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  Subjects -> METEOROLOGY (Total: 88 journals)
Showing 1 - 36 of 36 Journals sorted alphabetically
Acta Meteorologica Sinica     Hybrid Journal   (Followers: 3)
Advances in Atmospheric Sciences     Hybrid Journal   (Followers: 28)
Advances in Climate Change Research     Open Access   (Followers: 6)
Advances in Meteorology     Open Access   (Followers: 18)
Advances in Statistical Climatology, Meteorology and Oceanography     Open Access   (Followers: 1)
Aeolian Research     Hybrid Journal   (Followers: 5)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 13)
American Journal of Climate Change     Open Access   (Followers: 12)
Atmósfera     Open Access   (Followers: 1)
Atmosphere     Open Access   (Followers: 20)
Atmosphere-Ocean     Full-text available via subscription   (Followers: 12)
Atmospheric Chemistry and Physics (ACP)     Open Access   (Followers: 27)
Atmospheric Chemistry and Physics Discussions (ACPD)     Open Access   (Followers: 8)
Atmospheric Research     Hybrid Journal   (Followers: 47)
Atmospheric Science Letters     Open Access   (Followers: 23)
Boundary-Layer Meteorology     Hybrid Journal   (Followers: 21)
Bulletin of the American Meteorological Society     Open Access   (Followers: 31)
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   (Followers: 2)
Climate Dynamics     Hybrid Journal   (Followers: 27)
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: 5)
Climate Risk Management     Open Access  
Climate Services     Open Access  
Climate Summary of South Africa     Full-text available via subscription  
Climatic Change     Hybrid Journal   (Followers: 51)
Current Climate Change Reports     Hybrid Journal   (Followers: 1)
Developments in Atmospheric Science     Full-text available via subscription   (Followers: 10)
Dynamics and Statistics of the Climate System     Open Access   (Followers: 1)
Dynamics of Atmospheres and Oceans     Hybrid Journal   (Followers: 10)
Earth Perspectives - Transdisciplinarity Enabled     Open Access  
Energy & Environment     Full-text available via subscription   (Followers: 16)
Environmental and Climate Technologies     Open Access   (Followers: 3)
Global Meteorology     Open Access   (Followers: 6)
International Journal of Atmospheric Sciences     Open Access   (Followers: 9)
International Journal of Biometeorology     Hybrid Journal   (Followers: 1)
International Journal of Climate Change Strategies and Management     Hybrid Journal   (Followers: 12)
International Journal of Climatology     Hybrid Journal   (Followers: 23)
International Journal of Image and Data Fusion     Hybrid Journal   (Followers: 1)
Journal of Applied Meteorology and Climatology     Full-text available via subscription   (Followers: 26)
Journal of Atmospheric and Oceanic Technology     Full-text available via subscription   (Followers: 28)
Journal of Atmospheric and Solar-Terrestrial Physics     Hybrid Journal   (Followers: 52)
Journal of Atmospheric Chemistry     Hybrid Journal   (Followers: 8)
Journal of Climate     Full-text available via subscription   (Followers: 38)
Journal of Hydrology and Meteorology     Open Access   (Followers: 13)
Journal of Hydrometeorology     Full-text available via subscription   (Followers: 5)
Journal of Integrative Environmental Sciences     Hybrid Journal   (Followers: 4)
Journal of Meteorology and Climate Science     Full-text available via subscription   (Followers: 7)
Journal of Space Weather and Space Climate     Open Access   (Followers: 10)
Journal of the Atmospheric Sciences     Full-text available via subscription   (Followers: 52)
Journal of the Meteorological Society of Japan     Partially Free   (Followers: 1)
Journal of Weather Modification     Full-text available via subscription  
Large Marine Ecosystems     Full-text available via subscription  
Mathematics of Climate and Weather Forecasting     Open Access   (Followers: 4)
Mediterranean Marine Science     Open Access  
Meteorologica     Open Access   (Followers: 1)
Meteorological Applications     Hybrid Journal   (Followers: 4)
Meteorologische Zeitschrift     Full-text available via subscription   (Followers: 2)
Meteorology and Atmospheric Physics     Hybrid Journal   (Followers: 16)
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: 25)
Nature Climate Change     Full-text available via subscription   (Followers: 57)
Nature Reports Climate Change     Full-text available via subscription   (Followers: 23)
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: 3)
Space Weather     Full-text available via subscription   (Followers: 8)
Studia Geophysica et Geodaetica     Hybrid Journal   (Followers: 1)
Tellus A     Open Access   (Followers: 11)
Tellus B     Open Access   (Followers: 10)
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: 21)
Theoretical and Applied Climatology     Hybrid Journal   (Followers: 5)
Weather     Hybrid Journal   (Followers: 11)
Weather and Climate Extremes     Open Access   (Followers: 7)
Weather and Forecasting     Full-text available via subscription   (Followers: 15)
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]   [52 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1364-6826
   Published by Elsevier Homepage  [2969 journals]
  • Long-Term Variations of Noctilucent Clouds at ALOMAR
    • Abstract: Publication date: Available online 20 August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Jens Fiedler, Gerd Baumgarten, Uwe Berger, Franz-Josef Lübken
      Noctilucent clouds (NLC) are measured by the Rayleigh/Mie/Raman-lidar at the ALOMAR research facility in Northern Norway (69°N, 16°E) since 1994. The data set contains about 2860 hours of NLC detections and is investigated for the first time regarding trends. NLC properties depend on cloud brightness which is taken into account by the use of several cloud classes, related to brightness ranges. For NLC brighter than the long-term detection limit and strong NLC, respectively, the trend terms show increasing occurrence frequency (+9%/dec, +5%/dec) and brightness (+1.7×10−10/dec, +1.5×−10/dec) from 1998–2015. In the same period the altitude of faint and long-term limit clouds decreases (−66m/dec and −108m/dec). Over the entire time period of 22 years strong clouds show an increasing altitude by +76m/dec. NLC properties are affected differently by solar and atmospheric parameters. In general, Lyman-α and stratospheric ozone impact all three NLC parameters, temperature at 83km impacts mainly the NLC altitude. Time series of RMR lidar and SBUV satellite instruments match best for NLC occurrence frequency and brightness when restricting SBUV to the morning data at longitudes around ALOMAR (64°N–74°N,8°E–24°E/0–9LT). This suggests longitudinal dependent trends, which is confirmed by trend investigations of longitudinal subsets of the SBUV data set.


      PubDate: 2016-08-23T12:45:10Z
       
  • Formationof the small-scale structure of auroral electron precipitations
    • Abstract: Publication date: Available online 20 August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): A.P. Kropotkin
      This paper is aimed at physical causes of the small-scale transverse structure in the flows of auroral electrons, generating the corresponding small-scale structure of discrete auroras. The parallel electric field existing in the lower part of the auroral magnetosphere, in the auroral cavity region, in the presence of a strong upward field-aligned current, accelerates magnetospheric electrons to energies of ∼ 1 − 10 keV. The flow of these particles while maintaining the high density of the field-aligned current, produces a current-driven instability, which generates Alfvénic turbulence at short perpendicular wavelengths ≤ 1 km. These short-wavelength inertial Alfvén disturbances possess a nonzero parallell electric field, which modulates the electron flow velocity. The modulation occurring at high altitudes ≥ 10 4 km leads to a nonlinear effect of formation of strong density peaks at low altitudes of electron precipitation. The transverse, horizontal scales of the corresponding electron flow structure coincide with the small scales of the Alfvénic turbulence; and this structuring leads to non-uniformities in the auroral luminosity on the same scales, i.e., to small-scale structure of discrete auroras.


      PubDate: 2016-08-23T12:45:10Z
       
  • Hurricanes in the Gulf of Mexico and the Caribbean Sea and their
           Relationship with Sunspots
    • Abstract: Publication date: Available online 20 August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Berenice Rojo-Garibaldi, David Alberto Salas-de-León, Norma Leticia Sánchez-Santillan, María Adela Monreal-Gómez
      We present the results of a time series analysis of hurricanes and sunspots occurring from 1749 to 2010. Exploratory analysis shows that the total number of hurricanes is declining. This decline is related to an increase in sunspot activity. Spectral analysis shows a relationship between hurricane oscillation periods and sunspot activity. Several sunspot cycles were identified from the time series analysis.


      PubDate: 2016-08-23T12:45:10Z
       
  • Scattering of Relativistic and Ultra-relativistic Electrons by Obliquely
           Propagating Electromagnetic Ion Cyclotron Waves
    • Abstract: Publication date: Available online 12 August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Bogdan Uzbekov, Yuri Y. Shprits, Ksenia Orlova
      Electromagnetic Ion Cyclotron (EMIC) waves are transverse plasma waves that are generated in the Earth magnetosphere by ring current protons with temperature anisotropy in three different bands: below the H + , He + and O + ion gyrofrequencies. EMIC events are enhanced during the main phase of a geomagnetic storm when intensifications in the electric field result in enhanced injections of ions and are usually confined to high-density regions just inside the plasmapause or within drainage plumes. EMIC waves are capable of scattering radiation belt electrons and thus provide an important link between the intensification of the electric field, ion populations, and radiation belt electrons. Bounce-averaged diffusion coefficients computed with the assumption of parallel wave propagation are compared to the results of the code that uses the full cold plasma dispersion relation taking into account oblique propagation of waves and higher-order resonances. We study the sensitivity of the scattering rates to a number of included higher-order resonances, wave spectral distribution parameters, wave normal angle distribution parameters, ambient plasma density, and ion composition. Inaccuracies associated with the neglect of higher-order resonances and oblique propagation of waves are compared to potential errors introduced by uncertainties in the model input parameters.


      PubDate: 2016-08-17T12:29:04Z
       
  • Fluorescence caused by ionizing radiation from ball lightning: observation
           and quantitative analysis
    • Abstract: Publication date: Available online 16 August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Karl D. Stephan, Rozlyn Krajcik, Rolf J. Martin
      Ball lightning is a rare phenomenon, typically appearing as a glowing sphere associated with thunderstorms. In 2008 one of the authors witnessed a blue ball-lightning object hover in front of a glass window that appeared to glow yellow. Calibrated quantitative fluorometry measurements of the window show that the glow was probably due to fluorescence caused by ionizing radiation (UV or possibly X rays). Based on the measurements performed, estimates of the total ionizing-radiation power emitted by the object range upward from about 10W. These are among the most reliable semi-quantitative measurements so far of ionizing-radiation output from a ball-lightning object.
      Graphical abstract image

      PubDate: 2016-08-17T12:29:04Z
       
  • IFC-Ed. board
    • Abstract: Publication date: September 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 147




      PubDate: 2016-08-17T12:29:04Z
       
  • foF2 vs Solar Indices for the Rome station: looking for the best general
           relation which is able to describe the anomalous minimum between cycles 23
           and 24
    • Abstract: Publication date: Available online 9 August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): L. Perna, M. Pezzopane
      Analysesof the dependence of the F2layer critical frequency, foF2,on five widely used solar activity indices (F10.7,Lym–α, MgII, R and EUV0.1–50)are carried out considering noon values manually validated at the ionospheric station of Rome (41.8°N, 12.5°E,Italy) between January 1976and December 2013,a period of time covering the last three solar cycles and including the prolonged and anomalous minimum of solar cycle 23/24(years 2008–2009).After applying a 1–yearrunning mean to both foF2 and solar activity indices time series, a second order polynomial fitting proves to perform better than a linear one, and this is specifically due to the very low solar activity of the last solar minimum and to the remaining saturation effect characterizing the high solar activity. A comparison between observed and synthetic foF2 values, the latter calculated by using the analytical relations found for every index, and some considerations made on the R parameter introduced by Solomon et al. (2013), suggest that MgII is the best index to describe the dependence of foF2 on the solar activity. Three main reasons justify this result: (1) the good sensibility of MgII to the variations of foF2 for low solar activity; (2) the reduced saturation effect characterizing MgII at high solar activity; (3) the poor influence of the hysteresis effect characterizing MgII at medium solar activity. On the other hand, the F 10.7 index, widely used as input parameter for numerous ionospheric models, does not represent properly the last minimum; specifically, it is not able to describe the variations of foF2 under a solar activity level of F 10.7 = 82·10–22 [J Hz–1 s–1 m–2].


      PubDate: 2016-08-12T12:20:19Z
       
  • Relevance of long term time – series of atmospheric parameters at a
           mountain observatory to models for climate change
    • Abstract: Publication date: Available online 5 August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): M. Kancírová, K. Kudela, A.D. Erlykin, A.W. Wolfendale
      A detailed analysis has been made based on annual meteorological and cosmic ray data from the Lomnicky stit mountain observatory (LS, 2634 masl; 49.40°N, 20.22°E; vertical cut-off rigidity 3.85GV), from the standpoint of looking for possible solar cycle (including cosmic ray) manifestations. A comparison of the mountain data with the Global average for the cloud cover in general shows no correlation but there is a possible small correlation for low clouds (LCC in the Global satellite data). However, whereas it cannot be claimed that cloud cover observed at Lomnicky stit (LSCC) can be used directly as a proxy for the Global LCC, its examination has value because it is an independent estimate of cloud cover and one that has a different altitude weighting to that adopted in the satellite-derived LCC. This statement is derived from satellite data (http://isccp.giss.nasa.gov/climanal7.html) which shows the time series for the period 1983 to 2010 for 9 cloud regimes. There is a significant correlation only between cosmic ray (CR) intensity (and sunspot number (SSN)) and the cloud cover of the types cirrus and stratus. This effect is mainly confined to the CR intensity minimum during the epoch around 1990, when the SSN was at its maximum. This fact, together with the present study of the correlation of LSCC with our measured CR intensity, shows that there is no firm evidence for a significant contribution of CR induced ionization to the local (or, indeed, Global) cloud cover. Pressure effects are the preferred cause of the cloud cover changes. A consequence is that there is no evidence favouring a contribution of CR to the Global Warming problem. Our analysis shows that the LS data are consistent with the Gas Laws for a stable mass of atmosphere.


      PubDate: 2016-08-07T11:59:25Z
       
  • Long-term (2004-2015) tendencies and variabilities of tropical UTLS water
           vapour mixing ratio and temperature observed by AURA/MLS using
           multivariate regression analysis
    • Abstract: Publication date: Available online 2 August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): S. Sridharan, M. Sandhya
      Long-termvariabilities and tendencies in the tropical (30°N-30°S)monthly averaged zonal mean upper troposphere and lower stratosphere (UTLS) water vapour mixing ratio (WVMR) and temperature, obtained from the Microwave Limb Sounder (MLS) instrument onboard Earth Observing System (EOS) satellite for the period October 2004-September 2015,are studied using multivariate regression analysis. It is found that the WVMR shows a decreasing trend of 0.02-0.1ppmv/year in WVMR below 100hPa while the trend is positive (0.02-0.035ppmv/year) above 100hPa. There is no significant trend at 121hPa. The WVMR response to solar cycle (SC) is negative below 21hPa. However, the magnitude decreases with height from 0.13ppmv/100sfu(solar flux unit) at 178hPa to 0.07ppmv/100sfuat 26hPa. The response of WVMR to multivariate El Niño index (MEI), which is a proxy for El Niño Southern Oscillation (ENSO), is positive at and below 100hPa and negative above 100hPa. It is negative at 56-46hPa with maximum value of 0.1ppmv/MEI at 56hPa. Large positive (negative) quasi-biennial oscillation (QBO) in WVMR at 56-68hPa reconstructed from the regression analysis coincide with eastward (westward) to westward (eastward) transition of QBO winds at that level. The trend in zonal mean tropical temperature is negative above 56hPa with magnitude increasing with height. The maximum negative trend of 0.05K/yearis observed at 21-17hPa and the trend insignificant around tropopause. The response of temperature to SC is negative in the UTLS region and to ENSO is positive below 100hPa and mostly negative above 100hPa. The negative response of WVMR to MEI in the stratosphere is suggested to be due to the extended cold trap of tropopause temperature during El Niño years that might have controlled the water vapour entry into the stratosphere. The WVMR response to residual vertical velocity at 70hPa is positive in the stratosphere, whereas the temperature response is positive in the UTLS region and negative above 56hPa. Besides, the interannual variability and the response of the WVMR to the different parameters are explained based on the response of temperature at 100hPa (proxy for tropopause) to those parameters.


      PubDate: 2016-08-03T11:52:39Z
       
  • A satellite rainfall retrieval technique over northern Algeria based on
           the probability of rainfall intensities classification from MSG-SEVIRI
    • Abstract: Publication date: Available online 28 July 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Mourad Lazri, Soltane Ameur
      In this paper, an algorithm based on the probability of rainfall intensities classification for rainfall estimation from Meteosat Second Generation/Spinning Enhanced Visible and Infrared Imager (MSG-SEVIRI) has been developed. The classification scheme uses various spectral parameters of SEVIRI that provide information about cloud top temperature and optical and microphysical cloud properties. The presented method is developed and trained for the north of Algeria. The calibration of the method is carried out using as a reference rain classification fields derived from radar for rainy season from November 2006 to March 2007. Rainfall rates are assigned to rain areas previously identified and classified according to the precipitation formation processes. The comparisons between satellite-derived precipitation estimates and validation data show that the developed scheme performs reasonably well. Indeed, the correlation coefficient presents a significant level (r:0.87). The values of POD, POFD and FAR are 80%, 13% and 25%, respectively. Also, for a rainfall estimation of about 614mm, the RMSD, Bias, MAD and PD indicate 102.06(mm), 2.18(mm), 68.07(mm) and 12.58, respectively.


      PubDate: 2016-08-03T11:52:39Z
       
  • Unusual noon-time bite-outs in the ionospheric electron density around the
           anomaly crest locations over the Indian and Brazilian sectors during quiet
           conditions - a case study
    • Abstract: Publication date: Available online 1 August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): K. Venkatesh, P.R. Fagundes, A.J. de Abreu, V.G. Pillat
      The present case study reports the unusual noon-time electron density bite-out events during 12th to 18th April, 2004 around the anomaly crest locations which are not observed over the geomagnetic equator. These bite-out events at the crest locations occurred on three consecutive days under solar and geomagnetically quiet conditions over the Indian and Brazilian sectors. The bite-out events are observed with a delay of two days over the Brazilian sector when compared with those in the Indian sector. The duration of these TEC bite-outs is found to vary around 5hours in the Indian sector while it is around 3 hours in the Brazilian sector. Over Raipur in the Indian sector, the bite-out is found to be very strong (~30 TECU) on 13th April, 2004, where the TEC drops to nearly 50% of the corresponding day maximum TEC. The diurnal variations of dTEC have also shown significant differences during the occurrence of noon-time TEC bite-outs. Simultaneous Equatorial Electrojet (EEJ) variations over the Indian and Brazilian sectors have also been studied. The ionosonde data over the equatorial and anomaly crest locations has been analyzed to understand the F-layer behavior during the occurrence of TEC bite-outs. Significant drop in the F-layer peak density and heights are observed during the TEC bite-outs while the minimum height of the bottom side F-layer do not show considerable differences. Further, the variations of vertical electron density profiles are studied to explain the F-layer characteristics that resulted in the noon-time bite-outs over the anomaly crest locations.


      PubDate: 2016-08-03T11:52:39Z
       
  • Simulations of airglow variations induced by the CO2 Increase and solar
           cycle variation from 1980 to 1991
    • Abstract: Publication date: Available online 28 July 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Tai-Yin Huang
      Airglow intensity and Volume Emission Rate (VER) variations induced by the increase of CO2 gas concentration and F10.7variation (used as a proxy for the 11-yearsolar cycle variation) were investigated for the period of 1980to 1991,encompassing a full solar cycle. Two airglow models are used to simulate the induced variations of O(1S)greenline, O2(0,1)atmospheric band , and OH(8,3)airglow for this study. The results show that both the airglow intensities and peak VERs correlate positively with the F10.7solar cycle variation and display a small linear trend due to the increase of CO2gas concentration. The solar-cycle induced airglow intensity variations show that O(1S)greenline has the largest variation (~26%)followed by the O2(0,1)atmospheric band (~23%)and then OH(8,3)airglow (~8%)over the 11year timespan. The magnitudes of the induced airglow intensity variations by the increase of CO2gas concentration are about an order of magnitude smaller than those by the F10.7solar cycle variation. In general, the F10.7solar cycle variation and CO2increase do not seem to systematically alter the VER peak altitude of the airglow emissions, though the OH(8,3)VER peak altitude moves up slightly during the years when the F10.7value falls under 100SFU.


      PubDate: 2016-08-03T11:52:39Z
       
  • Similarity analysis of the streamer zone of blue jets
    • Abstract: Publication date: Available online 5 July 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): N.A. Popov, M.N. Shneider, G.M. Milikh
      Multiple observations of Blue Jets (BJ) and Gigantic Blue Jets (GBJ) show that BJ and GBJ emits a fan of streamers similar to a laboratory leader. Moreover, in the exponential atmosphere those long streamers grow preferentially upward, producing a narrow cone confined by the aperture angle. It was also noticed that BJ are similar to the streamer zone of a leader (streamer corona) and the modeling studies based on the streamers fractal structure were conducted. Objective of this paper is to study the fractal dimension of the bunch of streamer channels emitted by BJ and GBJ, at different altitude and under the varying electric field. This similarity analysis has been done in three steps: First we described the dendritic structure of streamers in corona discharge applying the fractal theory. Then using this model and the data from existing laboratory experiments we obtained the fractal dimension of the branching streamer channels. Finally the model was validated by the observations of BJ available from the literature.


      PubDate: 2016-07-24T11:30:15Z
       
  • 3D model of small-scale density cavities in the auroral magnetosphere with
           field-aligned current
    • Abstract: Publication date: Available online 15 July 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): P.A. Bespalov, V.G. Misonova, O.N. Savina
      We propose a 3D model of small-scale density cavities stimulated by an auroral field-aligned current and an oscillating field-aligned current of kinetic Alfvén waves. It is shown that when the field-aligned current increases so that the electron drift velocity exceeds a value of the order of the electron thermal velocity, the plasma becomes unstable to the formation of cavities with low density and strong electric field. The condition of instability is associated with the value of the background magnetic field. In the case of a relatively weak magnetic field (where the electron gyro-radius is greater than the ion acoustic wavelength), the current instability can lead to the formation of one-dimensional cavities along the magnetic field. In the case of a stronger magnetic field (where the ion acoustic wavelength is greater than the electron gyro-radius, but still is less than the ion gyro-radius), the instability can lead to the formation of 3D density cavities. In this case, the spatial scales of the cavity, both along and across the background magnetic field, can be comparable, and at the earlier stage of the cavity formation they are of the order of the ion acoustic wavelength. Rarefactions of the cavity density are accompanied by an increase in the electric field and are limited by the pressure of bipolar electric fields that occur within them. The estimates of typical density cavity characteristics and the results of numerical solutions agree with known experimental data: small-scale structures with a sufficiently strong electric field are observed in the auroral regions with strong field-aligned current.


      PubDate: 2016-07-24T11:30:15Z
       
  • Testing the interactive computer method (IM) for producing K indices with
           the data of the Hurbanovo and Budkov magnetic observatories
    • Abstract: Publication date: Available online 18 July 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Fridrich Valach, Pavel Hejda, Miloš Revallo, Josef Bochníček, Magdaléna Váczyová
      It is generally accepted that the geomagnetic K indices derived by experienced observers are of great value. The interactive method (IM) based on the traditional hand-scaling methodology is tested in this study. The tests are performed utilising the data from the Hurbanovo and Budkov magnetic observatories. These data include both digital records of the geomagnetic field and hand-scaled K indices that had been derived by experienced observers. The authentic K indices from Hurbanovo cover the year 1997 and the same kind of data from Budkov cover the years 1994–1999. In addition to these data, hand-scaled K indices are used which were derived by the experienced observer from printed digital magnetograms for both of the observatories for the years 2000-2003. The results of this study indicate that for high values of K indices (the values being at least 5) the tested method follows the traditional hand-scaling better than the widely used computer methods FMI and AS. On the other hand, for the K indices less than 5 the tested method turns out to be the worst when compared with the FMI and AS methods. For very low geomagnetic activity (K-index values equal to 0) the performance of the tested method is comparable to the two computer methods.


      PubDate: 2016-07-24T11:30:15Z
       
  • Editor’s Note
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146




      PubDate: 2016-07-24T11:30:15Z
       
  • Editor's note
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146




      PubDate: 2016-07-24T11:30:15Z
       
  • On the seasonal variability of raindrop size distribution and associated
           variations in reflectivity - rainrate relations at Tirupati, a tropical
           station
    • Abstract: Publication date: Available online 22 July 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Y. Sulochana, T.N. Rao, K. Sunilkumar, P. Chandrika, M.Roja Raman, S.V.B. Rao
      Three years of continuous OTT Parsivel disdrometer measurements made at Tirupati (13.6°N, 79.4°E), a tropical station near the foothills of Nallamala mountains, have been used to examine the climatological seasonal differences in bulk rainfall parameters, gamma parameters, raindrop size distributions (DSDs) and reflectivity - rainfall (Z-R) relationships. These relations are derived for both stratiform and convective rain during southwest and northeast monsoon (SWM and NEM) seasons, the two primary rainfall seasons for this region. The probability distribution functions for bulk rainfall and gamma parameters during the SWM and NEM suggest the dominance of evaporation and drop sorting during the SWM. The seasonal variations are also clearly apparent in DSD with fewer big drops and more small drops during the NEM than in SWM. These differences are seen more prominantely at smaller R. As a result, the retrieved Z-R relations are found to be distinctly different during the monsoon seasons. The seasonal variations in Z-R relations are not only observed for the total data but also for the rain type-segregated data. The prefactor of the Z-R relation is found to be larger for SWM and also for stratiform rain, consistent with earlier reports from southeast India, indicating that these features are robust and representative of southeast India. The observed differences in Z-R relations are discussed in the light of microphysical differences between the seasons and rain types.


      PubDate: 2016-07-24T11:30:15Z
       
  • IFC-Ed. board
    • Abstract: Publication date: August 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 146




      PubDate: 2016-07-24T11:30:15Z
       
  • Meteorological factors affecting lower tropospheric ozone mixing ratios in
           Bangkok, Thailand
    • Abstract: Publication date: September 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 147
      Author(s): S. Janjai, S. Buntoung, M. Nunez, K. Chiwpreecha, S. Pattarapanitchai
      This paper examines the influence of meteorological conditions in ozone mixing ratio measured at the Thai Meteorological Department (TMD) in Bangkok, Thailand. In addition to surface wind speed and direction, surface ozone concentrations, ozonesondes and CALIPSO Lidar images were collected during the study period extending from 01/01/2014 to 30/04/2015. Surface ozone concentrations show a strong seasonality, with maximum in the dry months of December to April and minimum during the wet southwest (SW) monsoon period extending from May to October. High ozone concentrations are related to biomass burning in the northeast highland regions of the country and neighboring Myanmar and southern China. These precursors travel in a southerly direction towards Bangkok in a well-defined aerosol layer which may be at ground level or at elevated heights. The growth of the daytime mixed layer scavenges some of the upper level aerosols, although local maxima in ozone concentrations at 1–2km are a frequent feature at Bangkok. There is an evidence of fumigation in the Gulf of Thailand and a return flow via the southerly sea breezes.


      PubDate: 2016-07-24T11:30:15Z
       
  • First observational evidence for the connection between the meteoric
           activity and occurrence of equatorial counter electrojet
    • Abstract: Publication date: September 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 147
      Author(s): C. Vineeth, N. Mridula, P. Muralikrishna, K.K. Kumar, T.K. Pant
      This paper presents the first direct observational evidence for the possible role of meteoric activity in the generation of the equatorial Counter Electrojets (CEJ), an enigmatic daytime electrodynamical process over the geomagnetic equatorial upper atmosphere. The investigation carried out using the data from Proton Precession Magnetometer and Meteor Wind Radar over a geomagnetic dip equatorial station, Trivandrum (8.5°N, 77°E, 0.5°N dip lat.) in India, revealed that the occurrence of the afternoon CEJ events during a month is directly proportional to the average monthly meteor counts over this location. The observation is found to be very consistent during the considered period of study, i.e the years 2006 and 2007. The study vindicates that the meteor showers play a major role in setting up the background condition conducive for the generation of CEJ by reducing the strength of the upward polarization field.


      PubDate: 2016-07-24T11:30:15Z
       
  • Solar irradiance observed at Summit, Greenland: Possible links to magnetic
           activity on short timescales
    • Abstract: Publication date: September 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 147
      Author(s): John E. Frederick
      Measurements of ground-level visible sunlight (400–600nm) from Summit, Greenland over the period August 2004 through October 2014 define the attenuation provided by cloudiness, including its dependence on solar elevation and season. The long-term mean cloud-attenuation increases with increasing solar zenith angle, consistent with radiative transfer calculations which treat a cloud as a plane parallel layer with a strong bias toward forward scattering and an albedo for diffuse radiation near 0.1. The ratio of measured irradiance to clear-sky irradiance for solar zenith angles greater than 66° has a small, but statistically significant, positive correlation with the previous day's magnetic activity as measured by the daily A p index, but no clear relationship exists between the irradiance ratio and daily changes in the ground-level neutron flux measured at Thule over the time frame considered. A high value of A p on one day tends to be followed by a day whose ground-level solar irradiance is slightly greater than would occur otherwise. In an average sense, the visible irradiance following a day with A p>16 exceeds that following a day with A p≤16 by 1.2–1.3% with a 95% confidence range of approximately ±1.0%. The results are broadly compatible with small changes in atmospheric scattering following magnetic disturbances.


      PubDate: 2016-07-24T11:30:15Z
       
  • Thermospheric atomic oxygen concentrations from WINDII O+(2P→2D)
           732nm emission: Comparisons with the NRLMSISE-00 and C-IAM models and with
           GUVI observations
    • Abstract: Publication date: September 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 147
      Author(s): Gordon G. Shepherd, Young-Min Cho, Victor I. Fomichev, Oleg V. Martynenko
      Thermospheric atomic oxygen concentrations have been retrieved from observations by the Wind Imaging Interferometer (WINDII) O+(2P→2D) 732 and 733nm emissions and are compared with results obtained by the Global Ultraviolet Imager (GUVI). Although the observations compared were taken ten years apart, the periods were selected on the basis of solar activity, using the Canadian Ionosphere and Atmosphere Model (C-IAM) to bridge the time gap. Results from all of these were compared with those from the Naval Research Laboratory Mass Spectrometer and Incoherent Scatter (NRLMSISE-00) model. Comparisons were made on the basis of F10.7 solar flux, day of year, local time, season, latitude and longitude. The WINDII local time variations showed enhanced values for the Northern spring season. Latitude and longitude plots showed smooth variations for NRLMSISE-00 and large variations for both WINDII and GUVI observations; in particular a depression in atomic oxygen concentration around 40°S latitude and 100°E longitude that is tentatively identified with a longitudinal wave 1 that does not propagate in local time but has an annual variation. The averaged values showed the WINDII values to be 0.75 that of NRLMSISE-00 compared with 0.80 for GUVI. Thus the WINDII values agreed with those of GUVI to within 6%, although taken 10 years apart.


      PubDate: 2016-07-24T11:30:15Z
       
  • Coordinated study of scintillations recorded by Chinese FY-2 geostationary
           meteorological satellite and VHF coherent radar observations over south
           china
    • Abstract: Publication date: September 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 147
      Author(s): Xiaomin Zuo, Tao Yu, Chunliang Xia, Jiang Huang, Jie Xu
      The first scintillation observations of Chinese FY-2 geostationary meteorological satellite (86.5°E) observed at Guangzhou (23.2°N, 113.3°E, dip 18°N) and simultaneous VHF (47.5MHz) coherent radar measurements from Sanya (18.3°N, 109.6°E, dip 13°N) during equinoctial months of 2011 and 2012 have been presented here. The observations are used for a coordinated study for the relationship between the L-band scintillation patches on the propagation path of FY-2 satellite and the extended 3-m irregularity structures known as plumes over South China. The statistical results showed that the plumes and the scintillation patches have nearly a one-to-one correspondence. In case study, the zonal drift velocity of the irregularities was estimated by comparison of the onset times of the scintillation and plume and the irregularities were found to drift eastwards at a speed ranging about tens of meters to one hundred meters per second. From the derived value of drift speed and duration of scintillation events, the irregularity patches were found to have east-west extent about a few hundred kilometers. On the other hand, the scintillation did not always occur following the appearance of plume which might be due to the associated irregularities occurring at lower altitudes failing to reach the region of the ionosphere through which the satellite to ground link passes. In addition, weak scintillations were observed on FY-2 link without any plume structure on radar backscatter maps occasionally.


      PubDate: 2016-07-24T11:30:15Z
       
  • The investigation of ionospheric response to total eclipses on 29th March,
           2006 and on 20th March, 2015 based on HF oblique sounding data
    • Abstract: Publication date: September 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 147
      Author(s): G.G. Vertogradov, E.G. Vertogradova
      The investigation of ionosphere response to solar eclipses was carried out. Maximum observable frequencies were analyzed during two eclipses on 29th March, 2006 and on 20th March, 2015 on several oblique sounding paths which were within the range of solar flux obscuration. The model describing local changes in the ionosphere, caused by the obscuration of solar flux during eclipse, is suggested. The computer simulation of HF radiowave propagation during the eclipses was carried out on the basis of this model, while quiet ionosphere was described by IRI-2012 model. It is shown that this approach gives adequate description of HF channel during eclipses for all propagation paths under consideration while the parameters of the model were the same for all paths. As the result of computer simulation time delays of ionosperic responses during eclipses were obtained (~1800–2000s). It was found that maximum depletion of electron concentration reached 85% in D-region for both eclipses. The electron density depletions at height of F2-peak were 48% and 34% for eclipse on 29th March, 2006 and on 20th March, 2015 respectively.


      PubDate: 2016-07-24T11:30:15Z
       
  • Solar flare impact on FUV based thermospheric O/N2 estimation
    • Abstract: Publication date: September 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 147
      Author(s): Y. Zhang, L.J. Paxton, H. Kil
      During/after intense solar flares, FUV based thermospheric O/N2 ratio decreases and recovers instantly, indicating that the decrease is not physical. Simulations with an increased solar X-ray (0–10nm) flux and a fixed O and N2 profiles show a significant 135.6nm/LBHS decrease that is sufficient to explain the O/N2 decrease. The false O/N2 decrease is mostly due to increased differences in O2 absorption at 135.6nm and LBHS caused by low-altitude emissions associated with enhanced X-rays. However, the heating from solar flares may cause a weak depletion in O/N2.


      PubDate: 2016-07-24T11:30:15Z
       
  • Solar activity variations of nocturnal thermospheric meridional winds over
           Indian longitude sector
    • Abstract: Publication date: September 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 147
      Author(s): M.K. Madhav Haridas, G. Manju, T. Arunamani
      The night time F-layer base height information from ionosondes located at two equatorial stations Trivandrum (TRV 8.5°N, 77°E) and Sriharikota (SHAR 13.7°N, 80.2°E) spanning over two decades are used to derive the climatology of equatorial nocturnal Thermospheric Meridional Winds (TMWs) prevailing during High Solar Activity (HSA) and Low Solar Activity (LSA) epochs. The important inferences from the analysis are 1) Increase in mean equatorward winds observed during LSA compared to HSA during pre midnight hours; 25m/s for VE (Vernal Equinox) and 20m/s for SS (Summer Solstice), AE (autumnal Equinox) and WS (Winter Solstice). 2) Mean wind response to Solar Flux Unit (SFU) is established quantitatively for all seasons for pre-midnight hours; rate of increase is 0.25m/s/SFU for VE, 0.2m/s/SFU for SS and WS and 0.08m/s/SFU for AE. 3) Theoretical estimates of winds for the two epochs are performed and indicate the role of ion drag forcing as a major factor influencing TMWs. 4) Observed magnitude of winds and rate of flux dependencies are compared to thermospheric wind models. 5) Equinoctial asymmetry in TMWs is observed for HSA at certain times, with more equatorward winds during AE. These observations lend a potential to parameterize the wind components and effectively model the winds, catering to solar activity variations.


      PubDate: 2016-07-24T11:30:15Z
       
  • Nonlinear responses of mesospheric emission layers to wave disturbances
    • Abstract: Publication date: September 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 147
      Author(s): Alexey Belyaev
      Model-based investigations of the wave-induced responses of O(1S), O2(b,0-0) and OH(8-3) emissions have been performed. A series of digital experiments performed using the one-dimensional simulation model proposed by Liu and Swenson (2003) demonstrated that, in addition to the variable component, the wave disturbance of airglow emissions has a constant component. This component is the enhancement/depletion of the background emission intensity of an emission layer. To interpret its appearance, the simplest analytical model of airglow disturbance due to a gravity wave has been constructed. This model indicates that enhancement/depletion of the background emission intensity is a nonlinear airglow response to a wave disturbance. Its magnitude depends quadratically on the wave amplitude and can reach a few dozen percent relative to the value of the zenith brightness of the unperturbed OH(8-3)/O(1S) emission layer.


      PubDate: 2016-07-24T11:30:15Z
       
  • Influence of photochemical processes on traffic-related airborne
           pollutants in urban street canyon
    • Abstract: Publication date: September 2016
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 147
      Author(s): Michal Střižík, Zdeněk Zelinger, Pavel Kubát, Svatopluk Civiš, Iva Bestová, Václav Nevrlý, Petr Kadeřábek, Jan Čadil, Pavel Berger, Alexandr Černý, Pavel Engst
      The urban street canyon of Legerova Street is part of the north-south trunk road that passes through the centre of Prague and remains an unresolved environmental issue for the capital of the Czech Republic. As many as one hundred thousand cars move through this region per day, and mortality has increased as a result of dust, NOx and other exhaust pollutants. The spatial distribution of pollutants (i.e., NO2, NO, and O3) during a day was measured by combined DIAL/SODAR techniques and spot analyzers that were appropriately located near the bottom of the street canyon. The measurements were performed under different meteorological conditions (autumn versus summer period). A purely physical approach does not provide a true description of reality due to photochemical processes that take place in the street canyon atmosphere. Sunlight in the summer triggers the production of ozone and thereby influences the concentration of NO2. The formation of an inverse non-diffuse vertical concentration distribution of NO2 in the morning hours was found to be related to the direct emission of O3 in the street and its background concentration. Rapid changes of NO2 concentrations were observed over time and in the vertical profile. An approach using a photochemical reactor to describe processes in a street canyon atmosphere was developed and verified as a useful tool for prediction purposes.


      PubDate: 2016-07-24T11:30:15Z
       
  • 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
           hemispheres
    • 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
           conditions
    • 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: http://www.izmiran.ru/ionosphere/sm-mit/ 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
       
  • 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
       
  • 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
       
  • 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
       
 
 
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