Atmospheric Gravity Waves (AGWs) play a crucial role in atmosphere-ionosphere coupling. Tropical cyclones (TCs) are considered one of the potential sources of AGWs. This study investigates four extreme category tropical cyclones from the last two decades over the Indian subcontinent: VSCS Phailin (2013), ESCS Fani (2019), SuCS Amphan (2020) over the Bay of Bengal, and ESCS Tauktae (2021) in the Arabian Sea. The meteorological observations confirmed the presence of deep convective activity during these TCs, which reached higher tropospheric altitudes during the TC's duration. The low cloud-top temperatures exhibited a positive correlation with the increasing lightning activity. Further, a notable increase in lightning activity was found during the intensification phases of the storm, particularly within the wind-field regions in all four cases, which could have led to an intensification of TCs. Simultaneously, an enhancement in AGW activity occurred in the mesosphere-lower thermosphere (MLT) region. Possibly, mesoscale convective system associated with the TC led to the formation of AGWs that propagated in both the vertical and horizontal domains to higher altitudes in the MLT region. The propagation of vertical and horizontal AGWs induced by TCs at higher altitudes has been validated and quantified by analyzing vertical temperature profiles obtained from SABER and day-night band DNB imagery from VIIRS satellites. Both vertical and horizontal wavelengths of AGWs showed peak power of waves during the maximum intensity stages of TCs. Both vertical and horizontal components of AGWs are quantified for the first time over the Indian region.

The study investigates Super Cyclone (SuCS) Amphan, which occurred over the Bay of Bengal (BoB) during 16-21 May 2020 as a possible source of lower ionospheric perturbations. INSAT-3D satellite observations confirmed intense convective activity through low Cloud Top Brightness Temperature (--80 degrees C) and suppressed Outgoing Longwave Radiation (below 100 W/m2). Lightning analysis indicated an increase in activity within 500 km of the cyclone center, with cloud-to-cloud (CC) lightning intensifying in the eyewall during the cyclone's peak. Over 60 % of positive CC flashes exceeded 10 kA, highlighting strong convective electrical dynamics. Temperature perturbations observed by the AIRS instrument onboard NASA's Aqua satellite appeared as concentric wave patterns at stratospheric altitudes, indicating atmospheric gravity waves (AGWs) activity in the northeast of the storm center. SABER temperature profiles further revealed enhanced wave amplitudes from May 17-20, confirming AGW propagation into the mesosphere-lower thermosphere (MLT) region. Nightglow emissions observed by the Suomi-NPP/DNB sensor provided additional evidence of concentric gravity waves at the MLT heights. This enhanced AGW activity coincided with Amphan's intensification. This multi-altitude observational analysis highlights the role of intense convection and lightning in AGW generation and their subsequent influence on upper atmospheric dynamics. The observations confirm that tropical cyclones serve as a source of lower ionospheric disturbances through AGW-driven energy and momentum deposition.

In the process of transient solar wind energy transfer into the near-Earth environment, extremely intense currents are often observed in the nightside polar ionosphere. Auroral brightening is generally accompanied with the current intensification. The westward electrojet leads to a sharp magnetic field depression in the horizontal component around 65 magnetic latitude in the midnight meridian. It typically marks the onset of a geomagnetic substorm. During the course of a substorm, the auroral electrojet expands in local time and also poleward from the location of onset. In our earlier study Singh et al. (2012), we presented the magnetic signatures of the polar substorms using about 100 days data from the Indian Antarctic station-Bharati (CGM coordinates 74 83 S, 98 60 E) in conjunction with the data from a near-conjugate station Hornsund (CGM coordinates 74 4 6 N, 107 34 E) in the Arctic. This study utilizes long-term (2013-22) magnetic field observations from the same stations. It is observed that the westward electrojet (WEJ) often expands to about similar to 75 magnetic latitudes in both hemispheres. A modified version of Newell and Gjerloev (2011) algorithm has been used to identify substorm-like WEJ intensification (hereafter substorm) over the stations. Their characteristics over a time scale of the solar cycle to the diurnal have been investigated. The hemispherical comparison of the time of onset, and occurrence and intensity of substorms with the solar illumination of the ionosphere has been carried out. (c) 2025 The Author(s). Published by Elsevier B.V. on behalf of COSPAR. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

The study presents detailed meteorological characteristics of extremely severe cyclonic storm (ESCS) Fani, and subsequent Atmospheric Gravity Waves (AGWs) induced D-region ionospheric perturbations and the role of lightning activity in it. The cyclone shaped as a weak disturbance over the north Indian Ocean (2.7 degrees N, 89.7 degrees E) on 25 April 2019. The disturbance intensified and evolved into ESCS Fani over Bay of Bengal (BoB) on 30 April, had landfall on 03 May, and dissipated after 04 May 2019. What makes Fani unique is its long life span of similar to 10 days, and only ESCS to occur after similar to 30 years over the BoB. Fani attained a minimum cloud top temperature of about -80 degrees C, and a corresponding maximum cloud top altitude of about similar to 17 km. Such meteorological conditions presented a strong convection process in the towering cumulonimbus in inner and outer rain bands, resulting in intense lightning activity. The peak lightning flash rate observed was similar to 375 min-1. SABER observations confirmed the coupling of atmosphere with ionosphere with strong AGWs in middle atmosphere during Fani. NWC (19.8 kHz) Very Low Frequency signal intersecting the track of Fani is used to decipher D-region ionospheric perturbations induced by AGWs from Fani. The results show the presence of increased AGW activity in D-region during the cyclone period when compared to that of the pre- and post-cyclone periods. The periods of the observed gravity waves are between similar to 13 and 20 min, highlighting the important role of lightning activity and AGWs in atmosphere-ionosphere coupling. A unique tropical cyclone "Fani" of the ESCS category from the Bay of Bengal with a life span of similar to 10 days is examined to understand the atmospheric gravity waves (AGWs) induced atmosphere-ionosphere coupling. The role of lightning discharges is specifically examined in the generation of AGWs in the lower atmosphere. These AGWs travel upwards from the lower atmosphere and play a significant role in transferring mass and energy during upward propagation through mesosphere to couple with ionosphere. The VLF data is used to understand the D-region ionospheric modulations by AGWs from Fani. Our analysis revealed increased AGW activity in the ionosphere during the cyclone period compared to pre- and post-cyclone days, which is strongly correlated with the lightning activity during the observational period. The findings contribute to a better understanding of how extreme weather events can affect the ionosphere. A unique extremely severe cyclonic storm Fani over the Bay of Bengal with 10-day life span is analyzed to understand the atmosphere-ionosphere coupling due to Atmospheric Gravity Waves (AGWs) Understand role of lightning activity in generation of AGWs, propagation via mesosphere, and consequent coupling with the ionosphere The results presented highlight the important role of lightning activity associated with AGWs in atmosphere-ionosphere coupling

AbstractOne of the most intense geomagnetic storms of recent times occurred on 10–11 May 2024. With a peak negative excursion of Sym‐H below −500 nT, this storm is the second largest of the space era. Solar wind energy transferred through radiation and mass coupling affected the entire Geospace. Our study revealed that the dayside magnetopause was compressed below the geostationary orbit (6.6 RE) for continuously ∼6 hr due to strong Solar Wind Dynamic Pressure (SWDP). Tremendous compression pushed the bow‐shock also to below the geostationary orbit for a few minutes. Magnetohydrodynamic models suggest that the magnetopause location could be as low as 3.3RE. We show that a unique combination of high SWDP (≥15 nPa) with an intense eastward interplanetary electric field (IEFY ≥ 2.5 mV/m) within a super‐dense Interplanetary Coronal Mass Ejection lasted for 409 min–is the key factor that led to the strong ring current at much closer to the Earth causing such an intense storm. Severe electrodynamic disturbances led to a strong positive ionospheric storm with more than 100% increase in dayside ionospheric Total Electron Content (TEC), affecting GPS positioning/navigation. Further, an HF radio blackout was found to occur in the 2–12 MHz frequency band due to strong D‐ and E‐region ionization resulting from a solar flare prior to this storm.

We report, in this work, the changes in the thermal structure of the mesosphere-lower thermosphere (MLT) region over an Indian Antarctic station Bharati (69.4 degrees S, 76.2 degrees E, CGM coordinates 75 degrees S, 97 degrees E) brought about by an intense geomagnetic storm of 23-24 March 2023 (Dst similar to -155 nT). We use the temperature and OH airglow measurements of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission satellite to compare the thermal field of the MLT region on these disturbed days with the neighbouring quietest days of 27-28 March. Such comparison reveals both warming and cooling in the MLT region associated with the storm. An extension of this comparative study in the latitude region located poleward of Bharati also shows similar behavior of the MLT region during this geomagnetic storm. Overall, this study reveals the maximum temperature enhancement of similar to 39-43 K to occur at around 99 km, a significant warming of similar to 4-43 K in 95-105 km, and a decrease of similar to 12-16 K in 80-87 km. While the enhancement of temperature in 95-105 km appears to be a consequence of the auroral heating associated with this storm; we are unable to account for the cooling below based on existing theories. Present observation of the development of cooling underneath the region of temperature enhancement during the geomagnetic storm is rare and demands further investigation.

We report F-region airglow imaging of fossil plasma depletions around midnight that revived afresh under persisting thermospheric gravity wave (GW) activity. An all-sky imager recorded these events in OI 630 nm imaging over Ranchi (23.3° N, 85.3° E; mlat. ∼19° N), India, on 16 April 2012. Northward-propagating and east–west-aligned GWs (λ∼210 km, v∼64 m s−1, and τ∼0.91 h) were seen around midnight. Persisting for ∼2 h, this GW activity revived two co-existing and eastward-drifting fossil depletions, DP1 and DP2. GW-driven revival was prominently seen in depletion DP1, wherein its apex height grew from ∼600 to >800 km, and the level of intensity depletion increased from ∼17 % to 50 %. The present study is novel in the sense that simultaneous observations of thermospheric GW activity and the associated evolution of depletion in OI 630 nm airglow imaging, as well as that around local midnight, have not been reported earlier. The current understanding is that GW phase fronts aligned parallel to the geomagnetic field lines and eastward-propagating are more effective in seeding Rayleigh–Taylor (RT) instability. Here, GW fronts were east–west-aligned (i.e., perpendicular to the geomagnetic field lines) and propagated northward, yet they revived fossil depletions.

Structuring on the west (east) wall of eastward (westward) drifting airglow depletion under quiet (storm) time is common. Here, we report for the first time the rare occurrence of the east wall structuring of an eastward drifting depletion near the crest of equatorial ionization anomaly (EIA) in India on 16 April 2012 under quiet geomagnetic conditions. We observed a linear depletion having a westward tilt of ∼25° and eastward drift speed of ∼129 m/s in the beginning. First prominent structuring occurred on its west wall that later swiftly surged poleward within next 6–12 min and bifurcated, that is, behaved like a secondary depletion growing on the primary one. Second west wall structuring then occurred but had considerably subdued growth. Meanwhile, main depletion bent slightly eastward above its branching node, and two structuring appeared on the east wall in succession. Secondary depletion then slightly contracted equatorward, and structuring emerged from its east wall, too, that later stretched eastward, got linked with main depletion and formed grid mesh shaped feature. Second structuring on the west wall started fading; while, those on the east wall swiftly evolved, surged poleward and gained prominence. Also, their westward tilt decreased. During the occurrence of these events, gravity waves (GWs) and the retreat of EIA were active overhead. Current study serves as first imaging evidence of Zalesak et al. (1982, https://doi.org/10.1029/JA087iA01p00151 ) simulations that the east wall of a westward tilted depletion can become unstable and host secondary instabilities. Possibly these structuring were excited by GWs via Rayleigh‐Taylor instability.

We report rare simultaneous observations of columniform sprites and associated gravity waves (GWs) using the Transient Luminous Events (TLEs) camera and All-sky imager at Prayagraj (25.5° N, 81.9° E, geomag. lat. ~ 16.5° N), India. On 30 May 2014, a Mesoscale Convective System generated a group of sprites over the north horizon that reached the upper mesosphere. Just before this event, GWs (period ~ 14 min) were seen in OH broadband airglow (emission peak ~ 87 km) imaging that propagated in the direction of the sprite occurrence and dissipated in the background atmosphere thereby generating turbulence. About 9–14 min after the sprite event, another set of GWs (period ~ 11 min) was observed in OH imaging that arrived from the direction of the TLEs. At this site, we also record Very Low Frequency navigational transmitter signal JJI (22.2 kHz) from Japan. The amplitude of the JJI signal showed the presence of GWs with ~ 12.2 min periodicities and ~ 18 min period. The GWs of similar features were observed in the ionospheric Total Electron Content variations recorded at a nearby GPS site. The results presented here are important to understand the physical coupling of the troposphere with the lower and upper ionosphere through GWs.

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.

Increasing resource degradation (soil) and resource scarcity (water) in Indo Gangetic Planes (IGP) had popularized the concept of conservation agriculture (CA). CA practices can alter the soil hydraulic properties by improving soil physical environment and hence water productivity (WP). Since CA practices are highly sites-pecific in nature, its worthiness under different cropping systems, soil types and agro-climatic zones must be studied. In the context of above-mentioned scenario of crop management practices, Hydrus-2D model was used to evaluate most suitable CA-based practice for north western (NW) IGP to understand the process of water transport. The experiment had 3-tillage and crop establishment practices [ZT-zero tillage; PB-permanent raised bed and CT-conventional tillage] in main plot and 4-cropping systems [MWMb-maize-wheat-mungbean; MCS-maize-chickpea-Sesbcrnia; MMuMb-maize-mustard-mungbean and MMS-maize-maize-Sesbania] in sub-plot. The validation of Hydrus-2D showed that nRMSE was observed between 0.19-0.25 and R2 value between 0.80-0.87 at P < 0.01. This indicates model is performing efficiently. The R2 value (0.87) was observed highest and RMSE ,(0.03) and nRMSE (0.15) was observed least in the CA-based PB plots. CA-based plots had 23%-37% less evaporation than CT plots. Cumulative root water uptake (CRWU) under PB was 11% and 15% lower, whereas CRWU under ZT was 20% and 30% higher than CT plots in 2012 and 2013, respectively. Cumulative deep drainage (CDD) in 2013 in PB was higher by 3.64 and 5.88 cm than ZT and CT, respectively. With 10-cm higher rainfall during 2013, variability in the soil water content (SWC) was increased by 22% in CT and 2% in ZT plots. PB had 14-35% and 30-36% higher water productivity than ZT and CT plots, respectively. Radiation use efficiency (RUE) for dry-matter was observed higher under CA based plots. However, RUE for grain yield was observed similar among CA and CT plots during 2012, but in 2013, ZT outperformed than CT plots. The outcome of this study is, the higher rainfall during 2013 mainly contributed to more CDD. Highly variable SWC was observed in the CT plots. With lesser deep drainage in ZT, root water uptake (RWU) was higher and WP was lower, whereas PB plots had comparatively less-moist soil profile and per unit of RWU + evaporation, a proportionately higher dry-matter was produced. In a well-drained soil profile of PB plots frequent and light irrigation may be advocated, whereas in ZT with better profile storage and lesser variability of SWC during both the year irrigation may be required less frequently. Therefore, adoption of CA-based practices leads to higher crop productivity and resource use efficiency, because of favorable soil hydrological property with less fluctuation in soil water content in maize under diversified cropping systems of IGP of south Asia.

Usual depletions in the Northern Hemisphere form a tree fork junction feature near the south (i.e., toward the equator) in all-sky airglow images, and its branches surge toward the north (i.e., poleward). We report in this paper unusual airglow depletions in OI 630.0-nm imaging over India that surged equatorward and formed an inverted tree fork junction feature on 3 January 2011. Airglow images showed faint signatures of medium-scale traveling ionospheric disturbances in the beginning that were east-west aligned and propagated toward equator. Within 06 to 18 min of its passing, turbulent structures were noted in the field of view, and two depleted patches appeared out of low airglow background over the off-equatorial edge. The apex height of the associated geomagnetic flux tubes varied from similar to 1,400 to 1,600 km. Later, these dark regions intensified and surged equatorward while drifting slowly toward west. While remaining almost steady, one of them further intensified and continued to surge equatorward. The second dark patch got linked up with another isolated depletion to form an elongated depleted feature. Next, the southern end of this attached feature surged equatorward. When two depletions were well formed, an inverted tree fork junction was noticeable. During this time, the equatorward motion of the equatorial ionization anomaly structure is also seen. To the best of our knowledge, this is the first imaging observation of an inverted tree fork junction feature and brings out the unknown facets of ionospheric irregularities. Plain Language Summary Usual depletions form a tree fork junction feature near the equatorial edge in all-sky airglow images; its branches surge poleward. On 3 January 2011, unusual depletions were noted over India that surged equatorward and formed an inverted tree fork junction. We present an independent usual depletion event. Such an inverted feature has been not reported earlier to the best of our knowledge and brings out the unknown facets of ionospheric irregularities.

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 study we present the behaviour of sporadic E-layer during a total solar eclipse (TSE) which occurred during the dawn/sunrise hours over a site located in the path of totality. A Canadian Advanced Digital Ionosonde (CADI) was operated at Allahabad (25.4 degrees N, 81.9 degrees E), a low latitude station located near the crest of equatorial ionization anomaly (EIA) in the Indian subcontinent to study the ionospheric effects of 22 July 2009 TSE. Corresponding to the eclipse period, a gradual increase of ftEs (top frequency of Es layer) in the 4-5 MHz range was seen on the control days. On 22 July (the TSE day), correlated changes in ftEs coinciding with the TSE progression was noted - (i) sharp decrease near first and second contact of TSE, (ii) an increase after first and second contact, and (iii) wavelike fluctuations in ftEs variation during eclipse hours and beyond. Much higher ftEs values were noted during the TSE hours in comparison to that seen on usual days. Strong blanketing Es layer developed during the TSE hours and persisted for slightly longer duration than its usual occurrence time. Near the TSE totality, slight lowering of the base height of Es layer was also noted. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.

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.

A greater energy grant in diesel-fed machinery driven farming substantiate the higher GHGs emission along with improper input (fertilizer, pesticide and irrigation) use and intensive soil management. Practicing conservation tillage, residue retention and diversified crop rotations were advocated because of their multiple benefits. Hence we explored the energy requirement and carbon footprint of conservation agriculture (CA) based maize production systems Coated N fertilizer [sulphur coated urea (SCU) and neem coated urea (NCU)] were compared with unfertilized and uncoated prilled urea (PU) in the scenario of with and without residue retention on permanent beds (PB) under diversified maize systems [MMuMb, maize-mustard-mungbean and MWMb, maize-wheat-mungbeanl in search of a sustainable and energy efficient production system with lesser C-footprint. Results of the 4-year study showed that crops planted on permanent bed with crop residue (PB+R) registered 11.7% increase in system productivity compared to PB without residue (PB-R). N management through Neem coated urea (NCU) recorded 2.3 and 10.9% higher system productivity compared with non-coated prilled urea plot under PB-R and PB+R, respectively. MMuMb was marginally superior than MWMb system in terms of cropping sequence yield, profitability, and energy and carbon use efficiency. Crop residue retention in zero tilled PB increased cost of cultivation by 125 and 147 USD/ha in MMuMb and MWMb systems, respectively. The quantified carbon footprint value was higher in MWMb system. In CA-based practices, crop residues management contributed the highest energy input (61.5-68.4%) followed by fertilizer application (17-20%). Among N management practices, neem coated urea (NCU) significantly improved system productivity and profitability in all the residue applied plots compared to un-fertilized and prillecl urea (PU) applied plots. Similarly, higher energy output was also observed in NCU treated plots. However, carbon footprint value was higher in PU (268-285 CO2-e kg/Mg) plots than NCU (259-264 CO2-e kg/Mg) treated plots. Thus, the study supports and recommends that the CA-based MMuMb system with efficient N management through NCU is an environmentally safe, clean and energy efficient one, hence can reduce carbon footprint, will ensure food security and will mitigate climate change. (C) 2019 Elsevier B.V. All rights reserved.

Simultaneous observations of OI 777.4 and OI 630.0 nm nightglow emissions were carried at a low-latitude station, Allahabad (25.5° N, 81.9° E; geomag. lat. ∼ 16.30° N), located near the crest of the Appleton anomaly in India during September–December 2009. This report attempts to study the F region of ionosphere using airglow-derived parameters. Using an empirical approach put forward by Makela et al. (2001), firstly, we propose a novel technique to calibrate OI 777.4 and 630.0 nm emission intensities using Constellation Observing System for Meteorology, Ionosphere, and Climate/Formosa Satellite Mission 3 (COSMIC/FORMOSAT-3) electron density profiles. Next, the electron density maximum (Nm) and its height (hmF2) of the F layer have been derived from the information of two calibrated intensities. Nocturnal variation of Nm showed the signatures of the retreat of the equatorial ionization anomaly (EIA) and the midnight temperature maximum (MTM) phenomenon that are usually observed in the equatorial and low-latitude ionosphere. Signatures of gravity waves with time periods in the range of 0.7–3.0 h were also seen in Nm and hmF2 variations. Sample Nm and hmF2 maps have also been generated to show the usefulness of this technique in studying ionospheric processes.

Ground-based observations of OH (6, 2) Meinel band nightglow were carried out at Ranchi (23.3° N, 85.3° E), India, during January–March 2011, December 2011–May 2012 and December 2012–March 2013 using an all-sky imaging system. Near the mesopause, OH temperatures were derived from the OH (6, 2) Meinel band intensity information. A limited comparison of OH temperatures (TOH) with SABER/TIMED measurements in 30 cases was performed by defining almost coincident criterion of ±1.5° latitude–longitude and ±3 min of the ground-based observations. Using SABER OH 1.6 and 2.0 µm volume emission rate profiles as the weighing function, two sets of OH-equivalent temperature (T1. 6 and T2. 0 respectively) were estimated from its kinetic temperature profile for comparison with OH nightglow measurements. Overall, fair agreement existed between ground-based and SABER measurements in the majority of events within the limits of experimental errors. Overall, the mean value of OH-derived temperatures and SABER OH-equivalent temperatures were 197.3 ± 4.6, 192.0 ± 10.8 and 192.7 ± 10.3 K, and the ground-based temperatures were 4–5 K warmer than SABER values. A difference of 8 K or more is noted between two measurements when the peak of the OH emission layer lies in the vicinity of large temperature inversions. A comparison of OH temperatures derived using different sets of Einstein transition probabilities and SABER measurements was also performed; however, OH temperatures derived using Langhoff et al. (1986) transition probabilities were found to compare well.

We analyze an equatorial plasma bubble (EPB) event observed in optical 630nm image data simultaneously from Gadanki (13.5 degrees N, 79.2 degrees E), Kolhapur (16.8 degrees N, 74.2 degrees E), India. The total electron content data from Gadanki together with the ionosonde data from an equatorial Indian station, Tirunelveli (8.7 degrees N, 77.8 degrees E) confirmed the association of observed EPB event with equatorial spread F (ESF). The optical 630nm images from a farther low-latitude Indian station Ranchi (23.3 degrees N, 85.3 degrees E) show clear signatures of tilted east-west wave structures propagating toward equator. Further, the upward wave energy noted in mesospheric airglow data was found to be negligible. These data suggest that possibly the off-equatorial tilted east-west structures triggered the observed EPB/ESF event.