lightning and transient luminous events by
           nadir spectrophotometric observation
    • Abstract: Publication date: July 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 145
      Author(s): Toru Adachi, Mitsuteru Sato, Tomoo Ushio, Atsushi Yamazaki, Makoto Suzuki, Masayuki Kikuchi, Yukihiro Takahashi, Umran S. Inan, Ivan Linscott, Yasuhide Hobara, Harald U. Frey, Stephen B. Mende, Alfred B. Chen, Rue-Ron Hsu, Kenichi Kusunoki
      We propose a new technique to identify the occurrence of lightning and transient luminous events (TLEs) using multicolor photometric data obtained by space borne nadir measurements. We estimate the spectral characteristics of lightning and TLEs by converting the optical data obtained by the ISUAL limb experiment to the GLIMS nadir geometry. We find that the estimated spectral shapes of TLE-accompanied lightning are clearly different from those of pure lightning. The obtained results show that (1) the intensity of FUV signals and (2) the ratio of 337/red (609–753nm) spectral irradiance are useful to identify the occurrence of TLEs. The occurrence probabilities of TLEs are 10%, 40%, 80%, in the case of lightning events having the 337/red spectral irradiance ratio of 0.95, 2.95, 14.79, respectively. By using the 60% criterion of the 337/red ratio and the existence of FUV emissions, we classify the 1039 GLIMS-observed lightning events into 828 pure lightning and 211 TLE-accompanied lightning. Since the GLIMS trigger level is adjusted to observe extremely-bright events, the occurrence probability of TLEs obtained here most probably reflects the characteristics of energetic lightning. The estimated global map is consistent with previously determined distributions: the highest activities of lightning and TLEs are found over the North/South American continents, African continent, and Asian maritime regions. While the absolute occurrence number of pure lightning and TLE-accompanied lightning are found to maximize in the equatorial region, the occurrence probability of TLEs possibly increase somewhat in the mid-latitude region. Since the occurrence probabilities of TLEs are higher over the ocean than over land, it is likely that the GLIMS-observed TLEs are due primarily to elves which tends to occur more frequently over the ocean.

      PubDate: 2016-05-04T20:27:09Z
  • Global structure of ionospheric TEC anomalies driven by geomagnetic storms
    • Abstract: Publication date: Available online 29 April 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): D. Pancheva, P. Mukhtarov, B. Andonov
      This study examines the structure and variability of the ionospheric TEC anomalies driven by geomagnetic storms. For this purpose the CODE global ionospheric TEC data from four geomagnetically disturbed periods (29 October-1 November 2003, 7–10 November 2004, 14-15 December 2006, and 5-6 August 2011) have been considered. By applying the tidal analysis to the geomagnetically forced TEC anomalies we made an attempt to identify the tidal or stationary planetary wave (SPW) signatures that may contribute to the generation of these anomalies. It has been found that three types of positive anomalies with different origin and different latitudinal appearance are observed. These are: (i) anomalies located near latitudes of ±40° and related to the enhancement and poleward moving of the equatorial ionization anomaly (EIA) crests; (ii) anomalies located near latitudes of ±60° and seen predominantly in the night-side ionosphere, and (iii) very high latitude anomalies having mainly zonally symmetric structure and related to the auroral heating and thermospheric expansion. The decomposition analysis revealed that these anomalies can be reconstructed as a result of superposition of the following components: zonal mean (ZM), diurnal migrating (DW1), zonally symmetric diurnal (D0), and stationary planetary wave 1 (SPW1).

      PubDate: 2016-05-04T20:27:09Z
  • Probing geomagnetic storm-driven magnetosphere-ionosphere dynamics in
           D-region via propagation characteristics of very low frequency radio
    • Abstract: Publication date: Available online 29 April 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Victor U.J. Nwankwo, Sandip K. Chakrabarti, Olugbenga Ogunmodimu
      The amplitude and phase of VLF/LF radio signals are sensitive to changes in electrical conductivity of the lower ionosphere which imprints its signature on the Earth-ionosphere waveguide. This characteristics makes it useful in studying sudden ionospheric disturbances, especially those related to prompt X-ray flux output from solar flares and gamma ray bursts (GRBs). However, strong geomagnetic disturbance and storm conditions are known to produce large and global ionospheric disturbances, which can significantly affect VLF radio propagation in the D region of the ionosphere. In this paper, using the data of three propagation paths at mid-latitudes (40° – 54°), we analyze the trend of aspects of VLF diurnal signal under varying solar and geomagnetic space environmental conditions in order to identify possible geomagnetic footprints on the D region characteristics. We found that the trend of variations generally reflect the prevailing space weather conditions in various time scales. In particular, the ‘dipping’ of mid-day signal amplitude (MDP) of VLF always occurs after geomagnetic perturbed or storm conditions in the time scale of 1–2days. The mean signal before sunrise (MBSR) and mean signal after sunset (MASS) also exhibit storm-induced dipping, but they appear to be influenced by event's exact occurrence time and highly variable conditions of dusk-to-dawn ionosphere. We observed fewer cases of the signals rise (e.g., MDP, MBSR or MASS) following a significant geomagnetic event, though this effect may be related to storms associated phenomena or effects arising from sources other than solar origin. The magnitude of induced dipping (or rise) significantly depends on the intensity and duration of event(s), as well as the propagation path of the signal. The post-storm day signal (following a main event, with lesser or significantly reduced geomagnetic activity), exhibited a tendency of recovery to pre-storm day level. In the present analysis, We do not see a well defined trend of the variations of the post-storm sunrise terminator (SRT) and sunset terminator (SST). The SRT and SST signals show more post-storm dipping in GQD-A118 propagation path but generally an increase along DHO-A118 propagation path. Thus the result could be propagation path dependent and detailed modeling is required to understand these phenomena.

      PubDate: 2016-05-04T20:27:09Z
  • Study of high-latitude ionosphere: One-year campaign over Husafell,
    • Abstract: Publication date: July 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 145
      Author(s): S.A. Bahari, M. Abdullah, A.M. Hasbi, B. Yatim, W. Suparta, A. Kadokura, G. Bjornsson
      This paper reports on the effects of diurnal, seasonal, geomagnetic and solar activity on GPS Vertical Total Electron Content (VTEC) measurements at a high-latitude station in Husafell, Iceland (64.7°N, 21.0°W) from March 2009 to February 2010. According to the diurnal VTEC pattern, there was generally a build-up region at sunrise (0500-1000 LT), a daytime plateau in the afternoon (1200-1400 LT), and a decay region from evening to pre-dawn (1800-0400 LT). The month-to-month analysis showed high VTEC variability, particularly in February 2010, due to an increase in solar activity. The VTEC showed a high variability during both winter and the equinoxes, with the highest value being 90%, but showed a low variability in summer. Two abnormal peaks appeared at sunrise and sunset in winter and the equinoxes. These peaks were the result of steep density gradients caused by the onset and turnoff of solar radiation. The correlation analysis yielded almost no correlation between the VTEC and geomagnetic activity but showed a high correlation with solar activity for all the seasons, particularly at night-time.

      PubDate: 2016-05-04T20:27:09Z
  • Temperature distribution and evolution characteristic in lightning return
           stroke channel
    • Abstract: Publication date: July 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 145
      Author(s): Yali Mu, Ping Yuan, Xuejuan Wang, Caixia Dong
      According to the time-resolved spectra of four lightning return strokes, the temperatures of arc core channel and the peripheral optical channel surrounding the arc core are investigated by different methods; the temperature distribution along the radial direction of channel on the peak current stage is discussed. The results show that a temperature gradient is formed along the radial direction of channel during the discharge process. With the increasing of the radius, the temperature decreases gradually. The temperature of arc core channel is about 4000–5000K higher than that of the peripheral optical channel. The time evolution of channel temperature shows that the falling of the temperature is very slow compared with the decreasing of the current after their peak values. After the peak current, the channel temperature is still maintained at around 20,000K up to 200–400 μ s . The heat effect resulting from such a long-time high temperature is the main source of most direct lightning disasters.

      PubDate: 2016-05-04T20:27:09Z
  • Large-scale traveling ionospheric disturbances using ionospheric imaging
           at storm time: A case study on 17 march 2013
    • Abstract: Publication date: July 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 145
      Author(s): Jun Tang, Yibin Yao, Jian Kong, Liang Zhang
      A moderate geomagnetic storm occurred on March 17, 2013, during which large-scale traveling ionospheric disturbances (LSTIDs) are observed over China by ionosondes and GPS from Crustal Movement Observation Network of China (CMONOC) and the International GNSS Service (IGS). Ionosonde data and computerized ionospheric tomography (CIT) technique are employed to analyze the disturbances in our study. The maximum entropy cross spectral analysis (MECSA) method is used to obtain the propagation parameters of the LSTIDs. Spatio-temporal variations of ionospheric electron density (IED) and total electron content (TEC) during this geomagnetic storm over China are investigated. Disturbance images of IED and TEC are also presented in the paper. The results show two LSTID events at about 12:00UT and 15:00UT during the main phase of the storm. Besides, the LSTIDs with a duration of 40min are detected over China. It is confirmed that the LSTIDs travel from north to south with a horizontal velocity of 400–500m/s, and moved southwestwards with a horizontal velocity of 250–300m/s, respectively.

      PubDate: 2016-05-04T20:27:09Z
  • Inter-hourly variability of total electron content during the quiet
           condition over Nigeria, within the equatorial ionization anomaly region
    • Abstract: Publication date: Available online 7 April 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): T.T. Ayorinde, A. B Rabiu, C. Amory-Mazaudier
      The inter-hourly variability (IHV) of the Total Electron Content (TEC) over Nigeria during the quiet days (Ap<4) of the year 2013 was examined using ground-based GPS receivers installed at seven (7) different locations across Nigeria by the Nigerian Global Navigation Satellite Systems (GNSS) Reference Network (NIGNET) operated by the office of the surveyor general of Nigeria. Nigeria is a country that lies within equatorial ionospheric anomaly (EIA) region. The IHV was calculated by converting the observed hourly slant TEC (STEC) value into the hourly vertical TEC (VTEC) and the differencing (∆TEC) with its corresponding hourly value from the previous day. There is a clear variation which depicts the expected temporal variability. The IHV in TEC in all the stations ranges between 0-20 TECU (TEC Units). The seasonal variation of the IHV of TEC over Nigeria maximizes (5-20 TECU) during Equinoctial months and minimizes (1-10 TECU) during the Solstice months. The IHV of TEC in September equinox period is higher than that of March equinox. Minimum value of IHV (~7 TECU at equinoxes and ~5 TECU at Solstice) was recorded at the Office of Surveyor General of the Federation (OSGF) station and the maximum value (~12 TECU at equinoxes and ~16 TECU at Solstice) was recorded at the Birni Kebbi Federal Polytechnic (BKFP) station which may be due to the fact that BKFP at 0.72° dip latitude is closer to the dip equator.

      PubDate: 2016-04-09T11:09:44Z
  • Cloud properties during active and break spells of the west african summer
           monsoon from CloudSat-CALIPSO measurements
    • Abstract: Publication date: Available online 3 April 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): E. Efon, A. Lenouo, D. Monkam, D. Manatsa
      High resolution of daily rainfall dataset from the Tropical Rainfall Measuring Mission (TRMM) was used to identify active and break cloud formation periods. The clouds were characterized based on CloudSat-CALIPSO satellite images over West Africa during the summer monsoon during the period 2006-2010. The active and break periods are defined as the periods during the peak monsoon months of June to August when the normalized anomaly of rainfall over the monsoon core zone is greater than 0.9 or less than − 0.9 respectively, provided the criteria is satisfied for at least three consecutive days. It is found that about 90% of the break period and 66.7% of the active spells lasted 3-4 days. Active spells lasting duration of about a week were observed while no break spell had such a long span. Cloud macrophysical (cloud base height (CBH), cloud top height (CTH) and cloud geometric depth (∆H), microphysical (cloud liquid water content, (LWC), liquid number concentration (LNC), liquid effective radius, ice water content (IWC), ice number concentration (INC) and ice effective radius) and radiative (heating rate properties) over South Central West Africa (5°−15°N; 15°W-10°E) during the active and break spells were also analyzed. High-level clouds are more predominant during the break periods compared to the active periods. Active spells have lower INC compared to the break spells. Liquid water clouds are observed to have more radiative forcing during the active than break periods while ice phase clouds bring more cooling effect during the break spells compared to the active spells.

      PubDate: 2016-04-07T10:59:03Z
  • Locating narrow bipolar events with single-station measurement of
           low-frequency magnetic fields
    • Abstract: Publication date: Available online 30 March 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Hongbo Zhang, Gaopeng Lu, Xiushu Qie, Rubin Jiang, Yanfeng Fan, Ye Tian, Zhuling Sun, Mingyuan Liu, Zhichao Wang, Dongxia Liu, Guili Feng
      We developed a method to locate the narrow bipolar events (NBEs) based on the single-station measurement of low-frequency (LF, 40-500kHz) magnetic fields. The direction finding of a two-axis magnetic sensor provides the azimuth of NBEs relative to the measurement site; the ionospheric reflection pairs in the lightning sferics are used to determine the range and height. We applied this method to determine the three-dimensional (3D) locations of 1475 NBEs with magnetic signals recorded during the SHandong Artificially Triggered Lightning Experiment (SHATLE) in summer of 2013. The NBE detections are evaluated on a storm basis by comparing with radar observations of reflectivity and lightning data from the World Wide Lightning Location Network (WWLLN) for two mesoscale convective systems (MCSs) of different sizes. As revealed by previous studies, NBEs are predominately produced in the convective regions with relatively strong radar echo (with composite reflectivity ≥30dBZ), although not all the convections with high reflectivity and active lightning production are in favor of NBE production. The NBEs located by the single-station magnetic method also exhibit the distinct segregation in altitude for positive and negative NBEs, namely positive NBEs are mainly produced between 7km and 15km, while negative NBEs are predominantly produced above 14km. In summary, the results of comparison generally show that the single-station magnetic method can locate NBEs with good reliability, although the accuracy of 3D location remains to be evaluated with the traditional multi-station method based on the time-of-arrival technique. This method can be applied to track the motion of storm convection within 800km, especially when they move out to ocean beyond the detection range (typically <400km) of meteorological radars, making it possible to study NBEs in oceanic thunderstorms for which the location with multiple ground-based stations is usually not feasible.

      PubDate: 2016-04-03T05:08:31Z
  • Multifractal analysis of lightning channel for different categories of
    • Abstract: Publication date: Available online 2 April 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): F.J. Miranda, S.R. Sharma
      A study from the point of view of complex systems is done for lightning occurred at Diamantina, Sete Lagoas and São José dos Campos, during the summer from September 2009 to April 2010. For the first time, multifractal analyses were performed for different lightning categories: two-dimensional, three-dimensional, non-branched, branched, cloud, cloud-to-ground, single and multiple. We found that when using two-dimensional images of natural lightning embedded in three dimensions to perform multifractal analysis, the interpretation of the multifractal spectrum must be restricted to identification of the multi (mono) fractal character of lightning channel and to estimation of fractal dimension. We have also observed that, on the average, each category has a specific value of fractal dimension. Categories in which branches and tortuosity are more usual, like branched and cloud categories, exhibited largest fractal dimensions due to more complexity of lightning channels. The results suggest that single and multiple lightning have similar complexities in their channels, leading to the same average values of fractal, information and correlation dimensions for both categories.

      PubDate: 2016-04-03T05:08:31Z
  • Evaluation of the inter-annual variability of stratospheric chemical
           composition in chemistry-climate models using ground-based multi species
           time series
    • Abstract: Publication date: Available online 1 April 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): V. Poulain, S. Bekki, M. Marchand, M.P. Chipperfield, M. Khodri, S. Dhomse, G.E. Bodeker, R. Toumi, M. De Maziere, J.-P. Pommereau, A. Pazmino, F. Goutail, D. Plummer, E. Rozanov, E. Mancini, H. Akiyoshi, J.-F. Lamarque, J. Austin
      The variability of stratospheric chemical composition occurs on a broad spectrum of timescales, ranging from day to decades. A large part of the variability appears to be driven by external forcings such as volcanic aerosols, solar activity, halogen loading, levels of greenhouse gases (GHG), and modes of climate variability (quasi-biennial oscillation (QBO), El Niño-Southern Oscillation (ENSO)). We estimate the contributions of different external forcings to the interannual variability of stratospheric chemical composition and evaluate how well 3-D chemistry-climate models (CCMs) can reproduce the observed response-forcing relationships. We carry out multivariate regression analyses on long time series of observed and simulated time series of several traces gases in order to estimate the contributions of individual forcings and unforced variability to their internannual variability. The observations are typically decadal time series of ground-based data from the international Network for the Detection of Atmospheric Composition Change (NDACC) and the CCM simulations are taken from the CCMVal-2 REF-B1 simulations database. The chemical species considered are column O3, HCl, NO2, and N2O. We check the consistency between observations and model simulations in terms of the forced and internal components of the total interannual variability (externally forced variability and internal variability) and identify the driving factors in the interannual variations of stratospheric chemical composition over NDACC measurement sites. Overall, there is a reasonably good agreement between regression results from models and observations regarding the externally forced interannual variability. A much larger fraction of the observed and modelled interannual variability is explained by external forcings in the tropics than in the extratropics, notably in polar regions. CCMs are able to reproduce the amplitudes of responses in chemical composition to specific external forcings. However, CCMs tend to underestimate very substantially the internal variability and hence the total interannual variability for almost all species considered. This lack of internal variability in CCMs might partly originate from the surface forcing of these CCMs by analysed SSTs. The results illustrate the potential of NDACC ground-based observations for evaluating CCMs.

      PubDate: 2016-04-03T05:08:31Z
  • Visibility effect on the availability of a terrestrial free space optics
           link under a tropical climate
    • Abstract: Publication date: Available online 25 March 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Ahmed Basahel, Islam Md. Rafiqul, Mohamad Hadi Habaebi, A.Z. Suriza
      Haze, fog and rain limit the visibilities and acts as dominant parameter for free space optics availability estimation. Low visibilities increase atmospheric attenuation and reduce the availability of optical signals from free space optics (FSO) links. Thus, this study determines the effect of visibility on FSO link availability in a tropical climate. Visibility data were measured in Malaysia for three years and used to estimate availability of FSO links. Rain and haze are two phenomena which reduces the visibility in tropical climate like Malaysia. Hence three cases were considered for measured data analysis: rain with dense haze, dense haze, and normal haze cases. In Malaysia, seasonal dense haze is mainly attributed to forest fires in Indonesia and in parts of Malaysia. The atmospheric attenuations predicted based on measured visibility (km) were compared across the three cases. The attenuations in the first two cases are found severe (almost 155dB/km); while in the third case it is very low (almost 6dB/km). The worst case (dense haze) is equivalent to a thick fog in temperate regions and must be examined carefully with respect to FSO deployment in a tropical environment.

      PubDate: 2016-03-29T04:46:56Z
  • Spatiotemporal analysis of snow cover variations at mt. Kilimanjaro using
           multi-temporal Landsat images during 27 years
    • Abstract: Publication date: Available online 28 March 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Sung-Hwan Park, Moung-Jin Lee, Hyung-Sup Jung
      The Landsat TM and ETM+ images have been acquired for the long period from the 1980s until the present with the temporal resolution of a 16-day repeat cycle from the visible, near infrared (NIR), short wave infrared (SWIR) and thermal infrared (TIR) bands. The Landsat multi-temporal images have been successfully used to monitor variations of the Earth surface during 27 years. In this paper, we observe the variations of 1) the snow cover area, 2) the snowline height and 3) the land surface temperature (LST) lapse rate at Mt. Kilimanjaro using a total number of 15 Landsat-5 TM and Landsat-7 ETM+ images from June 1984 to July 2011. Segmentation of normalized difference snow index (NDSI) images with a threshold of 0.6 is used to extract snow cover. Snowline altitude is then determined by combining the snow cover classification maps with a digital elevation model (DEM). And the LST lapse rate is also calculated from the TIR band in the forest area. The results from this study show that 1) the snow cover area largely decreases from 10.1km2 to 2.3km2 during about 27 years, which corresponds to a 77.2% reduction, 2) the snowline height rose from 4,760m to 5,020m by about 260m, and 3) the LST lapse rate shifted from −5.2°C/km to −2.7°C/km. This study demonstrates that multi-temporal Landsat images can be successfully used for the spatiotemporal analysis of long-term snow cover changes.

      PubDate: 2016-03-29T04:46:56Z
  • Variability of mesospheric water vapor above Bern in relation to the
           27-day solar rotation cycle
    • Abstract: Publication date: Available online 29 March 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Martin Lainer, Klemens Hocke, Niklaus Kämpfer
      Many studies investigated solar-terrestrial responses (thermal state, O3, OH, H2O) with emphasis on the tropical upper atmosphere. In this paper the focus is switched to water vapor in the mesosphere at a mid-latitudinal location. Eight years of water vapor profile measurements above Bern ( 46.88 ° N / 7.46 ° E ) are investigated to study oscillations with the focus on periods between 10 to 50 days. Different spectral analyses revealed prominent features in the 27-day oscillation band, which are enhanced in the upper mesosphere (above 0.1 hPa , ∼ 64 km ) during the rising sunspot activity of solar cycle 24. Local as well as zonal mean Aura MLS observations support these results by showing a similar behavior. The relationship between mesospheric water and the solar Lyman-α flux is studied by comparing the similarity of their temporal oscillations. The H2O oscillation is negatively correlated to solar Lyman-α oscillation with a correlation coefficient of up to − 0.3 to − 0.4 , and the phase lag is 6–10 days at 0.04 hPa . The confidence level of the correlation is ≥ 99 % . This finding supports the assumption that the 27-day oscillation in Lyman-α causes a periodical photodissociation loss in mesospheric water. Wavelet power spectra, cross-wavelet transform and wavelet coherence analysis (WTC) complete our study. More periods of high common wavelet power of H2O and solar Lyman-α are present when amplitudes of the Lyman-α flux increase. Since this is not a measure of physical correlation a more detailed view on WTC is necessary, where significant (two sigma level) correlations occur intermittently in the 27 and 13-day band with variable phase lock behavior. Large Lyman-α oscillations appeared after the solar superstorm in July 2012 and the H2O oscillations show a well pronounced anti-correlation. The competition between advective transport and photodissociation loss of mesospheric water vapor may explain the sometimes variable phase relationship of mesospheric H2O and solar Lyman-α oscillations. Generally, the WTC analysis indicates that solar variability causes observable photochemical and dynamical processes in the mid-latitude mesosphere.

      PubDate: 2016-03-29T04:46:56Z
  • Characterisation of GPS-TEC in the african equatorial and low latitude
           region and the regional evaluation of the IRI model
    • Abstract: Publication date: Available online 22 March 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): S.J. Adebiyi, I.A. Adimula, O.A. Oladipo
      With the increasing application of Global Navigation Satellite System (GNSS) products and services, knowledge of the Total Electron Content (TEC) variation is vital, particularly in historically under-sampled regions. The ionospheric induced-error, which is the largest and most variable error source of GNSS applications, is proportional to TEC along the satellite-receiver path. Simultaneous Global Positioning System (GPS) measurements from six African equatorial and low latitude stations in the southern hemisphere are used to investigate the latitudinal variation of TEC over the region during the year 2013, a year of moderate solar activity. The analysis reveals some detailed features of seasonal, month-to-month and solar activity dependence of TEC. The seasonal variation of TEC revealed that the daytime and the pre-midnight values of TEC for stations located close to the geographic equator is considerably higher in equinoxes and June solstice compared to stations farther from the equator, however, the difference is insignificant during the December solstice. The month-to-month variation of TEC shows semi-annual symmetry/asymmetry in TEC values for stations closer/farther from the equator. TEC sensitivity to solar activity shows significant seasonal and latitudinal characteristics. Generally, a relatively good correlation exists between TEC and F10.7 for stations around the Equatorial Ionization Anomaly (EIA) region compared to those found at stations close to the equator. Beyond the EIA region, the correlation coefficients drop in all seasons. TEC predicted by the three topside options of the International Reference Ionosphere (IRI) 2012 model [i.e. the NeQuick (NeQ), IRI-2001 Corrected (IRI-01 Corr) and the IRI-2001 (IRI-01) options] exhibits latitudinal and seasonal characteristics. The NeQ option performed better than the other two options at stations located within the equatorial region in most of the months and seasons. Outside the EIA region, the IRI-01 Corr and IRI-01 options give better predictions. Generally, the three model options give improved TEC representations with increasing latitude.

      PubDate: 2016-03-25T04:35:03Z
  • Time distribution of heavy rainfall events in south west of IRAN
    • Abstract: Publication date: Available online 24 March 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Zahra Ghassabi, G. Ali kamali, AmirHosein Meshkati, Sohrab Hajam, Nasrolah Javaheri
      Accurate knowledge of rainfall time distribution is a fundamental issue in many Meteorological-Hydrological studies such as using the information of the surface runoff in the design of the hydraulic structures, flood control and risk management, and river engineering studies. Since the main largest dams of Iran are in the south-west of the country (i.e. South Zagros), this research investigates the temporal rainfall distribution based on an analytical numerical method to increase the accuracy of hydrological studies in Iran. The United States Soil Conservation Service (SCS) estimated the temporal rainfall distribution in various forms. Hydrology studies usually utilize the same distribution functions in other areas of the world including Iran due to the lack of sufficient observation data. However, we first used Weather Research Forecasting (WRF) model to achieve the simulated rainfall results of the selected storms on south west of Iran in this research. Then, a three-parametric Logistic function was fitted to the rainfall data in order to compute the temporal rainfall distribution. The domain of the WRF model is 30.5N-34N and 47.5E-52.5E with a resolution of 0.08 degree in latitude and longitude. We selected 35 heavy storms based on the observed rainfall data set to simulate with the WRF Model. Storm events were scrutinized independently from each other and the best analytical three-parametric logistic function was fitted for each grid point. The results show that the value of the coefficient a of the logistic function, which indicates rainfall intensity, varies from the minimum of 0.14 to the maximum of 0.7. Furthermore, the values of the coefficient B of the logistic function, which indicates rain delay of grid points from start time of rainfall, vary from 1.6 in south-west and east to more than 8 in north and central parts of the studied area. In addition, values of rainfall intensities are lower in south west of IRAN than those of observed or proposed by the SCS values in the US.

      PubDate: 2016-03-25T04:35:03Z
  • Comparison of DMSP and SECS region-1 and region-2 ionospheric current
    • Abstract: Publication date: Available online 15 March 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): J.M. Weygand, S. Wing
      The region-1 and region-2 boundary has traditionally been identified using data from a single spacecraft crossing the auroral region and measuring the large scale changes in the cross track magnetic field. With data from the AUTUMN, CANMOS, CARISMA, GIMA, DTU MGS, MACCS, McMAC, STEP, THEMIS, and USGS ground magnetometer arrays we applied a state-of-art technique based on spherical elementary current system (SECS) method developed by Amm and Viljanen [1999) in order to calculate maps of region-1 and region-2 current system over the North American and Greenland auroral region. Spherical elementary current (SEC) amplitude (proxy for vertical currents) maps can be inferred at 10sec temporal resolution,~1.5° geographic latitude (Glat), and 3.5° geographic longitude (Glon) spatial resolution. We compare the location of the region-1 and region-2 boundary obtained by the DMSP spacecraft with the region-1 and region-2 boundary observed in the SEC current amplitudes. We find that the boundaries typically agree within 0.2°±1.3°. These results indicate that the location of the region-1 and region-2 boundary can reasonably be determined from ground magnetometer data. The SECS maps represent a value-added product from the magnetometer database and can be used for contextual interpretation in conjunction with other missions as well as help with our understanding of magnetosphere-ionosphere coupling mechanisms using the ground arrays and the magnetospheric spacecraft data.

      PubDate: 2016-03-20T04:21:15Z
  • Temporal variability patterns in solar radiation estimations
    • Abstract: Publication date: Available online 15 March 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): José M. Vindel, Ana A. Navarro, Rita X. Valenzuela, Luis F. Zarzalejo
      In this work, solar radiation estimations obtained from a satellite and a numerical weather prediction model in mainland Spain have been compared. Similar comparisons have been formerly carried out, but in this case, the methodology used is different: the temporal variability of both sources of estimation has been compared with the annual evolution of the radiation associated to the different study climate zones. The methodology is based on obtaining behavior patterns, using a Principal Component Analysis, following the annual evolution of solar radiation estimations. Indeed, the adjustment degree to these patterns in each point (assessed from maps of correlation) may be associated with the annual radiation variation (assessed from the interquartile range), which is associated, in turn, to different climate zones. In addition, the goodness of each estimation source has been assessed comparing it with data obtained from the radiation measurements in ground by pyranometers. For the study, radiation data from Satellite Application Facilities and data corresponding to the reanalysis carried out by the European Centre for Medium-Range Weather Forecasts have been used.

      PubDate: 2016-03-20T04:21:15Z
  • Parameterization of Large-Scale Turbulent Diffusion in the presence of
           both well-mixed and weakly mixed patchy layers
    • Abstract: Publication date: Available online 17 March 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): M.K. Osman, W.K. Hocking, D.W. Tarasick
      Vertical diffusion and mixing of tracers in the upper troposphere and lower stratosphere (UTLS) is not uniform, but primarily occurs due to patches of turbulence that are intermittent in time and space. The effective diffusivity of regions of patchy turbulence is related to statistical parameters describing the morphology of turbulent events, such as lifetime, number, width, depth and local diffusivity (i.e., diffusivity within the turbulent patch) of the patches. While this has been recognized in the literature, the primary focus has been on well-mixed layers, with few exceptions. In such cases the local diffusivity is irrelevant, but this is not true for weakly and partially mixed layers. Here, we use both theory and numerical simulations to consider the impact of intermediate and weakly mixed layers, in addition to well-mixed layers. Previous approaches have considered only one dimension (vertical), and only a small number of layers (often one at each time step), and have examined mixing of constituents. We consider a two-dimensional case, with multiple layers (10 and more, up to hundreds and even thousands), having well-defined, non-infinite, lengths and depths. We then provide new formulas to describe cases involving well-mixed layers which supersede earlier expressions. In addition, we look in detail at layers that are not well mixed, and, as in interesting variation on previous models, our procedure is based on tracking the dispersion of individual particles, which is quite different to the earlier approaches which looked at mixing of constituents. We develop an expression which allows determination of the degree of mixing, and show that layers used in some previous models were in fact not well mixed and so produced erroneous results. We then develop a generalized model based on two dimensional random-walk theory employing Rayleigh distributions which allows us to develop a universal formula for diffusion rates for multiple two-dimensional layers with general degrees of mixing. We show that it is the largest, most vigorous and less common turbulent layers that make the major contribution to global diffusion. Finally, we make estimates of global-scale diffusion coefficients in the lower stratosphere and upper troposphere. For the lower stratosphere, κ eff ≈ 2 x 10-2 m2 s-1, assuming no other processes contribute to large-scale diffusion.

      PubDate: 2016-03-20T04:21:15Z
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
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