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Found 22 entries in the Bibliography.
Showing entries from 1 through 22
| 2022 |
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An extensive intercomparison of ionospheric foF2 observations and NCAR Thermosphere-Ionosphere ElectrodynamicsGeneral Circulation Model(TIE-GCM)simulations has been carried out for the dip equatorial location of Thiruvananthapuram. Ionosonde measurements for geomagnetically quiet days of 2002, 2006 and 2008, representing solar maximum, solar minimum and deep solar minimum conditions have been used for the analysis. In general TIE-GCM simulations reproduced the temporal and seasonal characteristics of foF2 over Thiruvananthapuram reasonably well for all the three solar activity conditions. Seasonally the difference between the measured and the simulated foF2 tended to be higher during winter (maximum of 25\%). Additionally, it is found that TIE-GCM is not reproducing the reduction in the foF2 values in the noon hours i.e. the bite out, which is very prominent in the foF2 observations predominantly during 2002. A detailed analysis revealed that, there is good agreement between the modeled and measured values for the whole observation period, with an R value of 0.81. From the comparison it is clear that the model underestimates the observations in general but for the periods when bite out is prominent, the model gives an over estimation. The comprehensive comparisons during different solar activity conditions have shown that the difference between modeled and measured ionospheric peak densities lies in the range of. 10 to −25\%. This study brings out the efficacy of the model in simulating the temporal seasonal and solar cycle variability of ionospheric foF2 over the equatorial Indian region. Mridula, N.; Manju, G.; Sijikumar, S.; Pant, Tarun; Published by: Advances in Space Research Published on: may YEAR: 2022 DOI: 10.1016/j.asr.2022.02.018 |
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Total Electron Content Variations during an HSS/CIR driven storm at high and middle latitudes Geethakumari, Gopika; Aikio, Anita; Cai, Lei; Vanhamaki, Heikki; Pedersen, Marcus; Coster, Anthea; Marchaudon, Aurélie; Blelly, Pierre-Louis; Haberle, Veronika; Maute, Astrid; Ellahouny, Nada; Virtanen, Ilkka; Norberg, Johannes; Soyama, Shin-Ichiro; Grandin, Maxime; Published by: Published on: mar YEAR: 2022 DOI: 10.5194/egusphere-egu22-8194 |
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The ionospheric effects of six intense geomagnetic storms with Dst index ≤ −100 nT that occurred in 2012 were studied at a low-latitude station, Darwin (Geomagnetic coordinates, 21.96° S, 202.84° E), a low-mid-latitude station, Townsville (28.95° S, 220.72° E), and a mid-latitude station, Canberra (45.65° S, 226.30° E), in the Australian Region, by analyzing the storm–time variations in the critical frequency of the F2-region (foF2). Out of six storms, a storm of 23–24 April did not produce any ionospheric effect. The storms of 30 September–3 October (minimum Dst = −122 nT) and 7–10 October (minimum Dst = −109 nT) are presented as case studies and the same analysis was done for the other four storms. The storm of 30 September–3 October, during its main phase, produced a positive ionospheric storm at all three stations with a maximum percentage increase in foF2 (∆foF2\%) of 45.3\% at Canberra whereas during the recovery phase it produced a negative ionospheric storm at all three stations with a maximum ∆foF2\% of −63.5\% at Canberra associated with a decrease in virtual height of the F-layer (h’F). The storm of 7–10 October produced a strong long-duration negative ionospheric storm associated with an increase in h’F during its recovery phase at all three stations with a maximum ∆foF2\% of −65.1\% at Townsville. The negative ionospheric storms with comparatively longer duration were more pronounced in comparison to positive storms and occurred only during the recovery phase of storms. The storm main phase showed positive ionospheric storms for two storms (14–15 July and 30 September–3 October) and other three storms did not produce any ionospheric storm at the low-latitude station indicating prompt penetrating electric fields (PPEFs) associated with these storms did not propagate to the low latitude. The positive ionospheric storms during the main phase are accounted to PPEFs affecting ionospheric equatorial E × B drifts and traveling ionospheric disturbances due to joule heating at the high latitudes. The ionospheric effects during the recovery phase are accounted to the disturbance dynamo electric fields and overshielding electric field affecting E × B drifts and the storm-induced circulation from high latitudes toward low latitudes leading to changes in the natural gas composition [O/N2] ratio. Published by: Atmosphere Published on: mar YEAR: 2022 DOI: 10.3390/atmos13030480 Geomagnetic storms; \textbfE × \textbfB drifts; disturbance dynamo electric fields; prompt penetrating electric fields; storm-induced circulation |
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The ionospheric effects of six intense geomagnetic storms with Dst index ≤ −100 nT that occurred in 2012 were studied at a low-latitude station, Darwin (Geomagnetic coordinates, 21.96° S, 202.84° E), a low-mid-latitude station, Townsville (28.95° S, 220.72° E), and a mid-latitude station, Canberra (45.65° S, 226.30° E), in the Australian Region, by analyzing the storm–time variations in the critical frequency of the F2-region (foF2). Out of six storms, a storm of 23–24 April did not produce any ionospheric effect. The storms of 30 September–3 October (minimum Dst = −122 nT) and 7–10 October (minimum Dst = −109 nT) are presented as case studies and the same analysis was done for the other four storms. The storm of 30 September–3 October, during its main phase, produced a positive ionospheric storm at all three stations with a maximum percentage increase in foF2 (∆foF2\%) of 45.3\% at Canberra whereas during the recovery phase it produced a negative ionospheric storm at all three stations with a maximum ∆foF2\% of −63.5\% at Canberra associated with a decrease in virtual height of the F-layer (h’F). The storm of 7–10 October produced a strong long-duration negative ionospheric storm associated with an increase in h’F during its recovery phase at all three stations with a maximum ∆foF2\% of −65.1\% at Townsville. The negative ionospheric storms with comparatively longer duration were more pronounced in comparison to positive storms and occurred only during the recovery phase of storms. The storm main phase showed positive ionospheric storms for two storms (14–15 July and 30 September–3 October) and other three storms did not produce any ionospheric storm at the low-latitude station indicating prompt penetrating electric fields (PPEFs) associated with these storms did not propagate to the low latitude. The positive ionospheric storms during the main phase are accounted to PPEFs affecting ionospheric equatorial E × B drifts and traveling ionospheric disturbances due to joule heating at the high latitudes. The ionospheric effects during the recovery phase are accounted to the disturbance dynamo electric fields and overshielding electric field affecting E × B drifts and the storm-induced circulation from high latitudes toward low latitudes leading to changes in the natural gas composition [O/N2] ratio. Published by: Atmosphere Published on: mar YEAR: 2022 DOI: 10.3390/atmos13030480 Geomagnetic storms; \textbfE × \textbfB drifts; disturbance dynamo electric fields; prompt penetrating electric fields; storm-induced circulation |
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Ionospheric response of St. Patrick’s Day geomagnetic storm over Indian low latitude regions The current work shows the ionospheric response to an intense geomagnetic storm known as St. Patrick’s Day storm which occurred from 17-22 March 2015 using the ionospheric Chaurasiya, Sunil; Patel, Kalpana; Kumar, Sanjay; Singh, Abhay; Published by: Astrophysics and Space Science Published on: YEAR: 2022 DOI: 10.1007/s10509-022-04137-3 |
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This study presents multi-instrument observations of persistent large-scale traveling ionosphere/atmospheric disturbances (LSTIDs/LSTADs) observed during moderately increased auroral electrojet activity and a sudden stratospheric warming in the polar winter hemisphere. The Global Ultraviolet Imager (GUVI), Gravity field and steady-state Ocean Circulation Explorer, Scanning Doppler Imaging Fabry–Perot Interferometers, and the Poker Flat Incoherent Scatter Radar are used to demonstrate the presence of LSTIDs/LSTADs between 19 UT and 5 UT on 18–19 January 2013 over the Alaska region down to lower midlatitudes. This study showcases the first use of GUVI for the study of LSTADs. These novel GUVI observations demonstrate the potential for the GUVI far ultraviolet emissions to be used for global-scale studies of waves and atmospheric disturbances in the thermosphere, a region lacking in long-term global measurements. These observations typify changes in the radiance from around 140 to 180 km, opening a new window into the behavior of the thermosphere. Bossert, Katrina; Paxton, Larry; Matsuo, Tomoko; Goncharenko, Larisa; Kumari, Komal; Conde, Mark; Published by: Geophysical Research Letters Published on: YEAR: 2022 DOI: 10.1029/2022GL099901 |
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Nitric Oxide is a very important trace species which plays a significant role acting as a natural thermostat in Earth’s thermosphere during strong geomagnetic activity. In this paper, we present various aspects related to the variation in the NO Infrared radiative flux (IRF) exiting the thermosphere by utilizing the TIMED/SABER (Thermosphere Ionosphere Mesosphere Energetics and Dynamics/ Sounding of the Atmosphere using Broadband Emission Radiometry) observational data during the Halloween storm which occurred in late October 2003. The Halloween storm comprised of three intense-geomagnetic storms. The variability of NO infrared flux during these storm events and its connection to the strength of the geomagnetic storms were found to be different in contrast to similar super storms. Ranjan, Alok; Krishna, MV; Kumar, Akash; Sarkhel, Sumanta; Bharti, Gaurav; Bender, Stefan; Sinnhuber, Miriam; Published by: Advances in Space Research Published on: YEAR: 2022 DOI: 10.1016/j.asr.2022.07.035 |
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They based on the thermospheric O/N 2 density data measured by the global ultraviolet imager (GUVI) onboard the thermosphere, ionosphere, mesosphere energetics, and dynamics ( Published by: Atmosphere Published on: YEAR: 2022 DOI: 10.3390/atmos13030480 |
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They based on the thermospheric O/N 2 density data measured by the global ultraviolet imager (GUVI) onboard the thermosphere, ionosphere, mesosphere energetics, and dynamics ( Published by: Atmosphere Published on: YEAR: 2022 DOI: 10.3390/atmos13030480 |
| 2021 |
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The results presented in this paper are obtained from low-latitude ionospheric total electron content (TEC) variation during the chosen geomagnetic storm events happening during the solar cycle 24. We include the four intense geomagnetic storms that occurred on 26 September 2011, 15 July 2012, 19 February 2014 and 20 December 2015, depending upon the availability of TEC data. For this, we have used the TEC data from low-latitude station Varanasi (geographic latitude 25°, 16′N, geographic longitude 82°, 59′E and geomagnetic latitude 16°, 24′N) and an equatorial station Bengaluru (geographic latitude 13°, 02′N, geographic longitude 77°, 34′E and geomagnetic latitude 04°, 68′N). The storm-induced TEC changes at chosen stations have been discussed in terms of local time, storm wind effect, neutral wind, composition changes and variation in the dawn–dusk component of the interplanetary electric field (IEF Ey). Singh, Abha; Rathore, Vishnu; Kumar, Sanjay; Rao, S.; Singh, Sudesh; Singh, A.; Published by: Journal of Astrophysics and Astronomy Published on: aug YEAR: 2021 DOI: 10.1007/s12036-021-09774-8 geomagnetic storm; Global positioning system; low latitude; total electron contents |
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Statistical Analysis of Throat Aurora Using Long Term DMSP/SSUSI Observation Throat aurora is believed to be associated with magnetopause indentations and has direct implications on magnetopause reconnection. In this study, for the first time, we use Defense Meteorological Satellite Program/Special Sensor Ultraviolet Spectrographic Imager observations over ∼14 years to characterize the throat aurora occurrence, latitudinal extent, seasonal, and its solar cycle dependence. We identified 386 throat aurora cases during the different passes of the satellite over the northern hemisphere. The latitudinal extent of these throat aurorae are estimated and are divided into small, medium, and large categories. The small and medium latitudinal extent throat aurorae account for about 91\% of the total cases. The throat aurorae are found to occur most frequently in the post-noon hours. The throat aurorae were also observed more frequently during winter, likely due to summer-winter asymmetry in the ionospheric conductance. The occurrence of the throat aurora is also found to be anti-correlated with the solar cycle, likely because low solar activity gives good chances for sporadic reconnection that favors the occurrence of throat aurora. The dependence on interplanetary magnetic field reveals positive Bx favoring the occurrence of throat aurora. It also shows positive Bx (negative By) supports pre-noon (post-noon) occurrence. The difference in the trend and average values of background interplanetary magnetic field conditions with the throat aurora confirms the favorable conditions for the occurrence of throat aurora. Selvakumaran, R.; Han, De-Sheng; Gokani, Sneha; Zhang, Y.; Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2021 DOI: 10.1029/2021JA029164 |
| 2020 |
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Oberheide, J; Pedatella, NM; Gan, Q; Kumari, K; Burns, AG; Eastes, RW; Published by: Geophysical Research Letters Published on: |
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The observations of vertical total electron content (VTEC) and L1 and L2 band ionospheric scintillations at an equatorial station, Tarawa (Geomag. Coordinates, 2.68S, 114.26W), Kiribati Kumar, Sushil; Kumar, Sarvesh; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: YEAR: 2020 DOI: 10.1016/j.jastp.2020.105421 |
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The observations of vertical total electron content (VTEC) and L1 and L2 band ionospheric scintillations at an equatorial station, Tarawa (Geomag. Coordinates, 2.68S, 114.26W), Kiribati Kumar, Sushil; Kumar, Sarvesh; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: YEAR: 2020 DOI: 10.1016/j.jastp.2020.105421 |
| 2019 |
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In Figure 11, we present an analysis of daily thermospheric O/N 2 data measured by the GUVI onboard the TIMED satellite to see any change in thermospheric O/N 2 composition Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2019 DOI: 10.1029/2018JA025674 |
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In Figure 11, we present an analysis of daily thermospheric O/N 2 data measured by the GUVI onboard the TIMED satellite to see any change in thermospheric O/N 2 composition Published by: Journal of Geophysical Research: Space Physics Published on: YEAR: 2019 DOI: 10.1029/2018JA025674 |
| 2015 |
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The effect of geomagnetic storms on low latitude ionosphere has been investigated with the help of Global Positioning System Total Electron Content (GPS-TEC) data. The investigation has been done with the aid of TEC data from the Indian equatorial region, Port Blair (PBR) and equatorial ionization anomaly region, Agartala (AGR). During the geomagnetic storms on 24th April and 15th July 2012, significant enhancement up to 150\% and depression up to 72\% in VTEC is observed in comparison to the normal day variation. The variations in VTEC observed from equatorial to EIA latitudes during the storm period have been explained with the help of electro-dynamic effects (prompt penetration electric field (PPEF) and disturbance dynamo electric field (DDEF)) as well as mechanical effects (storm-induced equatorward neutral wind effect and thermospheric composition changes). The current study points to the fact that the electro-dynamic effect of geomagnetic storms around EIA region is more effective than at the lower latitude region. Drastic difference has been observed over equatorial region (positive storm impact) and EIA region (negative storm impact) around same longitude sector, during storm period on 24th April. This drastic change as observed in GPS-TEC on 24th April has been further confirmed by using the O/N2\ ratio data from GUVI (Global Ultraviolet Imager) as well as VTEC map constructed from IGS data. The results presented in the paper are important for the application of satellite-based communication and navigational system. Chakraborty, Monti; Kumar, Sanjay; De, Barin; Guha, Anirban; Published by: Journal of Earth System Science Published on: 07/2015 YEAR: 2015 DOI: 10.1007/s12040-015-0588-3 geomagnetic storm; Ionospheric total electron content; low latitude ionosphere |
| 2014 |
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Limb Viewing Hyper Spectral Imager (LiVHySI) for airglow measurements onboard YOUTHSAT-1 Bisht, R.S.; Hait, A.K.; Babu, P.N.; Sarkar, S.S.; Benerji, A.; Biswas, A.; Saji, A.K.; Samudraiah, D.R.M.; Kirankumar, A.S.; Pant, T.K.; Parimalarangan, T.; Published by: Advances in Space Research Published on: 08/2014 YEAR: 2014 DOI: 10.1016/j.asr.2014.01.016 airglow; Electron density; Ionosphere; Rayleigh; thermosphere; Volume emission |
| 2013 |
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Impacts of atmospheric ultrafast Kelvin waves on radio scintillations in the equatorial ionosphere We present a statistical analysis of the amplitudes of GPS scintillations (S4 index) observed throughout 2008\textendash2010 using the satellite radio occultation measurements of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC). Here, for the first time, periodic variability in the occurrence of S4 is investigated using these data. Significant variations of S4 with periods of 2.5\textendash4 days (quasi-3 days) are identified from the observations during postsunset hours (1900\textendash2400 local time) between 15\textdegreeS\textendash 15\textdegreeN magnetic latitude during this 3 year interval. Coherence analyses of these variations with the geomagnetic Ap index, solar EUV irradiance, and atmospheric wind measurements from an equatorial mesosphere meteor radar at Thumba, India ( 8.5\textdegreeN, 77\textdegreeE) are performed, providing a measure of the relationship between variations in the scintillations and potential drivers. The quasi-3 day variations in S4 are found to covary with the variations of the three drivers examined. In particular, the S4 signatures are found to be coherent with the atmospheric ultrafast Kelvin (UFK) planetary waves characterized by the zonal wind measurements of the radar. This study shows that these UFK waves are as important as the solar and geomagnetic drivers in forcing the day-to-day variations of the occurrence of equatorial spread F. Liu, Guiping; Immel, Thomas; England, Scott; Frey, Harald; Mende, Stephen; Kumar, Karanam; Ramkumar, Geetha; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2013 YEAR: 2013 DOI: 10.1002/jgra.50139 day-to-day variability; Equatorial ionosphere; scintillation; Ultra Fast Kelvin planetary wave |
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Impacts of atmospheric ultrafast Kelvin waves on radio scintillations in the equatorial ionosphere We present a statistical analysis of the amplitudes of GPS scintillations (S4 index) observed throughout 2008\textendash2010 using the satellite radio occultation measurements of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC). Here, for the first time, periodic variability in the occurrence of S4 is investigated using these data. Significant variations of S4 with periods of 2.5\textendash4 days (quasi-3 days) are identified from the observations during postsunset hours (1900\textendash2400 local time) between 15\textdegreeS\textendash 15\textdegreeN magnetic latitude during this 3 year interval. Coherence analyses of these variations with the geomagnetic Ap index, solar EUV irradiance, and atmospheric wind measurements from an equatorial mesosphere meteor radar at Thumba, India ( 8.5\textdegreeN, 77\textdegreeE) are performed, providing a measure of the relationship between variations in the scintillations and potential drivers. The quasi-3 day variations in S4 are found to covary with the variations of the three drivers examined. In particular, the S4 signatures are found to be coherent with the atmospheric ultrafast Kelvin (UFK) planetary waves characterized by the zonal wind measurements of the radar. This study shows that these UFK waves are as important as the solar and geomagnetic drivers in forcing the day-to-day variations of the occurrence of equatorial spread F. Liu, Guiping; Immel, Thomas; England, Scott; Frey, Harald; Mende, Stephen; Kumar, Karanam; Ramkumar, Geetha; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2013 YEAR: 2013 DOI: 10.1002/jgra.50139 day-to-day variability; Equatorial ionosphere; scintillation; Ultra Fast Kelvin planetary wave |
| 2012 |
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GPS-TEC variations during low solar activity period (2007--2009) at Indian low latitude stations The paper is based on the ionospheric variations in terms of vertical total electron content (VTEC) for the low solar activity period from May 2007 to April 2009 based on the analysis of dual frequency signals from the Global Positioning System (GPS) satellites recorded at ground stations Varanasi (Geographic latitude 25\textdegree16 \ N, Longitude 82\textdegree59 \ E), situated near the equatorial ionization anomaly crest and other two International GNSS Service (IGS) stations Hyderabad (Geographic latitude 17\textdegree20 \ N, longitude 78\textdegree30 \ E) and Bangalore (Geographic latitude 12\textdegree58 \ N, longitude 77\textdegree33 \ E) in India. We describe the diurnal and seasonal variations of total electron content (TEC), and the effects of a space weather related event i.e. a geomagnetic storm on TEC. The mean diurnal variation during different seasons is brought out. It is found that TEC at all the three stations is maximum during equinoctial months (March, April, September and October), and minimum during the winter months (November, December, January and February), while obtaining intermediate values during summer months (May, June, July and August). TEC shows a semi-annual variation. TEC variation during geomagnetic quiet as well as disturbed days of each month and hence for each season from May 2007 to April 2008 at Varanasi is examined and is found to be more during disturbed period compared to that in the quiet period. Monthly, seasonal and annual variability of GPS-TEC has been compared with those derived from International Reference Ionosphere (IRI)-2007 with three different options of topside electron density, NeQuick, IRI01-corr and IRI 2001. A good agreement is found between the GPS-TEC and IRI model TEC at all the three stations. Kumar, Sanjay; Priyadarshi, S.; Krishna, Gopi; Singh, A.; Published by: Astrophysics and Space Science Published on: 05/2012 YEAR: 2012 DOI: 10.1007/s10509-011-0973-6 geomagnetic storm; GPS; Ionospheric total electron contents; IRI model |
| 1998 |
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Swaminathan, PK; Strobel, DF; Kupperman, DG; Kumar, Krishna; Acton, L; DeMajistre, R; Yee, J-H; Paxton, L; Anderson, DE; Strickland, DJ; , others; Published by: Journal of Geophysical Research: Space Physics Published on: |
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