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  Subjects -> METEOROLOGY (Total: 82 journals)
Acta Meteorologica Sinica     Hybrid Journal   (Followers: 4)
Advances in Atmospheric Sciences     Hybrid Journal   (Followers: 9)
Advances in Climate Change Research     Open Access  
Advances in Meteorology     Open Access   (Followers: 7)
Aeolian Research     Hybrid Journal   (Followers: 3)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 7)
American Journal of Climate Change     Open Access   (Followers: 7)
Asian Journal of Earth Sciences     Open Access   (Followers: 19)
Atmósfera     Open Access  
Atmosphere     Open Access   (Followers: 4)
Atmosphere-Ocean     Full-text available via subscription   (Followers: 7)
Atmospheric Chemistry and Physics (ACP)     Open Access   (Followers: 14)
Atmospheric Chemistry and Physics Discussions (ACPD)     Open Access   (Followers: 8)
Atmospheric Research     Hybrid Journal   (Followers: 21)
Atmospheric Science Letters     Hybrid Journal   (Followers: 9)
Boundary-Layer Meteorology     Hybrid Journal   (Followers: 10)
Bulletin of the American Meteorological Society     Open Access   (Followers: 16)
Carbon Balance and Management     Open Access   (Followers: 5)
Change and Adaptation in Socio-Ecological Systems     Open Access  
Climate     Open Access   (Followers: 2)
Climate Change Economics     Hybrid Journal   (Followers: 16)
Climate Change Responses     Open Access  
Climate Dynamics     Hybrid Journal   (Followers: 15)
Climate law     Hybrid Journal   (Followers: 3)
Climate of the Past (CP)     Open Access   (Followers: 4)
Climate of the Past Discussions (CPD)     Open Access   (Followers: 2)
Climate Policy     Hybrid Journal   (Followers: 21)
Climate Risk Management     Open Access  
Climatic Change     Hybrid Journal   (Followers: 32)
Current Climate Change Reports     Hybrid Journal  
Developments in Atmospheric Science     Full-text available via subscription   (Followers: 5)
Dynamics of Atmospheres and Oceans     Hybrid Journal   (Followers: 3)
Earth Perspectives - Transdisciplinarity Enabled     Open Access   (Followers: 1)
Energy & Environment     Full-text available via subscription   (Followers: 18)
Environmental and Climate Technologies     Open Access   (Followers: 2)
Global Meteorology     Open Access  
International Journal of Atmospheric Sciences     Open Access   (Followers: 4)
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: 15)
International Journal of Image and Data Fusion     Hybrid Journal   (Followers: 1)
Journal of Applied Meteorology and Climatology     Full-text available via subscription   (Followers: 9)
Journal of Atmospheric and Oceanic Technology     Full-text available via subscription   (Followers: 10)
Journal of Atmospheric and Solar-Terrestrial Physics     Hybrid Journal   (Followers: 15)
Journal of Atmospheric Chemistry     Hybrid Journal   (Followers: 2)
Journal of Climate     Full-text available via subscription   (Followers: 29)
Journal of Climatology     Open Access   (Followers: 1)
Journal of Hydrology and Meteorology     Open Access   (Followers: 4)
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: 1)
Journal of Space Weather and Space Climate     Open Access   (Followers: 4)
Journal of the Atmospheric Sciences     Full-text available via subscription   (Followers: 28)
Journal of Weather Modification     Full-text available via subscription  
Large Marine Ecosystems     Full-text available via subscription  
Meteorologica     Open Access  
Meteorological Applications     Hybrid Journal   (Followers: 1)
Meteorologische Zeitschrift     Full-text available via subscription   (Followers: 2)
Meteorology and Atmospheric Physics     Hybrid Journal   (Followers: 5)
Mètode Science Studies Journal : Annual Review     Open Access  
Michigan Journal of Sustainability     Open Access  
Monthly Notices of the Royal Astronomical Society     Hybrid Journal   (Followers: 2)
Monthly Notices of the Royal Astronomical Society Letters     Hybrid Journal   (Followers: 3)
Monthly Weather Review     Full-text available via subscription   (Followers: 14)
Nature Climate Change     Full-text available via subscription   (Followers: 40)
Nature Reports Climate Change     Full-text available via subscription   (Followers: 16)
Open Journal of Modern Hydrology     Open Access   (Followers: 3)
Revista Brasileira de Meteorologia     Open Access   (Followers: 1)
Russian Meteorology and Hydrology     Hybrid Journal   (Followers: 4)
Space Weather     Full-text available via subscription   (Followers: 3)
Studia Geophysica et Geodaetica     Hybrid Journal   (Followers: 2)
Tellus A     Open Access   (Followers: 5)
Tellus B     Open Access   (Followers: 7)
The Cryosphere (TC)     Open Access   (Followers: 2)
The Cryosphere Discussions (TCD)     Open Access   (Followers: 1)
The Quarterly Journal of the Royal Meteorological Society     Hybrid Journal   (Followers: 8)
Theoretical and Applied Climatology     Hybrid Journal   (Followers: 3)
Weather     Hybrid Journal   (Followers: 3)
Weather and Climate Extremes     Open Access   (Followers: 2)
Weather and Forecasting     Full-text available via subscription   (Followers: 3)
Weatherwise     Hybrid Journal  
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]   [15 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1364-6826
   Published by Elsevier Homepage  [2800 journals]
  • Influence of the QBO and solar activity on interannual variability of the
           spring-time transition of stratosphere circulation
    • Abstract: Publication date: Available online 21 August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): E.V. Rakushina, A.Yu. Kanukhina, E.N. Savenkova, A.I. Pogoreltsev
      In this paper the influence of solar activity on variability of the springtime transition dates of stratospheric circulation is investigated. To detect the influence, the springtime transition and solar activity datasets were grouped according to the phases of the Quasi-Biennial Oscillation (QBO). It was obtained that there is a dependence of spring transition dates on solar activity. In case of dividing data on early and later spring transition, the stronger influence of solar signal is revealed at late spring transition. It was also shown that under high solar activity conditions, the relation between spring transition dates and solar activity is stronger than at low one.

      PubDate: 2015-08-24T04:41:46Z
  • Temporal and structural evolution of a tropical monsoon cloud system: A
           case study using X-band radar observations
    • Abstract: Publication date: Available online 22 August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Subrata Kumar Das, Sachin M. Deshpande, Siddarth Shankar Das, Mahen Konwar, Kaustav Chakravarty, Madhu Chandra Reddy Kalapureddy
      A mobile X-band (~9.535GHz) dual-polarization Doppler weather radar system was operated at a tropical site Pune (18.5386°N, 73.8089°E, 582m AMSL) by the Indian Institute of Tropical Meteorology, Pune, India for observing monsoon clouds. The measurement site was on the leeward (eastern) side of the Western Ghats (WG). This study focuses on the horizontal and vertical structure of monsoon precipitating clouds and its temporal evolution as observed by the X-band radar on August 27, 2011. The radar reflectivity factor (Z, dBZ) is used as a proxy for measure of intensity of cloud system. Result shows that the radar reflectivity has a strong temporal variation in the vertical, with a local peak occurring in the afternoon hours. Relatively shallow structure during the late night and early morning hours is noticed. The observed cloud tops were reached up to 8km heights with reflectivity maxima of about 35 dBZ at ∼5km. The spatial and vertical evolution of radar reflectivity is consistent with the large-scale monsoon circulation. The variations in the outgoing longwave radiation (OLR) from the Kalpana-1 satellite and vertical velocity and cloud-mixing ratio from the MERRA reanalysis data are also analyzed. As direct observations of clouds using radars are sparse over the Indian region, the results presented here would be useful to understand the processes related to cloud and precipitation formation in the tropical environment.

      PubDate: 2015-08-24T04:41:46Z
  • Study of fog in Bulgaria by using the GNSS tropospheric products and large
           scale dynamic analysis
    • Abstract: Publication date: Available online 20 August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): A. Stoycheva, G. Guerova
      The fog formation, development, and dissipation are studied by employing the synergy between surface observations and vertically Integrated Water Vapor (IWV) from Global Navigation Satellite Systems (GNSS). Selected are three fog cases in February and November 2012 and the fog development in 4 locations in north Bulgaria is analysed. It is found that the IWV tends to decrease during fog formation, and densification. Increase of IWV leads to fog dispersion and can be a result of evaporation or advection of new humid air mass. The mixing ratio also decreases during the fog formation and increases during dissipation but has a distinct diurnal variability, which limits its short range forecasting potential. IWV is found to have a very high sensitivity to both air mass transformation and/or advection at altitude. In one case it is found that the arrival time of a new air mass at altitude is of key importance for further fog development or suppression. The change of the air mass leads to change of the diurnal cycle of surface parameters like temperature thus controlling the fog life cycle. Further complication of fog diagnosis is introduced by a dynamic component, reflecting the orography difference in west and east part of Bulgaria. The behaviour of the IWV and mixing ratio can be a valuable additional tool in decision making processes for very short range fog diagnosis and prognosis. For monitoring fog life cycle hourly or sub-hourly data-sets will be an advantage.

      PubDate: 2015-08-20T04:25:02Z
  • Bi-decadal solar influence on climate, mediated by near tropopause ozone
    • Abstract: Publication date: Available online 19 August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): N.A. Kilifarska
      The Sun's contribution to climate variations was highly questioned recently. In this paper we show that bi-decadal variability of solar magnetic field, modulating the intensity of galactic cosmic ray (GCR) at the outer boundary of heliosphere, could be easily tracked down to the Earth's surface. The mediator of this influence is the lower stratospheric ozone, while the mechanism of signal translation consists of: (i) GCR impact on the lower stratospheric ozone balance; (ii) modulation of temperature and humidity near the tropopause by the ozone variations; (iii) increase or decrease of the greenhouse effect, depending on the sign of the humidity changes. The efficiency of such a mechanism depends critically on the level of maximum secondary ionisation created by GCR (i.e. the Pfotzer maximum) − determined in turn by heterogeneous Earth's magnetic field. Thus, the positioning of the Pfotzer max in the driest lowermost stratosphere favours autocatalytic ozone production in the extra-tropical Northern Hemisphere (NH), while in the SH − no suitable conditions for activation of this mechanism exist. Consequently, the geomagnetic modulation of precipitating energetic particles – heterogeneously distributed over the globe – is imprinted on the relation between ozone and humidity in the lower stratosphere (LS). The applied test for causality reveals that during the examined period 1957–2012 there are two main centers of action in the winter NH, with tight and almost stationary ozone control on the near tropopause humidity. Being indirectly influenced by the solar protons, the variability of the SH lower stratospheric ozone, however, is much weaker. As a consequence, the causality test detects that the ozone dominates in the interplay with ULTS humidity only in the summer extra-tropics.

      PubDate: 2015-08-20T04:25:02Z
  • Characterization of negative cloud-to-ground lightning in Florida
    • Abstract: Publication date: Available online 20 August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Yanan Zhu, Vladimir A. Rakov, Shreeharsh Mallick, Manh D. Tran
      We examined characteristics of negative cloud-to-ground lightning flashes using their electric field waveforms acquired at the Lightning Observatory in Gainesville (LOG), Florida in the summers of 2013 and 2014. Flash multiplicity, interstroke interval, flash duration, and first to subsequent stroke field peak ratio are determined for 478 flashes containing 2188 strokes and compared with previous results obtained in Florida and in other regions. We found that the average number of strokes per flash is 4.6 and the percentage of single-stroke flash is 12%. The geometric means of interstroke interval, flash duration, and first to subsequent stroke field peak ratio are 52ms, 223ms, and 2.4, respectively. About one-third (34%) of multiple-stroke flashes have at least one subsequent stroke whose field peak is greater than that of the first stroke. The geometric mean of normalized electric field peak shows a relatively weak tendency to decrease with increasing stroke order. We also found that the detectability of preliminary breakdown (PB) pulse train is affected by the signal/noise ratio, type of storm, peak current and distance. For 222 PB pulse trains, statistics on pulse duration, time interval between PB pulse train and return stroke (PB-RS interval), and PB to RS field peak ratio (PB/RS ratio) are presented. Very short PB-RS (≤6ms) intervals were observed to be associated with very high return-stroke peak currents and stepped-leader speeds.

      PubDate: 2015-08-20T04:25:02Z
  • Origin of high-frequency TEC disturbances observed by GPS over the
           European mid-latitude region
    • Abstract: Publication date: Available online 12 August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Gilles Wautelet, Rene Warnant
      High-frequency variability of the ionospheric Total Electron Content (TEC) can strongly affect precise positioning with GNSS. The occurrence rate as well as the amplitude of such disturbances have been extensively studied over the last decade. Mainly, one can distinguish disturbances due to space-weather events and the others, qualified as “quiet-time” as they are observed during quiet geomagnetic conditions. The latter, which represent more than 75% of the total number of disturbances over mid-latitudes, are then divided into two categories: the Winter Daytime (WD) and the Summer Nighttime (SN). The first category, representing the bulk of quiet-time disturbances, corresponds to classical Medium-Scale Traveling Ionospheric Disturbances (MSTIDs), that are the result of the interaction of gravity waves and the ionospheric plasma. On the other hand, SN disturbances are generally understood as non-classical MSTIDs of electrical origin. The paper investigates the origin of these two types of disturbance based on GPS measurements, ionospheric soundings and wind speed data at tropospheric level. If one cannot exclude the solar terminator as a potential source of gravity waves responsible for WD events, it is thought that the major contribution comes from the lower atmosphere. More precisely, tropospheric jetstream is considered as the favorite candidate for daytime MSTIDs. Turning to SN disturbances, our analysis reveals that they are related to spread-F phenomenon, linked to the appearance of sporadic E-layers. The related instabilities are responsible for field-aligned irregularities in the F-region, which are thought to be responsible for noise-like fluctuations of the GPS TEC observed during SN events.

      PubDate: 2015-08-16T04:21:25Z
  • Lightning-induced voltages caused by lighting strike to tall Objects
           considering the effect of frequency dependent soil
    • Abstract: Publication date: Available online 14 August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Qilin Zhang, Yuan Chen, Wenhao Hou
      In this paper we have analyzed the effect of frequency dependent soil (FDS) on the lightning-induced voltages caused by lightning subsequent return stroke for strike to tall objects ranging from 100m to 300m. It is found that the effect of FDS on the induced voltages peak can be approximately ignored when the low frequency conductivity (LFC) is equal to or larger than 0.01S/m, and with the decrease of LFC, the effect of FDS on the lightning induced voltages is more obvious. Compared with the constant LFC, the induced voltage peak becomes less for FDS. For example, for a constant LFC of 0.001S/m, the ratio of the induced voltages peak value for FDS to that for LFC is 83.2% at the line center and 66.8% at the line end for strike to 300-m-tall object, respectively. By using the decomposition method, we divide the lightning induced voltages into two components named by the incident induced waves (Vi) related with the vertical field and scattered induced waves (Vs) related with horizontal field, and it is found that FDS results into a less initial peak of tangential horizontal field along the overhead line and further results into a less induced voltage. Also, compared FDS with LFC, the FDS reduces the disparity of lightning induced voltages caused by different tall objects. For example, for the constant LFC, the induced voltage peak for strike to 300-m-tall object is 1.69 times larger than that for strike to 50-m-tall object. However, for the case of FDS, the corresponding ratio is about 1.2.

      PubDate: 2015-08-16T04:21:25Z
  • Wave like signatures in aerosol optical depth and associated radiative
           impacts over the central Himalayan region
    • Abstract: Publication date: Available online 3 August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): K.K. Shukla, D.V. Phanikumar, K. Niranjan Kumar, Kishore Reddy, V.R. Kotamarthi, Rob K Newsom, Taha B.M.J Ouarda
      Doppler Lidar and Multi Filter Rotating Shadow band Radiometer (MFRSR) observations are utilized to show wave like signatures in aerosol optical depth (AOD) during daytime boundary layer evolution over the Himalayan region. Fourier analysis depicted 60-80min periods dominant during afternoon hours, implying that observed modulations could be plausible reason for the AOD forenoon-afternoon asymmetry which was previously reported. Inclusion of wave amplitude in diurnal variation of aerosol radiative forcing estimates showed ~40% additional warming in the atmosphere relative to mean AOD. The present observations emphasize the importance of wave induced variations in AOD and radiation budget over the site.

      PubDate: 2015-08-07T03:24:44Z
  • IFC-Ed. board
    • Abstract: Publication date: September 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 132

      PubDate: 2015-08-03T03:21:35Z
    • Abstract: Publication date: Available online 31 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Marni Pazos, Blanca Mendoza, Luis Gimeno
      Three tropical cyclogenesis precursors, (absolute vorticity, relative humidity, vertical shear)and, the combined Genesis Potential Index are investigated in order to analyse their behaviour during three different phases(descending, minimum and ascending) of the solar cycle. The correlation between these tropical cyclogenesis precursors and the Dst geomagnetic index is also assessed, with the main finding being that the correlations between both the Genesis Potential Index and the vertical shear with the Dst index are statistically significant. This result suggests that the relationship between geomagnetic activity and tropical cyclones might be modulated by the influence of geomagnetic activity on the vertical wind shear.

      PubDate: 2015-08-03T03:21:35Z
  • Refinement of the background ionospheric conditions and plausible
           explanation based on neutral dynamics for the occurrence/non-occurrence of
           L-band scintillation patches against forecast.
    • Abstract: Publication date: Available online 26 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): R. Sridharan, Lijo Jose, Mala S. Bagiya, Surendra Sunda, R.K. Chaudhary, Tarun K. Pant
      The recently evolved L–band scintillation forecast mechanism based on the characteristic features of the daytime F-region electron density fluctuations and also on the basic ionospheric conditions had been successful to a reasonable extent in forecasting the spatio-temporal map of scintillation patches. There had been a few non-compliances in the expected pattern within/outside the forecast windows. The present paper attempts to address such non-compliances and offers a plausible explanation based on neutral dynamics, especially the local time variation of vertical winds over the magnetic equator, while at the same time refining the earlier stipulated background ionospheric conditions. With the above refinements, it is anticipated that the forecast mechanism would become very robust. The present results highlight the importance of the neutral dynamical parameters and the urgent need to concentrate on the efforts to make systematic measurements of the same in order to characterize their variability.

      PubDate: 2015-07-29T21:00:18Z
  • On the variability of the diurnal tide and coupling with planetary waves
           in the MLT over Cachoeira Paulista (22.7°S, 45°W)
    • Abstract: Publication date: Available online 20 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): A. Guharay, P.P. Batista, B.R. Clemesha
      Using meteor radar observations of four years in the mesosphere and lower thermosphere (MLT) over a subtropical Brazilian station, Cachoeira Paulista (22.7°S, 45°W), the temporal variability characteristics of the diurnal tide have been studied. In addition to the semiannual, annual and interannual variations, the diurnal tide amplitude exhibits clear intermittent modulation at periods of planetary waves. The tidal amplitude exhibits clear seasonal pattern with largest amplitude in fall equinox. The dominant periods of modulation of the diurnal tide are found to be greater than 10 days in the MLT. The diurnal tide, as detected in the power spectra of the horizontal winds, shows a spread in period around the central period (24h) which is an indication of nonlinear interactions between the diurnal tide and planetary waves. A bispectral analysis reveals prominent triplets (two primary waves and a secondary wave) confirming the interaction of the diurnal tide with planetary waves persistent over a broad spectral range. Also there is an indication of coupling of the diurnal tide with the intraseasonal oscillations at various times of the year.

      PubDate: 2015-07-21T22:05:34Z
  • Correlation between the sunspot number and tropospheric refractivity in a
           tropical environment
    • Abstract: Publication date: Available online 20 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Najib Yusuf, B.G. Ayantunji
      In this paper, a study of the tropospheric surface refractivity relationship with sunspots number variability on daily scale was carried out in a tropical region in Nigeria. The data was averaged to hourly mean from the initial five minutes update cycle and then to daily mean using spread sheet. The dependence of surface radio refractivity on sunspots number for the period considered in this work was established using linear regression coefficient and the results for Lagos and Anyigba are R2=0.019, R 2=0.004, R2=0.010, R 2=0.000 and R 2=0.000 for 2007, 2008, 2009, 2010 and 2011 and R 2=0.089, R 2=0.027 and R 2=0.007 for 2010, 2011 and 2012 respectively. However, when the spotless days were filtered the regression coefficient was obtained to be R 2=0.145, R 2=0.01261, R 2=0.00001, R 2=0.0012 and R 2=0.062 for 2007, 2008, 2009, 2010 and 2011 for Lagos and R 2=0.1155, R 2=0.0261 and R 2=0.0071 for 2010, 2011 and 2012 for Anyigba respectively. Meteorological data from 2007 to 2011 was employed for Lagos while meteorological data from 2010 to 2012 was employed for Anyigba. Sunspot data was also obtained from Royal Observatory of Belgium for the period under study. Results obtained show no correlation between Sunspot number and surface refractivity. The sunspot number data was filtered to remove noise due to spotless days. The result obtained after filtering did not show any significant difference.

      PubDate: 2015-07-21T22:05:34Z
  • Tropical upper tropospheric ozone enhancements due to potential vorticity
           intrusions over Indian sector
    • Abstract: Publication date: Available online 18 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): M. Sandhya, S. Sridharan, M. Indira Devi, H. Gadhavi
      Influence of potential vorticity (PV) intrusions at 13.5°N over and near Indian sector (50°E- 90°E) on tropical upper tropospheric ozone mixing ratio (OMR) variations is demonstrated based on two case studies. Increase of ECMWF (European Centre for Medium-range Weather Forecasting) reanalysis (ERA)-interim OMR in the upper troposphere (200–500hPa) is observed during the intrusion events consistently in both cases. The OMR also shows similar tongue like structure as PV and it even follows the spatial shift of the PV tongue. In addition, the enhancements in the upper tropospheric OMR during the intrusion events are confirmed using microwave limb sounder (MLS) ozone data at 216hPa. It is suggested that the existence of strong downdrafts, associated with the ageostrophic circulation due to jet stream, which is inferred from longitude-height cross-section of ERA-interim vertical velocity could bring the ozone further down, though high PV tongue remains only at higher level (above 400hPa). The importance of these results lies in demonstrating the role of PV intrusion events on the enhancement of tropical upper tropospheric ozone over Indian sector, where the impact of the PV intrusions is not well understood when compared to that over Pacfic and Atlantic sectors.

      PubDate: 2015-07-21T22:05:34Z
  • Propagation of short period (10-40min) atmospheric gravity waves from
           troposphere to mesosphere over Gadanki, India
    • Abstract: Publication date: Available online 18 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): S.C. Chakravarty, Kamsali. Nagaraja
      The Indian MST radar at Gadanki (13.5°N, 79.2°E) has been utilised to conduct a detailed study of the close coupling between the troposphere and the mesosphere through the vertically propagating atmospheric gravity waves. For this purpose two cases from a special campaign dedicated to the simultaneous measurement of the fluctuations in the UTLS (Upper Troposphere and Lower Stratosphere) and in the mesosphere during 2001 and one case from a follow up observation in 2002 have been investigated. By using both the FFT and wavelet techniques, the near simultaneous tropospheric and mesospheric data of radar return signal strengths and tropospheric wind fields are analysed. The signatures of relatively high frequency gravity waves with periods between ~10-40min have been clearly traced as propagating waves from the tropospheric turbulent layer heights (~8-18km) to the lower mesospheric heights (65-80km). Significant peak correlation coefficients of 0.56 and 0.45 have been found between the SNR time series of pairs of troposphere and mesosphere levels indicating the propagation of high speed gravity waves. The time series of wavelet spectra determined for the tropospheric SNR/zonal winds and the mesospheric SNR show that the detectability of the gravity waves increases at mesospheric heights. It is shown that the continuous SNR values received from the mesosphere can be used as an effective parameter for studies featuring mesospheric wave dynamics. Based on the observed values of vertical wavelengths and wave amplitudes, the horizontal wavelengths, wave phase and group velocities have been estimated for different wave periods. These results have implications on monitoring of the ubiquitous atmospheric gravity waves generated mainly by the tropospheric weather system of the tropical region from their imprint on the mesospheric turbulence structures.

      PubDate: 2015-07-21T22:05:34Z
  • “Characteristics of turbulence in the troposphere and lower
           stratosphere over the Indian Peninsula”
    • Abstract: Publication date: Available online 19 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): S.V. Sunilkumar, M. Muhsin, K. Parameswaran, M. Venkat Ratnam, Geetha Ramkumar, K. Rajeev, B.V. Krishna Murthy, K.V. Sambhu Namboodiri, K.V. Subrahmanyam, K. Kishore Kumar, Siddarth Sankar Das
      Characteristics of turbulence in the troposphere and lower stratosphere at Trivandrum (8.5°N, 76.9°E) and Gadanki (13.5°N, 79.2°E), two tropical stations located in the Indian Peninsula, are studied using GPS-radiosonde observations during the period of December 2010 to March 2014 as part of the Tropical Tropopause Dynamics (TTD) Experiment under the CAWSES-India program. This study relies on the detection of turbulence applying Thorpe analysis to the temperature profile, taking into account the impact of atmospheric moisture and instrumental noise on static stability. In general, the tropospheric turbulence is largely intermittent in space and time. The altitude region very close to the convective tropopause (COT), 10–15km, is relatively more turbulent than the lower troposphere from 3 to 8km. Though the occurrence of turbulence decreases significantly above the COT, occasionally a rather thin layer of turbulence (thickness <1km) is observed in the tropical tropopause layer (TTL) very close to the cold point tropopause (CPT). Even though broad turbulent layers, with thickness >2km, are the persisting features that can be observed in the 5–15km altitude region in multiple observations at both the sites at least during Asian Summer Monsoon (ASM) season, prominent multiple thin layers of stratified turbulence in the lower troposphere lasting for a day or less are observed only at Trivandrum in all seasons. In general, the turbulence strength in the 5–15km altitude region at Gadanki is generally larger than that at Trivandrum. Below 15km, while the turbulence is mainly governed by the convective instability at Gadanki, wind-shear driven (dynamic) instability also contributes considerably for the generation of turbulence at Trivandrum. While the generation of turbulence above 15km is dominated by dynamic instability, in the lower stratosphere (LS) it is mainly due to strong wind shears.

      PubDate: 2015-07-21T22:05:34Z
  • Extreme stratospheric springs and their consequences for the onset of
           polar mesospheric clouds
    • Abstract: Publication date: September 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 132
      Author(s): David E. Siskind, Douglas R. Allen, Cora E. Randall, V. Lynn Harvey, Mark E. Hervig, Jerry Lumpe, Brentha Thurairajah, Scott M. Bailey, James M. Russell
      We use data from the Aeronomy of Ice in the Mesosphere (AIM) explorer and from the NASA Modern Era Retrospective Analysis for Research and Applications (MERRA) stratospheric analysis to explore the variability in the onset of the Northern Hemisphere (NH) Polar Mesospheric Cloud (PMC) season. Consistent with recently published results, we show that the early onset of the NH PMC season in 2013 was accompanied by a warm springtime stratosphere; conversely, we show that the late onset in 2008 coincides with a very cold springtime stratosphere. Similar stratospheric temperature anomalies for 1997 and 2011 also are connected either directly, through observed temperatures, or indirectly, through an early PMC onset, to conditions near the mesopause. These 4 years, 2008, 1997, 2011, and 2013 represent the extremes of stratospheric springtime temperatures seen in the MERRA analysis and correspond to analogous extrema in planetary wave activity. The three years with enhanced planetary wave activity (1997, 2011 and 2013) are shown to coincide with the recently identified stratospheric Frozen In Anticyclone (FrIAC) phenomenon. FrIACs in 1997 and 2013 are associated with early PMC onsets; however, the dramatic FrIAC of 2011 is not. This may be because the 2011 FrIAC occurred too early in the spring. The link between NH PMC onset and stratospheric FrIAC occurrences represents a new mode of coupling between the stratosphere and mesosphere. Since FrIACs appear to be more frequent in recent years, we speculate that as a result, PMCs may occur earlier as well. Finally we compare the zonal mean zonal winds and observed gravity wave activity for the FrIACs of 2011 and 2013. We find no evidence that gravity wave activity was favored in 2013 relative to 2011, thus suggesting that direct forcing by planetary waves was the key mechanism in accelerating the cooling and moistening of the NH mesopause region in May of 2013.

      PubDate: 2015-07-17T21:49:37Z
  • The influence of PMCs on water vapor and drivers behind PMC variability
           from SOFIE observations
    • Abstract: Publication date: Available online 16 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Mark E. Hervig, David E. Siskind, Scott M. Bailey, James M. Russell III
      Observations from the Solar Occultation For Ice Experiment (SOFIE) are used to quantify relationships between polar mesospheric clouds (PMC) and their environment. Dehydration due to ice growth is found to be greatest ∼1.8km above the height of peak ice mass density on average, and H2O enhancement due to sublimation is greatest near the bottom of the PMC layer. The dehydration and hydration layers contain a similar amount of H2O, although less than is found in ice layers, a difference that may be due to meridional transport. Because PMCs modify the surrounding water vapor, PMC-H2O relationships can be misleading and recommendations are made for dealing with this issue. The dependence of PMCs on water vapor and temperature was quantified, accounting for the effects of ice on water vapor. The approach examined inter-annual variations and considered the subset of PMCs detected by the Solar Backscatter Ultraviolet (SBUV) instruments, which are less sensitive than SOFIE. Results in the Northern Hemisphere indicate that PMC variations are dominated by temperature, but that a combination of temperature and water vapor provides the best explanation of the observations. In the Southern Hemisphere PMC variability is attributed primarily to temperature, with water vapor playing a minor role. The subset of SBUV PMCs are found to be one third as sensitive to changing temperature as the entire PMC population observed by SOFIE. Finally, an approach is presented which allows temperature and water vapor anomalies to be estimated from various PMC data sets such as SBUV. Using recently reported SBUV PMC trends at 64–74°N latitude with the results of this study indicates a cooling trend of −0.27±0.14K decade−1 and a water vapor increase of +0.66±0.34% decade−1 (both at 80–84km). This cooling trend agrees with reports based on observations in the middle atmosphere at similar latitudes. The water vapor increase is lower than expected due to increasing methane, although this difference may be consistent with H2O loss due to photolysis at PMC altitudes.

      PubDate: 2015-07-17T21:49:37Z
  • Stratiform/convective rain delineation for TRMM microwave imager
    • Abstract: Publication date: Available online 14 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Tanvir Islam, Prashant K. Srivastava, Qiang Dai, Manika Gupta, Wan Zurina Wan Jaafar
      This article investigates the potential for using machine learning algorithms to delineate stratiform/convective (S/C) rain regimes for passive microwave imager taking calibrated brightness temperatures as only spectral parameters. The algorithms have been implemented for the Tropical Rainfall Measuring Mission (TRMM) microwave imager (TMI), and calibrated as well as validated taking the Precipitation Radar (PR) S/C information as the target class variables. Two different algorithms are particularly explored for the delineation. The first one is metaheuristic adaptive boosting algorithm that includes the real, gentle, and modest versions of the AdaBoost. The second one is the classical linear discriminant analysis that includes the Fisher's and penalized versions of the linear discriminant analysis. Furthermore, prior to the development of the delineation algorithms, a feature selection analysis has been conducted for a total of 85 features, which contains the combinations of brightness temperatures from 10GHz to 85GHz and some derived indexes, such as scattering index, polarization corrected temperature, and polarization difference with the help of mutual information aided minimal redundancy maximal relevance criterion (mRMR). It has been found that the polarization corrected temperature at 85GHz and the features derived from the “addition” operator associated with the 85GHz channels have good statistical dependency to the S/C target class variables. Further, it has been shown how the mRMR feature selection technique helps to reduce the number of features without deteriorating the results when applying through the machine learning algorithms. The proposed scheme is able to delineate the S/C rain regimes with reasonable accuracy. Based on the statistical validation experience from the validation period, the Matthews correlation coefficients are in the range of ~0.60–0.70. Since, the proposed method does not rely on any a priori information, this makes it very suitable to any other microwave sensors having similar channels to the TMI. The method could possibly benefit the constellation sensors in the Global Precipitation Measurement (GPM) mission era.

      PubDate: 2015-07-17T21:49:37Z
  • Comparison of peak height of the F2-layer (hmF2) measurements with
           IRI-2012, IRI-2007 and IRI-2001 models predictions above Roquetes station
           (Spain) during the ascending phase of the solar cycle 24
    • Abstract: Publication date: Available online 10 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Fahmi A. Mohammed
      This research aims to validate IRI-2012 program and examine its accuracy in predicting peak height of the F2- layer (hmF2) above Roquetes. The seasonal hourly means of the ionosphere F2 peak height parameter (hmF2) above Roquetes station, Spain, (located at latitude close to the latitude of Iraq, 41°N) were analyzed and the results were compared with IRI-2012, IRI-2007 and IRI-2001, using CCIR (Comite´ Consultatif International des Radio Communications) option. The analysis covered quiet and disturbed days during various seasons of 2013(the ascending phase of the solar cycle 24). In general, it is found that the predicted values of hmF2 overestimate the observed ones during all seasons, except Summer, whereas it underestimate at day hours. Also, it is found that the maximum percentage relative deviation of hmF2 occurred during Winter at 8LT, while the minimum occurred during Autumnat 22 LT.

      PubDate: 2015-07-13T17:59:33Z
  • Dynamics of vertical ionospheric inhomogeneities over Irkutsk during
           06:00-06:20UT 11/03/2011 caused by Tohoku earthquake
    • Abstract: Publication date: Available online 10 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): O.I. Berngardt , G.V. Kotovich , S.Ya. Mikhailov , A.V. Podlesnyi
      We study dynamics of vertical ionospheric irregularities caused by Tohoku earthquake 11/03/2011 (38.3N, 142.4E) at a distance of 3400km from the epicenter. Equivalent horizontal velocities of propagation in the ionosphere and vertical quasi-wavelength of the wave-like ionospheric irregularities, generated by the earthquake, are calculated. Based on the data of quasi-vertical sounding at Usolie-Tory path (midpoint - 52.3N, 103E, 120km distance), dynamics of vertical mid-scale inhomogeneities of the plasma frequency profile was reconstructed with a fine temporal resolution (60 seconds). As a result of numerical simulation involving the data from TALAYA seismic station (TLY, 51.7N, 103.7E) and comparison with the experiment it is shown that vertical ionospheric irregularities of 5-40km quasi-wavelength observed from 06:00 to 06:20 UT are qualitatively explained by traveling of the acoustic shock wave cone (Mach cone ) from a supersonic ground source - the seismic wave. It is demonstrated that the most likely sources of the shock wave were Z and E components of the seismic oscillations observed at TLY station. Irregularities observed after 06:20UT were apparently linked with other mechanisms. It is found that current temporal resolution of CHIRP ionosonde (60 seconds) and accuracy of the ionogram inversion technique used are not enough for detailed diagnosis of dynamics of the fine spatial vertical structures generated by the earthquake.

      PubDate: 2015-07-13T17:59:33Z
  • Size dependence of ozone lamina characteristics and their correlations
    • Abstract: Publication date: Available online 9 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Peter Krizan , Jan Lastovicka , Michal Kozubek
      Ozone profiles contain narrow layers of substantially enhanced or reduced ozone, called positive and negative laminae, respectively. They reflect both evolutions of stratospheric ozone content and stratospheric dynamics. Here we deal only with positive laminae. The following lamina characteristics are investigated in dependence on lamina size: the number of laminae per profile, the overall ozone amount in laminae per profile and the ozone amount in one lamina at the European ozonosonde stations. An important role of the vertical resolution of ozonesonde measurements is specified. Lamina characteristics for Legionowo and Lindenberg, and small lamina (< 2mPa) characteristics for all stations suffer with effects of vertical resolution of measurements. For this reason they are not used here for long-term trend investigations. The long-term evolution of the ozone amount in one lamina does not display a trend. The results for the three remaining stations, Hohenpeissenberg, Payerne and Uccle, are largely consistent with our previous results on lamina behaviour, which means that our previous results on trends in laminae (e.g., Krizan and Lastovicka, 2005; Lastovicka et al., 2014) are basically correct. The number of laminae per profile and the overall ozone amount in laminae per profile show negative trends before (1979-1995) and rather positive trends after (1996-2011) the reversal of trends in total columnar ozone over Europe. Both parameters reach the highest values for small laminae and with increasing size they decrease. Correlations between characteristics of laminae of different size ranges at individual stations are better for neighbour lamina ranges than for distant lamina ranges. The number of statistically significant correlations of laminae of the same size between pairs of stations is much higher for large laminae above 4mPa, probably due to processes responsible for their formation and their expected larger horizontal size.

      PubDate: 2015-07-13T17:59:33Z
  • Wave-3 and wave-4 patterns in the low- and mid-latitude ionospheric TEC
    • Abstract: Publication date: Available online 6 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Sicheng Wang , Sixun Huang , Hanxian fang
      The JPL global ionospheric maps (GIMs) from January 1, 1999 to December 31, 2013 are analyzed using the space-time spectral analysis method to obtain the tidal patterns in the ionospheric TEC. The results show that noticeable wave-3 and wave-4 signatures can be detected near the crests of equatorial ionospheric anomaly (EIA) regions. Wave-4 structure is comprised predominately by DE3 component, while wave-3 structure is comprised mainly by DE2 component. SPW4 (SPW3) component also accounts for the wave-4 (wave-3) signature. The absolute amplitude of all the aforementioned tidal and SPW signatures shows a saturation effect on the solar activity. The tidal components have significant seasonal variations, with the prominent latitudinal asymmetry. The relative amplitude of zonal mean TEC, however, shows persistent patterns with little solar activity dependence. DE3 is intense in March and September/October, and is weak in northern winter and southern summer. DE2 is strong in the southern hemisphere, and is weak in boreal winter. The amplitude of tide DE3 in TEC is smaller than that of DE2.

      PubDate: 2015-07-09T02:28:34Z
  • Spectral Analysis comparisons of Fourier-Theory-based methods and Minimum
           Variance (Capon) methods
    • Abstract: Publication date: Available online 6 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Marcial Garbanzo-Salas , Wayne. K. Hocking
      In recent years, adaptive (data dependent) methods have been introduced into many areas where Fourier spectral analysis has traditionally been used. Although the data-dependent methods are often advanced as being superior to Fourier methods, they do require some finesse in choosing the order of the relevant filters. In performing comparisons, we have found some concerns about the mappings, particularly when related to cases involving many spectral lines or even continuous spectral signals. Using numerical simulations, several comparisons between Fourier transform procedures and minimum variance method (MVM) have been performed. For multiple frequency signals, the MVM resolves most of the frequency content only for filters that have more degrees of freedom than the number of distinct spectral lines in the signal. In the case of Gaussian spectral approximation, MVM will always underestimate the width, and can misappropriate the location of spectral line in some circumstances. Large filters can be used to improve results with multiple frequency signals, but are computationally inefficient. Significant biases can occur when using MVM to study spectral information or echo power from the atmosphere. Artifacts and artificial narrowing of turbulent layers is one such impact.

      PubDate: 2015-07-09T02:28:34Z
  • The 27-day Rotational Variations in Total Solar Irradiance Observations:
    • Abstract: Publication date: Available online 4 July 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Jae N. Lee , Robert F. Cahalan , Dong L. Wu
      During the last decade, observations from SORCE (Solar Radiation and Climate Experiment)/TIM (Total Irradiance Monitor), ACRIMSAT (Active Cavity Radiometer Irradiance Monitor Satellite)/ACRIM III, and SOHO (SOlar and Heliospheric Observatory)/VIRGO (Variability of IRradiance and Gravity Oscillations Sun PhotoMeter) provided Total Solar Irradiance (TSI) measurements with unprecedented accuracy and stability to determine the amount of solar irradiance reaching the top of the atmosphere and how solar irradiance varies on different time scales. These three independent measurements are analyzed using the EEMD (Ensemble Empirical Mode Decomposition) method to characterize the phase and amplitude of the 27-day solar rotational variation in TSI. The mode decomposition clearly identifies a 27-day solar rotational signature on TSI measurements. The rotational variations of TSI from the three independent observations are generally consistent with each other, despite different mean TSI values. During the declining phase of solar cycle 23, the amplitude of TSI 27-day variations is as high as 0.8W/m2 (~0.05%), while during the rising phase of solar cycle 24, the amplitude is up to 0.4W/m2 (~0.04%). During the minimum phase (2008-2009), the amplitude of the rotational mode is only ~0.1W/m2. The correlation of this rotational mode between TIM and ACRIM III is ~0.92 and the slope of the local peak values is ~0.98. The correlation between TIM and VIRGO is ~0.96 and the slope of the local peak values is ~0.98, very similar to the slope with ACRIM III.

      PubDate: 2015-07-05T02:22:05Z
  • Application of aerosol optical properties to estimate aerosol type from
           ground-based remote sensing observation at urban area of northeastern
    • Abstract: Publication date: Available online 27 June 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Huizheng Che , Hujia Zhao , Yunfei Wu , Xiangao Xia , Jun Zhu , Oleg Dubovik , Victor Estelles , Yanjun Ma , Yangfeng Wang , Hong Wang , Yaqiang Wang , Xiaoye Zhang , Guangyu Shi
      Aerosol optical properties were derived from ground-based sunphotometer observations between 2009-2013 at three urban sites of Shenyang, Anshan, Fushun in northeastern China. The annual means for extinction aerosol optical depths (EAOD) at 500nm were 0.57±0.38, 0.52±0.35, and 0.41±0.31 at Shenyang, Anshan, Fushun, respectively. The corresponding annual means for the extinction Angstrom exponents (EAE) computed for the wavelengths of 440 and 870nm were 0.86±0.32, 0.86±0.34 and 0.91±0.35, respectively, indicating that urban area of Northeast China were affected by both coarse and fine particles. Hygroscopic growth in summer and incursions of dust aerosols in spring were evidently revealed from the analysis of the relationship between EAE and δEAE (the EAE difference, δEAE=EAE(440,670)- EAE(670,870)). The annual mean absorption aerosol optical depths (AAOD440nm) values at Shenyang, Anshan, Fushun were 0.15±0.11, 0.10±0.07, 0.08±0.04, respectively. The annual mean absorption Angstrom exponents (AAE440-870nm) values were 0.86±0.24, 1.19±0.39, 1.33±0.36 at Shenyang, Anshan, Fushun, respectively. When the AAEs were close to unity at Anshan, the absorption aerosol particles evidently consisted of black carbon from coal combustion and motor vehicles. Larger AAEs at Fushun were indicative of absorbing aerosols mainly from biomass burning and mineral dust. The AAE at Shenyang was<1 which may be consistent with black carbon particles with absorbing or non-absorbing coatings. Analysis of the relationship between the AAEs and extinction Angstrom exponents showed that the aerosol populations at these three sites could be classified as “mixed-small particles” including anthropogenic particles and secondary organic aerosol with highly variable sphericity fractions.

      PubDate: 2015-06-30T10:52:34Z
  • Review and Testing Analysis of Moupfouma rain rate Model for Southern
    • Abstract: Publication date: Available online 24 June 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Chandrika P , Vijaya Bhaskara Rao S , Kiran Kumar N.V.P , Narayana Rao T
      Suitability of the analytical model by Moupfouma in modeling the one-minute rain rate distributions at tropical stations of Thiruvananthapuram and Gadanki is studied. The Climatic dependent parameters of the model governing the slope of the one-minute rain rate distributions are acclimatized and validated. The paper also presents rain rate distributions for Thiruvananthapuram and Gadanki. Performance of the model with newly refined climatic dependent parameters is assessed. The Moupfouma model is observed to model the one minute rain rate distributions with a maximum percentage relative error of 14% at 0.001% of time, and with approximately zero relative error at 0.01% of time in an average year. The climatic dependent parameters governing the slope of one-minute rain rate distributions are proposed for Southern India.

      PubDate: 2015-06-25T11:12:12Z
  • Analysis of aerosol scattering properties measured by a nephelometer at a
           coastal-rural site in the Atlantic southwest of the Iberian Peninsula
    • Abstract: Publication date: Available online 24 June 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Juan F. López , Victoria E. Cachorro , Angel M. de Frutos
      Aerosol hemispherical scattering and the backscattering coefficients, σsp, σbsc, have been measured using a 3-wavelength(450, 550 and 700nm) integrating nephelometer over two years (January 2006 to May 2008) in the coastal area of the Gulf of Cádiz, in the southwest of the Iberian Peninsula. These coefficients have been carefully analyzed starting with the impact of corrections on the measurements of σsp: i.e., drift calibration constants do not modify the mean value in our data series. However, the selection of dry data (with RH less than 50%) modifies substantially the number of data and the resulting mean value of σsp is now 14% lower, which is compensated when the angular truncation correction is applied. The characterization and features of σsp, σbsc, and the derived parameters αsp (alpha Ångström exponent) and b (the backscatter ratio) has been analysed, as annual, seasonal and diurnal evolution. A general statistic based on hourly data gives mean values and standard deviation of σsp (500 nm) = 48 ±38Mm−1 with a median of 38 Mm-1, and σbsc(500nm)=5.6±3.8Mm-1 with a median of 4.6 Mm-1. Thus, these values show moderate-low values but with a large range of variation considering the existing measured values over the Iberian Peninsula. The median value of σsp (500nm) is an indicator that events of high aerosol burden are frequent presenting a substantial influence on the daily averages. The alpha Ångström exponent, αsp, derived from the pairs 450/700 nm gives a mean value 1.35±0.54 with a median of 1.47 and with the most frequent value of 1.7, thus indicating the prevalence of medium size particles but with a significant influence of fine particles. The b ratio has the same value for mean and median, 0.12±0.02, showing a decrease with increasing values of σsp. Annual and daily cycles have been also analyzed showing the complex behaviour of the optical properties at this coastal site where cold and warn periods show very different characteristics. Besides, the daily cycle is strongly influenced by the breeze conditions. According to the information extracted from the σsp-αsp relationship this rural Atlantic site presents prevalence of mixed marine-continental aerosols but with significant influence of local anthropogenic sources. Desert dust particles were also discriminated which are not frequently reported in the data of “in situ” aerosols.

      PubDate: 2015-06-25T11:12:12Z
  • IFC-Ed. board
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131

      PubDate: 2015-06-25T11:12:12Z
  • A statistical study of internal gravity wave characteristics using the
           combined Irkutsk incoherent scatter radar and Digisonde data
    • Abstract: Publication date: Available online 24 June 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): A.V. Medvedev , K.G. Ratovsky , M.V. Tolstikov , S.S. Alsatkin , A.A. Shcherbakov
      Using previously developed methods for determining the three-dimensional spatial-temporal structure of traveling ionospheric disturbances and the automatic detection of wave disturbances, we analyzed data obtained simultaneously with the Irkutsk Incoherent Scatter Radar and Irkutsk ionosonde. The analysis relies on long continuous series of observations acquired during winter seasons in 2010–2014. We obtained representative statistics of traveling ionospheric disturbances characteristics including the full velocity vector. We analyzed the characteristics of traveling ionospheric disturbances with 1–6 hour periods comparing them against the dispersion relations for internal gravity waves in the Boussinesq and Hines approximations. It was shown that, with due consideration for the horizontal neutral wind, most of the observed ionospheric disturbances agrees with the laws of internal gravity waves propagation in the upper atmosphere. It was found that azimuthal anisotropy of internal gravity waves characteristics allows us to obtain the diurnal variations of zonal and meridional neutral winds in the upper atmosphere.

      PubDate: 2015-06-25T11:12:12Z
  • Characteristics of second-order residual ionospheric error in GNSS radio
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): Xiaochuan Qu , Zhenghang Li , Jiachun An , Wenwu Ding
      In Global Navigation Satellite Systems (GNSS) radio occultation (RO), one of the most significant error sources is the ionospheric error, which is largely eliminated by dual-frequency linear combination. However, second-order residual ionospheric error (RIE) in excess phase still remains and affects the retrievals of neutral atmospheric parameters in RO. Second-order RIE varies with RO azimuth in a sinusoidal pattern for a set of simulated RO events occurring in the same location at different azimuths. The amplitude of the sinusoidal curve below 60km is at the order of sub-centimeter under moderate solar activity level. The retrieval biases of the neutral atmospheric parameters induced by second-order RIE also have sinusoidal features with RO azimuth, but have opposite variation trends to that of the second-order RIE. The RO azimuths of the maximum positive and negative retrieval biases correspond approximately to the azimuths of maximum negative and positive second-order RIEs, respectively. The order of the maximum bending angle bias induced by the second-order RIE is about 10−8 rad under moderate solar activity level. However, the retrieval errors at low latitude are larger than those at high and middle latitudes, and the maximum temperature bias at low latitude could be 0.35K at 40km. Based on the sinusoidal variation of second-order RIE, it is shown that even at the same RO point and under the same solar activity level, the second-order RIEs at different RO azimuths still have different effects on the retrieval precision of atmospheric parameters. This should be considered carefully when many RO profiles are averaged for climate trend detection, especially at low latitude.

      PubDate: 2015-06-20T13:39:38Z
  • Plasma bubble monitoring by TEC map and 630nm airglow image
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): H. Takahashi , C.M. Wrasse , Y. Otsuka , A. Ivo , V. Gomes , I. Paulino , A.F. Medeiros , C.M. Denardini , N. Sant’Anna , K. Shiokawa
      Equatorial ionosphere plasma bubbles over the South American continent were successfully observed by mapping the total electron content (TECMAP) using data provided by ground-based GNSS receiver networks. The TECMAP could cover almost all of the continent within ~4000km distance in longitude and latitude, monitoring TEC variability continuously with a time resolution of 10min. Simultaneous observations of OI 630nm all-sky image at Cachoeira Paulista (22.7°S, 45.0°W) and Cariri (7.4°S, 36.5°W) were used to compare the bubble structures. The spatial resolution of the TECMAP varied from 50km to 1000km, depending on the density of the observation sites. On the other hand, optical imaging has a spatial resolution better than 15km, depicting the fine structure of the bubbles but covering a limited area (~1600km diameter). TECMAP has an advantage in its spatial coverage and the continuous monitoring (day and night) form. The initial phase of plasma depletion in the post-sunset equatorial ionization anomaly (PS-EIA) trough region, followed by development of plasma bubbles in the crest region, could be monitored in a progressive way over the magnetic equator. In December 2013 to January 2014, periodically spaced bubble structures were frequently observed. The longitudinal spacing between the bubbles was around 600–800km depending on the day. The periodic form of plasma bubbles may suggest a seeding process related to the solar terminator passage in the ionosphere.

      PubDate: 2015-06-20T13:39:38Z
  • Statistical functions and relevant correlation coefficients of clearness
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): Diego Pavanello , Willem Zaaiman , Alessandra Colli , John Heiser , Scott Smith
      This article presents a statistical analysis of the sky conditions, during years from 2010 to 2012, for three different locations: the Joint Research Centre site in Ispra (Italy, European Solar Test Installation – ESTI laboratories), the site of National Renewable Energy Laboratory in Golden (Colorado, USA) and the site of Brookhaven National Laboratories in Upton (New York, USA). The key parameter is the clearness index k T , a dimensionless expression of the global irradiance impinging upon a horizontal surface at a given instant of time. In the first part, the sky conditions are characterized using daily averages, giving a general overview of the three sites. In the second part the analysis is performed using data sets with a short-term resolution of 1 sample per minute, demonstrating remarkable properties of the statistical distributions of the clearness index, reinforced by a proof using fuzzy logic methods. Successively some time-dependent correlations between different meteorological variables are presented in terms of Pearson and Spearman correlation coefficients, and introducing a new one.

      PubDate: 2015-06-20T13:39:38Z
  • Lidar observations of cirrus clouds in Buenos Aires
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): S. Gabriela Lakkis , Mario Lavorato , Pablo Canziani , Hector Lacomi
      Characterization of cirrus clouds over Buenos Aires (34.6°S, 58.5°W) using a ground based lidar is presented. The study, carried out for the period 2010–2011, reveals that cirrus are usually found in the altitude region 8–11km, with mid-cloud temperatures values varying between −75°C and 55°C. The clouds, whose bases altitudes display significant variability while their tops remains close to the tropopause, show geometrical thickness ranging from 1.2 to 5km, with on average value 3.0±0.9km. Most commonly observed cirri can be characterized as optically thin cirrus rather than dense ones, with a mean optical depth value of 0.26±0.11 and an applied multiple scattering factor η of 0.85±0.07. In this region, the optical depth increases with increasing geometrical thickness with a partially linear correlation. Lidar ratios are also analyzed and on average the value is 32±17sr.

      PubDate: 2015-06-20T13:39:38Z
  • Sensitivity of tropical stratospheric ozone to rotational UV variations
           estimated from UARS and Aura MLS observations during the declining phases
           of solar cycles 22 and 23
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): Sébastien Bossay , Slimane Bekki , Marion Marchand , Virginie Poulain , Ralf Toumi
      The correlation between tropical stratospheric ozone and UV radiation on solar rotational time scales is investigated using daily satellite ozone observations and reconstructed solar spectra. We consider two 3-year periods falling within the descending phases of two 11-year solar cycles 22 (1991–1994) and 23 (2004–2007). The UV rotational cycle is highly irregular and even disappears for half a year during cycle 23. For the 1991–1994 period, ozone and 205nm UV flux are found to be correlated between about 10 and 1hPa with a maximum of 0.29 at ~5hPa; ozone sensitivity (percentage change in ozone for 1% change in UV) peaks at ~0.4. Correlation during cycle 23 is weaker with a peak ozone sensitivity of 0.2. The correlation is found to vary widely, not only with altitude, but also from one year to the next with a rotational signal in ozone appearing almost intermittent. Unexpectedly, the correlation is not found to bear any relation with the solar rotational forcing. For instance, solar rotational fluctuations are by far the strongest during 1991–1992 whereas the correlation peaks at the end of 1993, a rotationally quiescent period. When calculated over sliding intervals of 1-year, the sensitivity is found to vary very strongly within both 3-year periods; it is almost negligible over the entire vertical profile during some 1-year intervals or reaches close to 1 around 2–5mb for other intervals. Other sources of variability, presumably of dynamical origin, operate on the rotational spectral range and determine to a large extent the estimated solar rotational signal. Even considering 3 years of observations (corresponding to about 40 solar cycles), the extraction of the rotational solar signal does not appear to be robust during declining phases of 11-year solar cycles. As observational studies cover at best three 11-year solar cycles, it must be challenging to produce a reliable estimation of the 11-year solar cycle signal in stratospheric ozone, especially in the presence of decadal climate variability.

      PubDate: 2015-06-20T13:39:38Z
  • Solar global horizontal and direct normal irradiation maps in Spain
           derived from geostationary satellites
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): J. Polo
      Solar radiation derived from satellite imagery is a powerful and highly accurate technique for solar resource assessment due to its maturity and to the long term database of observation images available. This work presents the methodology developed at CIEMAT for mapping solar radiation from geostationary satellite information and it also shows solar irradiation maps of global horizontal and direct normal components elaborated for Spain. The maps presented here have been developed from daily solar irradiation estimated for eleven years of satellite images (2001–2011). An attempt to evaluate the uncertainty of the presented maps is made using ground measurements from 27 meteorological stations available in Spain for global horizontal irradiation obtained from the World Radiation Data Centre. In the case of direct normal irradiation the ground measurement database was scarce, having available only six ground stations with measurements for a period of 4 years. Yearly values of global horizontal irradiation are around 1800kWhm−2 in most of the country and around 1950–2000kWhm−2 for annual direct normal irradiation. Root mean square errors in monthly means were of 11% and of 29% for global horizontal and direct normal irradiation, respectively.

      PubDate: 2015-06-20T13:39:38Z
  • Determining magnetotail reconnection location from polar rain energy
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): Yongliang Zhang , Simon Wing
      An improved algorithm was developed to estimate the polar rain electron path length from the magnetotail X-line to the polar ionosphere using the information of polar rain electron energy-latitude dispersion. Recent particle tracing simulations using APLOPM model (Applied Physics Laboratory – Open-field line particle Precipitation Model) (Wing et al., 2001 ; Wing and Zhang, 2015) indicate that an existing or traditional method underestimates the path length by at least 33%. A new method for estimating electron path length that introduces a new parameter (energy parameter) is proposed. The improved algorithm has been validated using the APLOPM simulation data. By applying the new algorithm to two real events measured by DMSP satellites, we found the polar rain electron path lengths of 67 and 114 R E, (X-lines estimated at X=−54 and −91 R E), respectively (assuming the distance from the X-line to the Earth is 80% of the electron path length). The associated IMF Bz were 1 and –11nT, respectively for the two events. This is consistent with the expected stretched magnetotail configuration under a strongly southward IMF. The results are also consistent with statistical results of the X-line locations from Geotail measurements.

      PubDate: 2015-06-20T13:39:38Z
  • Gravity waves-induced airglow temperature variations, phase relationships,
           and Krassovsky ratio for OH(8,3) airglow, O2(0,1) atmospheric band, and
           O(1S) greenline in the MLT region
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): Tai-Yin Huang
      The gravity wave-induced secular variations and fluctuations of airglow intensity-weighted temperatures for OH(8,3) nightglow, O2(0,1) atmospheric band, and O(1S) greenline in the MLT region were simulated to study the wave effects’ on airglow temperatures. They were investigated with a time-dependent OH Chemistry-Dynamics (OHCD) model and a Multiple Airglow Chemistry-Dynamics (MACD) model with a small-scale linear gravity wave packet. The largest wave-induced airglow temperature secular variations are found to be ~0.8% in the O2(0,1) temperature and the largest wave-induced airglow temperature fluctuations are found to be ~0.25% in the O(1S) temperature. We also investigated the phase relationships between the airglow intensities and temperatures. Our results show that the airglow intensities lead the airglow temperatures most of the time. Also, airglow located at a higher altitude leads the airglow located at a lower altitude, indicating a downward phase progression, which is consistent with the phase of the wave packet we used. The Krassovsky ratio for these airglow emissions were calculated and found to be decreasing with increasing altitude. The amplitude of the Krassovsky ratio for OH(8,3) airglow, O2(0,1) atmospheric band, and O(1S) greenline were ~10, 6, and 4, respectively.

      PubDate: 2015-06-20T13:39:38Z
  • Synoptic Kelvin type perturbation waves over Congo basin over the period
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): Zebaze Sinclaire , André Lenouo , Clément Tchawoua , Serge Janicot
      The synoptic structure and inter-annual variability of Kelvin waves over the Congo basin from 1979 to 2010 are explored using outgoing longwave radiation (OLR) and National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis data. Composite method shows that high values of synoptic Kelvin wave (SKW) index are located over Congo basin during March–June where the convective active phase favours the formation of convective synoptic systems. Mean composite SKWs structure shows that these waves propagate faster over land surface and dissipate with suppressed phase. Because convective instability is smaller, these waves cannot grow in Congo basin. High correlation between SKWs and precipitation time series occurs when the Kelvin waves lead the precipitation time series by about 4 days. The analysis of 32 years datasets (1979–2010) also shows that in some particular year, strong SKWs propagation exists with periods centred around 5 days. Otherwise, results show marked inter-annual variability of Kelvin wave activity over Congo basin associated with divergence and low level westerly trade winds.

      PubDate: 2015-06-20T13:39:38Z
  • Variability of the quasi-2-day wave and interaction with longer period
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): A. Guharay , P.P. Batista , B.R. Clemesha
      An exclusive study has been carried out with long term meteor wind data (2000–2014) to characterize the quasi-2-day wave (QTDW) in the mesosphere and lower thermosphere (MLT) and its interactions with the longer period planetary waves at Cachoeira Paulista (22.7°S, 45°W). The QTDW is observed to be dominant during late summer (January–February) all the years under consideration except 2013. All the wave parameters exhibit significant interannual variability. The maximum wave amplitude comes out to be 39m/s, which is significantly higher than the reported northern hemispheric findings. The mean MLT period exhibits a wide range of variability (36–70h) indicating the presence of multiple Rossby normal modes with varying zonal wave numbers. Modulations of the QTDW amplitude by the planetary waves with longer periodicities (>9 days) are evident, especially during summer. The nonlinear interactions between the 2-day wave and longer period waves are believed to give rise to a host of secondary waves with frequencies lying close to 2-day. The strong QTDW activity, as observed at this location, has potential to cause significant effect on the overlying ionosphere and hence the atmosphere-ionosphere dynamical coupling.

      PubDate: 2015-06-20T13:39:38Z
  • Simultaneous retrieval of T(p) and CO2 VMR from two-channel non-LTE limb
           radiances and application to daytime SABER/TIMED measurements
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): L. Rezac , A. Kutepov , J.M. Russell III , A.G. Feofilov , J. Yue , R.A. Goldberg
      The kinetic temperature, T k , and carbon dioxide, CO2 density, are key parameters that characterize the energetics and dynamics of the mesosphere and lower thermosphere (MLT) region. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on-board the Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (TIMED) satellite has been providing global, simultaneous measurements of limb radiance in 10 spectral channels continuously since late January 2002. In this paper we (1) present a methodology for a self-consistent simultaneous retrieval of temperature/pressure, T k (p), and CO2 volume mixing ratio (VMR) from the broadband infrared limb measurements in the 15 and 4.3 μ m channels, and (2) qualitatively describe the first results on the CO2 VMR and T k obtained from application of this technique to the SABER 15 and 4.3 μ m channels, including issues, which demand additional constraints to be applied. The self-consistent two-channel retrieval architecture updates parameters at all altitudes simultaneously, and it is built upon iterative switching between two retrieval modules, one for CO2 and one for T k . A detailed study of sensitivity, stability and convergence was carried out to validate the algorithm. The T k /CO2 VMR distribution can be reliably retrieved without biases connected with this non-linear inverse problem starting with an initial guess as far as ±20% of CO2 VMR and ±15K from the solution (as global shift, or somewhat larger if only local deviations are considered). In polar summer toward high latitudes the retrieved CO2 VMR profile shows a local peak around 90km. We discuss details of this feature and show that: (a) it is not an algorithm artifact or instability, (b) additional a priori constraints are needed in order to obtain a physical profile and to remove this peak, and (c) several possibilities are explored as to uncover the real cause of this feature, but no firm conclusion can be reached at this time. This algorithm has been applied to all available daytime SABER measurements since 2002, and the first results of the mean CO2 VMR profiles and their distribution is discussed. In particular, the CO2 VMR profiles depart from a well mixed value at altitudes of 65–70km during equinoxes at high and mid-latitudes, but in the summer hemisphere solstice period the SABER data is more consistent with a well mixed VMR conditions extend up to 87–90km especially toward high latitudes.

      PubDate: 2015-06-20T13:39:38Z
  • Wavelength dependence of the effective cloud optical depth
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): D. Serrano , M.J. Marín , M. Núñez , M.P. Utrillas , S. Gandía , J.A. Martínez-Lozano
      This study examines the wavelength dependence of cloud optical depth. To accomplish this task two different wavelength bands of the solar spectrum were considered in the cloud optical depth retrieval which was conducted in Valencia, Spain. The first retrieval used global irradiance measurements in the UVER range taken from a YES-UVB-1 radiometer in combination with multiple scattering model estimates; while the second retrieval was obtained in the Broadband range, with measurements of global solar surface irradiance from a CM6 pyranometer and a multiple scattering model. Whilst the dependence of the cloud optical depth (τ) on the wavelength is small, the best result was displayed by the SBDART model with less than 2% deviation between two ranges and moderately worse results were obtained with the LibRadtran model. Finally, seasonal statistical data for optical depth are presented for 2011 and 2012.

      PubDate: 2015-06-20T13:39:38Z
  • Ionospheric electron density profile estimation using commercial AM
           broadcast signals
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): De Yu , Hong Ma , Li Cheng , Yang Li , Yufeng Zhang , Wenjun Chen
      A new method for estimating the bottom electron density profile by using commercial AM broadcast signals as non-cooperative signals is presented in this paper. Without requiring any dedicated transmitters, the required input data are the measured elevation angles of signals transmitted from the known locations of broadcast stations. The input data are inverted for the QPS model parameters depicting the electron density profile of the signal’s reflection area by using a probabilistic inversion technique. This method has been validated on synthesized data and used with the real data provided by an HF direction-finding system situated near the city of Wuhan. The estimated parameters obtained by the proposed method have been compared with vertical ionosonde data and have been used to locate the Shijiazhuang broadcast station. The simulation and experimental results indicate that the proposed ionospheric sounding method is feasible for obtaining useful electron density profiles.

      PubDate: 2015-06-20T13:39:38Z
  • Studying the G condition occurrence in different latitudes under solar
           minimum: Observation and modeling
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): Polekh N.M. , Romanova E.B. , Ratovsky K.G. , Shi J.K. , Wang X. , Wang G.J.
      We analyzed the G condition occurrence, using data of ionospheric vertical sounding from stations Norilsk (69.4°N, 88.1°Е), Irkutsk (52.5°N, 104°Е) and Hainan (18.3°N, 109.3°Е) during the last extreme low solar activity period (2006–2009). In most cases, the three stations registered the G condition in May–August; in Norilsk, however, it was registered in March–April 2008. Under quiet geomagnetic conditions, the longest intervals (up to several hours) during which the G condition was continuously registered were observed in Irkutsk and Norilsk in June–July 2008. In Norilsk, it was registered almost every day in the morning and in the daytime (LT) during these months. We performed theoretical modeling of electron density distribution for the cases when the G condition was registered, taking into account the correction of the neutral atmosphere model. The obtained calculations are in good agreement with observed data. Besides, we showed that variations in thermospheric parameters (density, composition, temperature, and wind velocity) can promote formation of the G condition under quiet geomagnetic conditions during the last extreme low solar activity.

      PubDate: 2015-06-20T13:39:38Z
  • Double core of ozone valley over the Tibetan Plateau and its possible
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): Dong Guo , Yucheng Su , Chunhua Shi , Jianjun Xu , Alfred M. Powell
      In this study, the three-dimensional structure of the ozone valley (e.g. ozone depletion) over the Tibetan Plateau (TP) in summer (June–August) has been investigated using Microwave Limb Sounder (MLS) ozone (O3) data from 2005 to 2013. A double core structure of the ozone valley over the TP is found with one depletion center in upper stratosphere (10–2hPa) named the upper core, and another depletion center, named the lower core, is observed in the upper troposphere/lower stratosphere (200–50hPa). The analysis indicates that the zonal deviation of ozone O3 * (O3 *=O3–[O3], here [O3] is the zonal mean of O3) at the upper core is nearly −1DU while its counterpart's deviation at the lower core is nearly –15DU. Large scale atmospheric circulation and terrain effects play an important role in the ozone valley at the lower core. In contrast, photochemistry reactions of odd chlorine including chlorine atoms (Cl) and chlorine monoxide (ClO) dominate the ozone valley at the upper core. Based on the MLS products, support for a chemical driver at the upper core is based on: (1) the significant diurnal variability of ozone suggests possible photochemistry reactions impacting the ozone valley; (2) the positive center of the ClO zonal deviation (CLO*) and hydrogen chloride (HCl) zonal deviation (HCl*) are found at the bottom of the upper core, which means the higher odd chlorine may accelerate the ozone loss.

      PubDate: 2015-06-20T13:39:38Z
  • First results of the high-resolution multibeam ULF wave experiment at the
           Ekaterinburg SuperDARN radar: Ionospheric signatures of coupled poloidal
           Alfvén and drift-compressional modes
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): Pavel N. Mager , Oleg I. Berngardt , Dmitri Yu. Klimushkin , Nina A. Zolotukhina , Olga V. Mager
      A continuous experiment was carried out at the Ekaterinburg (EKB) stereoradar of the Russian segment of SuperDARN in order to examine the spatio-temporal characteristics of radar-detected magnetospheric ULF waves. The study of magnetospheric oscillations is based on analysis of scattering from field-aligned F-layer irregularities. Their E × B drift Doppler velocity at F-layer heights is associated with the background electric field in the ionosphere. During the experiment one of the radar channels operates in 0–2 beam scanning, with an integration time of 6s, which corresponds to the total 18-s time resolution at each beam. This allows detecting magnetospheric ULF waves with periods of 40s and up. Beam 0 is along the 132 magnetic meridian, so the registered velocity oscillations correspond to the wave electric field azimuthal component. Operation of the radar in this mode was started in December 2013. The first ULF wave events observed in the experiment and presented here occurred on 14 December 2013 and 2 January 2014 in the nightside magnetosphere during two geomagnetic disturbances classified as small magnetic storms and associated with high speed streams from coronal holes. Both the ULF events occurred after substorm-like auroral disturbances. The ULF waves observed during these events are classified as Pc5 geomagnetic pulsations. Two oscillation branches were observed, the higher and the lower frequency ones. As the azimuthal wave numbers m increase, the branches converge and merge into a single oscillation branch at some critical azimuthal wave number value m ⋆ . This ω ( m ) dependence is characteristic of the coupled Alfvén and drift-compressional waves which according to theory merge if the azimuthal wave number exceeds some critical value. This merged single oscillation branch represents an unstable drift ballooning coupling mode. Thus, the following interpretation of the observed events can be suggested; at m < m ⋆ the higher and lower frequency branches can be identified with the Alfvén and drift-compressional modes, respectively, and at m > m ⋆ the single branch can be identified with the drift ballooning coupling mode.

      PubDate: 2015-06-20T13:39:38Z
  • Night-time light ion transition height behaviour over the Kharkiv
           (50°N, 36°E) IS radar during the equinoxes of 2006–2010
    • Abstract: Publication date: September 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 132
      Author(s): Dmytro V. Kotov , Vladimír Truhlík , Phil G. Richards , Stanimir Stankov , Oleksandr V. Bogomaz , Leonid F. Chernogor , Igor F. Domnin
      This research investigates anomalous nighttime ion density behaviour over the Kharkiv, Ukraine incoherent scatter radar (49.6° N, 36.3° E, 45.3° inv) during the equinoxes of 2006–2010. The observations show that the altitude of the transition from O+ to lighter ions was much lower than empirical and physical models predict. The standard physical model produces very good agreement for the O+ densities but underestimates the H+ densities by a factor of 2 in March 2006 and a factor of 3 in March 2009. The anomalously low transition height is a result of similar lowering of the ionospheric peak height and also of significantly increased H+ density. The lower ionospheric peak height may be caused by weaker nighttime neutral winds. The calculations indicate that the higher measured topside ionosphere H+ densities are most likely due to higher neutral hydrogen densities. Both factors could be the result of weaker than usual magnetic activity, which would reduce the energy input to high latitudes. Prolonged low activity periods could cause a global redistribution of hydrogen and also allow more neutral hydrogen to settle down from the exosphere into the mid-latitude ionosphere. The finding of the need for higher H densities agrees well with recent H-alpha airglow measurements and it is important for accurate modelling of plasmasphere refilling rates and night-time N m F 2 values.

      PubDate: 2015-06-20T13:39:38Z
  • Statistical investigation of the noise added to a model of the effect of
           solar activities on the plasma of the ionosphere using DEMETER satellite
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): Mahmoud Sharzehei , M.A. Masnadi-Shirazi , Sh. Golbahar-Haghighi
      Although a relation between ionospheric anomalies and occurrence of strong earthquake has been studied for several decades, the issue of finding anomalies in ionospheric parameter before earthquakes has been always a matter of controversy among scientific community. In this way, the study of the ionosphere by satellite observers plays a significant role in assessing the feasibility of finding anomalies in ionospheric parameters as short-term precursors of earthquakes. Regardless of whether this assertion about ionospheric precursor is true or false, the ionosphere has been shown to be affected more by solar activities than other events such as seismic activities; thus, the modeling of ionospheric variation caused by solar activities is valuable in assessing the possibility of ionospheric precursors. One of the most famous satellites launched to investigate the ionospheric plasma perturbation associated with solar and seismic activities is the DEMETER, the French micro-satellite. To carry on such investigation, one of its payloads, the onboard IAP experiment, allows for the measurement of important plasma parameters including ion composition densities and their temperature. The current work presents a statistical distribution for the noise added to the proposed model describing the regular effect of solar activities on the ionospheric plasma above Iran during one half-orbit time of the DEMETER (~35min) in the absence of an earthquake and a quiet time condition. The results of this study show that the proposed modeling noise statistically agrees with the Gaussian distribution; however, its variance may vary from one day to another. In other words, the noise is a non-stationary random process. The proposed model is then evaluated by a set of experimental data. The results of this evaluation show that the measured data follow the proposed model.

      PubDate: 2015-06-20T13:39:38Z
  • Aerosol optical properties over a coastal site in Goa, along the west
           coast of India.
    • Abstract: Publication date: August 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 130–131
      Author(s): Shilpa Shirodkar , Harilal B. Menon
      Spectral characteristics of the Aerosol optical depths (AODs) measured over a coastal site in Goa (15.46°N and 73.83°E), from a plateau ~50m above mean sea level, for the period 2008–2010, are analyzed to understand the inter-seasonal and intra-seasonal variability and to delineate different aerosol sources. A Microtops-II sunphotometer having five different wavelengths centered at 0.380, 0.440, 0.500, 0.675 and 0.870µm was used to estimate AODs in different seasons classified as: winter monsoon season from December to March (WMS), spring inter-monsoon season from April to May (SIMS), summer monsoon season from June to September (SMS) and fall inter-monsoon season from October to November (FIMS). The number of data (AODs) generated in each season is 569 in WMS, 131 in SIMS, 38 in SMS and 256 in FIMS. The highest AOD at 500nm (AOD500) was recorded in SIMS (0.43±0.18) while the lowest value was observed in SMS (0.32±0.10). The seasonal mean values of Ångström α computed from the least-square method in the wavelength range 0.440–0.870μm showed higher values (1.23±0.20) in FIMS than those in SMS (0.75±0.34). The highest Ångström β values were noticed in SIMS (0.25±0.10) and lowest in FIMS (0.17±0.06). To make a source appropriation and thus to resolve the complexity of aerosols in the study area, α was computed in different wavelength ranges, viz: short wavelengths (0.440–0.500μm) and long wavelengths (0.675–0.870μm), which revealed differing α values for different ranges of wavelengths. To account for the curvature, a second order polynomial fit is introduced. Subsequently, the second-order Ångström exponent (ά) and the coefficient of the second-order polynomial fit are analyzed to understand the dominant aerosol type.
      Graphical abstract image

      PubDate: 2015-06-20T13:39:38Z
  • A comparison of stratospheric photochemical response to different
           reconstructions of solar ultraviolet radiative variability
    • Abstract: Publication date: Available online 15 June 2015
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Cassandra Bolduc , Michel S. Bourqui , Paul Charbonneau
      We present calculations of stratospheric chemical abundances variations between different levels of solar activity using a simple photochemistry model in transient chemistry mode. Different models for the reconstruction of the solar spectrum, as well as observations from the SOLar STellar Irradiance Comparison Experiment (SOLSTICE) and Spectral Irradiance Monitor (SIM) on the SOlar Radiation and Climate Experiment (SORCE) satellite, are used as inputs to the calculations. We put the emphasis on the MOnte CArlo Spectral Solar Irradiance Model (MOCASSIM) reconstructions, which cover the spectral interval from 150 to 400nm and extend from 1610 to present. We compare our results with those obtained with the Naval Research Laboratory Solar Spectral Irradiance (NRLSSI) model as well as with the Magnesium-Neutron Monitor (MGNM) model over a period of time spanning the ascending phase of Cycle 22. We also perform the calculations using SORCE composite spectra for the descending phase of Cycle 23 and with the reconstructed MOCASSIM, NRLSSI and MGNM spectra for the same period for comparison. Finally, we compare the chemical abundances obtained for the Maunder Minimum with those obtained for the Cycle 23 minimum (in March 2009) and find that stratospheric ozone concentration was slightly higher during the recent minimum, consequent to the small positive variability between the MOCASSIM spectra for both epochs, especially below 260nm. We find that the response in stratospheric ozone is not only dependent on the variability amplitude in the solar spectrum (especially in the 200–240nm band), but also significantly on the base level of the minimum solar spectrum.

      PubDate: 2015-06-20T13:39:38Z
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