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  Subjects -> METEOROLOGY (Total: 79 journals)
Acta Meteorologica Sinica     Hybrid Journal   (Followers: 2)
Advances in Atmospheric Sciences     Hybrid Journal   (Followers: 4)
Advances in Meteorology     Open Access   (Followers: 4)
Aeolian Research     Hybrid Journal   (Followers: 2)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 6)
American Journal of Climate Change     Open Access   (Followers: 5)
Asian Journal of Earth Sciences     Open Access   (Followers: 17)
Atmósfera     Open Access  
Atmosphere     Open Access   (Followers: 2)
Atmosphere-Ocean     Full-text available via subscription   (Followers: 4)
Atmospheric Chemistry and Physics (ACP)     Open Access   (Followers: 11)
Atmospheric Chemistry and Physics Discussions (ACPD)     Open Access   (Followers: 7)
Atmospheric Research     Hybrid Journal   (Followers: 19)
Atmospheric Science Letters     Hybrid Journal   (Followers: 6)
Boundary-Layer Meteorology     Hybrid Journal   (Followers: 9)
Bulletin of the American Meteorological Society     Open Access   (Followers: 13)
Carbon Balance and Management     Open Access   (Followers: 6)
Change and Adaptation in Socio-Ecological Systems     Open Access  
Climate     Open Access   (Followers: 1)
Climate Change Economics     Hybrid Journal   (Followers: 17)
Climate Dynamics     Hybrid Journal   (Followers: 14)
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: 19)
Climate Risk Management     Open Access  
Climatic Change     Hybrid Journal   (Followers: 31)
Developments in Atmospheric Science     Full-text available via subscription   (Followers: 3)
Dynamics of Atmospheres and Oceans     Hybrid Journal   (Followers: 3)
Earth Perspectives - Transdisciplinarity Enabled     Open Access  
Energy & Environment     Full-text available via subscription   (Followers: 15)
Environmental and Climate Technologies     Open Access   (Followers: 1)
Global Meteorology     Open Access  
International Journal of Atmospheric Sciences     Open Access   (Followers: 2)
International Journal of Biometeorology     Hybrid Journal   (Followers: 1)
International Journal of Climate Change Strategies and Management     Hybrid Journal   (Followers: 7)
International Journal of Climatology     Hybrid Journal   (Followers: 13)
International Journal of Image and Data Fusion     Hybrid Journal  
ISRN Meteorology     Open Access  
Journal of Applied Meteorology and Climatology     Full-text available via subscription   (Followers: 7)
Journal of Atmospheric and Oceanic Technology     Full-text available via subscription   (Followers: 10)
Journal of Atmospheric and Solar-Terrestrial Physics     Hybrid Journal   (Followers: 14)
Journal of Atmospheric Chemistry     Hybrid Journal   (Followers: 2)
Journal of Climate     Full-text available via subscription   (Followers: 24)
Journal of Climatology     Open Access   (Followers: 1)
Journal of Hydrology and Meteorology     Open Access   (Followers: 2)
Journal of Hydrometeorology     Full-text available via subscription   (Followers: 3)
Journal of Integrative Environmental Sciences     Hybrid Journal   (Followers: 4)
Journal of Meteorology and Climate Science     Full-text available via subscription  
Journal of Space Weather and Space Climate     Open Access   (Followers: 4)
Journal of the Atmospheric Sciences     Full-text available via subscription   (Followers: 23)
Journal of Weather Modification     Full-text available via subscription  
Large Marine Ecosystems     Full-text available via subscription   (Followers: 1)
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: 2)
Michigan Journal of Sustainability     Open Access  
Monthly Notices of the Royal Astronomical Society     Hybrid Journal   (Followers: 1)
Monthly Notices of the Royal Astronomical Society Letters     Hybrid Journal   (Followers: 2)
Monthly Weather Review     Full-text available via subscription   (Followers: 12)
Nature Climate Change     Full-text available via subscription   (Followers: 34)
Nature Reports Climate Change     Full-text available via subscription   (Followers: 15)
Open Journal of Modern Hydrology     Open Access   (Followers: 1)
Revista Brasileira de Meteorologia     Open Access   (Followers: 1)
Russian Meteorology and Hydrology     Hybrid Journal   (Followers: 3)
Space Weather     Full-text available via subscription   (Followers: 3)
Studia Geophysica et Geodaetica     Hybrid Journal   (Followers: 3)
Tellus A     Open Access   (Followers: 4)
Tellus B     Open Access   (Followers: 7)
The Cryosphere (TC)     Open Access   (Followers: 1)
The Cryosphere Discussions (TCD)     Open Access   (Followers: 1)
The Quarterly Journal of the Royal Meteorological Society     Hybrid Journal   (Followers: 5)
Theoretical and Applied Climatology     Hybrid Journal   (Followers: 2)
Weather     Hybrid Journal   (Followers: 2)
Weather and Climate Extremes     Open Access   (Followers: 2)
Weather and Forecasting     Full-text available via subscription   (Followers: 1)
Weatherwise     Hybrid Journal  
气候与环境研究     Full-text available via subscription  
Journal Cover Journal of Atmospheric and Solar-Terrestrial Physics
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   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1364-6826
     Published by Elsevier Homepage  [2571 journals]   [SJR: 0.955]   [H-I: 56]
  • Diurnal tide in the low-latitude troposphere and stratosphere: Long-term
           trends and role of the extended solar minimum
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): M. Venkat Ratnam , N. Venkateswara Rao , C. Vedavathi , B.V. Krishna Murthy , S. Vijaya Bhaskara Rao
      In the present study, long-term trends in the diurnal tide in the troposphere and stratosphere over a tropical station Gadanki (13.5°N, 79.2°E) are investigated using ERA-Interim wind and temperature products available since 1979. Suitability of the ERA-Interim data for the present study is ascertained using simultaneous radiosonde and MST radar observations over Gadanki and good consistency was found between the two. In general, diurnal tide amplitudes are found to increase from troposphere to stratosphere, as expected. Amplitude of the diurnal tide shows a long-term linear increasing trend, which becomes prominent in the stratosphere. Interestingly, convection over Gadanki also exhibits an increasing trend suggesting that they are related. Role of solar cycle on the diurnal tide is investigated by separating the tidal amplitudes during minimum and maximum of solar cycles 21, 22 and 23. Significantly higher amplitudes in the recent extended solar minimum are noticed though no consistent relation is found between solar activity and tides, in general. These results are discussed in the light of role of convection on the generation of the diurnal tide and their propagation to the higher altitudes, coupling lower and middle atmospheres. Special emphasis is made on the observed large amplitudes of the diurnal tide in the extended solar minimum while relating the observed changes to the background circulation.


      PubDate: 2014-11-24T04:55:42Z
       
  • Solar control on the cloud liquid water content and integrated water vapor
           associated with monsoon rainfall over India
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): Animesh Maitra , Upal Saha , Arpita Adhikari
      A long-term observation over three solar cycles indicates a perceptible influence of solar activity on rainfall and associated parameters in the Indian region. This paper attempts to reveal the solar control on the cloud liquid water content (LWC) and integrated water vapor (IWV) along with Indian Summer Monsoon (ISM) rainfall during the period of 1977–2012 over nine different Indian stations. Cloud LWC and IWV are positively correlated with each other. An anti-correlation is observed between the Sunspot Number (SSN) and ISM rainfall for a majority of the stations and a poor positive correlation obtained for other locations. Cloud LWC and IWV possess positive correlations with Galactic Cosmic Rays (GCR) and SSN respectively for most of the stations. The wavelet analyses of SSN, ISM rainfall, cloud LWC and IWV have been performed to investigate the periodic characteristics of climatic parameters and also to indicate the varying relationship of solar activity with ISM rainfall, cloud LWC and IWV. SSN, ISM rainfall and IWV are found to have a peak at around 10.3 years whereas a dip is observed at that particular period for cloud LWC.


      PubDate: 2014-11-24T04:55:42Z
       
  • IFC-Ed. board
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B




      PubDate: 2014-11-24T04:55:42Z
       
  • A brief overview on the special issue on CAWSES-India Phase II program
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): Duggirala Pallamraju , Subramanian Gurubaran , Madineni Venkat Ratnam



      PubDate: 2014-11-24T04:55:42Z
       
  • Solar cycle effects on Indian summer monsoon dynamics
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): M. Venkat Ratnam , Y. Durga Santhi , P. Kishore , S. Vijaya Bhaskara Rao
      Solar activity associated with sunspot number influences the atmospheric circulation on various time scales. As Indian summer monsoon (ISM) is the manifestation between warmer Asian continent and the cooler Indian Ocean, changes in the solar cycle are expected to influence the ISM characteristics. Among several elements of ISM, Tropical Easterly Jet (TEJ), Low Level Jet (LLJ), and rainfall are important features. As a part of CAWSES India Phase II theme 1 (solar influence on climate (0–100km)) programme, we made an attempt to investigate the role of solar cycle variability on these ISM features using long-term data available from NECP/NCAR (1948–2010) and ERA-Interim (1979–2010) re-analysis products. To check the suitability of these data sets, ground based observations available over the Indian region are also considered. ISM characteristics are studied separately for the maximum and minimum as well as increasing and decreasing solar cycle conditions. Amplitudes corresponding to the solar cycle observed in TEJ, LLJ and rainfall are extracted using advanced statistical tool known as intrinsic mode function. Long-term trends in TEJ reveal decreasing trend at the rate of 0.13m/s/yr (between 1948 and 2000) and no perceptible trend in LLJ. There exists inverse relation between TEJ strength and Central India rainfall. Large difference of 2m/s (5m/s) in the zonal winds of TEJ between solar maximum and minimum (increasing and decreasing trend) is noticed. There exists a difference of ~2m/s in LLJ winds between solar maximum and minimum and increasing and decreasing trend of the solar cycle. However, no consistent relation between the ISM rainfall and solar cycle is noticed over Indian region unlike reported earlier but there exists a delayed effect around 13 years. We attribute the observed features as linear and non-linear relation between dynamics of ISM, rainfall and solar cycle, respectively.


      PubDate: 2014-11-24T04:55:42Z
       
  • Comparative analysis of nocturnal vertical plasma drift velocities
           Inferred from ground-based ionosonde measurements of hmF2 and h’F
    • Abstract: Publication date: Available online 22 November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): B.O. Adebesin , J.O. Adeniyi , I.A. Adimula , O.A. Oladipo , A.O. Olawepo , B.W. Reinisch
      Variations in the evening/nighttime ionosonde vertical plasma drift velocities inferred from the time rate of change of both the base of the F-layer height (Vz(h’F)) and height of the peak electron density (Vz(hmF2)) from an equatorial station were compared for better description of the E x B drifts. For better interpretation, both results were compared with the Incoherent Scatter (IS) radar observations (Vz(ISR)) which is taken to be the most accurate method of measuring drift, and therefore the data of reference level. An equinoctial maximum and June solstice minimum in post-sunset pre-reversal enhancement (PRE) was observed for Vz(hmF2), Vz(ISR), and Vz(h’F). The percentage correlation between VzhmF2 and Vzh’F ranges within 55–70%. While PRE for Vz(hmF2) peaked at 19 LT for all seasons, Vz(h’F) peaked at 18 LT for September equinox and December solstice, and start earlier. The nighttime downward reversal peak magnitudes for Vz(hmF2) and Vz(h’F) are respectively within the range of −4 to −14 and −2 to −14m/s; whereas Vz(ISR) ranges within −12 and −34m/s; and the peak time was reached earlier with the ionosonde observations than for the ISR. The PRE peak magnitude for Vz(hmF2), Vz(h’F) and Vz(ISR) varies between 3–14, 2–14, and 4–14m/s for the entire seasons. Our results revealed higher drift correlation coefficients in both Vz(hmF2) versus Vz(ISR) (0.983) and Vz(h’F) versus Vz(ISR) (0.833) relationships during the equinoxes between 16–20 LT, at which time the F-layer altitude is higher than the 300km threshold value; and lower for solstice period (0.326 and 0.410 in similar order). A better linear relationship between Vz(hmF2) and Vz(h’F2) was observed during the reversal (19–21 LT) phase period. PRE velocity was shown to be seasonal and solar activity dependent. Both VzhmF2 and Vzh’F compares almost equally with the ISR measurement. However, the PRE peak magnitude for the drift inferred using h’F2 is closer to the corresponding ISR magnitude during the equinoxes; whereas the drift inferred from hmF2 best represent the ISR magnitude for solstices. We established that both VzhmF2 and Vzh’F are governed by the same mechanism at nighttime, and as such any of them can be used to infer vertical drift as long as the 300km threshold value condition is considered, otherwise chemical correction may be required for the F-layer uplift.


      PubDate: 2014-11-24T04:55:42Z
       
  • On the occurrence of the coldest region in the stratosphere and tropical
           tropopause stability: A study using COSMIC/FORMOSAT-3 satellite
           measurements
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): V. Kumar , S.K. Dhaka , R.K. Choudhary , Shu-Peng Ho , S. Yoden , K.K. Reddy
      The occurrence of coldest region in the lower and middle stratosphere has been investigated using COSMIC/FORMASAT-3 radio occultation measurements. Observations from January 2007 to December 2011, comprising of 2,871,811 numbers of occultations uniformly spread over land and sea, have been used in this study. Using vertical profiles of temperature upto 40km altitude, zonally averaged at each 5° latitude band between 90°N and 90°S, it is shown that the coldest region in the upper atmosphere occurs during winter in high latitude stratosphere (latitudes >45°) in both the hemispheres with southern hemisphere (temperature less than <−85°C) cooler than northern hemisphere (temperature ~−75°C). The spatial extent of the region of low temperature region found between 10km and 30km altitude, indicating a 20km vertical thick layer of cold temperature. In the southern hemisphere, such a region of coldest temperature remains for more than six months (April–October), in the Northern hemispheric polar region (~−75°C) it is seen mostly during four winter months between October and January. Using NCEP-DOE reanalysis data, we show that cold temperature in the stratospheric region coexists with the jet streams prevalent in those regions. Strong wind jet is surmised to make stratosphere colder. The absence of sunlight in the coldest region is known to cause jet streams. Impact of stratospheric quasi-biennial oscillation (QBO) on the sharpness of tropical tropopause (stability) has also been investigated. Observations suggest that during westerly phase of QBO, the stability of the tropopause increases.


      PubDate: 2014-11-24T04:55:42Z
       
  • Dry phase of tropical lower stratospheric water vapor: Role of BDC,
           convection and ozone variability
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): Shipra Jain , A.R. Jain , T.K. Mandal
      In the present paper, the relationship between dry phase of water vapor in the tropical lower stratosphere (TLS) and 100hPa temperatures (T 100) has been examined. Role of various processes, such as Brewer–Dobson circulation (BDC), convective activities and seasonal minimum of ozone mixing ratio, has been quantified to explain the reason of low T 100 over Indonesian-Australian western Pacific region (IAWPR). Aura MLS data show that low water vapor mixing ratio (WVMR) first appears over the western Pacific during northern hemisphere (NH) winters and directs the dry phase of TLS. Observations of low T 100 (~188K), close association between WVMR and T 100, slow transport of water vapor in TLS and saturation of air close to 82.5–100hPa over IAWPR indicate conditions favorable for 'freeze drying'. Present analysis has brought out several interesting features (a) in addition to BDC, convective activities and low ozone mixing ratio near the tropopause level seems to be contributing to the low T 100 over IAWPR during NH winter/spring, (b) apart from the seasonal decrease, T 100 over IAWPR is noted to be continually low throughout the year by ~1.2K than the zonal mean value where part of such decrease in T 100 (i.e. ~0.7K) can be understood in terms of water vapor feedback process and (c) wave activity of different temporal scale and amplitude (~1–2K) also modulate T 100 over IAWPR. MLS observations also provide an evidence of coupling between the surface and TLS processes, if the sea surface temperature over IAWPR is more than 301.7K.


      PubDate: 2014-11-24T04:55:42Z
       
  • Characteristics of cirrus clouds and tropical tropopause layer: Seasonal
           variation and long-term trends
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): Amit Kumar Pandit , Harish Gadhavi , M. Venkat Ratnam , A. Jayaraman , K. Raghunath , S. Vijaya Bhaskara Rao
      In the present study, characteristics of tropical cirrus clouds observed during 1998–2013 using a ground-based lidar located at Gadanki (13.5°N, 79.2°E), India, are presented. Altitude occurrences of cirrus clouds as well as its top and base heights are estimated using the advanced mathematical tool, wavelet covariance transform (WCT). The association of observed cirrus cloud properties with the characteristics of tropical tropopause layer (TTL) is investigated using co-located radiosonde measurements available since 2006. In general, cirrus clouds occurred for about 44% of the total lidar observation time (6246h). The most probable altitude at which cirrus clouds occurr is 14.5km. The occurrence of cirrus clouds exhibited a strong seasonal dependence with maximum occurrence during monsoon season (76%) and minimum occurrence during winter season (33%) which is consistent with the results reported recently using space-based lidar measurements. Most of the time, cirrus top was located within the TTL (between cold point and convective outflow level) while cirrus base occurred near the convective outflow level. The geometrical thickness of the cirrus cloud is found to be higher during monsoon season compared to winter and there exists a weak inverse relation with TTL thickness. During the observation period the percentage occurrence of cirrus clouds near the tropopause showed an 8.4% increase at 70% confidence level. In the last 16 years, top and base heights of cirrus cloud increased by 0.56km and 0.41km, respectively.


      PubDate: 2014-11-24T04:55:42Z
       
  • Detection of tropopause altitude using Indian MST radar data and
           comparison with simultaneous radiosonde observations
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): S. Ravindrababu , M. Venkat Ratnam , S.V. Sunilkumar , K. Parameswaran , B.V. Krishna Murthy
      The structure and variability of tropical tropopause over Gadanki (13.5°N, 79.2°E) are delineated using data obtained from Indian MST radar operated in the vertical mode as a part of intense Tropical Tropopause Dynamics (TTD) campaigns conducted under the CAWSES India Phase II (Theme 3) program. Radar measurements for 72h in each month from December 2010 to September 2013 have been considered. The identified tropopause altitude with radar (RTH) is compared with the cold point (CPH) and lapse rate tropopause altitudes (LRH) obtained from simultaneous radiosonde data at three hourly intervals during these campaigns. Most of the time, a very good agreement between the RTH and CPH and/or LRH from radiosonde measurements is observed. The mean difference between RTH and CPH and RTH and LRH is found to be 0.1±1km and 0.5±1km, respectively. The smaller differences between RTH and CPH noticed in the present work when compared to other mid- and polar latitudes might be due to the well defined tropopause structure in the tropical latitudes. As the radar provides reliable data on the tropopause, its long-term variability is investigated using the data from 2007 to 2012 available from the MST radar.


      PubDate: 2014-11-24T04:55:42Z
       
  • Tropical tropopause dynamics (TTD) campaigns over Indian region: An
           overview
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): M. Venkat Ratnam , S.V. Sunilkumar , K. Parameswaran , B.V. Krishna Murthy , Geetha Ramkumar , K. Rajeev , Ghouse Basha , S. Ravindra Babu , M. Muhsin , Manoj Kumar Mishra , A. Hemanth Kumar , S.T. Akhil Raj , M. Pramitha
      It is widely accepted that the tropical tropopause is closely linked to climate change. Several campaigns have already been conducted and also are being planned to address various issues related to the tropical tropopause layer (TTL). Despite many campaigns, several scientific issues still remain unexplained including Indian summer monsoon dynamics, cirrus clouds and the trace gas distribution across the tropopause etc. In order to address some of the issues, particularly over the Indian region, intensive observational campaigns called ‘tropical tropopause dynamics (TTD)’ are being conducted since December 2010 at two stations namely Gadanki (13.5°N, 79.2°E) and Trivandrum (8.5°N, 76.9°E) under CAWSES India Phase-II programme. This overview article aims to bring out the current understanding on the tropical tropopause, issues addressed through the TTD campaigns and the details of the data collected in these campaigns using collocated instruments as well as complementary satellite data. So far 32 campaigns have been completed successfully and in this paper main focus is given for describing the systematic data collected using various techniques (MST radar, Mie lidar, Radiosonde, ozonesonde) simultaneously in each month. In general, over the study region affected by the monsoon, a prominent updraft prevails in the middle and upper troposphere regions covering TTL affecting the transport of minor species across the tropopause. The behavior of the cold point tropopause (CPT) at Gadanki and Trivandrum reveals that there are significant differences in the CPT characteristics even within the monsoon region. Cold point tropopause shows stronger sub-daily scale variation over Trivandrum than Gadanki though no indication of deep convection is present at the former location particularly in winter.


      PubDate: 2014-11-24T04:55:42Z
       
  • Whistlers detected and analyzed by Automatic Whistler Detector (AWD) at
           low latitude Indian stations
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): Abhay K. Singh , S.B. Singh , Rajesh Singh , Sneha A. Gokani , Ashok K. Singh , Devendraa Siingh , János Lichtenberger
      Recently, at three Indian low latitude stations: Varanasi (geomag. lat. 14°55′N, geomag. long. 153°54′E, L: 1.078), Allahabad (geomag. lat. 16.05°N; geomag. long. 155.34°E, L: 1.081) and Lucknow (geomag. lat. 17.6°N, geomag. long. 154.5°E, L: 1.104) an Automatic Whistler Detector (AWD) has been installed in December, 2010 for detection and analysis of whistlers. This instrument automatically detects and collects statistical whistlers data for the investigation of whistlers generation and propagation. Large numbers of whistlers have been recorded at Varanasi and Allahabad during the year 2011 which is analyzed in the present study. Different types of whistlers have been recorded at Varanasi and Allahabad. The correlation between recorded whistlers and causative lightning strikes were analyzed using data provided by World-Wide Lightning Location Network (WWLLN). We observed that for both the stations more than 50% of causative sferics of whistlers were observed to match closely with the times of WWLLN detected lightning strikes within the propagation times of causative tweeks. All of these lightning strikes originated from the region within 500–600km radius circle from the conjugate point of Varanasi and Allahabad supports the ducted propagation at low latitude stations. The dispersion of the observed whistlers varies between 8 and 18s1/2, which shows that the observed whistlers have propagated in ducted mode and whole propagation path of whistlers lies in the ionosphere. The ionospheric columnar electron contents of these observed whistlers vary between 13.21 TECU and 56.57 TECU. The ionospheric parameters derived from whistler data at Varanasi compare well with the other measurements made by other techniques.


      PubDate: 2014-11-24T04:55:42Z
       
  • Prediction of horizontal component of earth's magnetic field over Indian
           sector using neural network model
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): K. Unnikrishnan
      Present work is the first attempt to predict horizontal component of earth's magnetic field (H) and range in H (ΔH) over Indian sector by considering the stations, namely, Trivandrum, Pondicherry, Visakhapatnam, and Nagpur, using the concept of neural network (NN). Through training procedure, solar flux (F10.7), latitude, longitude, day of the year, local time, Ap index, IMF Bz, and ion number density are identified as the optimum choice of input parameters, whereas the inclusion of solar wind pressure and velocity has not significantly improved the performance of the model. Thus an appropriate neural network model, NSSHC has been developed with 12 hidden neurons and 500 iterations to predict H component and range in H (ΔH) during the period 1996–2001, to capture diurnal, seasonal, latitudinal, magnetic and solar activity effects.


      PubDate: 2014-11-24T04:55:42Z
       
  • Simultaneous optical measurements of equatorial plasma bubble (EPB) from
           Kolhapur (16.8°N, 74.2°E) and Gadanki (13.5°N, 79.2°E)
           
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): R.N. Ghodpage , A. Taori , P.T. Patil , S. Gurubaran , S. Sripathi , S. Banola , A.K. Sharma
      In this paper, we study the Equatorial Plasma Bubble (EPB) features using All sky imager (ASI) observations of O(1D) 630.0nm night airglow emission from Kolhapur (16.8°N, 74.2°E, 10.6°N dip lat.) and Gadanki (13.5°N, 79.2°E, 6.5°N dip lat.) during March 2012. The optical data was supported by the ionosonde measurements from Tirunelveli (8.7°N, 77.8°E, 0.5°N dip lat.) which revealed the occurrence of equatorial spread-F. The EPBs were monitored at both locations as nearly north–south aligned intensity depleted regions. We computed east–west plasma drift velocity over Kolhapur and Gadanki for the nights having coordinated measurements. Also, the observed plasma bubble drift velocities are compared with the zonal neutral wind velocities obtained from the HWM-07 model and the empirical drift model of England and Immel (2012). We observed that, generally, the mean zonal drift velocities of the plasma bubbles tend to decrease with local time (after midnight). Our results reveal the drift velocity noted in Kolhapur data varies from 124m/s to 181.8m/s, while from the Gadanki data show the drift velocity to range from 116.3m/s to 160.3m/s.


      PubDate: 2014-11-24T04:55:42Z
       
  • Observation of ionospheric irregularities around midnight and
           post-midnight near the northern crest of the Equatorial Ionization Anomaly
           in the Indian longitude sector: Case studies
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): T. Das , K.S. Paul , A. Paul
      Multistation and multi-technique observation of equatorial ionospheric irregularities from locations over the magnetic equator through the northern crest of the Equatorial Ionization Anomaly (EIA) and beyond is one of the important objectives of the Indian CAWSES program. For this purpose, multistation observational campaign was conducted during September 2011, April 2012 and September 2012 involving GPS TEC and S4 from Calcutta situated virtually underneath the northern crest of the EIA, and GPS S4 measurements from Siliguri, located beyond the northern crest of the EIA. Intense amplitude scintillation observations have been noted around midnight and post-midnight hours on certain GPS links located north of Siliguri with no scintillation patches during pre-midnight period. Satellite links experiencing scintillations from Siliguri were unaffected at Calcutta. Day-to-day variability has been noted in the maximum northern observation of GPS scintillations at different S4 levels from both Calcutta and Siliguri. Simultaneous observations from Siliguri and Calcutta indicate that post-midnight GPS amplitude scintillations are possibly associated with interaction of traveling ionospheric disturbances from mid-latitudes towards the equator, with transionospheric GPS links contrary to early evening hours when such movement are usually from over the magnetic equator towards the northern and southern crests of EIA. The present paper reports three cases of ionospheric irregularity tracking using the above stations on September 25, 2012, April 12, 2012 and September 11, 2011, all magnetically quiet days. Information related to the variabilities of latitudinal extent of scintillation observations along 88°E meridian at different times during 13–19UT and different levels of intensities of scintillation could provide useful information for transionospheric satellite link design and Satellite-based Augmentation System (SBAS).


      PubDate: 2014-11-24T04:55:42Z
       
  • On the pre-midnight ascent of F-layer in the June solstice during the deep
           solar minimum in 2008 over the Indian sector
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part B
      Author(s): D. Chakrabarty , B.G. Fejer , S. Gurubaran , Tarun K. Pant , M.A. Abdu , R. Sekar
      Investigations on the variations of the virtual height ( h ' F ) of the base of the F-layer over Thumba (8.5°N, 77°E, dip lat 0.5°N) in 2002 (high solar activity) and 2008 (very low solar activity) under quiet geomagnetic conditions show characteristic pre-midnight rise of h ' F in the June solstice of 2008. Comparison of the h ' F variations in 2008 over Thumba and Fortaleza (3.9°S, 38.4°W, dip lat 1.8°S), Brazil, reveals that the pre-midnight rise of h ' F is significantly more over Thumba during the June solstice. Drift measurements on-board the Communication/Navigation Outage Forecasting System (C/NOFS) satellite elicit that the midnight upward drift over the Indian sector during the northern summer months of 2009 is the largest, a feature that significantly weakens in 2010. C/NOFS measurements also confirm the electro-dynamical nature of the pre-midnight h ' F rise over the Indian sector in the June solstice during the low solar activity. As the equatorial F-region vertical drifts during nighttime are controlled by E-region dynamo driven by tidal wind system, systematic wind measurements at upper mesospheric heights by an MF radar (1.98MHz) from Tirunelveli (8.7°N, 77.8°E, dip lat 0.5°S), India, during 2000–2011 are used to derive the tidal components. This reveals that the phases of both the meridional and zonal components of the diurnal tide regress while the phase of the meridional component of the semidiurnal tide significantly advances with decreasing solar activity with concomitant increases in amplitudes during the summer months. These observations suggest the possible semidiurnal tidal influence on the pre-midnight h ' F rise over the Indian sector in the June solstice during low solar activity.


      PubDate: 2014-11-24T04:55:42Z
       
  • Studies on some characteristics of rain-induced depolarization of Ku-band
           signal over an earth-space path at a tropical location
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): Animesh Maitra , Arpita Adhikari
      The rain-induced depolarization of a Ku-band satellite signal has been studied at a tropical location, Kolkata (22°34′N, 88°29′E). The depolarization phenomenon is observed in terms of an enhancement of cross-polar component of a horizontally polarized Ku-band satellite signal at the present location. The differential phase shifts, dominantly responsible for causing depolarization caused by scattering of oblate spheroidal rain drops at Ku-band, are computed by employing the point matching technique and utilizing rain drop size distribution data, experimentally obtained at the present location. The differential phase shift is significant for large rain drops resulting in greater depolarization of signal. Consequently, rain drop size distribution plays an important role in determining the depolarization of the satellite signal. The relationship of cross-polar enhancement with rain rate shows a seasonal variation indicating higher extent of depolarization during the pre-monsoon period than during the monsoon period, the reason being the dominance of larger rain drops in the pre-monsoon period compared to the monsoon months for identical rain rates.


      PubDate: 2014-11-20T04:35:36Z
       
  • Observational study on melting layer characteristics over Palau in Pacific
           Ocean
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): U.V. Murali Krishna , K. Krishna Reddy , R. Mastanaiah , Ryuichi Shirooka , Chen-Jeih Pan
      In this paper, four years (April, 2003–March, 2007) of wind profiler radar (WPR) observations, Tropical Rainfall Measuring Mission measurements, radiosonde and automatic weather station data are utilized to characterize melting layer/bright band (caused due to the melting of hydrometeors when the precipitation has a significant stratiform cloud contribution) variability during easterly and westerly monsoon periods over Palau in Western Pacific Ocean. Four years observational results show that presence of stratiform precipitation is more in Westerly monsoon compared to Easterly monsoon. However, bright band height (BBH) is lower in Westerly monsoon. It is also observed that the BBH during the year 2006 is higher than 2005 possibly due to El Nino effect.


      PubDate: 2014-11-20T04:35:36Z
       
  • Temporal asymmetry in aerosol optical characteristics: A case study at a
           high-altitude station, Hanle, in Ladakh region
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): Shantikumar S. Ningombam , S.P. Bagare , A.K. Srivastava , V.P. Kanawade , Rajendra B. Singh , Sangita K. Padhy
      Diurnal features of aerosol optical depth (AOD) at a high-altitude station, Hanle (4500m amsl) in the western Himalayas, were studied using direct/diffuse solar irradiance measurement from a Skyradiometer (Prede) during October 2007 to December 2010. The study reveals a diurnal asymmetry in the measured aerosol characteristics, with three types of diurnal variation in AOD. Among them, Types I and II are prominent during pre-monsoon, while Type III dominates during post-monsoon. Type I appears to be associated with new-particle formation process from gaseous precursors, in addition to the combination of anthropogenic and desert-dust aerosols, probably brought by the prevailing westerly/south-westerly winds during the pre-monsoon season. The diurnal feature of the Type II may be attributed by the transported desert-dust aerosols brought by the prevailing winds. Further, Type III may be associated with the aged background aerosols over the region, pertaining to a small contribution from gaseous precursors.


      PubDate: 2014-11-20T04:35:36Z
       
  • Fluctuations in the ionosphere related to Honshu Twin Large Earthquakes of
           September 2004 observed by the DEMETER and CHAMP satellites
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): Kwangsun Ryu , Jang-Soo Chae , Ensang Lee , Michel Parrot
      While investigating possible precursory signatures of large earthquakes in the ionospheric data measured by the DEMETER and CHAMP satellites, we found ionospheric disturbances related to large earthquakes (M=7.2 and 7.4) that occurred on September 2004 near the south coast of Honshu, Japan. The satellite data were statistically compared with an empirical model and local averages of the large set of data in the study period. A fluctuation in the electron density above the epicenter was observed roughly 2weeks before the main earthquakes. Surveys of the space weather and geomagnetic activities suggest that these fluctuations were not caused by changes in space conditions or by a geomagnetic storm. The features were also distinct from well-known natural ionospheric anomalies. In addition, a peak-like profile in the ion temperature and lowered O + density around the region of the epicenter was observed a week before the main earthquakes along the satellite passes whose longitudes are close to the epicenter. The features are more apparent when they are compared with the data more distant from the epicenter, suggesting that the disturbances occur along the geomagnetic field lines. The concurrent measurements of the ion drift velocity suggest the fluctuations were triggered by the vertical plasma drift. The observed anomalies disappeared ∼ 2 weeks after the quakes. According to the current theories on the seismo-ionospheric coupling, the horizontal electric field at the lower boundary of the ionosphere should have been strengthened by the seismic activity in order for the ionospheric plasma movements above the epicenter and its geomagnetic conjugate regions to trigger the observed ionospheric anomalies.


      PubDate: 2014-11-20T04:35:36Z
       
  • The location and rate of occurrence of near-Earth magnetotail reconnection
           as observed by Cluster and Geotail
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): K.J. Genestreti , S.A. Fuselier , J. Goldstein , T. Nagai , J.P. Eastwood
      A statistical characterization of the location and rate of occurrence of magnetic reconnection in the near-Earth magnetotail is performed by analyzing the set of ion diffusion region (DR) observations made by the Cluster and Geotail spacecraft during solar maximum and the declining phase. The occurrence rate is analyzed in terms of its dependence on both X GSM ⁎ and Y GSM ⁎ (where coordinates are in the solar wind aberrated geocentric solar magnetospheric system). Within the limits of the statistics available to this study, we find the purely X GSM ⁎ - dependent occurrence rate to be roughly constant over a large portion of the near-Earth magnetotail. In contrast, we find the purely Y GSM ⁎ - dependent occurrence rate to be biased towards dusk with a local maximum between 0 R E ≤ Y GSM ⁎ ≤ 5 R E . The Y GSM ⁎ - dependent occurrence rate is then used to construct a quasi-2D formulation of the DR occurrence rate, which has explicit dependence on X GSM ⁎ and implicit dependence on Y GSM ⁎ . The quasi-2D occurrence rate is then used to examine the predicted ephemeris of the Magnetospheric MultiScale (MMS) spacecraft. We estimate that, during its near-Earth magnetotail survey phase, MMS will likely observe 11±4 DR events.
      Highlights • Cluster and Geotail observations of the nightside ion diffusion region are analyzed. • The occurrence rate of events is calculated as a function of XGSM and YGSM. • The occurrence rate is used to estimate the number of events MMS will observe.

      PubDate: 2014-11-20T04:35:36Z
       
  • Guided radio-wave propagation in the equatorial ionosphere according to
           the topside sounding onboard Interkosmos-19
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): A.T. Karpachev , G.A. Zhbankov , V.P. Kuleshova , V.A. Telegin
      In addition to normal vertical-incident ionogram traces, strongly remote (up to 2000km) traces of HF-radio-signal reflections observed on topside-sounder ionograms of the Interkosmos-19 satellite obtained in the equatorial ionosphere are presented. Such traces are connected with waveguides (ducts). These waveguides are field-aligned irregularities of the ionospheric plasma with electron density depletions of a few percent and cross-field dimension of a few to several kilometers. Ray tracing confirms this supposition and allows an estimate of typical waveguide parameters: diameter ≤10–15km and amplitude ΔN/N ≥10%, where N is the electron density. The waveguide traces usually start at the cutoff frequencies of the main traces. However, sometimes they begin at much lower frequencies which indicates the satellite was transitioning through an equatorial plasma bubble during the recording of the ionogram. The X-mode of ducted echoes is more distinct then the O-mode. Only one ducted trace is usually observed on the Interkosmos-19 ionograms; a second conjugate trace is rarely recorded. The same is true for combination modes which is a combination of an oblique-incidence and guided propagation. Waveguides are observed at all heights of Interkosmos-19 (500–1000km) inside the equatorial anomaly region (from −40° to +40° Dip). Waveguides are usually associated with other irregularities of various sizes in the equatorial ionosphere, some of which cause additional traces and spread F on the topside-sounding ionograms. Ducted-echo characteristics observed with Interkosmos-19 are different from those observed earlier with the Alouette and ISIS satellites. This difference is discussed. It is shown that the ionospheric plasma irregularities responsible for the waveguides are observed much more often during nighttime than during daytime.


      PubDate: 2014-11-20T04:35:36Z
       
  • The role of altitudinal variation of scale height in determining the
           
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): K. Venkatesh , P.V.S. Rama Rao , Paulo R. Fagundes
      Studies on the topside electron density profile variations have gained significant importance in the recent past in view of the trans-ionospheric communication and navigation applications particularly over the equatorial and low latitude sectors. The determination of scale height to be used in analytical functions has become more important in estimating the vertical electron density profile in the topside ionosphere. The incoherent scatter radar data over an equatorial station Jicamarca and a low latitude station Arecibo during the high solar activity years 2001 and 2002 are used to estimate the altitudinal dependence of topside ionospheric scale height. These scale height values at different altitudes are used to reconstruct the topside electron density profiles to study the changes in the shape of the topside profile due to the varying scale height values. It has been observed that a closer estimates of the electron density profiles in the topside ionosphere can be derived by using scale height values around 550km over Jicamarca and around 500km over Arecibo. The IRI-2012 modeled electron density profiles have been derived by giving F-layer peak density and height as inputs and those modeled profiles are compared with ISR measured and reconstructed profiles. Further, the scale height values in the topside ionosphere are computed using the IRI-2012 modeled electron and ion temperatures around 550km altitudes over Jicamarca and around 500km altitude over Arecibo. The scale height values thus derived have been used to reconstruct the topside electron density profiles over Jicamarca and Arecibo, the results of which have also been discussed in this paper.


      PubDate: 2014-11-20T04:35:36Z
       
  • Insight into wintertime aerosol characteristics over Beijing
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): Xiaolin Zhang , Mao Mao , Matthew J. Berg , Wenbo Sun
      Aerosol particle pollution in northern China has crucial impact on regional and global climate. The monthly mean aerosol optical depth (AOD) at 550nm in the northern China had its minimum in winter. Surface measurements of aerosol microphysical and optical properties over the Beijing urban area from December 3, 2011 to January 1, 2012 are presented here. The aim of this study was to evaluate wintertime aerosol characteristics, which were impacted by wind and relative humidity. The following mean values were observed: scattering coefficient (293±283Mm−1, 1Mm−1=10−6 m−1), absorption coefficient (136±125Mm−1), backscattering ratio (0.15±0.02), single scattering albedo (0.65±0.08), at 550nm, and scattering Angstrom exponent (2.01±0.22), with mean relative humidity of (47±24)%. Wintertime values of scattering and absorption coefficients had wind dependence, showing that high values occurred with calm winds while the dilution effect of strong winds was obtained for wind speed larger than 4ms−1. Based on air mass backward trajectories, wintertime haze episodes in Beijing were induced by local-pollution emissions, whereas clear periods were dominated by air masses from clean, continental, northwestern areas. Our study indicates that the main challenge to improve wintertime air quality in Beijing is to control local emissions of particulate pollution.


      PubDate: 2014-11-20T04:35:36Z
       
  • On the altitude of initiation of the gradient drift waves at different
           longitude sectors in the vicinity of the dip equator
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): R. Sekar , S.P. Gupta , D. Chakrabarty
      In order to understand the variation in the altitudes of initiation ( h aoi ) of E region gradient drift (GD) waves at different longitude sectors in the vicinity of the dip equator, the linear growth rate expression was examined. This revealed that the growth rate of the primary GD waves in an altitude region of 85–93km depends on the square of the geomagnetic field strength (B). This is shown to explain the lower h aoi of GD waves over Indian longitude vis-a-vis American longitudes. The available observations on the GD waves from different longitude sectors reveal that the h aoi is inversely proportional to B 2.


      PubDate: 2014-11-20T04:35:36Z
       
  • Cosmogenic production and climate contributions to nitrate record in the
           TALDICE Antarctic ice core
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): S. Poluianov , R. Traversi , I. Usoskin
      This paper presents the results of a comparative wavelet coherence analysis of a multimillennial nitrate record with a number of climatic and solar activity proxies. Distinguishing between these factors is important in the view of a possibility of nitrate deposited in a polar region to represent galactic cosmic ray flux and, consequently, solar activity. We used the data from the TALDICE drilling project (Talos Dome, Antarctica), which covers the age range 12,000–700 BP (years before present, i.e. before 1950) and includes records of nitrate as well as climatic proxies, such as Na+, Ca2+, MSA (methanesulphonic acid), δ 18O, SO 4 2 − . The solar activity series is represented by reconstructions of the heliospheric modulation parameter from the 14C and 10Be data. We found (1) a confirmation of multimillennial relation between nitrate and galactic cosmic ray flux; (2) no clear signature of long-term variations of nitrate transport from lower latitudes. We suggest that variations in the nitrate record in the time scale of hundreds–thousands years are most likely caused by local production, deposition and post-deposition processes.


      PubDate: 2014-11-20T04:35:36Z
       
  • Response of surface boundary layer parameters during the formation of
           thunderstorms over Cochin
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): C.A. Babu , P.R. Jayakrishnan
      In the present study we made a detailed analysis of the surface ABL parameters associated with three thunderstorms that occurred over Cochin during pre-monsoon season. The high-resolution sonic anemometer data can provide microscale evolution of the surface boundary layer processes. The parameters studied are momentum flux, sensible heat flux, Turbulent Kinetic Energy (TKE), friction velocity and variance of u, v, w, T. Momentum flux anomalously increases from 0.1Nm−2 to 1Nm−2 during the occurrence of thunderstorm. Correspondingly, sensible heat flux decreases anomalously to a value of −200Wm−2 from 10Wm−2. TKE increases abruptly to 3m2 s−2 from 0.5m2 s−2 during convective activity. Friction velocity also changes abruptly to 1ms−1 from 0.1ms−1. The thermodynamic parameters and stability indices were investigated prior to the occurrence of thunderstorms and found that the atmospheric characteristics were conducive for the formation of convective activity.


      PubDate: 2014-11-20T04:35:36Z
       
  • Global simulation of extremely fast coronal mass ejection on 23 July 2012
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): Kan Liou , Chin-Chun Wu , Murray Dryer , Shi-Tsan Wu , Nathan Rich , Simon Plunkett , Lynn Simpson , Craig D. Fry , Kevin Schenk
      The July 23, 2012 CME was an extremely fast backside event, reaching ∼1AU (STEREO-A) within 20h as compared to ∼3–6 days for typical CME events. Here, we present results from a simulation study of the CME and its driven shock using a combined kinematic and magnetohydrodynamic (MHD) simulation model, H3DMHD. In general, the model results match well with in situ measurements in the arrival time of the CME-driven shock and the total magnetic field strength, assuming an initial CME speed of 3100km/s. Based on extrapolation of an empirical model, the fast CME and its large magnetic field ( B ∼120nT) are capable of producing an extremely large geomagnetic storm (Dst∼−545nT), comparable to the well-known Halloween storm in 2003, if the CME had made a direct impact to the Earth. We investigated the effect of the adiabatic index (γ). It is found that the shock tends to arrive slightly later for a smaller γ value, and γ=5/3 provides the best agreement for the shock arrival time. We also demonstrate that the strength (the Mach number) of the CME-driven fast-mode shock is not the largest at the “nose” of the CME. This is mainly due to the manifestation of fast-mode wave speed upstream of the shock.


      PubDate: 2014-11-20T04:35:36Z
       
  • Superposed epoch analyses of HILDCAAs and their interplanetary drivers:
           Solar cycle and seasonal dependences
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): Rajkumar Hajra , Ezequiel Echer , Bruce T. Tsurutani , Walter D. Gonzalez
      We study the solar cycle and seasonal dependences of high-intensity, long-duration, continuous AE activity (HILDCAA) events and associated solar wind/interplanetary external drivers for ~ 3 1 2 solar cycle period, from 1975 to 2011. 99 HILDCAAs which had simultaneous solar wind/interplanetary data are considered in the present analyses. The peak occurrence frequency of HILDCAAs was found to be in the descending phase of the solar cycle. These events had the strongest time-integrated AE intensities and were coincident with peak occurrences of high-speed solar wind streams. The event initiations were statistically coincident with high-to-slow speed stream interactions, compressions in the solar wind plasma and interplanetary magnetic field (IMF). The latter were corotating interaction regions (CIRs). The signatures of related CIRs were most prominent for the events occurring during the descending and solar minimum phases of the solar cycles. For these events, the solar wind speed increased by ~41% and ~57% across the CIRs, respectively. There was weak or no stream–stream interaction or CIR structure during the ascending and solar maximum phases. HILDCAAs occurring during spring and fall seasons were found to occur preferentially in negative and positive IMF sector regions (toward and away from the Sun), respectively.


      PubDate: 2014-11-20T04:35:36Z
       
  • IFC-Ed. board
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A




      PubDate: 2014-11-20T04:35:36Z
       
  • Assessment of IRI-2012 profile parameters by comparison with the ones
           inferred using NeQuick2, ionosonde and FORMOSAT-1 data during the high
           solar activity over Brazilian equatorial and low latitude sector
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 121, Part A
      Author(s): K. Venkatesh , P.R. Fagundes , R. de Jesus , A.J. de Abreu , V.G. Pillat , S.G. Sumod
      The equatorial and low latitude ionosphere exhibits large variability in the electron density distribution. This variability is manifested by a typical dynamical phenomenon namely, the Equatorial Ionization Anomaly (EIA). In the presence of significant variabilities, accurate estimation of ionospheric Total Electron Content (TEC) has gained more importance in view of the communication and navigation applications. In the present study, the ionospheric electron density as well as the profile thickness and shape parameters of the latest available IRI (IRI-2012) and NeQuick (NeQuick2) models over the equatorial and low latitude sectors have been compared with experimental values for understanding their performance. The ground based ionosonde data in conjunction with the FORMOSAT-1(formerly called ROCSAT) measured in-situ electron density in the topside ionosphere have been used to derive the vertical electron density profiles over three identified locations in the Brazilian equatorial and low latitude sectors during the high solar activity year of 2002. Profiles reconstructed from the combination of ionosonde and FORMOSAT-1 data are compared with profiles derived from both IRI-2012 and NeQuick2 models. The diurnal and seasonal variations of TEC, F-layer peak density (NmF2), F-layer peak height (hmF2), bottom side thickness parameter (B0), shape parameter (B1) and topside effective scale height (H T) have been studied to validate the IRI-2012 and NeQuick2 model simulations. It has been noticed that these models underestimate the experimental TEC during day-time hours of the equinoctial and summer months of the high solar activity. The models perform better in the prediction of NmF2 and hmF2 than in the prediction of TEC during day-time hours. Further, it is observed that both IRI-2012 and the NeQuick2 models show considerable deviations in the estimation of the bottom side profile parameters while more discrepancies are observed in the prediction of topside effective scale height values particularly during day-time hours.


      PubDate: 2014-11-20T04:35:36Z
       
  • Role of surface and boundary layer processes in the temporal evolution of
           monsoon low level jet (MLLJ) observed from High resolution Doppler wind
           lidar measurements
    • Abstract: Publication date: Available online 2 October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): R.D. Ruchith , P. Ernest Raj , M.C.R. Kalapureddy , T. Dharmaraj
      Monsoon Low Level Jet (MLLJ) is one of the important components of Indian summer monsoon. Using high-resolution measurements of boundary layer wind profiles from a Doppler wind lidar at Mahbubnagar (16.73°N, 77.98°E and 445m above mean sea level), India, the temporal evolution of the MLLJ has been investigated. Both jet core height and jet speed show clear diurnal variation during the monsoon season. Jet core starts descending down in the evening hours and remains at a height between 600m – 900m (above surface level) during nighttime. Soon after local sunrise, jet core starts ascending and reaches heights above 1800m by afternoon hours. Jet core speed starts strengthening in the nighttime and attains maximum intensity in the early morning hours and then the core speeds decrease around the time when the jet core is at its maximum height. Simultaneous diurnal variations of surface temperature, sensible heat flux, latent heat flux and Richardson number show that daytime heating and turbulence in surface layers enhance mixing in the daytime boundary layer which helps in lifting of the jet core. Shear produced turbulence and momentum fluxes also play a significant role in the diurnal variation of MLLJ. Factors influencing the evolution of the convective boundary layer and factors responsible for formation of nocturnal boundary layer are closely associated with the diurnal variation of MLLJ occurring over the low-latitude south Indian peninsular region during monsoon season. The results emphasize the importance of continuous and high spatial-temporal resolution wind profile measurements in the monsoon boundary layer from a Doppler wind lidar.


      PubDate: 2014-10-06T07:47:17Z
       
  • Atmospheric surface layer responses to the extreme lightning day in
           plateau region in India
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): Arun K. Dwivedi , Sagarika Chandra , Manoj Kumar , Sanjay Kumar , N.V.P. Kiran Kumar
      This paper discusses the observations of the atmospheric surface layer (ASL) parameters during the lightning event. During this event behaviour of surface layer parameters has been observed. Other derived parameters like Monin–Obukhov stability parameter (z/L), turbulent kinetic energy (TKE), momentum flux (MF) and sensible heat flux (SHF) have also been considered during this stochastic phenomenon. Characteristics of these surface layer parameters have been analysed during lightning period and compared with the clear weather day. During the peak period of the lightning, the incoming solar irradiance was reduced by one third of its normal value, resulting in an air-temperature decrement near the surface in the range of 4°C to 6°C. In addition to that a significant reduction in energy exchanges between surface and lower lying atmosphere (viz. TKE, MF and SHF), has also been observed. The rate of instantaneous decay in solar irradiance and SHF from the first strike to its peak strike time was larger than that seen during clear day hours. The normalized standard deviations of wind components during clear day were studied using Monin–Obukhov similarity theory (MOST) and the results have been compared with earlier studies reported in the literature.


      PubDate: 2014-10-01T06:39:25Z
       
  • Improved performance over time of integration in momentum flux estimation
           using Postset Beam Steering technique
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): V.K. Anandan , Shridhar Kumar , V.N. Sureshbabu , T. Narayana Rao , M. Purnachandra Rao , Toshitaka Tsuda
      Using time series of vertical data collected from middle and upper atmospheric (MU) radar, the adaptive Capon beamforming technique is used to synthesize beams in the desired pointing directions within the radar beamwidth. Beam synthesis has been performed at the tilt angle of 1.5° with different beam configurations (4 beams, 8 beams, 16 beams, 32 beams, 48 beams and 64 beams), which are equally separated azimuth plane. The Power Spectral Density (PSD) is obtained from the synthesized beam using the eigenvector (EV) sub-space based spectral estimation method. The first moment is derived from the EV produced spectrum using the adaptive moment estimation method. From the first order moments derived along equally spaced pointing directions, radial wind velocities are readily obtained in the corresponding directions. From radial velocity obtained in various pointing directions, momentum flux of short duration (<2h) is estimated using the symmetric beam method (SBM) which requires 4 symmetric beams separated by 90° in the azimuth plane. A comparative study has been performed to study the optimum beam configuration, required for the flux estimation, which shows that 32 beam configuration is sufficient to estimate the flux with least error. Study with 32 beam configuration, gives 8 sets of symmetric beams (8×4). Using 8 set of beams, the flux is estimated for each set of beams and averaged. The averaged flux is further integrated over different lengths of time up to 14h. This systematic method for the estimation of momentum flux reveals that spatial averaging of beams in azimuth and integration over different lengths of time have reduced the time of integration from 15 to 16h for the conventional approach to 8–9h for the new approach using Postset Beam Steering (PBS) technique. The flux estimated with spatial-averaging of beam using PBS technique has been compared with other standard methods.


      PubDate: 2014-10-01T06:39:25Z
       
  • IFC-Ed. board
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120




      PubDate: 2014-10-01T06:39:25Z
       
  • Clustering of atmospheric data by the deterministic annealing
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): Alexander Ruzmaikin , Alexandre Guillaume
      The Deterministic Annealing (DA) clustering method, which determines the cluster centers, their sizes, and probability with which data are associated with each cluster, is tested using artificial data and applied to atmospheric satellite data. It is also shown how the method can be advantageously used to characterize data outliers. The method is based on the optimization of a cost function that depends both on the averaged distance of data points to cluster centers and the Shannon entropy of the data. The cost function uses two independent parameters in a close analog to the Gibbs' thermodynamics (with the averaged distance similar to the internal energy) allowing a sufficient control of the formation of new clusters as “phase transitions” by changing the clustering parameter similar to the thermodynamical temperature. The satellite data used are a temperature–water vapor data set and the positions of deep convective clouds obtained from the measurements of the Atmospheric InfraRed Sounder (AIRS) on the Aqua satellite. The clustering of these data is demonstrated for the 2D case (at fixed pressure level) and for the 3D case at multiple pressure levels indicating potential applications to investigation of distributions of atmospheric profiles.


      PubDate: 2014-10-01T06:39:25Z
       
  • Latitudinal effect on the diurnal variation of the F2 layer at low solar
           activity
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): J.O. Adeniyi , B.W. Joshua
      The latitudinal effect on the diurnal variation of the F2 layer peak parameters at low solar activity was investigated. Our results reveal that the likelihood of the occurrence of a noon-bite out is reduced with increase in latitude. Beyond 21.770°N geomagnetic latitude, it is hardly noticed. Daytime maximum NmF2 peak occurs mostly after midday in the northern hemisphere. Similar variations occur in the southern hemisphere, although it varies with the seasons, and latitudes. The maximum ionization decreases with increase in latitude and NmF2 values during the equinoxes are higher than those of the solstice seasons, in the northern hemisphere. It is entirely different in the southern hemisphere. The rate of decay is faster during the solstice than during the equinoxes. Maximum hmF2 values occur at the equatorial ionosphere; the least is in the mid-latitude region. The time of formation and position of the EIA crests is observed to be asymmetric. It appears to be more consistent in the northern hemisphere than the south. These types of seasonal variations have been attributed to the daytime meridional wind, equatorial fountain effect and the location of the subsolar point in relation to the magnetic equator.


      PubDate: 2014-09-25T05:32:46Z
       
  • Influence of hadron and atmospheric models on computation of cosmic ray
           ionization in the atmosphere—Extension to heavy nuclei
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): A.L. Mishev , P.I.Y. Velinov
      In the last few years an essential progress in development of physical models for cosmic ray induced ionization in the atmosphere is achieved. The majority of these models are full target, i.e. based on Monte Carlo simulation of an electromagnetic-muon-nucleon cascade in the atmosphere. Basically, the contribution of proton nuclei is highlighted, i.e. the contribution of primary cosmic ray α-particles and heavy nuclei to the atmospheric ionization is neglected or scaled to protons. The development of cosmic ray induced atmospheric cascade is sensitive to the energy and mass of the primary cosmic ray particle. The largest uncertainties in Monte Carlo simulations of a cascade in the Earth atmosphere are due to assumed hadron interaction models, the so-called hadron generators. In the work presented here we compare the ionization yield functions Y for primary cosmic ray nuclei, such as α-particles, Oxygen and Iron nuclei, assuming different hadron interaction models. The computations are fulfilled with the CORSIKA 6.9 code using GHEISHA 2002, FLUKA 2011, UrQMD hadron generators for energy below 80GeV/nucleon and QGSJET II for energy above 80GeV/nucleon. The observed difference between hadron generators is widely discussed. The influence of different atmospheric parametrizations, namely US standard atmosphere, US standard atmosphere winter and summer profiles on ion production rate is studied. Assuming realistic primary cosmic ray mass composition, the ion production rate is obtained at several rigidity cut-offs – from 1GV (high latitudes) to 15GV (equatorial latitudes) using various hadron generators. The computations are compared with experimental data. A conclusion concerning the consistency of the hadron generators is stated.


      PubDate: 2014-09-25T05:32:46Z
       
  • Lidar observations of the middle atmospheric thermal structure over north
           China and comparisons with TIMED/SABER
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): Chuan Yue , Guotao Yang , Jihong Wang , Sai Guan , Lifang Du , Xuewu Cheng , Yong Yang
      According to the observational data for over 120 nights of the Rayleigh lidar located in Beijing, China (40.5°N, 116.2°E), the middle atmospheric thermal structure (35–85km) over North China was obtained. Lidar observation results show good agreements with SABER temperature data sets, which justify that both the two instruments are reliable. Lidar results show significant difference with the NRLMSISE-00 empirical model and lidar temperatures are usually colder than the model data during the observational time, which may be due to the associations of high level of solar activity, greenhouse gases and the frequent haze weather in North China. To characterize the seasonal variations of the atmospheric temperature structure over Beijing, the amplitude and phase profiles of the annual, semi-annual and 3-month sinusoidal oscillations were extracted by multi-parameter sinusoidal regression. A stratospheric temperature enhancement (STE) event and a long-term mesospheric temperature inversion layer (MIL) are observed in the early winter of 2012/2013. The observed STE event could be due to the enhancement of planetary wave (k=1) activity while the long-term MIL could be due to gravity wave-planetary wave interactions in the masopause region.


      PubDate: 2014-09-20T04:55:45Z
       
  • Validation and revision of far-field-current relationship for the
           lightning strike to electrically short objects
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): Qilin Zhang , Wenhao Hou , Tongtong Ji , Lixia He , Jianfeng Su
      In this paper we have validated and revised the general expressions for far-field-current factors presented by Bermudez et al. (2005, 2007) for lightning strike to tall objects on perfectly and finitely conducting ground, respectively. For the perfectly conducting ground, it is found that when the risetime of lightning return stroke current (RT) is larger than 5h/c (h is the height of tall object and c is the light speed), the overestimation caused by the traditional method predicting the lightning current peak is within 10% beyond a distance of 20km from the lightning channel, and with the decrease of observed horizontal distance d, the error will increase due to the effect of induction field component. For example, when d is 10km, the overestimation is about 20% for strike to a 300-m-tall object. For the finite conductivity ranging from 0.01S/m to 0.001S/m, when the lightning strikes the 300-m-tall object, the lightning current peak predicted from the measured magnetic field peak according to the traditional method is overestimated ranging from about +5% to +20% (positive means overestimation while negative means underestimation) and the derivation value is more within a distance of 20km because of induction field component; When the lightning strikes the 50-m-tall object, the predicted current peak according to the traditional method has an error ranging from about +5% to −15%.


      PubDate: 2014-09-20T04:55:45Z
       
  • A new South American network to study the atmospheric electric field and
           its variations related to geophysical phenomena
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): J. Tacza , J.-P. Raulin , E. Macotela , E. Norabuena , G. Fernandez , E. Correia , M.J. Rycroft , R.G. Harrison
      In this paper we present the capability of a new network of field mill sensors to monitor the atmospheric electric field at various locations in South America; we also show some early results. The main objective of the new network is to obtain the characteristic Universal Time diurnal curve of the atmospheric electric field in fair weather, known as the Carnegie curve. The Carnegie curve is closely related to the current sources flowing in the Global Atmospheric Electric Circuit so that another goal is the study of this relationship on various time scales (transient/monthly/seasonal/annual). Also, by operating this new network, we may also study departures of the Carnegie curve from its long term average value related to various solar, geophysical and atmospheric phenomena such as the solar cycle, solar flares and energetic charged particles, galactic cosmic rays, seismic activity and specific meteorological events. We then expect to have a better understanding of the influence of these phenomena on the Global Atmospheric Electric Circuit and its time-varying behavior.


      PubDate: 2014-09-20T04:55:45Z
       
  • Observations of the intraseasonal oscillations over two Brazilian low
           latitude stations: A comparative study
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): A. Guharay , P.P. Batista , B.R. Clemesha , R.A. Buriti
      A comparative study of intraseasonal oscillations (ISO) in the period range 20–110 days is carried out in the mesosphere and lower thermosphere (MLT) zonal wind at two low latitude stations, Cariri (7.4°S, 36.5°W) and Cachoeira Paulista (22.7°S, 45°W) located far from the convective anomaly region. Considerable seasonal and interannual variability is observed. The ISO in the MLT and lower atmosphere are found to be well correlated during winter and spring indicating a coupling of the atmospheric regions through the ISO. On the other hand, relatively less correlation during summer and fall may suggest a dominance of the in situ excitation of the ISO in the MLT relative to the lower atmospheric contribution. The correlation between the MLT and lower atmosphere is found to be a little higher at Cachoeira Paulista than Cariri. The ISO in the MLT shows good correlation between the two stations, but correlation is insignificant in the case of lower atmosphere. The ISO is most prominent in the upper troposphere, upper stratosphere and MLT. The waves responsible for communicating the ISO signature from the troposphere to the middle atmosphere in the tropics are believed to refract through mid-latitudes in course of their propagation. An evident height variation of the high amplitude ISO in the upper troposphere is observed with a clear annual oscillation at Cariri. The observed behaviors of the ISO at the present sites are discussed in the light of plausible physical mechanisms.


      PubDate: 2014-09-20T04:55:45Z
       
  • Physical mechanisms responsible for forming the 4-peak longitudinal
           structure of the 135.6nm ionospheric emission: First results from the
           Canadian IAM
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): O.V. Martynenko , V.I. Fomichev , K. Semeniuk , S.R. Beagley , W.E. Ward , J.C. McConnell , A.A. Namgaladze
      The Canadian Ionosphere and Atmosphere Model (Canadian IAM or C-IAM) is a new project aimed at the development of whole atmosphere modeling capabilities in Canada. The first version of the C-IAM is comprised of the extended Canadian Middle Atmosphere (CMAM) and the Murmansk's Upper Atmosphere Model (UAM), currently coupled in a one-way manner. The model extends from the surface to the inner magnetosphere and is able to describe the impact on the upper atmosphere and ionosphere of self-consistently generated lower atmosphere dynamical variability. In the current study, the C-IAM has been used to investigate the physical mechanisms responsible for forming the 4-peak longitudinal structure of the 135.6nm ionospheric emission observed by the IMAGE satellite over the tropics at 20:00 local time from March 20 to April 20, 2002. To perform this study, the C-IAM has been run for this whole observation period taking into account a realistic day-to-day variation in solar and geomagnetic activity. The 4-peak longitudinal structure produced by the model and averaged over the observation period is in a good agreement with the observations. Analysis of the model results suggests that the main mechanism for generating the longitudinal structure in the ionospheric emission after sunset is a modification of the ionospheric electric field in the E region caused in the course of the daytime by differences in the diurnal evolution of the zonal wind in different longitudinal sectors due to waves penetrating from the lower atmosphere. In agreement with the earlier findings, our study showed that this mechanism is driven mainly by the diurnal eastward propagating tide with zonal number 3. A small contribution to the formation of the 4-peak structure is also provided by longitudinal variations in meridional wind and neutral composition at the F2 layer altitudes. The 4 peaks being clearly visible in the monthly mean result are not, however, present every day. Day-to-day variability of both the diurnal wind evolution and geomagnetic activity can significantly modify the longitudinal structure of the ionospheric emission.


      PubDate: 2014-09-20T04:55:45Z
       
  • Long-term trends in the northern extratropical ozone laminae with focus on
           European stations
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): Jan Lastovicka , Peter Krizan , Michal Kozubek
      Narrow layers of substantially enhanced ozone concentration in ozonesonde-observed ozone profiles, called positive ozone laminae, reveal much stronger trend than the stratospheric and total ozone itself. They seem to be sensitive to both the ozone concentration and even more to changes in the stratospheric dynamics. We are studying long-term trends of strong positive laminae based on balloon-borne ozone sounding in Europe, Japan, North America and Arctic over 1970–2011 with focus on European stations due to their highest frequency of ozone sounding. Laminae characteristics exhibit strong negative trend till the mid-1990s (decrease by 50% or more). In more recent years this negative trend reverses to a positive trend. According to regression analysis, several factors play a role in the trend in laminae in Europe, namely NAO, EESC and the behavior of the winter polar stratospheric vortex represented here by the 10hPa polar temperature. On the other hand, several factors are found not to play a significant role in the long-term trend in laminae.


      PubDate: 2014-09-20T04:55:45Z
       
  • Statistics of ionospheric scintillation occurrence over European high
           latitudes
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): V. Sreeja , M. Aquino
      Rapid fluctuation in the amplitude and phase of transionospheric radio signals caused by small scale ionospheric plasma density irregularities is known as scintillation. Over the high latitudes, irregularities causing scintillation are associated with large scale plasma structures and scintillation occurrence is mainly enhanced during geomagnetic storms. This paper presents a statistical analysis of scintillation occurrence on GPS L1C/A signal at a high latitude station located in Bronnoysund (geographic latitude 65.5°N, geographic longitude 12.2°E; corrected geomagnetic (CGM) latitude 62.77°N), Norway, during the periods around the peaks of solar cycles 23 (2002–2003) and 24 (2011–2013). The analysis revealed that the scintillation occurrence at Bronnoysund during both the solar maximum periods maximises close to the midnight magnetic local time (MLT) sector. A higher occurrence of scintillation is observed on geomagnetically active days during both the solar maximum periods. The seasonal pattern of scintillation occurrence indicated peaks during the summer and equinoctial months. A comparison with the interplanetary magnetic field (IMF) components B y and B z showed an association of scintillation occurrence with the southward IMF B z conditions.


      PubDate: 2014-09-20T04:55:45Z
       
  • Long-term variabilities and tendencies in zonal mean TIMED–SABER
           ozone and temperature in the middle atmosphere at 10–15°N
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): Oindrila Nath , S. Sridharan
      Long-term variabilities and trends of middle atmospheric (20–100km) ozone volume mixing ratio (OVMR) and temperature and their responses towards quasi-biennial oscillation (QBO), solar cycle (SC) and El Niño-southern oscillation (ENSO) have been investigated using monthly averaged zonal mean Sounding of Atmosphere by Broadband Emission Radiometry (SABER) observations at 10–15°N for the years 2002–2012. Composite monthly mean of OVMR shows semi-annual oscillation (SAO) predominantly in the lower stratosphere (20–30km) and in the upper mesosphere (above 90km), whereas that of temperature shows SAO in the upper stratosphere (45–55km) and lower mesosphere (60–75km). Amplitudes of SAO and annual oscillation (AO) in OVMR show enhancement above 80km and 90km respectively in the mesosphere and both show maximum around 30km in the stratosphere. The amplitudes of SAO and AO in temperature show maxima just below and above 80km in the mesosphere, whereas in the stratosphere, they show maxima around 40km and 20km respectively. The phase profiles of SAO and AO in temperature show downward progressions below 80km, whereas the phase profile of SAO in OVMR shows downward progression only below 40km and the phase remains constant above 80km. Regression analysis of OVMR shows increasing trend at 23km, and small decreasing trend at 30km, 34km and above 80km. Above 92km, the trend sharply decreases. OVMR response to QBO winds at 30hPa shows negative maxima at 30km and 91km, positive maximum at 26km and is insignificant at other heights. The OVMR response to SC is positive in the middle stratosphere peaking at 31km and in the upper mesosphere peaking at 95km. The OVMR response to ENSO shows mixed behavior in stratosphere and positive in the upper mesosphere. It is positive in the lower height region 20–27km with maximum at 25km. The response to ENSO is insignificant up to 70km and it is positive above 80km with two maxima at 87km and 97km. Regression analysis of temperature shows cooling trends in most of the stratosphere and the mesosphere (40–90km). The temperature response to SC is increasingly positive above 40km. The temperature response to ENSO is negative in the middle stratosphere and positive in the lower and upper stratosphere. In mesosphere, it is largely negative in the height range 60–80km and positive above 80km.


      PubDate: 2014-09-16T04:18:17Z
       
  • Ball lightning caused by a semi-relativistic runaway electron avalanche
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): Geron S. Paiva , Carlton A. Taft , Nelson C.C.P. Furtado , Marcos C. Carvalho , Eduardo N. Hering , Marcus Vinícius , F.L. Ronaldo Jr. , Neil M. De la Cruz
      Ball lightning (BL) is observed as a luminous sphere in regions of thunderstorm activity. There are many reports of BL forming in total absence of thunderclouds, associated with earthquakes and volcanoes. In this latter case, BL has been known to appear out of “nowhere”. In this work, a hypothesis on BL formation is presented involving the interaction between very low frequency (VLF) radio waves and atmospheric plasmas. High-velocity light balls are produced by ionic acoustic waves (IAWs) interacting with a stationary plasma. Several physical properties (color, velocity, and fragmentation) observed in the BL phenomenon can be explained through this model.


      PubDate: 2014-09-16T04:18:17Z
       
  • Vlasiator: First global hybrid-Vlasov simulations of Earth's foreshock and
           magnetosheath
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): S. von Alfthan , D. Pokhotelov , Y. Kempf , S. Hoilijoki , I. Honkonen , A. Sandroos , M. Palmroth
      We present results from a new hybrid-Vlasov simulation code, Vlasiator, designed for global magnetospheric simulations. Vlasiator represents ions by a six-dimensional distribution function propagated using a finite volume approach. The distribution functions are self-consistently coupled to electromagnetic fields with electrons modeled as a charge-neutralizing fluid. A novel sparse representation of the distribution function reduces the computational demands of the problem by up to two orders of magnitude. The capabilities of the code are demonstrated by reproducing characteristics of the ion/ion right-hand resonant beam instability, as well as key features of the collisionless bow shock and magnetosheath in front of the Earth's magnetosphere in global five-dimensional (two in ordinary space, three in velocity space) simulations. We find that Vlasiator reproduces the ion velocity distribution functions with quality comparable to spacecraft observations.


      PubDate: 2014-09-16T04:18:17Z
       
  • Ionospheric effects of sudden stratospheric warmings in eastern Siberia
           region
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): A.S. Polyakova , M.A. Chernigovskaya , N.P. Perevalova
      Ionospheric effects observed in Russia's Asia region during sudden stratospheric warmings (SSWs) in the winters 2008/2009 and 2012/2013 corresponding to both extreme solar minimum and moderate solar maximum conditions have been examined. To detect the ionospheric effects which must have been induced by the SSWs, we have carried out a joint analysis of total electron content (TEC) global ionospheric maps (GIM), MLS (Microwave Limb Sounder, EOS Aura) measurements of vertical temperature profiles, as well as NCEP/NCAR and UKMO Reanalysis data. It has been revealed for the first time that during strong SSWs the amplitude of diurnal variation of TEC decreases nearly by half in the mid-latitude ionosphere. Besides, the intensity of TEC deviations from the background level increases during SSWs. It has also revealed that during SSW peak the midday TEC maximum considerably decreases, and the night/morning TEC increases compared to quiet days. The pattern of TEC response to SSW is shown to be identical for both quiet and disturbed geophysical conditions.


      PubDate: 2014-09-11T03:24:26Z
       
  • The effect of the Earth׳s optical shadow on thermal plasma
           measurements in the plasmasphere
    • Abstract: Publication date: December 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 120
      Author(s): G. Kotova , M. Verigin , V. Bezrukikh
      The data processing technique was developed for thermal plasma measurements by wide-angle plasma analyzers, which was successfully used for the Interball mission instruments. This technique considers the effect of spacecraft potential on plasma measurements. When the spacecraft enters the optical shadow of the Earth, the evaluated spacecraft potential suddenly drops, but no abrupt changes of plasma density or temperature are observed. Often observed decrease in temperature of protons in the Earth's shadow is actually associated with shading of ionospheric feet of magnetic field line passing through the spacecraft. This suggests that ionospheric photoelectrons are an important heat source for the plasmasphere. Besides, the Interball 1 data suggest that photoelectrons coming from the nearest ionosphere are more effective in plasmaspheric ion heating than photoelectrons from the conjugate hemisphere.


      PubDate: 2014-09-11T03:24:26Z
       
 
 
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