Dibyendu Chakrabarty

Physical Research Laboratory | PRL · Space and Atmospheric Sciences Division

Coronal mass ejections (CMEs) are primary drivers of space weather, and studying their evolution in the inner heliosphere is vital to prepare for a timely response. Solar wind streams, acting as background, influence their propagation in the heliosphere and associated geomagnetic storm activity. This study introduces SWASTi-CME, a newly developed M...

Plain Language Summary The enhanced solar wind‐magnetosphere‐thermosphere energetics, and subsequent NO radiative cooling in lower thermosphere during extreme space weather events regulate the energy equilibrium of Earth's upper atmosphere. Enhance Joule heating and energetic particle precipitation in high‐latitude regions during these events resul...

The study highlights the hemispheric asymmetry of the ionospheric response to the solstice storms of 2015 from conjugate point measurements. It was found that the asymmetry manifests mostly in the recovery phase when thermospheric drivers are dominant. A clear reversal of quiet time asymmetry due to the equatorward turning of winter-side meridional...

Coronal mass ejections (CMEs) are primary drivers of space weather and studying their evolution in the inner heliosphere is vital to prepare for a timely response. Solar wind streams, acting as background, influence their propagation in the heliosphere and associated geomagnetic storm activity. This study introduces SWASTi-CME, a newly developed MH...

The Aditya-L1 is the first space-based solar observatory of the Indian Space Research Organization (ISRO). The spacecraft will carry seven payloads providing uninterrupted observations of the Sun from the first Lagrangian point. Aditya-L1 comprises four remote sensing instruments, viz. a coronagraph observing in visible and infrared, a full disk im...

Although the enhancements in the alpha-proton ratio in the solar wind (expressed as AHe = Na/Np*100) in the Interplanetary Coronal Mass Ejections (ICMEs) have been studied in the past, AHe enhancements at the stream interface region received very little attention so far. In this letter, by extensively analyzing the stream interaction region (SIR) e...

The origin of nonradial solar wind flows and their effect on space weather are poorly understood. Here we present a detailed investigation of 12 nonradial solar wind events during solar cycles 23-24, covering the period 1995-2017. In all these events the azimuthal flow angles of the solar wind exceed 6°as measured at the L1 Lagrangian point of the...

During a weak geomagnetic storm (Ap = 15) on 24 December 2014, the penetration electric field perturbations over the Indian dip equatorial sector are found to be anomalous on a number of occasions during postsunset hours. The event is anomalous as the magnitude and polarity of penetration electric fields do not obey the existing paradigm. The penet...

The characteristics of X-class flares of solar cycles 23 and 24 are examined based on the soft X-ray (0.1–0.8 nm) and EUV (26–34 nm) light curves. First, the commonly used correction factors for the center-to-limb variation of EUV flux are compared. Subsequently, enhancements in X-ray and EUV levels are used to calculate the relative apportionment...

The Aditya-L1 is the first space-based solar observatory of the Indian Space Research Organization (ISRO). The spacecraft will carry seven payloads providing uninterrupted observations of the Sun from the first Lagrangian point. Aditya-L1 comprises four remote sensing instruments, {\it viz.} a coronagraph observing in visible and infrared, a full d...

Solar wind streams, acting as a background, govern the propagation of space weather drivers in the heliosphere, which induce geomagnetic storm activities. Therefore, predictions of the solar wind parameters are the core of space weather forecasts. This work presents an indigenous three-dimensional (3D) solar wind model (SWASTi-SW). This numerical f...

Investigations on the solar cycle variation of the properties of suprathermal populations (H and other heavy ions like 4He, 3He, C, O and Fe) in the solar wind are sparse and hence, poorly understood. In the present investigation, solar cycle variations of "quiet" time suprathermal elements are investigated using < ∼ 1 MeV/n particle flux data obta...

We present a statistical investigation (September 2012 - September 2017) of pitch angle distribution (PAD) of energetic electrons (∼30 keV - 1 MeV) in the outer radiation belt (L ≥ 3) during CME- and CIR-driven geomagnetic storms using Van Allen Probe measurements. We selected geomagnetic storms based on minimum of SYM-H being less than -50 nT and...

Solar wind streams, acting as background, govern the propagation of space weather drivers in the heliosphere, which induce geomagnetic storm activities. Therefore, predictions of the solar wind parameters are the core of space weather forecasts. This work presents an indigenous three-dimensional (3D) Solar Wind model (SWASTi-SW). This numerical fra...

Based on 10 years' of vertical total electron content (VTEC) data in solar cycle 24 from Ahmedabad (23.0°N, 72.6°E, dip angle 35.2°), a station under the crest region of equatorial ionization anomaly (EIA), it is shown that both the integrated residual and total post‐sunset enhancements in VTEC are conspicuous during Equinox and December solstice w...

Despite helium abundance (AHe = nH/nHe) being ∼8 per cent at the solar photospheric/chromospheric heights, AHe can be found to exceed 8 per cent in interplanetary coronal mass ejections (ICMEs) on many occasions. Although various factors like interplanetary shocks, chromospheric evaporation, and ‘sludge removal’ have been separately invoked in the...

The hemispherical asymmetry of the low latitude region along 100°E±5°E is scrutinized for the year 2015 at magnetically conjugate points on seasonal and intra-seasonal time scales. Two conjugate Ionosonde station pairs are selected- one pair in the inner valley (from SEALION) and the other in the outer edges of the EIA region. The anomaly in the st...

Despite helium abundance (AHe = nH/nHe) is ~ 8 % at the solar photospheric/chromospheric heights, AHe can be found to exceed 8% in interplanetary coronal mass ejections (ICMEs) on many occasions. Although various factors like interplanetary shocks, chromospheric evaporation and "sludge removal" have been separately invoked in the past to address th...

A geomagnetic storm is a phenomenon of weakening of Earth's magnetic field from a few hours to several days, which directly or indirectly affects navigation, transportation, communication, power grids, satellite electronics, etc. In general, the duration of the recovery phase is larger. Thus, its cumulative effect is greater than the main phase. Th...

On a geomagnetic quiet night of October 29, 2018, we captured an observational evidence of the onset of dark band structures within the field‐of‐view of an all‐sky airglow imager operating at 630.0 nm over a geomagnetic low‐mid latitude transition region, Hanle, Leh Ladakh. Simultaneous ionosonde observations over New Delhi shows the occurrence of...

We present, for the first time, a plasmaspheric hiss event observed by the Van Allen probes in response to two successive interplanetary (IP) shocks occurring within an interval of ∼2 h on December 19, 2015. The first shock arrived at 16:16 UT and caused disappearance of hiss for ∼30 min. Combined effect of plasmapause crossing, significant Landau...

In this paper, we study the interaction between a nighttime Medium Scale Traveling Ionospheric Disturbance (MSTID) and geomagnetic north-south oriented field-aligned plasma depletion structure over Hanle, Leh Ladakh (32.7°N, 78.9°E; Mlat. ∼24.1°N), India on a geomagnetically quiet night (06 May 2019, Ap = 4). The results are based on the observatio...

Based on 10 years' (2010–2019) of vertical total electron content (VTEC) data from Ahmedabad (23.0°N, 72.6°E, dip angle 35.2°) and campaign based OI 630.0 nm airglow intensity measurements from Mt. Abu (24.6°N, 72.7°E, dip angle 38.0°), it is shown that plasma density over the equatorial ionization anomaly (EIA) crest region increases in varying de...

A detailed investigation on longitudinal and decadal variations of general characteristics (amplitude, width, peak altitude) of the equatorial electrojet (EEJ) is carried out using a physics-based model of electrojet. A few important aspects that emerge from this investigation include (i) changes in the half-width of EEJ with longitude and it’s dep...

The relative abundance of alpha particles with respect to protons, usually expressed as AHe = (nα/np)*100, is known to respond to solar activity, although changes in its behaviour in the last four solar cycles are not known. In this letter, by systematically analysing inter-calibrated AHe data obtained from the first Lagrangian point of the Sun–Ear...

The relative abundance of alpha particles with respect to proton, usually expressed as $A_{He}$ = ($n_\alpha/n_p$)*100, is known to respond to solar activity although changes in its behaviour in the last four solar cycles are not known. In this letter, by systematically analysing inter-calibrated $A_{He}$ data obtained from the first Lagrangian poi...

Solar X-ray Monitor (XSM) instrument of India’s Chandrayaan-2 lunar mission carries out broadband spectroscopy of the Sun in soft X-rays. XSM, with its unique features such as low background, high time cadence, and high spectral resolution, provides the opportunity to characterize transient and quiescent X-ray emission from the Sun even during low...

On a geomagnetically quiet night of July 07, 2018, the allsky imager at Hanle, Leh Ladakh (32.7°N, 78.9°E; Mlat. ∼24.1°N), India captured a number of plasma structures in O (¹D) 630.0 nm airglow emission. In a short observational period of around 3 h, two different medium scale traveling ionospheric disturbances and two different mid‐latitude plasm...

In this paper, we have evaluated the role of interplanetary magnetic field (IMF) By on the asymmetry of the ring current during the main phase of geomagnetic storms. The mean H variations have been calculated using 31 ground magnetic stations over magnetic latitudes of 09–45° following the methodology of Li et al. (2011, https://doi.org/10.1029/201...

Solar X-ray Monitor (XSM) instrument of India's Chandrayaan-2 lunar mission carries out broadband spectroscopy of the Sun in soft X-rays. XSM, with its unique features such as low background, high time cadence, and high spectral resolution, provides the opportunity to characterize transient and quiescent X-ray emission from the Sun even during low...

An observational evidence of a unique plasma depletion event was captured by an O(¹D) 630.0 nm airglow imager on 13 June 2018 over a transition region of geomagnetic low‐mid latitude, Hanle, Leh Ladakh, India (32.77°N, 78.97°E; Mlat. ~24.1°N). The observed plasma depletion structures are tilted at an angle of 13° ± 2° west of the geomagnetic north...

Three different episodes of prompt penetration electric field (PPEF) disturbances are observed during the main phase of the St. Patrick's Day storm on 17 March 2015 under steady southward interplanetary magnetic field (IMF) Bz conditions unlike the conventional PPEF associated with southward or northward turnings of IMF Bz. These PPEF events took p...

This investigation shows that the significant electric field disturbances in the dip‐equatorial ionosphere during the geomagnetic storm of 6–8 September 2017 are due to the passage of two consecutive interplanetary coronal mass ejections (ICMEs). During the passage of the first ICME sheath, a long duration (∼10 hr) prompt penetration (PP) event is...

In order to understand the characteristics of long‐lasting “C‐type” structure in the Sodium (Na) lidargram, six cases from different observational locations have been analyzed. The Na lidargram, collected from low‐, middle‐, and high‐latitude sites, show long lifetime of the C‐type structures which is believed to be the manifestation of Kelvin‐Helm...

During the geomagnetic storm periods, the convection electric field penetrates promptly to equatorial latitudes, causing an eastward electric field in the dayside ionosphere. Occasionally, the polarity of the dayside ionospheric electric field is inverted when the Interplanetary Magnetic Field (IMF) turns northward. In this paper, interesting obser...

This review article briefly brings out the historical development of atmospheric sodium (Na) measurements over India and the importance of coordinated measurements with multiple techniques to address physical processes in the Earth's upper atmosphere. These measurements were initiated in the early 1970s by observing Na airglow emission intensities...

An observational evidence of medium‐scale traveling ionospheric disturbances (MSTIDs) reaching to magnetic latitude as low as ~3.5° over the Indian sector is provided for the first time based on OI 630‐nm airglow imaging observation from a low‐latitude station, Gadanki (13.5°N, 79.2°E; 6.6° magnetic latitude), on 12 January 2016. The horizontal wav...

Aditya Solar-wind Particle EXperiment (ASPEX) is one of the seven scientific experiments onboard the Aditya-L1 mission (the forthcoming Indian solar mission), to be placed in a halo orbit around the L1 Lagrangian point of the Sun-Earth system, at a distance of 1.5 million km from the Earth, along the Sun-Earth line. ASPEX will carry out the in-situ...

Based on careful analysis of 16 years of hourly variations of the strength of equatorial electrojet (EEJ) derived using the ground-based magnetometers over the Indian sector, the role played by disturbance dynamo electric field disturbances on equatorial ionosphere is identified. It is found that most prominent cases of the effects of disturbance d...

Low latitude ionospheric behavior during solar transient disturbances of solar flares and storm time penetrating electric fields comprises an important part of the Earth's space weather. The flares enhance the electron density of the sunlit ionosphere by supplying excess solar radiation. However, the degree of these density changes is subjective if...

On 13 April 2013, the ACE spacecraft detected arrival of an interplanetary shock at 2250 UT, which is followed by the passage of the sheath region of an interplanetary coronal mass ejection (ICME) for a prolonged (18-hr) period. The polarity of interplanetary magnetic field Bz was northward inside the magnetic cloud region of the ICME. The ring cur...

Studies made earlier using ground-based observations of geomagnetic field over the Indian longitudes revealed that the occurrence of equatorial counter electrojet (CEJ) events in afternoon hours is more frequent during June solstice (May-June-July-August) in solar minimum than in other periods. In general, the June solstice solar minimum CEJ events...

We report on the kinematics of two interacting CMEs observed on 13 and 14 June 2012. Both CMEs originated from the same active region NOAA 11504. After their launches which were separated by several hours, they were observed to interact at a distance of 100 Rs from the Sun. The interaction led to a moderate geomagnetic storm at the Earth with Dst i...

Aditya-L1, the first ever Indian scientific space mission dedicated to probe the Sun, our nearest star, is slated for launch by the Indian Space Research Organisation (ISRO) most likely in 2020, the year coinciding with the expected start of the rising phase of solar cycle 25. Of the seven science payloads on-board Aditya- L1, three are in situ ins...

Based on TEC observations by India’s GPS Aided Geo Augmentation Network (GAGAN), we report the dayside low latitude ionospheric variations over the Indian region during the moderate main phase step-I of the 17 March 2015 geomagnetic storm. In addition, we assess the efficacy of GPS inferred TEC maps by International GNSS service (IGS) in capturing...

A total of 43 CIR-induced geomagnetic storms during the unusually deep solar minimum of solar cycle 23 (2006-2010) were identified using a super-posed epoch analysis technique. Of these 43 events, a detailed cross spectrum analyses, between the variations in the Z-component of the interplanetary magnetic field (IMF Bz) and the equatorial electrojet...

The threshold vertical plasma drifts and their polarities are inferred from E-region irregularities reported earlier using different experiments conducted from India during geomagnetically quiet time. In addition, the hourly variations of magnetometer data sets are used in conjunction with an equatorial electrojet model (Anandarao, 1976) to deduce...

This study tries to bring out the fact that storm-time substorms can compete and at times significantly contribute to the geomagnetically disturbed time prompt penetration electric field effects on low and equatorial latitudes. Observations of unusual equatorial plasma drift data from JULIA (Jicamarca Unattended Long-term Investigations of the Iono...

A detailed investigation is carried out to estimate the nighttime ionospheric current over the Indian dip-equatorial sector using an electrojet model (Anandarao, 1976) and in-situ measurements (Subbaraya et al., 1983; Gupta, 2000) of nighttime electron densities. The estimated E-region current density is of the order of ∼0.3 Akm-2 during pre-midnig...

On January 7, 2005 (Ap= 40), prompt penetration electric field perturbations of opposite polarities were observed over Thumba and Jicamarca on a few occasions during 13:45-16:30 UT. However, the electric field was found to be eastward during 14:45-15:30 UT over both Thumba and Jicamarca contrary to the general expectation wherein opposite polaritie...

The effects of the St. Patrick's Day geomagnetic storms of 2013 and 2015 in the equatorial and low latitude regions of both hemispheres in the 100°E longitude sector is investigated and compared with the response in the Indian sector at 77°E. The data from a chain of ionosondes and GPS/GNSS receivers at magnetic conjugate locations in the 100°E sec...

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 28-29 June 2013 is presented. The GPS Total Electron Content (TEC) observations from a network of stations in the Indian equatorial, low and mid latitude regions along with the ra...

Aditya Solar wind Particle EXperiment (ASPEX) is one of the scientific experiments onboard the Aditya-L1 mission, the first Indian solar mission planned to be launched in the year of 2019. The primary objective of the ASPEX experiment is to carry out in-situ, multi-directional measurements of solar wind ions in the energy range of 100 eV/n to 5 MeV...

The existence of the possible ionospheric current during nighttime over low-equatorial latitudes is one of the unresolved issues in ionospheric physics and geomagnetism. A detailed investigation is carried out to estimate the same over Indian longitudes using in situ measurements from Thumba , empirical plasma drift model (Fejer et al., 2008) and e...

Before the onset of a geomagnetic storm on 22 January 2012 (Ap = 24), an enhancement in solar wind number density from 10/cm3 to 22/cm3 during 0440–0510 UT under northward interplanetary magnetic field (IMF Bz) condition is shown to have enhanced the high-latitude ionospheric convection and also caused variations in the geomagnetic field globally....

A detailed investigation was carried out to understand a prolonged (~44 hours) weakly southward interplanetary magnetic field (IMF-Bz) condition during May 02--04, 1998. In-situ observations, during the period, showed the passage of an expanding magnetic cloud embedded in an interplanetary coronal mass ejection (ICME), followed up by a shock and an...

Determination of daytime dip-equatorial E-region electric field based on magnetometer measurements makes use of the nighttime base value of the horizontal component of the magnetic field over a dip equatorial and off-equatorial station that is sufficiently away from the influence of equatorial electrojet. This technique inherently assumes the night...

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 occured during 18-21 February 2014. GPS Total Electron Content (TEC) data from the Indian Antarctic station, Bharti...

Large variations in the horizontal component of magnetic field recorded on ground based magnetometers over dip equator during daytime are well known and are attributed to strong current flow over equatorial E-region. However, during nighttime, it is believed that ionospheric conductivity is not large enough to support the substantial current. As a...

Coordinated digisonde and OI 630.0 nm airglow observations from Thumba (TVM), an Indian dip equatorial station, in conjunction with magnetic and geosynchronous particle flux measurements, reveal three different types of electric field disturbances in the equatorial ionosphere-thermosphere system (ITS) occurring in succession over a period of 6 h on...

The height-time-concentration map of neutral sodium (Na) atoms measured by a Na lidar during the night of 18 to 19 March 2007 over Gadanki, India (13.5? N, 79.2? E) reveals an unusual structure in the Na layer for around 30 min in the altitude range of 92 to 98 km which is similar to the usual `C? type structures observed at other locations. In ord...

A GNU Radio Beacon Receiver (GRBR) system for Total Electron Content (TEC) measurements using 150 and 400 MHz transmissions from Low-Earth Orbiting Satellites (LEOS) is fabricated in-house and made operational at Ahmedabad (23.04°N, 72.54°E geographic, dip latitude 17°N) since May 2013. This system receives the 150 and 400 MHz transmissions from hi...

In order to understand the variation in the altitudes of initiation ( ) of E region gradient drift (GD) waves at different longitude sectors in the vicinity of the dip equator, the linear growth rate expression was examined. This revealed that the growth rate of the primary GD waves in an altitude region of 85–93 km depends on the square of the geo...

Understanding of the kinematic evolution of Coronal Mass Ejections (CMEs) in the heliosphere is important to estimate their arrival time at the Earth. It is found that kinematics of CMEs can change when they interact or collide with each other as they propagate in the heliosphere. In this paper, we analyze the collision and post-interaction charact...

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 400 km north of Thumba. Another r...

The present work describes the low latitude ionospheric variability during an unusually prolonged (~33 hours) geomagnetically disturbed condition that prevailed during 15-16 July 2012. The low latitude electron density in summer hemisphere, investigated using ground and satellite based observations, responded to this by generating strong negative i...

We studied three interplanetary coronal mass ejections associated with solar eruptive filaments. Filament plasma remnants embedded in these structures were identified using plasma, magnetic and compositional signatures. These features when impacted the Earth's terrestrial magnetosphere - ionosphere system, resulted in geomagnetic storms. During the...

The present investigation brings out, in contrast to the earlier works, the changes in the equatorial electrojet (EEJ) current in response to a few moderate (M-class) and low (C and B class) intensity solar flares during 2005–2010. Special care is taken to pick these flare events in the absence of prompt electric field perturbations associated with...

On 5 January 2005, SoHO/LASCO observed the launch of two successive coronal mass ejections (CMEs) associated with the filament (active region and quiescent) structures. The eruptions resulted in two distinct magnetic clouds whose embedded flux-rope topology is modeled by the Grad-Shafranov (G-S) reconstruction technique. Filament plasma remnants in...

On 5 January 2005, SoHO/LASCO observed two CMEs associated with eruptive filaments with different initial velocities and acceleration. The second CME accelerates much faster than the previous and the resulting interaction has been revealed in in-situ spacecraft measurements by the presence of magnetic holes at the border of the two distinct magnetic...

Meteor characteristics during shower and non-shower periods in 2005–2008 have been studied using narrow beam (HPBW ~ 3°) VHF radar at Gadanki (13.5°N, 79.2°E). Various interesting echoes are illustrated and probable explanations for their behaviour are also provided. Doppler spectra of the Range Spread Trail Echo indicate a probable plasma converge...

Possible precursor signatures in the quasi-periodic variations of solar photospheric fields were investigated in the build-up to one of the deepest solar minima experienced in the past 100 years. This unusual and deep solar minimum occurred between Solar Cycles 23 and 24. We used both wavelet and Fourier analysis to study the changes in the quasi-p...

Meteor characteristics during shower and non-shower periods in 2005-2008 have been studied using narrow beam (HPBW ~ 3°) VHF radar at Gadanki (13.5°N, 79.2°E). Various interesting echoes are illustrated and probable explanations for their behaviour are also provided. Doppler spectra of the Range Spread Trail Echo indicate a probable plasma converge...

A case of the drastic effects of an eastward prompt penetration and a westward overshielding electric field successively affecting the daytime equatorial ionosphere during the space weather event that occurred on 24 November 2001 is presented. Under the influence of the strong eastward prompt penetration electric field starting from 11:25 Indian st...

Optical signature for shear in the zonal plasma flow is obtained along with a tilted plasma plume structure in VHF radar map during a space weather event on 11 February 2004 (AP=28). A multi-wavelength photometer with a narrow spectral band-width and a narrow field-of-view was operated from Gadanki (13.5°N, 79.2°E, dip lat 6.3°N) to measure airglow...

The daily peak total electron content (TEC), recorded from Rajkot (22.29°N, 70.74°E, 31.6°N dip angle), is analyzed to investigate the combined roles of the solar cycle effect and neutral dynamical processes on the TEC variation over the equatorial ionization anomaly (EIA) crest region during the deep minimum between solar cycle 23 and 24. It is fo...

Observations using a narrow spectral band (0.3nm) airglow photometer with a narrow field-of-view (3°) developed recently enabled to capture the impact of space weather events on neutral airglow emission over low latitudes and also opened up new vistas to characterize different plasma structures associated with Equatorial Spread F (ESF). Plasma enha...

Observations of OI 630.0 nm dayglow intensity from Mt. Abu (magnetic latitude (MLAT): 16.2°N; magnetic longitude (MLONG): 148°E) at two different directions corresponding to two different magnetic latitudes (MLATZenith: 16.2°N and MLAT20°Elevation: 22.2°N) revealed nearly simultaneous intensity enhancements on 2 February 2002 (Ap = 19) during 0554–...

Simultaneous observations of a narrowband sodium (Na) airglow photometer corresponding to the D2 line in conjunction with a Na lidar from Gadanki (13.5°N, 79.2°E), India, reveal episodic enhancements in Na airglow intensity during 1930–0142 Indian standard time (IST; IST = UT + 5.5 h) on 18–19 March 2007. This variation is drastically different fro...

In order to identify the dominant modes of mesospheric gravity waves, sodium (Na) airglow mea-surements were carried out in campaign modes during November, 2006 -February, 2009 over Mt. Abu (24.6o N, 72.7o E) and Gadanki (13.5o N, 79.2o E) using a narrow-band and narrow field-of-view Na airglow photometer. The airglow observations yield the tempora...

In order to understand the substantial variation of sodium (Na) airglow intensity from one night to another, a case study is performed using simultaneous, campaign-based measurements of Na airglow and Na lidar during March 2007 from Gadanki (13.5°N, 79.2°E), India, during postmidnight hours. The altitude profiles of mesospheric ozone, temperature,...

In order to investigate the relation between the sodium airglow emission and sodium atoms, a narrow-band and narrow field-of-view sodium airglow photometer was operated in campaign modes from Gadanki (13.5° N, 79.2° E) in conjunction with sodium lidar during March, 2007 and 2008. The airglow observations yielded the temporal variation of altitude-i...

An investigation involving nonlinear numerical simulation has been undertaken based on the observations of two events involving the reversal of nighttime zonal electric field to eastward direction over equatorial region due to the overshielding effect associated with interplanetary electric field. In one of the events, the ionospheric alterations b...

Co-ordinated campaigns have been conducted from Gadanki (13.5° N, 79.2° E, dip lat 6.4° N) by operating simultaneously the Indian MST radar in ionospheric coherent backscatter mode and by monitoring thermosphere airglow line emissions (630.0 nm and 777.4 nm) using a narrow band multi-wavelength scanning photometer during January-March for the past...

1] A geomagnetic storm event is identified wherein the base of the equatorial F layer (h 0 F) over dip equator moved unusually upward till premidnight hours and descended thereafter. The h 0 F variation is linearly correlated with the variation in the smoothed auroral electrojet index (AE) which varies slowly. The fast fluctuations (residuals) with...

The Equatorial Spread-F (ESF) is a complex phenomenon encompassing a wide range of scale sizes (covering more than six orders of magnitude) of irregularities in electron and ion densities as well as in electric fields. The generation mechanisms involve not only the plasma processes but also neutral processes. Thus, to understand the different facet...

Plasma irregularity structures associated with an Equatorial Spread-F (ESF) event were recorded by the Indian VHF Radar on 26?27 April 2006 near midnight hours. The plasma structures were found to be isolated without having bottomside structure. They moved predominantly downward and the structures were found to be less turbulent than their post-sun...