This study investigates the interaction between Equatorial Plasma Bubbles (EPBs) and Medium Scale Traveling Ionospheric Disturbances (MSTIDs) observed on 31 January 2017 over low-latitude India using a multi-instrumental approach. OI Nightglow images from Panhala (16.48 degrees N, 74.6 degrees E, and 11.1 degrees N MLAT) and Gadanki (13.5 degrees N, 79.2 degrees E; similar to 6.6 degrees MLAT), ionosonde measurements from Tirunelveli, GPS TEC measurements from Hyderabad & Bangalore and geomagnetic data from India were analyzed to examine how MSTIDs influence EPB morphology, drift, and evolution. EPBs, typically drifting eastward after post-sunset pre-reversal enhancement of the zonal electric field via Rayleigh-Taylor instability, exhibited modulation by a south to north-westward propagating MSTID observed simultaneously at both ASI locations. This MSTIDs, induced elongation, intensification, and in some cases, dissipation of EPBs depending on their phase alignment. Keograms from both sites revealed consistent plasma perturbations, with Gadanki data confirming the presence and propagation of the same MSTID front, even near the magnetic equator. The h'F obtained from Canadian Advanced Digital Ionosonde observations from Tirunelveli (8.73 degrees N, 77.7 degrees E, and 1.6 degrees N MLAT) supported strong PRE-driven vertical uplift coinciding with EPB onset. Dual-frequency GPS-TEC analysis over Hyderabad (HYDE) and Bangalore (IISC) revealed quasi-periodic MSTIDs signatures with northwestward propagation indicating large-scale ionospheric disturbances likely driven by gravity waves. These results confirm MSTID-induced modulation of EPBs, validating gravity wave seeding as one of the key mechanism influencing equatorial ionospheric irregularities. The findings underscore the value of coordinated optical and radio measurements for understanding the horizontal and vertical coupling processes occurring at ionospheric altitudes.

In the present study, we examine the response of equatorial plasma bubbles (EPBs) and total electron content (TEC) to the geomagnetic storm of 19–21 January 2026. This analysis is based on coordinated all-sky airglow observations over Kolhapur (16.8°N, 74.2°E) along with GNSS-derived TEC and Rate of TEC Index (ROTI) measurements across the Indian longitude sector. The geomagnetic activity, as indicated by the SYM-H index, reached a minimum of −251 nT, signifying an intense storm. A storm sudden commencement (SSC) was observed around 19–20 UT on 19 January, followed by a rapid transition into the main phase of the storm.Well-developed EPBs were observed prior to and during the early phase of the storm sudden commencement (SSC), exhibiting typical eastward drift under quiet-time conditions. Around ∼20 UT, the EPBs showed a brief westward displacement, accompanied by a rapid reduction in their zonal and vertical extent. The depleted structures subsequently fragmented and collapsed abruptly, leaving only isolated, blob-like plasma features. After this collapse, no further EPB activity was observed for the rest of the night. The estimated EPB drift velocities ranged from 174 to −21 m/s, indicating a clear reversal in zonal motion, similar to drift reversals reported during the strong geomagnetic storm of 17 March 2015. Notably, EPBs remained suppressed until 25 January, suggesting a prolonged post-storm stabilization of the ionosphere. Multi-station ROTI observations corroborated this suppression, with irregularity activity declining sharply following the drift reversal and remaining below the scintillation threshold over subsequent nights, consistent with disturbance dynamo-driven inhibition of post-sunset instability growth. In contrast, TEC exhibited a predominantly positive storm-time response, with significant enhancement at mid-latitudes and no clear or sustained negative phase. The simultaneous occurrence of TEC enhancement and EPB suppression indicates that increased plasma density alone is not sufficient for EPB development. Instead, these observations highlight the dominant role of rapid storm-time electrodynamic forcing in controlling EPB dynamics over the Indian longitude sector.

Lightning is an intriguing natural phenomenon and understanding its characteristics while the passage of the cyclone remains mostly unraveled. In this research, we aim to investigate how the cloud-to-ground (CG) lightning activity is getting influenced by the cyclone and vice-versa. We use NRSC- LDSN data and INSAT-3D data over the ocean for the first time to analyze this inter- relationship. We use ERA5 ECMWF reanalysis dataset to verify the occurrence conditions and impact of the lightning. The key parameters analyzed include, Total column cloud ice water (TCIW), Total column cloud liquid water (TCLW), Vertical integral of kinetic energy (VIKE), and Convective Inhibition (CIN). Our analysis suggests that though TCIW indicates the potential of lightning occurrences over and near by the cyclone path, the CIN remained the controlling factor. Also, the sudden enhancements in the kinetic energy in and around the cyclone following the lightning occurrences give a possible clue that thermal energy produced by the lightning may have converted into kinetic energy.

We present evidence of the merging of Equatorial Plasma Bubbles (EPBs) with Medium-Scale Travelling Ionospheric Disturbances (MSTIDs) during the post-midnight sector over the Indian region, observed on the night of 28th January 2011, a typical spread F event. The wavefront of the MSTIDs was aligned from northwest to southeast, propagating southwestward. In this study, we analyze airglow data from OI 630.0 nm emission recorded by an all-sky imager (ASI) located at Kolhapur (16.8 degrees N, 74.2 degrees E). The onset of EPBs was observed around 13:30 UT. Notably, eastward-moving EPBs began to merge with the dark wavefronts of MSTIDs around 19:50 UT, with the process completing by 21:45 UT. During this merging process, the drift velocity of EPBs decreased from 100 m/s to 50 m/s which later merged with the dark fronts of MSTIDs, as noted in OI 630.0 nm images. This interaction resulted in structural changes to the eastward drifting EPBs. The electrodynamics associated with this novel event is elaborated in this paper. (c) 2025 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Space based radio wave communication and navigation has become need of the society. Atmospheric (thermospheric-ionospheric) processes, such as Equatorial Plasma Bubbles (EPBs), affect the radio waves propagating through this region, causing heavy perturbations on signals received at ground. This paper investigates the causative mechanism of EPB through the ground based remotely sensed imaging observations of O (1S) 557.7 nm and O (1D) 630.0 nm emissions emanating from the upper mesosphere (-100 km altitudes) and thermosphere-ionosphere (-250 km altitudes) over a low-latitude station, Kolhapur (16.8 degrees N, 74.2 degrees E, and dip lat. 10.6 degrees N). Our investigation revealed that the gravity waves evident in OI557.7 nm images exhibit a close association with the observed EPB structures. These mesospheric gravity waves were found to travel from the South to North with horizontal wavelengths -35 and -56 km on 13-14 April and 26-27 April 2015, respectively. The thermosphere-ionosphere measurements exhibited occurrence of the North-South aligned EPB moving to the east with an inter depletion distance (IDD) equal to -44 km and -64 km. These results provide evidences on association of the gravity waves with the EPB. (c) 2023 COSPAR. Published by Elsevier B.V. All rights reserved.

The current study investigates the application of the photogrammetric technique, commonly used for satellite measurements, on the All Sky Imager (ASI), which is used for night airglow observations from Kolhapur (16.8 degrees N, 74.2 degrees E), India. Using image processing methods, the current study spanning from the year 2016 to 2020 (March - May months) estimates the cloud speeds to range from 10 m s(-1) to 18 m s(-1) during the period under consideration. The slowest speed of 10 +/- 3 m s(-1) was evidenced in 2017, while it takes value of 15 +/- 3 m s(-1) over other years. The clouds are found to move in a south-westerly direction during the time period under consideration. The cloud cover fraction varies in between similar to 0.178 to 0.594 from 2016 to 2020. Our analysis indicates systematic changes in the pre-monsoon cloud fraction and direction of the cloud movement. The observed trend indicates that the monsoon pattern is somewhat changing

Atmospheric lightning is an outcome of extreme complex physical processes occurring in the atmosphere. Cloud-to-ground (CG) lightning is considered as a natural disaster. Understanding the importance of CG lightning and implication of the lightning phenomena, Global Climate Observing System (GCOS), world meteorological organization, in its report in the year 2016, introduced the lightning as an Essential Climate Variable (ECV). The present report uses the Lightning Detection Sensor Network (LDSN) established by the National Remote Sensing Centre, Indian Space Research Organization over India to generate the Lightning ECV. A use case of these ECVs are also showcased for an event in Bihar, India, when 42 deaths were reported at locations with large number of CG occurrences.

We report an interesting Equatorial Plasma Bubbles (EPBs) event during the night of March 22–23, 2017. To investigate the dynamics of observed EPBs, we utilize multi‐instrument data obtained with all‐sky imager (ASI) from Panhala (16.48°N, 74.6°E, 11.1°N Dip. Lat.), Canadian Advanced Digital Ionosonde (CADI) from Tirunelveli (8.73°N, 77.7°E, 1.6°N Dip. Lat.) and ionospheric backscatter echoes data of Gadanki Ionospheric Radar Interferometer (GIRI) radar from Gadanki (13.5°N, 79.2°E, 6.5°N Dip. Lat.) over Indian regions. The optical observations from Panhala reveal clear signatures of EPBs from ∼1600 UT onwards and corresponding ESF occurrence is noted in CADI at Tirunelveli as well. Backscatter echoes are also recorded in Range time intensity map obtained by GIRI after ∼17:45 UT. On this night, two EPBs (EPB1 and EPB2) are observed with inter‐depletion distance of ∼600 km. The EPB1 drifts eastward throughout the night and evolves with time as bifurcated structures while the trailing EPB2 drifts eastward initially and eventually drifts westward. We believe that this is the first evidence of differential drifts of EPBs imaged through ASI over a narrow longitudinal zone over the Indian region.

In this paper, the occurrence characteristics of the equatorial plasma bubbles (EPBs) using OI 630.0 nm all sky imager (ASI) night airglow observations over Kolhapur (16.8o N, 74.2o E, 10.6o dip. Lat.) during the solar cycle-24 are presented. These results are discussed in terms of season, solar and magnetic activity during years 2011 to 2018. The ASI observations were only carried out during January to May and October to December months due to unfavorable weather conditions. The results suggest that while January, February and December are the only months where EPBs were found to occur over Kolhapur in any year, but the percentage of occurrence of EPBs during these months suggests their low occurrence rate during solar minimum. A total of 683 nights of observations were carried, out of which, 93 nights are found to be magnetically disturbed nights having Ap>18. In addition, the ASI observations are also correlated with Pre-Reversal Enhancement of the vertical drift of the evening sector at Tirunelveli on few storm events for comparison. The important findings of this study are: 1) increase in the occurrence of EPBs with respect to the solar activity; 2) suppression of EPBs on 71 disturbed nights, while enhancement of EPBs on 22 nights under magnetic disturbance; 3) EPBs occurrence during equinox months is found to be higher than winter months during ascending phase of solar cycle-24.; and, 4) EPBs are mostly observed in the pre-midnight sector in the high solar activity (HSA) period, while they are seen in the post-midnight to dawn sector during the low solar activity (LSA) period. We also noticed non-occurrence of EPBs during equinox month in the year 2018 which seems to be peculiar and needs further investigations.

The Kumbh mela is a huge public gathering event in Hindu tradition. During 2019 Kumbh which was organized at Prayagraj/Allahabad, India, large infrastructure was created to facilitate the visitors. To monitor impact of such gathering and infrastructure on the atmospheric composition, a road campaign was conducted from Nagpur (21.15 N, 79.03 E) to Prayagraj (25.42 N, 81.87 E) during 17-23 February 2019 with a hand-held microtop sun photometer as a primary instrument. Data revealed AOD variation to be higher by about 19% at the centre of the event. The derived angstrom exponent suggests that the mass gathering and large infrastructure may have raised the dust level in the ambient atmosphere which was reflected in the enhanced Aerosol optical depth values and size distribution.

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 wavelength, horizontal phase velocity, and period of the MSTID are found to be 160 ± 6 km, 138 ± 14 m/s, and 19.5 ± 3 min, respectively. These phase fronts are observed to move toward southwest with a propagation angle of ~235° ± 1° with respect to north. In addition to the MSTID, a strong quasiperiodic southward moving wave (QPSMW) from the evening to midnight interval and a small‐scale southward moving wave structure with wavelength and periodicity different from the QPSMW are also detected on the same night. Horizontal wavelength, horizontal phase velocity, and period of the QPSMW are estimated to be 367 ± 14 km, 131 ± 18 m/s, and 46.7 ± 13 min, respectively, and those of the small‐scale southward moving wave are found to be 157 ± 4 km, 121 ± 17.8 m/s, and 21.7 ± 3.4 min, respectively. Global Positioning System‐total electron content maps suggest that the weak and asymmetric equatorial ionization anomaly helped deep ingression of the MSTID on this night. The descent of the F layer seems to have caused the dissipation of the MSTID and QPSMW closer to the dip equator on this night. Therefore, the present investigation shows that the midlatitude MSTIDs can influence the F region plasma processes even over very low latitudes under favorable background conditions.

In this paper, we report first-time observations of total column ozone (TCO), aerosol optical thickness (AOT) and precipitable water content (PWC) at five different wavelengths using compact, handheld, multichannel sun photometer (Microtops II ozonometer) at Atigre village (16.74°N latitude, 74.37°E longitude, 604 ms altitude above sea level). The three optical filters at wavelengths 305 nm, 312 nm and 320 nm are used to detect the TCO, while two optical filters 936 nm and 1020 nm are used to detect the PWC and AOT, respectively. We have been collecting data from September 1, 2017, and 122 days are selected from September 1, 2017, to December 31, 2017, to present as first observations of TCO, AOD and PWC. The mean values of TCO, AOT and PWC are found to be 261.2 (± 9.22) DU, 0.25 (± 0.04) and 1.98 (± 0.79) cm, respectively, during this period. The TCO measurements taken by the Microtops II ozonometer are compared with the ozone monitoring instrument satellite data over Atigre. We found that PWC and AOT values are negatively correlated (− 0.54) during monsoon season, while they show positive correlation (0.63) during other seasons with 90% significance level. The diurnal variation of TCO, PWC and AOT differ in monsoon and the post-monsoon season.

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 wavelength, horizontal phase velocity, and period of the MSTID are found to be 160 ± 6 km, 138 ± 14 m/s, and 19.5 ± 3 min, respectively. These phase fronts are observed to move toward southwest with a propagation angle of ~235° ± 1° with respect to north. In addition to the MSTID, a strong quasiperiodic southward moving wave (QPSMW) from the evening to midnight interval and a small‐scale southward moving wave structure with wavelength and periodicity different from the QPSMW are also detected on the same night. Horizontal wavelength, horizontal phase velocity, and period of the QPSMW are estimated to be 367 ± 14 km, 131 ± 18 m/s, and 46.7 ± 13 min, respectively, and those of the small‐scale southward moving wave are found to be 157 ± 4 km, 121 ± 17.8 m/s, and 21.7 ± 3.4 min, respectively. Global Positioning System‐total electron content maps suggest that the weak and asymmetric equatorial ionization anomaly helped deep ingression of the MSTID on this night. The descent of the F layer seems to have caused the dissipation of the MSTID and QPSMW closer to the dip equator on this night. Therefore, the present investigation shows that the midlatitude MSTIDs can influence the F region plasma processes even over very low latitudes under favorable background conditions.

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 wavelength, horizontal phase velocity, and period of the MSTID are found to be 160 ± 6 km, 138 ± 14 m/s, and 19.5 ± 3 min, respectively. These phase fronts are observed to move toward southwest with a propagation angle of ~235° ± 1° with respect to north. In addition to the MSTID, a strong quasiperiodic southward moving wave (QPSMW) from the evening to midnight interval and a small‐scale southward moving wave structure with wavelength and periodicity different from the QPSMW are also detected on the same night. Horizontal wavelength, horizontal phase velocity, and period of the QPSMW are estimated to be 367 ± 14 km, 131 ± 18 m/s, and 46.7 ± 13 min, respectively, and those of the small‐scale southward moving wave are found to be 157 ± 4 km, 121 ± 17.8 m/s, and 21.7 ± 3.4 min, respectively. Global Positioning System‐total electron content maps suggest that the weak and asymmetric equatorial ionization anomaly helped deep ingression of the MSTID on this night. The descent of the F layer seems to have caused the dissipation of the MSTID and QPSMW closer to the dip equator on this night. Therefore, the present investigation shows that the midlatitude MSTIDs can influence the F region plasma processes even over very low latitudes under favorable background conditions.

An observational evidence of medium-scale traveling ionospheric disturbances (MSTIDs) reaching to magnetic latitude as low as similar to 3.5 degrees 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 degrees N, 79.2 degrees E; 6.6 degrees magnetic latitude), on 12 January 2016. The horizontal wavelength, horizontal phase velocity, and period of the MSTID are found to be 160 +/- 6 km, 138 +/- 14 m/s, and 19.5 +/- 3 min, respectively. These phase fronts are observed to move toward southwest with a propagation angle of similar to 235 degrees +/- 1 degrees with respect to north. In addition to the MSTID, a strong quasiperiodic southward moving wave (QPSMW) from the evening to midnight interval and a small-scale southward moving wave structure with wavelength and periodicity different from the QPSMW are also detected on the same night. Horizontal wavelength, horizontal phase velocity, and period of the QPSMW are estimated to be 367 +/- 14 km, 131 +/- 18 m/s, and 46.7 +/- 13 min, respectively, and those of the small-scale southward moving wave are found to be 157 +/- 4 km, 121 +/- 17.8 m/s, and 21.7 +/- 3.4 min, respectively. Global Positioning System-total electron content maps suggest that the weak and asymmetric equatorial ionization anomaly helped deep ingression of the MSTID on this night. The descent of the F layer seems to have caused the dissipation of the MSTID and QPSMW closer to the dip equator on this night. Therefore, the present investigation shows that the midlatitude MSTIDs can influence the F region plasma processes even over very low latitudes under favorable background conditions. Plain Language Summary Medium-scale traveling ionospheric disturbances (MSTIDs) generated in the midlatitude are found to propagate toward the equator. While crossing the equatorial ionization anomaly crest region most of these structures dissipate due to ion drag. A deep ingression of the MSTID to a very low geomagnetic latitude (near to the geomagnetic equator) over the Indian sector is noted during the descending phase of the 24th solar cycle. Weak and asymmetric equatorial ionization anomaly formation is believed to support the deep ingression processes. On the observational night quasiperiodic southward moving waves and a small-scale southward moving wave signature are also observed in addition with the MSTID. The dissipation of all these features is possibly due to existence of the midnight pressure bulge. Present study provides an observational evidence of the midlatitude MSTID propagation into the low latitudes and their interaction with the low-latitude ionospheric/thermospheric processes, for example, midnight pressure bulge.

Total column ozone (TCO) distribution and its variation over the Indian region at different stations for the period of about 30 years from 1986 to 2015 are studied. TCO data is taken from the merged ozone data set (MOD) overpass data for 15 different stations over India. The average correlation between TCO and solar proxies such as sunspot number and F10.7 cm solar flux is more than 0.5. We further divided the time series of TCO according to solar cycle as 22nd solar cycle (September 1986 to July 1996), 23rd solar cycle (August 1996 to November 2008) and 24th solar cycle (December 2008 to December 2015) (on going cycle) for a period of 1986-2015. Herein, for the long term trend analysis of TCO, we have removed the seasonal effect by the deseasonalization process, the effects of solar activities, stratospheric waves (quasi-biennial-oscillation-QSO and El Nino-Southern Oscillation-ENSO) by the multifunction linear regression method (MLR). We have compared both the linear trends in TCO which are calculated by the simple linear regression (SLR) and deseasonalised multifunction linear regression (DMLR) analysis. It is found that the direction of the trend in 22nd and the 23rd solar cycle is similar while, it is opposite in the 24th solar cycle. We observed a more negative trend in the 22nd solar cycle and less negative trend in the 23rd solar cycle while the trend is positive in the 24th solar cycle. The results indicate that after the DMLR process, the trend values are decreased by a large factor. Therefore, it is found that the role of natural variability is more than that of the ozone depleting substances (ODS) on long term variability in TCO over India. This statistical analysis provides better analysis of trend variation in TCO series over India. The main objective of this work is to analyze the variations in trend in the TCO with respect to the recent three solar cycles.

Antarctica provides an opportunity to study natural forcing and background values of various constituents in the atmosphere, in particular, aerosols. In a recent effort during the 36th Indian Scientific Expedition to Antarctica (36th ISEA), a Dual Imager System was installed at Indian station Bharati (69.4 degrees S, 76.18 degrees E) to study round-the-clock variations of aerosol optical thickness (AOT). The data reveal a weak diurnal pattern in the AOT variability and the values vary from 0.07 to 0.10 during daytime while they reach0.12 during nighttime. The daytime (solar zenith angle <70 degrees) results compare well with collocated sun photometer as well as space based estimates, while the higher solar zenith angle (>70 degrees) AOT values are reported for the first time over Antarctica. The observed higher AOT values at higher zenith angles, i.e. during nighttime are suggested to be due to variations in wind speed and temperature.