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  Subjects -> METEOROLOGY (Total: 76 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: 1)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 5)
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: 3)
Atmospheric Chemistry and Physics (ACP)     Open Access   (Followers: 11)
Atmospheric Chemistry and Physics Discussions (ACPD)     Open Access   (Followers: 7)
Atmospheric Research     Hybrid Journal   (Followers: 14)
Atmospheric Science Letters     Hybrid Journal   (Followers: 5)
Boundary-Layer Meteorology     Hybrid Journal   (Followers: 8)
Bulletin of the American Meteorological Society     Open Access   (Followers: 12)
Carbon Balance and Management     Open Access   (Followers: 5)
Climate     Open Access   (Followers: 1)
Climate Change Economics     Hybrid Journal   (Followers: 16)
Climate Dynamics     Hybrid Journal   (Followers: 13)
Climate law     Hybrid Journal   (Followers: 1)
Climate of the Past (CP)     Open Access   (Followers: 4)
Climate of the Past Discussions (CPD)     Open Access   (Followers: 2)
Climate Policy     Hybrid Journal   (Followers: 18)
Climate Risk Management     Open Access  
Climatic Change     Hybrid Journal   (Followers: 28)
Developments in Atmospheric Science     Full-text available via subscription   (Followers: 3)
Dynamics of Atmospheres and Oceans     Hybrid Journal   (Followers: 3)
Energy & Environment     Full-text available via subscription   (Followers: 14)
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: 6)
International Journal of Climatology     Hybrid Journal   (Followers: 11)
International Journal of Image and Data Fusion     Hybrid Journal  
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: 1)
Journal of Climate     Full-text available via subscription   (Followers: 20)
Journal of Climatology     Open Access  
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: 3)
Journal of Meteorology and Climate Science     Full-text available via subscription  
Journal of Space Weather and Space Climate     Open Access   (Followers: 3)
Journal of the Atmospheric Sciences     Full-text available via subscription   (Followers: 20)
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: 1)
Monthly Weather Review     Full-text available via subscription   (Followers: 10)
Nature Climate Change     Full-text available via subscription   (Followers: 29)
Nature Reports Climate Change     Full-text available via subscription   (Followers: 14)
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: 6)
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
   [16 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1364-6826
     Published by Elsevier Homepage  [2563 journals]   [SJR: 0.955]   [H-I: 56]
  • The role of electric fields in sporadic E layer formation over low
           latitudes under quiet and magnetic storm conditions
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
      Author(s): M.A. Abdu , J.R. de Souza , I.S. Batista , A.M. Santos , J.H.A. Sobral , R.G. Rastogi , H. Chandra
      Sporadic E layers are formed dominantly by wind shear mechanism, but their formation and dynamics are driven also by ionospheric electric fields. Investigation of low latitude sporadic E layers under quiet conditions shows that Es layer formation during post sunset hours can be disrupted or enhanced depending upon the vertical structure of the vertical electric field arising from sunset electrodynamic processes. During magnetic storms the formation and disruption of these layers are also strongly controlled by vertical Hall electric field induced by the zonal magnetospheric electric fields that penetrates to equatorial/low latitude ionosphere. Observational results on storm time Es layer responses in the Brazilian and Indian-Asian longitudes are compared. An under-shielding prompt penetration electric field (PPEF) of westward polarity that dominate the night side ionosphere, or an over-shielding electric field also of westward polarity in the evening sector can cause formation of sporadic E layers near 100km, while an eastward polarity electric field, (under-shielding/over-shielding depending upon local time) can lead to disruption of an Es layer in progress. Ionization convergence/divergence leading to the Es layer formation/disruption is driven by a vertical Hall electric field, induced by the primary zonal PPEF, in the presence of storm associated enhanced ratio of field line integrated Hall to Pedersen conductivity (∑ H )/(∑ P ). A downward polarity of the Hall electric field leads to Es layer formation, while an upward polarity causes the Es layer disruption. An enhancement in the ∑ H /∑ P ratio can result from E layer conductivity enhancement due to energetic particle precipitation peculiar to the longitude of the South Atlantic Magnetic Anomaly (SAMA) and/or from a drastic reduction in integrated Pederson conductivity in the form of reduced foF2 that is observed in all longitudes.
      Graphical abstract image

      PubDate: 2014-06-14T18:17:08Z
       
  • Wavelength dependence of solar irradiance enhancement during X-class
           flares and its influence on the upper atmosphere
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
      Author(s): Yanshi Huang , Arthur D. Richmond , Yue Deng , Phillip C. Chamberlin , Liying Qian , Stanley C. Solomon , Raymond G. Roble , Zuo Xiao
      The wavelength dependence of solar irradiance enhancement during flare events is one of the important factors in determining how the Thermosphere–Ionosphere (T–I) system responds to flares. To investigate the wavelength dependence of flare enhancement, the Flare Irradiance Spectral Model (FISM) was run for 61 X-class flares. The absolute and the percentage increases of solar irradiance at flare peaks, compared to pre-flare conditions, have clear wavelength dependences. The 0–14nm irradiance increases much more (~680% on average) than that in the 14–25nm waveband (~65% on average), except at 24nm (~220%). The average percentage increases for the 25–105nm and 122–190nm wavebands are ~120% and ~35%, respectively. The influence of 6 different wavebands (0–14nm, 14–25nm, 25–105nm, 105–120nm, 121.56nm, and 122–175nm) on the thermosphere was examined for the October 28th, 2003 flare (X17-class) event by coupling FISM with the National Center for Atmospheric Research (NCAR) Thermosphere–Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) under geomagnetically quiet conditions (Kp=1). While the enhancement in the 0–14nm waveband caused the largest enhancement of the globally integrated solar heating, the impact of solar irradiance enhancement on the thermosphere at 400km is largest for the 25–105nm waveband (EUV), which accounts for about 33K of the total 45K temperature enhancement, and ~7.4% of the total ~11.5% neutral density enhancement. The effect of 122–175nm flare radiation on the thermosphere is rather small. The study also illustrates that the high-altitude thermospheric response to the flare radiation at 0–175nm is almost a linear combination of the responses to the individual wavebands. The upper thermospheric temperature and density enhancements peaked 3–5h after the maximum flare radiation.


      PubDate: 2014-06-14T18:17:08Z
       
  • Height-integrated Pedersen conductivity in both E and F regions from
           COSMIC observations
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
      Author(s): Cheng Sheng , Yue Deng , Xinan Yue , Yanshi Huang
      Altitudinal distribution of Joule heating is very important to the thermosphere and ionosphere, which is roughly proportional to the Pedersen conductance at high latitudes. Based on the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites observations from 2008 to 2011, the height-integrated Pedersen conductivities in both E (100–150km) and F (150–600km) regions and their ratio γ P ( ∑ PE / ∑ PF ) have been calculated. The result shows that the maximum ratio in the northern summer hemisphere is ~5.5, which is smaller than that from the Thermosphere–Ionosphere–Electrodynamics General Circulation Model (TIE-GCM v1.94) simulation (~9). This indicates that the energy inputs into the F region may be underestimated in the model. The seasonal variations of the ratio have been investigated for both hemispheres, and an interhemispheric asymmetry has been identified. The variational trend of the ratio is similar in both hemispheres, which reaches minimum at local summer and maximum at local winter. However, the difference of the ratio from local summer to local winter in the southern hemisphere is larger than that in the northern hemisphere.


      PubDate: 2014-06-14T18:17:08Z
       
  • Superposed epoch analyses of ion temperatures during CME- and
           CIR/HSS-driven storms
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
      Author(s): A.M. Keesee , J.G. Elfritz , M.-C. Fok , D.J. McComas , E.E. Scime
      Coronal mass ejections (CMEs) and corotating interaction regions associated with high speed solar wind streams (CIR/HSSs) drive geomagnetic storms in the terrestrial magnetosphere. Each type of storm driver yields different dynamics of storm evolution. We present results from comparative superposed epoch analyses of global ion temperatures calculated from TWINS energetic neutral atom (ENA) data and simulations using the comprehensive ring current model (CRCM). During the June 2008–April 2012 timeframe, 48 geomagnetic storms (minimum Dst≤−40nT) occurred. Of these, 21 storms were CME-driven and 15 were driven by CIR/HSSs. Superposed epoch analysis results demonstrate that ion temperatures increase during the recovery phase of CIR/HSS-driven storms, while ions are rapidly heated at the commencement of CME-driven storms then cool over the main phase, particularly for intense (minimum Dst≤−78nT) CME-driven storms. Higher energy ions are convected to lower L-shells during CME-driven storms, while CIR/HSS-driven storms tend to have average ion temperatures that are higher on the dayside than nightside.


      PubDate: 2014-06-14T18:17:08Z
       
  • The ionospheric outflow feedback loop
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
      Author(s): T.E. Moore , M.-C. Fok , K. Garcia-Sage
      Following a long period of observation and investigation beginning in the early 1970s, it has been firmly established that Earth׳s magnetosphere is defined as much by the geogenic plasma within it as by the geomagnetic field. This plasma is not confined to the ionosphere proper, defined as the region within a few density scale heights of the F-region plasma density peak. Rather, it fills the flux tubes on which it is created, and circulates throughout the magnetosphere in a pattern driven by solar wind plasma that becomes magnetically connected to the ionosphere by reconnection through the dayside magnetopause. Under certain solar wind conditions, plasma and field energy is stored in the magnetotail rather than being smoothly recirculated back to the dayside. Its release into the downstream solar wind is produced by magnetotail disconnection of stored plasma and fields both continuously and in the form of discrete plasmoids, with associated generation of energetic Earthward-moving bursty bulk flows and injection fronts. A new generation of global circulation models is showing us that outflowing ionospheric plasmas, especially O+, load the system in a different way than the resistive F-region load of currents dissipating energy in the plasma and atmospheric neutral gas. The extended ionospheric load is reactive to the primary dissipation, forming a time-delayed feedback loop within the system. That sets up or intensifies bursty transient behaviors that would be weaker or absent if the ionosphere did not “strike back” when stimulated. Understanding this response appears to be a necessary, if not sufficient, condition for us to gain accurate predictive capability for space weather. However, full predictive understanding of outflow and incorporation into global simulations requires a clear observational and theoretical identification of the causal mechanisms of the outflows. This remains elusive and requires a dedicated mission effort.


      PubDate: 2014-06-14T18:17:08Z
       
  • IMF By-controlled field-aligned currents in the magnetotail during
           northward interplanetary magnetic field
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
      Author(s): Z.W. Cheng , J.K. Shi , M. Dunlop , Z.X. Liu
      The influence of the interplanetary magnetic field (IMF) B y component on the field-aligned currents (FACs) in the plasma sheet boundary layer (PSBL) in the magnetotail during the northward IMF were investigated using the data from Cluster. There are 748 FACs cases selected to do analysis. We present that the IMF B y component plays a very important role in controlling the flow direction of the FACs in the PSBL in the magnetotail. In the northern hemisphere, the influence of the positive (negative) IMF B y is an earthward (tailward) FACs. To the contrary, in the southern hemisphere, the effect of the positive (negative) IMF B y is a tailward (earthward) FACs. There is a clear north–south asymmetry of the polarity of the FACs in the PSBL when IMF B y is positive or negative, and this asymmetry of the polarity is more distinct when IMF B y is positive. The FAC density is controlled by IMF B y only when IMF B y is large. When IMF B y is more than 10nT the absolute FAC density in the PSBL has an obvious positive correlation with the IMF B y . When IMF B y is less than 10nT, there is no correlation between the absolute FAC density and IMF B y . There is a clear dusk–dawn asymmetry in the current densities for the FACs in the PSBL, with the dawn currents appearing larger than the dusk currents. The FAC with the largest (smallest) density is located in the range of 0100≤MLT<0200 (2100≤MLT<2200).


      PubDate: 2014-06-14T18:17:08Z
       
  • Ionospheric TEC, thermospheric cooling and Σ[O/N2] compositional
           changes during the 6–17 March 2012 magnetic storm interval (CAWSES
           II)
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
      Author(s): O.P. Verkhoglyadova , B.T. Tsurutani , A.J. Mannucci , M.G. Mlynczak , L.A. Hunt , L.J. Paxton
      A series of four geomagnetic storms (the minimum SYM-H~−148nT) occurred during the March 6–17, 2012 in the ascending phase of the solar cycle 24. This interval was selected by CAWSES II for its campaign. The GPS total electron content (TEC) database and JPL's Global Ionospheric Maps (GIM) were used to study vertical TEC (VTEC) for different local times and latitude ranges. The largest response to geomagnetic activity is shown in increases of the low-latitude dayside VTEC. Several GPS sites feature post-afternoon VTEC “bite-outs”. During Sudden Impulse (SI+) event on March 8th a peak daytime VTEC restores to about quiet-time values. It is shown that the TIMED/SABER zonal flux of nitric oxide (NO) infrared cooling radiation correlates well with auroral heating. A factor of ~5 cooling increase is noted in some storms. The cooling radiation intensifies in the auroral zone and spreads towards the equator. Effects of the storm appear at lower latitudes ~18.6h later. The column density ratio Σ[O/N2] is analyzed based on TIMED/GUVI measurements. Both increases (at low latitudes) and decreases (from auroral to middle latitudes) in the ratio occurs during the geomagnetic storms. We suggest that the column density ratio could be enhanced at low to middle latitudes on the dayside partially due to the superfountain effect (atomic oxygen uplift due to ion-neutral drag). It is suggested that decreases in the Σ[O/N2] ratio at high to middle-latitudes may be caused by high thermospheric temperatures. During SI+s, there is an increase in Σ[O/N2] ratio at auroral latitudes.


      PubDate: 2014-06-14T18:17:08Z
       
  • Plasma pressure distribution in the surrounding the Earth plasma ring and
           its role in the magnetospheric dynamics
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
      Author(s): E.E. Antonova , I.P. Kirpichev , M.V. Stepanova
      We analyzed the characteristics of the plasma region surrounding the Earth at the geocentric distances between 6 and 15R E using the data of THEMIS mission from April 2007 to September 2012. The obtained averaged distributions of plasma pressure, of pressure anisotropy, and of magnetic field near the equatorial plane showed the presence of a ring-shaped structure surrounding the Earth. It was found that for quiet geomagnetic conditions the plasma pressure is nearly isotropic for all magnetic local times at geocentric distances >6R E . Taking into consideration that the minimal values of the magnetic field at the field lines near noon are shifted from the equatorial plane, we estimate the value of plasma beta parameter in the region of minimal values of the magnetic field using the Tsyganenko-2001 magnetic field model. It was found that the values of plasma beta parameter are of the order of unity for the nightside part of the ring-shaped structure in the equatorial plane and for the region of minimal values of the magnetic field in the dayside, indicating that the ring-shaped structure should play an active role in the magnetic field distortion. Comparison of obtained distribution of plasma pressure at the equatorial plane with the values of plasma pressure at low altitudes, showed that the considerable part of the auroral oval can be mapped into the analyzed plasma ring. The role of the high-beta plasma ring surrounding the Earth for Earth–Sun System disturbances is discussed.


      PubDate: 2014-06-14T18:17:08Z
       
  • Permutation entropy analysis of complex magnetospheric dynamics
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
      Author(s): Giuseppe Consolini , Paola De Michelis
      The present study is focused on the emergence of dynamical complexity in the Earth's magnetospheric dynamics during magnetic storms as monitored by SYM-H index. A long time series of SYM-H index covering the period from January 2000 to December 2004 is analyzed using a quite novel technique, the permutation entropy analysis. We show that the normalized permutation entropy values of the SYM-H time series decrease during geomagnetic disturbed periods revealing a gradual increase in the temporal correlation of the fluctuations which generates a gradual increase in the complexity degree of the magnetosphere response to the solar wind magnetic field and plasma parameter changes. These large changes in the normalized permutation entropy values and complexity degree observed during the disturbed periods can be interpreted as the signature of dynamical phase transitions happening in proximity to the occurrence of geomagnetic storms and substorms confirming results previously found using different methods. The dependence of the degree of complexity on both the magnitude of the geomagnetic disturbance and the IMF B y GSM and B z GSM components is investigated and discussed.


      PubDate: 2014-06-14T18:17:08Z
       
  • Evidence for two types of dipolarization in the earth's magnetotail
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
      Author(s): A.T.Y. Lui
      There is a long history in the study of current-disruptions/dipolarizations (CDDs) in the Earth's magnetotail. A recent trend for this topic is the focus on very transient (~1–2min) positive pulses of the B z component in the magnetotail coined as dipolarization fronts (DFs). We reviewed several salient features of CDDs reported previously and compare them with those of DFs. We find several major differences between them. First, their temporal profiles differ significantly—DFs have pulse-like form while CDDs have the sustained dipolarization lasting for many minutes. Second, CDDs are typically associated with initial large magnetic fluctuations having the characteristics of turbulence while DFs are not. Third, DFs typically propagate Earthward while CDDs spread tailward. Fourth, DFs are mainly spatial structures acting as discontinuities to separate the regions ahead and behind them with a north–south oriented thin current sheet. On the other hand, CDDs are mainly temporal manifestations of a local dynamic process that reduces the east–west cross-tail current near the neutral sheet. There is indication that CDDs in the near-Earth region (within the downstream distance of ~15 R E) occur prior to substorm onset and DFs are typically found in the midtail region after substorm onsets. These differences justify renaming DFs as dipolarization pulses so that the fronts of CDDs can be distinguished from dipolarization pulses without the confusion brought about by the present terminology.


      PubDate: 2014-06-14T18:17:08Z
       
  • Interplanetary magnetic field By control of prompt total electron content
           increases during superstorms
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
      Author(s): A.J. Mannucci , G. Crowley , B.T. Tsurutani , O.P. Verkhoglyadova , A. Komjathy , P. Stephens
      Large magnitude increases in ionospheric total electron content (TEC) that occur over 1–3h on the dayside are a significant manifestation of the main phases of superstorms. For the largest superstorms of solar cycle 23 (based on the Dst index), ground networks of GPS receivers measured peak total electron content increases greater than a factor of 2 relative to quiet time TEC averaged over the broad latitude band ±40° for local times 1200–1600LT. Near 30° latitude, the Halloween storms of October 29–30, 2003 appeared to produce storm-time TEC exceeding quiet time values by a factor of 5 within 2–3h of storm onset, at 1300LT. The physical cause of these large positive phase ionospheric storms is usually attributed to prompt penetration electric fields (PPEFs) initiated by Region 1 current closure through the ionosphere (Nopper and Carovillano, 1978 mechanism). An unresolved question is what determines variation of the TEC response for different superstorms. It has been suggested that the cross polar cap potential and Region 1 currents are significant factors in determining PPEF in the equatorial ionosphere, which are related to the solar wind reconnection electric field estimated by Kan–Lee and others. In this paper, we show evidence that suggests B y may be a significant factor controlling the TEC response during the main phase of superstorms. We analyzed the interplanetary conditions during the period that TEC was increasing for eight superstorms. We find that increasing daytime TEC during superstorms only occurs for large reconnection electric fields when B y magnitude is less than B z . The data suggest that B z is a far more important factor in the TEC response than the reconnection electric field. We also find that TEC decreases following its peak storm-time value for two superstorms, even though B z remains large and B y magnitudes are less than B z . Such decreases during the geomagnetic disturbance may indicate the role of magnetospheric shielding currents, or of changes in the thermosphere that have developed over the prolonged period of large solar wind electric field. Further analysis is warranted covering a wider range of storm intensities on the role of B y in affecting the daytime TEC response for a range of storm intensities.


      PubDate: 2014-06-14T18:17:08Z
       
  • IFC-Ed. board
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116




      PubDate: 2014-06-14T18:17:08Z
       
  • Introduction to this special issue: “Sun–Earth system
           exploration: Moderate and extreme disturbances”
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
      Author(s): P.T. Newell , B.T. Tsurutani



      PubDate: 2014-06-14T18:17:08Z
       
  • On the propagation of sudden impulses through the magnetosphere
    • Abstract: Publication date: August 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
      Author(s): U. Villante , M. Piersanti
      On the basis of a simple geometrical approach, we evaluated some aspects of the propagation time of SI disturbances between the magnetopause and geostationary orbit for variable impact points at the magnetopause, focusing attention on the expected lag time between the SI manifestation at spacecraft located ≈4h a part along geostationary orbit. We also examined a set of events identified by GOES8 and GOES10 during 2001–2004. The experimental observations reveal a clear local time (LT) dependence of the lag time between spacecraft that is consistent with that one predicted for disturbances determined by the first launch from the impact point and propagating in different directions approximately with the same speed. In addition, the comparison with the expected LT pattern suggests that most of the events might be related with pressure fronts impacting on the subsolar magnetopause; this aspect is consistent with the dominant orientation of the interplanetary shock fronts for this set of events.


      PubDate: 2014-06-14T18:17:08Z
       
  • 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: Available online 15 May 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      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: 2014-06-14T18:17:08Z
       
  • Intercomparison of various SA Techniques on wind estimation using multi
           receiver phased array radar
    • Abstract: Publication date: Available online 16 May 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Shridhar Kumar , V.K. Anandan , V.N. Sureshbabu , T. Narayana Rao , M. Purnachandra Rao , Toshitaka Tsuda
      In this paper we have applied various spaced antenna (SA) techniques to derive horizontal winds with Middle and Upper (MU) atmospheric radar observations. SA techniques comprise different analysis method like Full Correlation Analysis (FCA), Cross Correlation Ratio (CCR), Slope at Zero lag (SZL) and Intersection (INT) methods etc. Among these methods, FCA is considered one of the classical approaches. In the present study, the MU radar antenna array is regrouped (in software) into three different antenna segments, each segment consists of 8 channels and forming an equilateral triangle. Grouping of antenna has been done with 4 different orientations by interchanging the channels. FCA wind has been estimated with an equilateral triangle grouping of antenna array in all orientations. With the same grouping in different orientation, winds are estimated with CCR, SZL and INT method. Winds estimated with different orientation are averaged to obtain the mean winds component. In most of studies reported earlier using CCR, SZL and INT method, winds have been estimated with pair of antenna having baseline parallel to the antenna array plane. We have retrieved the zonal wind with a pair of antennas having baseline parallel to the antenna array plane in East-west direction and meridional wind is estimated with a pair of antennas having baseline parallel to the antenna array plane in North-south direction.The mean winds obtained with various SA techniques are compared with that observed by the Doppler Beam swinging (DBS) technique and GPS-sonde. It is observed that mean winds obtained with the approach adopted using different spatially distributed array grouping has yielded higher height coverage up to ∼20km and in good agreement with the results obtained using DBS observations even with a temporal resolution of ∼1.3min in clear air condition. Various statistical analyses like correlation analysis, standard deviation, Root mean square error (RMSE) and error analysis have been performed to understand the performance of other techniques in comparison with FCA. The analysis is carried out for an observation of 6hours for two different observation periods.


      PubDate: 2014-06-14T18:17:08Z
       
  • Tropical tropopause dynamics (TTD) campaigns over Indian region: An
           overview
    • Abstract: Publication date: Available online 20 May 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      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: 2014-06-14T18:17:08Z
       
  • 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: Available online 22 May 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      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: 2014-06-14T18:17:08Z
       
  • Prefa Recent progress from networked studies based around MST radar
    • Abstract: Publication date: Available online 29 May 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Wayne K. Hocking , Volker Lehmann , Werner Singer , Masayuki Yamamoto



      PubDate: 2014-06-14T18:17:08Z
       
  • Hybrid model for long-term prediction of the ionospheric global TEC
    • Abstract: Publication date: Available online 24 May 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): P. Mukhtarov , D. Pancheva , B. Andonov
      A new hybrid climatological model for long-term prediction of the global TEC was developed. It is based on the global empirical background TEC model constructed by Mukhtarov et al. (2013a,b) and the availability of regularly/new observations from CODE TEC data. The cornerstone of the hybrid model consists of applying the method of autocorrelation prediction of the error and the respective correction of the background model with the predicted error. An important question is how the efficiency of the correction procedure depends on the given offset, i.e. the time distance between the dates for which the prediction is made to that with real data. It was found that the correction is really effective if the error prediction is made for a date with a distance up to 60 days from the date with real data. Then the RMSE decreases from 3.2 TECU (for the global background TEC model) to 2.76 TECU (for the hybrid model) which demonstrates the advantage of the presented in this paper hybrid model for long-term prediction with respect to the originally built background TEC model.


      PubDate: 2014-06-14T18:17:08Z
       
  • Electric field signatures of the IAR and Schumann resonance in the upper
           ionosphere detected by Chibis-M microsatellite
    • Abstract: Publication date: Available online 3 June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): D. Dudkin , V. Pilipenko , V. Korepanov , S. Klimov , R. Holzworth
      We tried to find with the ULF/ELF electric field sensor onboard Chibis-M microsatellite signatures of the IAR (Ionospheric Alfvén Resonator) and Schumann Resonance (SR) in the upper ionosphere. Whereas observations of the IAR and SR multi-band emissions with ground magnetometers are ubiquitous, in-situ satellite observations of their signatures are very rare. ULF events detected by the Chibis-M show a possibility of triggered excitation of IAR. In contrast to dominating view, IAR has been found to be effectively excited on the dayside, too. Chibis-M observations also supported the possibility of the SR leakage into the upper ionosphere.


      PubDate: 2014-06-14T18:17:08Z
       
  • Comparison of GPS-TEC measurements with IRI-2007 and IRI-2012 modeled TEC
           at an equatorial latitude station, Bangkok, Thailand
    • Abstract: Publication date: Available online 9 June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Sanit Arunpold , Nitin K. Tripathi , V. Rajesh Chowdhary , Durairaju Kumaran Raju
      This paper presents the first vertical total electron content (VTEC) data derived from a dual-frequency GPS receiver installed at the Asian Institute of Technology in Bangkok, as part of project SCINDA (Scintillation Network and Decision Aid). with a magnetic dip latitude of 14°N, The diurnal, monthly, and seasonal variation in TEC, measured between August 2010 and July 2012, was compared with values derived from two International Reference Ionosphere (IRI) models: the IRI-2007 and the recently released IRI-2012. The highest diurnal TEC always occurred between 08:00 and 12:00 Universal Time (UT). The diurnal pattern of GPS-TEC reached its maximum values during equinoctial months (March, April, September, and October) and minimum values during solstice months (June, July, December, and January), which can be attributed to the solar extreme ultra-violet ionization coupled with the upward vertical ExB drift. The modeled TEC was underestimated in 2010 and 2011 and overestimated in 2012, especially with the IRI-2007 model. The measured values were better correlated with the IRI-2012 model, especially in 2012. However, neither of the IRI models responded to geomagnetic activity, despite the selection of the “storm” option, generally showing a smooth curve and underestimating TEC during a storm. To verify this phenomenon, the impacts of geomagnetic storms were considered.


      PubDate: 2014-06-14T18:17:08Z
       
  • Equinoctial asymmetry in low latitude ionosphere as observed by SROSS-C2
           satellite
    • Abstract: Publication date: Available online 11 June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Ananna Bardhan , Malini Aggarwal , D.K. Sharma , J. Rai
      The ionospheric plasma parameters (electron, ion temperatures and ion composition-Te, Ti, O+ and H+) measured by SROSS-C2 satellite at an average altitude of ~500km has been investigated to study the behaviour of the ionosphere in equinoxes during half a solar cycle (year 1995 to 2000, F10.7~70 to 195). The region under study spans over 5°–35°N geog. latitude and 65°–95°E geog. longitude in the Indian sector. We found an equinoctial asymmetry in the diurnal behaviour of Te, Ti, O+ and H+ varying with increase in solar activity. The strength of equinoctial asymmetry in Te and Ti is strong during early morning and daytime and strength decreases with increase in solar activity whereas during night time no asymmetry/weaker is observed in low/high solar activity respectively. During the day time, a very strong equinoctial asymmetry in O+ is observed during solar minimum which diminishes with increase in solar activity. The similar diurnal behaviour of H+ as that of O+ is observed during low solar activity but no clear equinoctial asymmetry is observed during solar maximum, as H+ being highly dynamic. The transition height (O+/H+) is lowest in early morning during solar minimum, which increases during local day-time. The rate of increase in transition height is different in both the equinoxes (higher in vernal than autumn) with respect to dependence on the solar activity, during daytime. Hence equinoctial asymmetry is stronger during solar minimum period than maximum, with higher/lower transition height in vernal during daytime/nighttime respectively.


      PubDate: 2014-06-14T18:17:08Z
       
  • Diurnal tide in the low-latitude troposphere and stratosphere: Long-term
           trends and role of the extended solar minimum
    • Abstract: Publication date: Available online 12 June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      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 (13.5oN, 79.2oE) 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. Significant 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: 2014-06-14T18:17:08Z
       
  • On the characteristic parameters of magnetic storms during two solar
           cycles
    • Abstract: Publication date: July 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 114
      Author(s): R. Monreal MacMahon , C. LLop-Romero
      Relationships between characteristic parameters of geomagnetic storms like the pressure corrected Dst index (Dst ⁎), the solar wind speed, the southward component of the interplanetary magnetic field B S , and their associated times were studied during two solar cycles and for approximately 300 storm events extracted from the OMNI database (1974–1996) to further analyze what drives Dst ⁎ not only during storms but also during non-storm times. Analyzing the whole data set, that is considering storm time and the less disturbed (nonstorm) times, we infer that outside the storm phases the dominant driver role is played by the solar wind speed and that its role during storms is usually not negligible. However, as expected, during the main and recovery phases of magnetic storms the driving parameter is the dawn-dusk component of the interplanetary electric field vB S , where the main role is played by B S . We found that the Dst ⁎ peak grows monotonically with the peak of B S . The duration time t B s that B S remains over a certain threshold value grows linearly with the peak of Dst ⁎ for weak, moderate and some intense storms. For more intense events the growth rate diminishes and probably vanishes. Significant differences appear when the correlation between the peaks of Dst ⁎ and B S is analyzed during the different solar cycle phases. That correlation and also the recurrence of our chosen storms have a periodic behavior, similar to the solar cycle. The most of storms are registered during the ascending phases of the solar cycle and sunspot maxima, however the higher correlations between the peaks of B S and Dst ⁎ are found during minima and ascending phases of the solar cycle.


      PubDate: 2014-06-14T18:17:08Z
       
  • New types of simple non-linear models to compute solar global irradiance
           from cloud cover amount
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): Viorel Badescu , Alexandru Dumitrescu
      Most simple solar radiation models are built with reference to a basic model calibrated for clear sky conditions. New models are built in this paper with reference to two basic models, calibrated for clear sky and overcast sky conditions, correspondingly. The models are illustrated with measurements data from five meteorological stations in Romania (South-Eastern Europe), where the ratio between the solar irradiance on overcast sky and clear sky, respectively, ranges between 0.27 and 0.55. A three-parameter model is used for both basic models. Three new types of regression models were developed from the two basic models. They are non-linear generalizations of the Angstrom–Savinov model. Their accuracy decreases by increasing the cloud cover amount. One model has been further tested. A set of regression coefficients has been obtained by fitting that model to all available data, for all stations. The model based on this set of regression coefficients has good accuracy in any particular station, when low and intermediate cloudy skies are considered. The model based on a set of regression coefficients obtained in a given station was tested in other stations. Its accuracy is good (or marginally, good enough) on skies with low and intermediate cloudy skies. Its accuracy is good for intermediate zenith angles, ranging between 30° and 70°.


      PubDate: 2014-06-14T18:17:08Z
       
  • IFC-Ed. board
    • Abstract: Publication date: July 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 114




      PubDate: 2014-06-14T18:17:08Z
       
  • Characteristics of E-region background ionosphere and plasma waves
           measured over the dip equator during total solar eclipse campaign
    • Abstract: Publication date: July 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 114
      Author(s): R. Sekar , S.P. Gupta , D. Chakrabarty
      A unique set of rocket flight measurements of plasma parameters from the dip equator (Thumba; 8.5°N, 76.5°E, dip 0.5°S) was carried out at two obscuration levels (40% and 72%) on a total solar eclipse day (16 February 1980) which was also under a moderately disturbed geomagnetic condition. The path of totality was 400km north of Thumba. Another rocket flight was conducted on 17 February 1980 to obtain the control day measurement at the same local time. As expected, the electron densities are found to be less throughout the measured altitude region on a solar eclipse day with the 72% obscuration level compared to the control day at the same local time (same solar zenith angle). In the presence of average electron density scale length of 10 and 9km in the altitude region of 88–100km, the initiation of the gradient drift waves is observed at altitudes of 91 and 93km during 40% and 72% obscuration levels respectively on a solar eclipse day. However, on a control day, in the presence of average electron density scale length of 9km, these waves are found at altitude as low as 88km. In addition, the amplitude of the gradient drift waves is found to be the largest during the 72% obscuration level compared to those during the 40% obscuration level and control day. In the absence of electric field measurements, the magnetometer observations are used to infer an increase in the polarization electric field when the obscuration level is around 72%. This along with steeper gradient can account for the increase in the amplitude of gradient drift waves during 72% obscuration compared to 40% obscuration. The relative role of the growth and decay of the gradient drift waves is discussed in the context of these observations.


      PubDate: 2014-06-14T18:17:08Z
       
  • Signatures of ultra fast Kelvin waves in low latitude ionospheric TEC
           during January 2009 stratospheric warming event
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): D.V. Phanikumar , K. Niranjan Kumar , Sanjay Kumar
      In this study, for the first time, planetary wave signatures in ionospheric Total Electron Content (TEC) retrieved from global positioning service (GPS), mesospheric wind and temperature at low latitude station has been identified during January–February 2009. Our investigations revealed that planetary waves with 3–5 days periodicity characterized as ultrafast Kelvin (UFK) waves caused by stratospheric warming event during January 2009. The UFK waves are observed to be propagated from lower atmosphere to ionosphere. The UFK perturbations during SSW event are discussed in the light of current understanding of role of non linear interaction of planetary waves to modulate low latitude ionosphere.


      PubDate: 2014-06-14T18:17:08Z
       
  • On the vertical distribution of carbon monoxide over Bay of Bengal during
           winter: Role of water vapour and vertical updrafts
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): I.A. Girach , Prabha R. Nair
      The differences in the spatial pattern of column carbon monoxide (CO) and in-situ measured near-surface CO over Bay of Bengal (BoB) during winter were examined in the light of vertical distribution of CO as retrieved from MOPITT (Measurements Of Pollution In The Troposphere) on board Terra spacecraft. The column CO showed relatively high values over southern-BoB whereas the near-surface CO showed low mixing ratio indicating the existence of significant amount of CO at higher altitudes. The vertical profiles of CO over the BoB region retrieved from MOPITT exhibit a high altitude peak around ~9km altitude region. The role of water vapour and convective activity/vertical updrafts in establishing the observed vertical profile of CO was investigated. It is found that CO got uplifted to the higher altitude due to updrafts and water vapour caused depletion of CO at lower altitudes which appeared as an apparent high in CO mixing ratio at higher altitude relative to that over lower altitude. The role of water vapour in the destruction of CO was confirmed by box model simulations. Airmass back-trajectory analysis showed that the long range transport from lower troposphere/boundary layer was also partially responsible for higher mixing ratios at higher altitude. In addition, a comparison of in-situ measured near-surface CO and those retrieved from MOPITT using retrieval algorithm Versions 4 and 5 showed that the points of discrepancy have reduced in the Version 5. Biomass burning and anthropogenic activities taking place over the Myanmar landmass was found to be responsible for the hot spots of near-surface-CO over the northeast-BoB.


      PubDate: 2014-06-14T18:17:08Z
       
  • A study on wind dynamics during convective processes using the
           Postset-beam-steering technique
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): V.K. Anandan , V.N. Sureshbabu , S. Vijayabhaskara Rao , Shridhar Kumar
      This paper demonstrates the potential of the Postset-beam-steering (PBS) technique on a VHF multi receiver profiler radar for studying convective processes over the Middle and Upper (MU) atmospheric radar located at Shigaraki (34.85°N, 136.10°E), Japan. During times of convection, it is difficult to study the atmospheric processes by normal radar observational methods due to instantaneous changes in the wind fields over the position and time. Meanwhile, it is important to know the simultaneous changes in vertical and horizontal wind fields for studying the evolution of atmospheric processes and the dynamics associated with it. PBS, as a means of software beam steering, overcomes such difficulties in estimating atmospheric wind parameters because of a number of inherent signal processing algorithms associated with the technique itself. The main objective of the present work includes major investigations of fast changing 3-D wind fields and the processes associated with it. Further, the advantages of the PBS for studying the spatial variability in winds, circulation patterns, mixing process, momentum flux and vorticity during the atmospheric convection are presented through a set of examples.


      PubDate: 2014-06-14T18:17:08Z
       
  • Transmission of planetary wave effects to the upper atmosphere through
           eddy diffusion modulation
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): Vu Nguyen , S.E. Palo
      Past observations have shown that the effects of planetary waves can travel beyond their dissipation region and into the thermosphere and ionosphere. One possible mechanism through which this event can occur is the modulation of turbulent mixing near the turbopause. Because turbulent mixing in the mesosphere–lower thermosphere is strongly dependent on the amount of wave dissipation, planetary wave filtering of gravity waves from below can indirectly modulate the amount of turbulent mixing. This study uses the NCAR TIE-GCM to investigate how this mechanism induces variability in upper atmospheric composition and density. It is shown that varying the amount of turbulent mixing at discrete planetary wave periods induces similar periodicities in neutral and electron density. This process is driven by species diffusive flux through isobaric (constant pressure) levels, resulting in atmospheric contraction or expansion. Results also indicate that the mechanism studied has a wave frequency dependence and is most effective for long period planetary waves.


      PubDate: 2014-06-14T18:17:08Z
       
  • Traveling planetary wave ionospheric disturbances and their role in the
           generation of equatorial spread-F and GPS phase fluctuations during the
           last extreme low solar activity and comparison with high solar activity
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): A.J. de Abreu , P.R. Fagundes , M.J.A. Bolzan , M. Gende , C. Brunini , R. de Jesus , V.G. Pillat , J.R. Abalde , W.L.C. Lima
      This investigation studies traveling planetary wave ionospheric disturbance (TPWID) type oscillations on the modulation of the F region virtual height rise during the E×B electric field pre-reversal enhancement (PRE), near sunset hours. We also studied their role in the generation of equatorial spread F (ESF) and GPS phase fluctuations during periods of the last extreme low solar activity (LSA) of January 2009 to April 2010 ( F 10.7 ¯ = 73 ) . A comparison is made with periods of high solar activity (HSA) in 2003 and 2004 near equatorial region. The ionospheric irregularities investigated are medium (bottom-side) and large (plasma bubble) scales. Ionospheric F region oscillations with period of days are due to the TPWIDs, which play an important role in producing favorable or unfavorable conditions for equatorial ionospheric irregularities, changing the electron vertical profile and F region height. In this paper, we present simultaneous ionospheric sounding (ionosonde) and GPS vertical total electron content (vTEC) observations carried out near equatorial region (Palmas 10.2°S, 48.2°W) and low latitude region (São José dos Campos 23.2°S, 45.9°W; located under the southern crest of the equatorial ionospheric anomaly), Brazil. Observations show that the occurrence of fresh ESF during LSA and HSA and fresh GPS phase fluctuations at equatorial region follow the trend of day-to-day variations in the F region virtual height, which are due to electric field PRE modulated by TPWID wave like oscillations. During LSA, the altitude of 250km acts as a threshold height for the generation of fresh ionospheric irregularities, whereas during HSA, the threshold height is 300km. The observations also found a strong increase in the generation of fresh ionospheric irregularities from October 2009 to March 2010 during LSA and from September 2003 to March 2004 during the HSA. Furthermore, in LSA, the period of fresh ionospheric irregularities was less than during HSA, though both periods followed a similar seasonal pattern. In the low-latitude, we observed more ESFs than phase fluctuations because ionosonde is more sensitive than GPS. We also observed periods with and without day-to-day oscillations in the F region virtual height. The observations made by GPS stations and ionosondes in the equatorial region, for much of the period analyzed, presented similar results with regard to the generation of equatorial ionospheric irregularities. In the low latitude, some nights of January, February, October, and December 2009 also showed a similarity.


      PubDate: 2014-06-14T18:17:08Z
       
  • Subseasonal variability of water vapor in the upper stratosphere/lower
           mesosphere over Northern Europe in winter 2009/2010
    • Abstract: Publication date: Available online 13 April 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): D.H.W. Peters , K. Hallgren , F.-J. Lübken , P. Hartogh
      For the upper stratosphere and lower mesosphere (USLM) we used microwave spectrometer measurements of water vapor to investigate the cause of subseasonal variability over Northern Europe: at ALOMAR (Andenes, 69.3°N, 16.1°E), Northern Norway, and at the Leibniz Institute of Atmospheric Physics, (Kühlungsborn, 54.2°N, 11.8°E), Northern Germany, for winter 2009/ 2010. The MERRA data set of NASA is applied to study the dynamical link between the local variability of H2O and transport in the USLM. Beside a slow increase in January and a stronger decrease in February and March 2010, episodes of significant increase and decrease of H2O were found over Northern Germany. These structural changes are in good agreement with MERRA which show similar patterns induced by a dominant conservative horizontal transport of H2O. Due to the strong negative meridional gradient and mixing barrier, higher values of water vapor have been observed outside the polar vortex and lower values inside. We found that the complex polar vortex evolution over Northern Germany during the minor stratospheric sudden warming (mSSW) in the beginning of December 2009 and the major warming (MSSW) at the end of January 2010, as well as between the two, fit well into this relationship. An episode of strong increase in water vapor over ALOMAR at about 55–60km altitude was observed during the MSSW on the 27th of January 2010 resulting in a significant double peak in altitude. Based on MERRA data we show that this dual peak was caused by a relatively strong regional northward propagation of more moist air in the lower mesosphere. In the lower mesosphere strong polar intrusion of warm and moist air occurred mainly over Northern Europe resulting in a well-mixed polar anticyclone on the 30th of January. In comparison with observations the local maxima of H2O in MERRA are underestimated by approximately 1–2ppmv. After the MSSW, the vertical descent rate of the MERRA reanalysis is half as much as the observed one over Kühlungsborn. Nevertheless the high coherence between local water vapor measurements over Northern Germany and Northern Norway, and MERRA support the extended use of MERRA for subseasonal transport studies in the USLM. We conclude that the observed strong subseasonal variability of H2O in the USLM over Northern Europe, especially over Kühlungsborn and over ALOMAR, during the winter 2009/2010 was caused by the passage of the edge of polar vortex and linked transport of H2O.


      PubDate: 2014-04-29T13:47:17Z
       
  • Correlations between Sunspot numbers, Interplanetary Parameters and
           geomagnetic trends over solar cycles 21, 22 and 23
    • Abstract: Publication date: Available online 18 April 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Kusumita Arora , N.Phani Chandrasekhar , Nandini Nagarajan , Ankit Singh
      We have analyzed correlations between sunspot numbers, solar wind, ion density, interplanetary magnetic field vis-à-vis magnetic activity. Planetary geomagnetic index (Ap) and local residual measure of magnetic activity (IΔH) from low-latitude Magnetic Observatory, CSIR-NGRI, Hyderabad (IMO-HYB) spanning solar cycles 21 – 23 are used for this study. Using correlation coefficients between and wavelet decomposition of sunspot numbers, interplanetary parameters and measures of magnetic activity, the complex and time varying nature of these inter-relationships are brought out. The overall influence of sunspot number could be separated and combined episodic effects of other solar parameters could be distinguished. The demonstrated correlation or lack of it, between measures of magnetic activity (Ap and IΔH), and all the parameters of solar activity, presented here corroborate established mechanisms as well as delineated clearly the relative impact of different solar mechanisms over phases of three solar cycles. The possible role of non-sunspot related activity from high latitude regions of the sun is indicated.


      PubDate: 2014-04-29T13:47:17Z
       
  • Storm-time behaviors of O/N2 and NO variations
    • Abstract: Publication date: Available online 25 April 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Y. Zhang , L.J. Paxton , D. Morrison , D. Marsh , H. Kil
      Algorithms have been developed to extract net nitric oxide (NO) radiances in the wavelength range of 172–182nm from the dayside TIMED/GUVI spectrograph data and convert them to NO column density (100–150km). The thermospheric O/N2 column density ratios (referenced from an altitude ~135km with a N2 column density of 1017 cm−2) are also obtained from the spectrograph data. The spatial resolution of the NO and O/N2 products along the GUVI orbit is 240km. The coincident O/N2 ratio and NO column density maps during a few geomagnetic storms reveal two major features: (1) Storm-time O/N2 depletion and NO enhancement extend from high to mid and low latitudes. They are anti-correlated on a global scale, (2) the NO enhancement covers a wider longitude and latitude region than O/N2 depletion on a local scale. The similarity between O/N2 depletion and NO enhancement on global scale is due to storm-time equatorward meridional wind that brings both O/N2 depleted and NO enhanced air from high to low latitudes. The altitude dependence of the storm-time meridional wind, different peaks altitudes of the local O/N2 and NO variations, and long life time of NO (one day or longer) may explain the different behaviors of O/N2 and NO on a local scale.


      PubDate: 2014-04-29T13:47:17Z
       
  • Investigation of localized 2D convection mapping based on artificially
           generated swarm ion drift data
    • Abstract: Publication date: Available online 26 April 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): R.A.D. Fiori , D.H. Boteler , A.V. Koustov , D. Knudsen , J.K. Burchill
      Ionospheric plasma flow is an indicator of the interconnection between the solar wind, interplanetary magnetic field (IMF), and Earth's magnetosphere. Ionospheric convection has been mapped in the past using either a widespread data set for instantaneous convection mapping over a short time period or data from an instrument measuring convection in a spatially confined region over a long time period for the purpose of building a statistically-averaged convection pattern. This study explores convection mapping using a spherical cap harmonic analysis (SCHA) technique within a localized spherical cap based on data that will be available from the Swarm three-satellite constellation. Convection is mapped in the vicinity of hypothetical Swarm satellite tracks where it is adequately constrained by data. By using statistical models to emulate Swarm measurements, we demonstrate that such mapping can be successful based on data from the Swarm A and Swarm B satellites. Convection is divided into well constrained and poorly constrained subsets to determine parameters characterizing goodness-of-fit based on known quantities. Using the subset of well constrained maps, it is determined that convection is best mapped for a spherical cap having an angular radius of θ c =10°. The difference between the maximum mapped convection and the maximum velocity measured along the satellite track (Δv) is introduced to evaluate goodness-of-fit. For the examples presented in this paper, we show that a threshold value of Δv=281m/s successfully differentiates between well and poorly constrained maps 77.6% of the time. It is shown that convection can be represented over a larger region through the use of multiple spherical caps.


      PubDate: 2014-04-29T13:47:17Z
       
  • SBAS operation in the Indian sector under simultaneous scintillation on
           different GNSS links
    • Abstract: Publication date: Available online 26 April 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): S.K. Chakraborty , S. Chatterjee , A. DasGupta
      Scintillation observations of transionospheric signals from two GEOs (55°E and 140°E) and from the satellite constellations of GPS and GLONASS are carried out simultaneously during the equinoctial months of high solar activity years (2011–2012) from Raja Peary Mohan College (RPMC) center situated near the equatorial ionization anomaly (EIA) crest to study the vulnerability conditions of SBAS operation. Scintillations in excess of∼10dB are recorded simultaneously in the two GEO links in∼8% of the observing days with an average duration of∼28minutes. Under this condition the availability of GPS and GLONASS also falls below the optimum number (4) necessary for navigation solution, rendering the SBAS operation doubtful. GPS is found to be more susceptible to exhibit receivers’ loss of lock than the GLONASS. The study reveals that two GEO links with pierce point longitude separation of∼10° are not suitable for maintaining faithful SBAS opeartion around the EIA crest. Occurrence of GEO scintillations are found to be associated with the strength and duration of the emerging post sunset EIA structure.


      PubDate: 2014-04-29T13:47:17Z
       
  • Study of local regularities in solar wind data and ground magnetograms
    • Abstract: Publication date: May 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 112
      Author(s): Virginia Klausner , Arian Ojeda González , Margarete Oliveira Domingues , Odim Mendes , Andres Reinaldo Rodriguez Papa
      Interplanetary coronal mass ejections (ICMEs) can reach the Earth׳s magnetosphere causing magnetic disturbances. For monitoring purposes, some satellites measure the interplanetary parameters which are related to energy transfer from solar wind into magnetosphere, while ground-based magnetometers measure the geomagnetic disturbance effects. Data from the ACE satellite and from some representative magnetometers were examined here via discrete wavelet transform (DWT). The increase in the amplitude of wavelet coefficients of solar wind parameters and geomagnetic field data is well-correlated with the arrival of the shock and sheath regions, and the sudden storm commencement and main phase, respectively. As an auxiliary tool to verify the disturbed magnetic fields identified by the DWT, we developed a new approach called effectiveness wavelet coefficient (EWC) methodology. The first interpretation of the results suggests that DWT and EWC can be effectively used to characterize the fluctuations on the solar wind parameters and their contributions to the geomagnetic field. Further, this kind of technique could be implemented in quasi real-time to facilitate the identification of the shock and the passage of the sheath region which sometimes can be followed by geoeffective magnetic clouds. Also, the technique shows to be very useful for the identification of time intervals in the dataset during geomagnetic storms which are associated to interplanetary parameters under very well defined conditions. It allows selecting ideal events for investigation of magnetic reconnection in order to highlight in a more precise manner the mechanisms existing in the electrodynamical coupling between the solar wind and the magnetosphere.


      PubDate: 2014-04-29T13:47:17Z
       
  • A statistical analysis of occurrence characteristics of Spread-F
           irregularities over Indian region
    • Abstract: Publication date: May 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 112
      Author(s): A.K. Upadhayaya , Sumedha Gupta
      We investigate the regularities of a change in Spread-F F probability during day-to-day, under varying solar variability, latitudinal behavior and their response to geomagnetic storm in equatorial and low-mid latitude stations. The occurrence characteristics of Spread-F irregularities, is obtained from daily hourly ionosonde data from a low-mid latitude station, Delhi (28.6°N, 77.2°E), for more than half a solar cycle (2001 to 2007). The latitudinal behavior of Spread-F is studied using ionosonde data from anomaly crest station, Ahmedabad (23.01°N, 72.36°E) and equatorial station, Kodaikanal (10.2°N, 77.5°E) for low, moderate and high solar activity periods. The maximum percentage occurrences of Spread-F were observed during the low solar activity year 2007, we believe, the low plasma and neutral density during 23/24 solar cycle minimum could be an important factor leading to the generation and propagation of TIDs and gravity waves. An anti-solar activity correlation to Spread-F occurrence is reported during all the seasons at different stations which are because of instability generated by the trans-equatorial meridional winds. There is a substantial variation during pre and post midnight hours in F region height from equatorial to low latitudes in response to magnetic disturbances. Concurrence was observed in the occurrence time of Spread-F to different storm events during different storm phases. The established irregularities and their behavior in Indian region are qualitatively interpreted and discussed.


      PubDate: 2014-04-29T13:47:17Z
       
  • IFC-Ed. board
    • Abstract: Publication date: May 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 112




      PubDate: 2014-04-29T13:47:17Z
       
  • The role of the traveling planetary wave ionospheric disturbances on the
           equatorial F region post-sunset height rise during the last extreme low
           solar activity and comparison with high solar activity
    • Abstract: Publication date: June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 113
      Author(s): A.J. de Abreu , P.R. Fagundes , M.J.A. Bolzan , R. de Jesus , V.G. Pillat , J.R. Abalde , W.L.C. Lima
      This investigation studies traveling planetary wave ionospheric disturbance (TPWID) type oscillations on the modulation of the F region post-sunset height rise during the electric field pre-reversal enhancement (PRE). The studied period, from January 2009 to April 2010, occurred during the extremely low solar activity, when the averaged F10.7 was 73 [W/m2 Hz]. In addition, the results are compared with those for a high solar activity period of 2003. We present ionospheric sounding observations carried out near equatorial region (Palmas 10.2°S, 48.2°W, dip latitude 5.5°S) and low latitude region (São José dos Campos 23.2°S, 45.9°W, dip latitude 17.6°S; located under the southern crest of the equatorial ionospheric anomaly) in the Brazilian sector. The studies found that the magnitude of the electric field during PRE time and consequently the day-to-day variations of the F region virtual height at equatorial region and low latitude are modulated by waves with periods of around 3–4, 5–6, 10–15, and 24–35 days. The observations show that during low solar activity, the TPWID oscillations are lower than during high solar activity, but with the same amplitude around 200km. The TPWID long period oscillations of around 27 days present very distinct characteristics at the equatorial region and low latitude, indicating that these regions are not directly connected. Our study also shows that the response to the TPWID short period of around 3–4, 5–6, and 10–15 days at the equatorial region and low latitude present very clear coupling during January–February, 2009, possibly due to the sudden stratospheric warming and TPWID mechanisms.


      PubDate: 2014-04-29T13:47:17Z
       
  • The occurrence of coronal holes during the sunspot cycle
    • Abstract: Publication date: June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 113
      Author(s): H. Machiya , S.-I. Akasofu
      In order to learn the nature of coronal holes for a long period, magnetic disturbances represented by the geomagnetic index C9 (though proxy for coronal holes) for the period from 1884 to 2002 are examined, selecting only those that recur every 27 days during at least six solar rotation periods and separating the rising and declining phases, and also distinguishing one and two coronal holes in one solar rotation. It was found that the occurrence of coronal holes per year (N) during both the rising and the declining phases tends to be more frequent for greater numbers of the peak value of sunspots (R) in each sunspot cycle. The frequency per year is about twice as large for the declining phase as for the rising phase. The N–R relationship is 0.0080R+0.302 for the rising phase and 0.0152R+0.203 for the declining phase.


      PubDate: 2014-04-29T13:47:17Z
       
  • Modification of lightning quasi-electrostatic signal by mesospheric halo
           generation
    • Abstract: Publication date: June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 113
      Author(s): A.J. Bennett
      Current induced by the electrostatic component of lightning on a conductor exposed to the atmosphere was measured at 100Hz by detectors at two sites in southern England. These detectors were separated by 120km and capable of lightning detection to a range of approximately 100km. Signals from the same flash detected by both receivers were generally of the same shape, as expected if the source was charge neutralisation by lightning of relatively small horizontal extent. For approximately 1% of flashes detected the signal shape received at both sites was considerably different, indicating that the small vertical dipole approximation was not sufficient to explain the detected charge reconfiguration during the flash. This discrepancy was explained by the addition of a short pulse of horizontally extensive charge above the flash, consistent with a mesospheric halo. The effect of this halo superimposed on the signal from the parent lightning is described. The observations support previous evidence that quasi-static current measurement can be used to identify flashes which produce halos and so complement existing optical halo detection instrumentation.


      PubDate: 2014-04-29T13:47:17Z
       
  • A new procedure for obtaining vertical total electron content from two
           frequency LEOS beacons
    • Abstract: Publication date: June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 113
      Author(s): Dmitry Shatskiy , Ludmila M. Kagan , John W. MacDougall
      A new procedure is suggested for obtaining VTEC from slant TEC two frequency measurements. To verify the procedure an inexpensive portable digital receiver was used to measure ionospheric total electron content (TEC). Experimental results agree well with the data from a nearby ionosonde and the International Reference Ionosphere (IRI) model. Orientations of traveling ionospheric disturbances (TIDs) present in the area at the time of the recording were obtained from the small-scale variations of TEС in a two-station configuration. The results are consistent with the diurnal TID pattern.


      PubDate: 2014-04-29T13:47:17Z
       
  • Long-term evolution of corrected NOAA/MEPED energetic proton fluxes and
           their relation to geomagnetic indices
    • Abstract: Publication date: June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 113
      Author(s): Timo Asikainen , Kalevi Mursula
      We study the relationship between energetic 120–250keV proton fluxes and geomagnetic Ap, AE, Dxt indices using the recently corrected measurements of the MEPED instrument onboard the low-altitude NOAA/POES satellites. Corrected database spans from 1979 to present, and allows us to reliably study the long-term variation of energetic proton fluxes over several solar cycles. Contrary to uncorrected fluxes, which can be more than an order of magnitude too low, the corrected fluxes display a systematic solar cycle variation closely resembling the variation of Ap and AE indices with a maximum in the declining solar cycle phase and a minimum in solar minimum. We also find that trapped fluxes are enhanced relative to precipitating fluxes in the declining phases and solar minima. This supports the fact that high-speed solar wind streams are the most significant driver of energetic proton fluxes. We compute the correlations between fluxes and indices in a range of time scales, and show that they are significantly improved by the flux correction. We find that precipitating fluxes correlate better than trapped fluxes with Ap/AE indices at all time scales, and the highest correlation is found with Ap. For precipitating fluxes these correlations depend weakly on time scale, but for trapped fluxes the correlation significantly increases from daily scale to solar rotation and longer time scales. Comparing the fluxes to Dxt index shows a complex relationship, where the fluxes depend not only on Dxt value but also on its time derivative.


      PubDate: 2014-04-29T13:47:17Z
       
  • Variation of OC, EC, WSIC and trace metals of PM10 in Delhi, India
    • Abstract: Publication date: June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 113
      Author(s): S.K. Sharma , T.K. Mandal , Mohit Saxena , Rashmi , A. Sharma , A. Datta , T. Saud
      Variation of organic carbon (OC), elemental carbon (EC), water soluble inorganic ionic components (WSIC) and major and trace elements of particulate matter (PM10) were studied over Delhi, an urban site of the Indo Gangatic Plain (IGP), India in 2010. Strong seasonal variation was noticed in the mass concentration of PM10 and its chemical composition with maxima during winter (PM10: 213.1±14.9µgm−3; OC: 36.05±11.60µgm−3; EC: 9.64±2.56µgm−3) and minima during monsoon (PM10: 134.7±39.9µgm−3; OC: 14.72±6.95µgm−3; EC: 3.35±1.45µgm−3). The average concentration of major and trace elements (Na, Mg, Al, P, S, Cl, K, CA, Cr, Ti, Fe, Zn and Mn) was accounted for ~17% of the PM10 mass. Average values of K+/EC (0.28) and Cl−/EC (0.59) suggest the influences of biomass burning in PM10, whereas, higher concentration of Ca2+ suggests the soil erosion as possible source from the nearby agricultural field. Fe/Al ratio (0.34) indicates mineral dust as a source at the sampling site, similarly, Ca/Al ratio (2.45) indicates that aerosol over this region is rich in Ca mineral compared to average upper continental crust. Positive matrix factorization (PMF) analysis quantifies the contribution of soil dust (20.7%), vehicle emissions (17.0%), secondary aerosols (21.7%), fossil fuel combustion (17.4%) and biomass burning (14.3%) to PM10 mass concentration at the observational site of Delhi.


      PubDate: 2014-04-29T13:47:17Z
       
  • IFC-Ed. board
    • Abstract: Publication date: June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 113




      PubDate: 2014-04-29T13:47:17Z
       
  • X-rays and solar proton event induced changes in the first mode Schumann
           resonance frequency observed at a low latitude station Agra, India
    • Abstract: Publication date: June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 113
      Author(s): Birbal Singh , Rajesh Tyagi , Yasuhide Hobara , Masashi Hayakawa
      Effects of two events of X-ray bursts followed by solar proton events (SPEs) occurred on 22 September, 2011 and 06 July, 2012 on the variation of first mode Schumann resonance (SR) frequency monitored at a low latitude station, Agra (Geograph. lat. 27.2°N, long. 78°E) India are examined. The variation of average first mode SR frequency shows a sudden increase in coincidence with the X-ray bursts and a decrease associated with the peak flux of SPE. The increases in the frequency in the two cases are 8.4% and 10.9% and corresponding decreases are 4.3% and 3.3% respectively. The increases in the frequency are interpreted in terms of growth of ionization in the upper part of D-region ionosphere due to X-ray bursts and decreases during SPE are caused by the high ionization in the lower D-region (altitude about 50–60km) in the polar region. The variation of SR frequency is observed to be consistent with other observatories at middle and high latitudes. The effects of X-ray flares on the D-region of the ionosphere at low and equatorial latitudes are also examined by analyzing the amplitude data of VLF transmitter signal (NWC, f=19.8kHz) monitored at Agra. The flare effect observed prior to sun-set hours shows increase of electron density above 60km in the ionosphere.


      PubDate: 2014-04-29T13:47:17Z
       
  • Ionospheric irregularities during a substorm event: Observations of ULF
           pulsations and GPS scintillations
    • Abstract: Publication date: July 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 114
      Author(s): H. Kim , C.R. Clauer , K. Deshpande , M.R. Lessard , A.T. Weatherwax , G.S. Bust , G. Crowley , T.E. Humphreys
      Plasma instability in the ionosphere is often observed as disturbances and distortions of the amplitude and phase of the radio signals, which are known as ionospheric scintillations. High-latitude ionospheric plasma, closely connected to the solar wind and magnetospheric dynamics, produces very dynamic and short-lived Global Positioning System (GPS) scintillations, making it challenging to characterize them. It is observed that scintillations in the high-latitude ionosphere occur frequently during geomagnetic storms and substorms. In addition, it is well known that Ultra Low Frequency (ULF) pulsations (Pi2 and Pi1B) are closely associated with substorm activity. This study reports simultaneous observations of Pi2 and Pi1B pulsations and GPS phase scintillations during a substorm using a newly designed Autonomous Adaptive Low-Power Instrument Platform (AAL-PIP) installed at the South Pole. The magnetic field and GPS data from the instruments appear to be associated in terms of their temporal and spectral features. Moreover, the scintillation events were observed near the auroral latitudes where Pi1B pulsations are commonly detected. The temporal, spectral and spatial association between the scintillation and geomagnetic pulsation events suggests that the magnetic field perturbations and enhanced electric fields caused by substorm currents could contribute to the creation of plasma instability in the high-latitude ionosphere, leading to GPS scintillations.


      PubDate: 2014-04-29T13:47:17Z
       
 
 
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