Bibliography

The geoeffectiveness of TIE-GCM simulations of ionospheric critical frequency foF2 at the equatorial station of Thiruvananthapuram in the Indian sector

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

Comparison; foF2; TIE-GCM

Signatures of Equatorial Plasma Bubbles and Ionospheric Scintillations from Magnetometer and GNSS Observations in the Indian Longitudes during the Space Weather Events of Early September 2017

Scintillation due to ionospheric plasma irregularities remains a challenging task for the space science community as it can severely threaten the dynamic systems relying on space-based navigation services. In the present paper, we probe the ionospheric current and plasma irregularity characteristics from a latitudinal arrangement of magnetometers and Global Navigation Satellite System (GNSS) stations from the equator to the far low latitude location over the Indian longitudes, during the severe space weather events of 6–10 September 2017 that are associated with the strongest and consecutive solar flares in the 24th solar cycle. The night-time influence of partial ring current signatures in ASYH and the daytime influence of the disturbances in the ionospheric E region electric currents (Diono) are highlighted during the event. The total electron content (TEC) from the latitudinal GNSS observables indicate a perturbed equatorial ionization anomaly (EIA) condition on 7 September, due to a sequence of M-class solar flares and associated prompt penetration electric fields (PPEFs), whereas the suppressed EIA on 8 September with an inverted equatorial electrojet (EEJ) suggests the driving disturbance dynamo electric current (Ddyn) corresponding to disturbance dynamo electric fields (DDEFs) penetration in the E region and additional contributions from the plausible storm-time compositional changes (O/N2) in the F-region. The concurrent analysis of the Diono and EEJ strengths help in identifying the pre-reversal effect (PRE) condition to seed the development of equatorial plasma bubbles (EPBs) during the local evening sector on the storm day. The severity of ionospheric irregularities at different latitudes is revealed from the occurrence rate of the rate of change of TEC index (ROTI) variations. Further, the investigations of the hourly maximum absolute error (MAE) and root mean square error (RMSE) of ROTI from the reference quiet days’ levels and the timestamps of ROTI peak magnitudes substantiate the severity, latitudinal time lag in the peak of irregularity, and poleward expansion of EPBs and associated scintillations. The key findings from this study strengthen the understanding of evolution and the drifting characteristics of plasma irregularities over the Indian low latitudes.

Vankadara, Ram; Panda, Sampad; Amory-Mazaudier, Christine; Fleury, Rolland; Devanaboyina, Venkata; Pant, Tarun; Jamjareegulgarn, Punyawi; Haq, Mohd; Okoh, Daniel; Seemala, Gopi;

Published by: Remote Sensing      Published on: jan

YEAR: 2022     DOI: 10.3390/rs14030652

space weather; equatorial plasma bubbles; ionospheric irregularity; global navigation satellite system; magnetometer; poleward drift; rate of change of TEC index; scintillations; storm-time electric currents

The impact of a stealth CME on the Martian topside ionosphere

Solar cycle 24 is one of the weakest solar cycles recorded, but surprisingly the declining phase of it had a slow coronal mass ejection (CME) that evolved without any low coronal

Thampi, Smitha; Krishnaprasad, C; Nampoothiri, Govind; Pant, Tarun;

Published by: Monthly Notices of the Royal Astronomical Society      Published on:

YEAR: 2021     DOI: 10.1093/mnras/stab494

Geomagnetic storm-induced plasma density enhancements in the southern polar ionospheric region: A comparative study using St. Patrick s Day storms of 2013 and 2015

order to examine if the variations in the TEC were caused by thermospheric composition changes in the southern high-latitude regions, we present O/N 2 maps obtained from the GUVI

Shreedevi, PR; Choudhary, RK; Thampi, Smitha; Yadav, Sneha; Pant, TK; Yu, Yiqun; McGranaghan, Ryan; Thomas, Evan; Bhardwaj, Anil; Sinha, AK;

Published by: Space Weather      Published on:

YEAR: 2020     DOI: 10.1029/2019SW002383

Signatures of Sudden Storm Commencement on the equatorial thermospheric dayglow

It has been observed that the OI 630.0\ nm dayglow emission over a dip equatorial station, Trivandrum (8.5\textdegree\ N, 77\textdegree\ E, dip 0.5\textdegree\ N), India registered an abrupt increase of\ ~\ 2000\ R during the compression phase of the magnetosphere as dictated by a sudden increase in solar wind ram pressure. Furthermore, an unusual depletion of these emissions has been observed during the eastward interplanetary electric field (IEF), concomitant with southward excursion of IMF Bz. The ionosonde and magnetometer observations confirmed the effects of prompt penetration electric field (PPEF). Associated with the eastward PPEF, formation of F3 layers were also noticed. These unique results, which emphasize the effect of Sudden Storm Commencement/IEF on these equatorial daytime airglow emissions are discussed in context of changes in the equatorial zonal electric field and F region height variations associated with polar/auroral activities due to the magnetosphere-ionosphere coupling.

Sumod, Sukumarn; Pant, Tarun; Ajesh, Asokan;

Published by: Journal of Space Weather and Space Climate      Published on: 06/2019

YEAR: 2019     DOI: 10.1051/swsc/2019026

Ionosphere VHF scintillations over Vaddeswaram (Geographic Latitude 16.31° N, Geographic Longitude 80.30° E, Dip 18° N), a latitude Indian station--A case study

This research reports the 250\ MHz amplitude ionosphere scintillations recorded at Vaddeswaram (Geographic Latitude 16.31\textdegreeN, Geographic Longitude 80.30\textdegreeE, Dip 18\textdegreeN), a low-latitude station in India. Though amplitude scintillations were recorded for four continuous days (05\textendash08 November 2011), the presence of intense and long-duration scintillations on 06 November 2011 instigated us to verify the ionosphere background conditions. This research, therefore, is also used important databases including, diurnal variations of h F (virtual height of the F-layer) and the vertical drifts as measured by an advanced digital ionosonde radar located at an Indian equatorial station i.e. Trivandrum (Geographic Latitude 8.5\textdegreeN, Geographic Longitude 77\textdegreeE, Dip 0.5\textdegreeN), equatorial Electrojet (EEJ) ground strength measured using magnetometers and the total electron content (TEC) maps provided by the International GPS Service (IGS) to study the background ionosphere conditions. The interesting observations are higher E\ \texttimes\ B drifts, the occurrence of long-duration range-type spread F signatures at Trivandrum and, thereafter, intense scintillations over Vaddeswaram. It was found a secondary peak at around 1600 LT in EEJ strength followed by a higher upward drift velocity (more than 60\ m/s) with a significant raise of the F region up to 470\ km over the magnetic equator on 06 November 2011. The possible physical mechanisms of these important observational results are discussed in the light of available literature.

Brahmanandam, P.S.; Uma, G.; Pant, T.K.;

Published by: Advances in Space Research      Published on: 10/2017

YEAR: 2017     DOI: 10.1016/j.asr.2017.06.051

Direct observational evidence for disturbance dynamo on the daytime low-latitude ionosphere: A case study based on the 28 June 2013 space weather event

A case of the westward disturbance dynamo (DD) electric field, influencing the daytime equatorial and low-latitude ionosphere, during a geomagnetic storm that occurred on 28\textendash29 June 2013 is presented. The GPS total electron content (TEC) observations from a network of stations in the Indian equatorial, low and middle latitude regions along with the radio beacon TEC, ionosonde, and magnetic field observations are used to study the storm time behavior of the ionosphere. Negative ionospheric storm effects were seen over the low and middle latitudes during the storm time due to the presence of a westward DD electric field. Observations show that the suppression of the equatorial ionization anomaly (EIA) from the morning hours itself on 29 June 2013 took place due to the prevailing westward DD electric field, providing evidence for the model calculations by Balan et al. (2013). Simulations using the GITM model also agree well with our results. The present study gains importance as the direct observational evidences for disturbance dynamo effects on the daytime low-latitude ionosphere and the EIA are sparse, as it has been difficult to delineate it from the compositional disturbances.

Thampi, Smitha; Shreedevi, P.; Choudhary, R.; Pant, Tarun; Chakrabarty, D.; Sunda, S.; Mukherjee, S.; Bhardwaj, Anil;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2016

YEAR: 2016     DOI: 10.1002/2016JA023037

On the latitudinal changes in ionospheric electrodynamics and composition based on observations over the 76--77 E meridian from both hemispheres during a geomagnetic storm

The relative contributions of the composition disturbances and the disturbance electric fields in the redistribution of ionospheric plasma is investigated in detail by taking the case of a long-duration positive ionospheric storm that occurred during 18\textendash21 February 2014. GPS total electron content (TEC) data from the Indian Antarctic station, Bharti (69.4\textdegreeS, 76.2\textdegreeE geographic), the northern midlatitude station Hanle (32.8\textdegreeN, 78.9\textdegreeE geographic), northern low-latitude station lying in the vicinity of the anomaly crest, Ahmedabad (23.04\textdegreeN, 72.54\textdegreeE geographic, dip latitude 17\textdegreeN), and the geomagnetic equatorial station, Trivandrum (8.5\textdegreeN, 77\textdegreeE geographic, dip latitude 0.01\textdegreeS) are used in the study. These are the first simultaneous observations of TEC from Bharti and Hanle during a geomagnetic storm. The impact of the intense geomagnetic storm (Dst\~-130\ nT) on the southern hemisphere high-latitude station was a drastic reduction in the TEC (negative ionospheric storm) starting from around 0330 Indian standard time (IST) on 19 February which continued till 21 February, the maximum reduction in TEC at Bharti being \~35 TEC units on 19 February. In the northern hemisphere midlatitude and equatorial stations, a positive ionospheric storm started on 19 February at around 0900 IST and lasted for 3\ days. The maximum enhancement in TEC at Hanle was about \~25 TECU on 19 February while over Trivandrum it was \~10 TECU. This long-duration positive ionospheric storm provided an opportunity to assess the relative contributions of disturbance electric fields and composition changes latitudinally. The results indicate that the negative ionospheric storm over Bharti and the positive ionospheric storm over Hanle are the effect of the changes in the global wind system and the storm-induced composition changes. At the equatorial latitudes, the positive ionospheric storm was due to the interplay of prompt penetration electric field and disturbance dynamo electric field.

Shreedevi, P.; Thampi, Smitha; Chakrabarty, D.; Choudhary, R.; Pant, Tarun; Bhardwaj, Anil; Mukherjee, S.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 02/2016

YEAR: 2016     DOI: 10.1002/2015JA021841

Geomagnetic storms; High latitude low latitude coupling; Ionosphere; positive ionospheric storm

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

First observational evidence of the modulation of the threshold height h'Fc for the occurrence of equatorial spread F by neutral composition changes

[1]\ In the present study, the seasonal and solar activity variations of the threshold height for equatorial spread F occurrence irrespective of the polarity of the meridional winds during magnetically disturbed period are presented for the first time. The modulation of the seasonal pattern of the threshold height by the seasonal mean O/N₂ values is also examined. The Ionosonde data of magnetic equatorial location Trivandrum (8.5\textdegreeN, 76.5\textdegreeE) and low latitude station SHAR (13.7\textdegreeN, 80.2\textdegreeE) in the Indian longitude sector during equinoxes, winter, and summer seasons of 2002 to 2006 and the corresponding Thermosphere Ionosphere Mesosphere Energetics and Dynamics/GUVI (Global Ultra Violet Imager) O/N₂ data are used for the study. The important findings that have emerged from this study are (i) the substantial increase of threshold height with magnetic activity for all the seasons and (ii) the modulation of h\textquoterightF_c by neutral density changes, irrespective of season, solar, or magnetic activity.

Haridas, M.; Manju, G.; Pant, Tarun;

Published by: Journal of Geophysical Research: Space Physics      Published on: 06/2013

YEAR: 2013     DOI: 10.1002/jgra.50331

Equatorial Spread F; O/N2; solar activity; Threshold height

Ionospheric response to a geomagnetic storm during November 8--10, 2004

This paper investigates the response of the equatorial, and near equatorial, ionosphere to geomagnetic disturbances during the period November 8-10, 2004. Ionosonde data from Trivandrum (8.5\textdegreeN 77\textdegreeE and dip 0.5\textdegreeN) and SHAR (13.5\textdegreeN, 80.2\textdegreeE, dip \~5.5\textdegreeN), magnetic field data from Tirunelveli (8.7\textdegreeN, 76.9\textdegreeE, dip latitude 0.5\textdegreeS) and Alibag (18.64\textdegreeN, 72.87\textdegreeE), and GUVI O/N₂ data in the Indian longitude sector, are used for the study. The behavior of interplanetary parameters is also examined in conjunction with the ionospheric data. On 8 November, the EIA around noontime is not fully inhibited even though the electrojet strength an indicates inhibition of EIA due to a disturbance dynamo electric field effect. It is the enhanced O/N₂ over TRV and SHAR, with a larger increase over SHAR, which results in a larger (than expected) value of the EIA proxy parameter. On 9 November, the comparable values of f_oF₂ at TRV and SHAR around noon time is due to the combined effect of a weakened anomaly in the presence disturbance dynamo electric field effects leading to the EIA crest being near SHAR, and increased O/N₂ values at TRV and SHAR with a larger increase at TRV. On 10 November, the very strong values of the EIA proxy-SHAR parameter is attributed to the combined effects of prompt penetration electric field related modulations of EIA, and significant O/N₂ changes at the equatorial, and near equatorial, latitude. Thus, the study reveals the important role of storm-induced O/N₂ changes, along with prompt penetration electric fields and disturbance dynamo electric fields in modulating the ionization distribution in the equatorial ionization anomaly (EIA) region during this period.

Simi, K.; Manju, G.; Haridas, M.; Nayar, S.; Pant, Tarun; Alex, S.;

Published by: Earth, Planets and Space      Published on: 05/2013

YEAR: 2013     DOI: 10.5047/eps.2012.09.005

Equatorial Electrojet; Equatorial ionization anomaly; geomagnetic storm; O/N2 ratio

Equatorial and low-latitude ionosphere-thermosphere system response to the space weather event of August 2005

, Sreeja; Ravindran, Sudha; Pant, Tarun; Devasia, CV; Paxton, LJ;

Published by: Journal of Geophysical Research: Space Physics      Published on:

YEAR: 2009     DOI: