Upper mesospheric wind data acquired by the medium frequency radar at Kolhapur (16.7oN, 74.2oE) and Modern–Era Retrospective analysis for Research and Application version 2 (MERRA-2) temperature and wind reanalysis datasets are used to investigate the dynamical response of the low-latitude middle atmosphere to the sudden stratospheric warming (SSW) events that occurred during the 2017–18 and 2018–19 winters. When the amplitude of the high-latitude stratospheric planetary wave (PW) of zonal wavenumber one reduces considerably with the onset of the SSW event, the low-latitude mesospheric PW over Kolhapur also shows a considerable reduction in the PW activity. It is noteworthy that the upper mesospheric winds are eastward for approximately 3 weeks after the onset of SSW. The reduced PW activity is associated with the enhanced gravity wave activity in the meridional wind during the SSW 2018–19 event. The plane of propagation of gravity waves obtained from the perturbation ellipse method suggests that their predominant plane of propagation is in the north–south direction. The persistence of the eastward winds is suggested to be due to the interaction of the northward propagating gravity waves with the mean flow, leading to the eastward acceleration due to the Coriolis force.

We present the study of mesospheric winds in the 78–98 km height range using observations by a partial reflection radar station (MF–radar) situated at Kolhapur (16.8° N, 74.2° E), India. The sequential wind profiles over the period of 2014–2019 obtained from this radar operated at 1.98 MHz are used for this study. To delineate the behaviour of the winds in the mesosphere and lower thermosphere (MLT) region, we use wind data providing horizontal wind velocities averaged for an hour. Details of the seasonal, annual, and inter-annual variations and also the climatology of mean motion in zonal (East-West) and meridional (North-South) components in the MLT region over the aforementioned period are presented. The zonal wind below 90 km has been observed with eastward flow for the period of solstices and westward flow at equinoxes, showing strong semi-annual oscillations (SAO). While above 90 km, annual oscillations (AO) are seen to be dominant. Annual oscillations (AO) are observed in the mean meridional wind, with poleward motion during winter and equatorward motion during the remaining seasons. At higher altitudes (above 92 km), the poleward motion weakens and the equatorward wind flow becomes strong.

The strong quasi 2‐day wave (Q2DW) event that occurred during January 2015 was studied by employing medium frequency and meteor radar observations of winds from three different locations at low latitudes with considerable longitudinal separation. The large‐amplitude wave activity that occurred in mid‐January is the focus of this study. Using the advantage offered by the longitudinal separation among the stations, the zonal structure of the Q2DW has been examined. The presence of a dominant westward propagating zonal wavenumber 3 (W3) mode was revealed in the analysis. The availability of geomagnetic field data from a number of stations at low latitudes enabled us to observe the wave event at ionospheric dynamo region heights. The phase‐longitude cross‐section of the quasi 2‐day oscillation in the Y component of the geomagnetic field reiterates the presence of the dominant W3 mode observed at lower altitudes. Similar zonal characteristics and periods of the wave signatures found at mesospheric altitudes and in the manifestation of quiet‐time ionospheric currents in geomagnetic field are in conformity with the notion of the wave coupling of the atmosphere‐ionosphere system.

This study presents the analysis of planetary waves (PWs) using daily mean wind velocities for four years (August 2013 to July 2017) of continuous measurements using MF radar over the low latitude Indian region Kolhapur (16.8 degrees N; 74.2 degrees E). The MF radar at Kol-hapur was upgraded in 2013. These are the first results of PWs after the upgradation of MF radar. The seasonal and intra-seasonal vari-abilities of East-West (EW) traveling PWs in the MLT region have been studied. In the present work, the data was analyzed to study the waves with various periodicities (e.g. 3-4, 5-8, 15-17, and 30-60 days). The 3.5 day [Ultra-Fast Kelvin (UFK)] wave shows semiannual variability with burst like wave activity observed during the summer months and December solstice. In addition, it is observed to be stronger in the spring equinoctial period. A strong semiannual oscillation (SAO) has been observed in a 6.5-day wave with peaks near the equinoxes. Similar to SAO over the low latitude MLT region, the wave activity is stronger in April/May than in September/October. The 6.5-day waves are observed to be stronger when the background mean wind is westward. From the analysis, it has been seen that the period before and after the equinoctial period is favorable for the 6.5-day wave propagation. The 16-day wave has no significant seasonal dependence; instead, the waves spread to almost all seasons. The Madden-Julian Oscillations (MJOs) have been observed to be propa-gating with an average wind speed of 5 m/s when the background mean wind is eastward. The occurrence of MJO is observed during the summer and winter months. These results are the first of their kind in two aspects: first, they show the PWs with enhanced altitude coverage covering up to 110 km, and second, they show the PWs not contaminated due to equatorial electro jet influence. (c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.

ABSTRACT Airglow emissions which originate from the mesospheric and thermospheric altitudes have been routinely being monitored at Kolhapur (16.8° N, 74.2° E), Maharashtra, India, using ground base remote sensing imagers. We note that the observable amplitudes of very small-scale waves during April 2020 were significantly smaller than the regular observations. We investigate the reason for these low observable amplitudes. It is noted that drastic improvement in the quality of images was due to better contrast, which is attributed to significant reduction in greenhouse gases and aerosol loading in the atmosphere by the complete shutdown of local man-made emissions. Results suggest that lockdown had an important repercussion on the visibility through the improved air quality and thus better viewing conditions, which were reflected in the remotely sensed observations made with airglow imager.

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.

We analyzed the mesospheric winds and temperature data for investigating the waves scaling from the period of few hours to several hours (and few days) based on the airglow observations at Kolhapur (16.8 degrees N, 74.2 degrees E, 10.6 degrees N dip. lat.). The data presented in this study are collected using medium frequency radar and Multispectral Scanning Photometer at low latitude station Kolhapur. We scrutinized the wind and temperature relation of these waves for the observed period from January to May 2011. The data of 56 clear nights were collected and out of which 22 nights of data shows a conspicuous wavelike features. The nocturnal variability reveals the prominent wave signatures with a period which range from 7 to 12 h (h) as a dominant nocturnal wave. The presence of quasi 2.8-4 days waves with significant amplitudes is also detected. The comparison of the winds and temperatures suggests the temperature waves to be near in phase with meridional wind component and a time delayed relation with the zonal wind component. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.

The ground-based all sky imager (ASI) is an advanced optical technique, capable of measuring the strong F-region nightglow in CH 630.0 nm emission from atomic oxygen. This emission is used to study the large-scale F-region plasma irregularities; called as Equatorial Plasma Bubbles (EPBs) which often disturbs the communication and navigation systems over low latitudes. The observations of OI 630.0 nm nightglow emission have been carried out from low latitude station Kolhapur (16.8 degrees N, 74.2 degrees E, 10.6 degrees dip. lat.) using ASI during moonless nights for the period of 2011 to 2015. We have analyzed images recorded by ASI during this period and found some interesting features of EPBs on few nights (08 cases). This paper reports the analysis and the dynamics of EPBs features such as bifurcation, merging and detachment. The bifurcation in EPBs occurs before mid-night and extends to couple of hours towards dawn. Also, the secondary structures are seen as evolving features on the eastern wall of EPBs. In one of the case, the EPBs are seen to merge with each other due to their opposite tilts. Also, some EPBs detach due to unequal drifts along the meridian indicating the presence of strong latitudinal gradient in zonal neutral winds or altitudinal shear in zonal plasma drift which might be responsible for this detachment. In some cases we note that the EPBs shrink. Some of these features support the previous findings and some are new which needs further detailed investigation. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.

This study presents the quasi-two-day wave (Q2DW) characteristics of the mesosphere and lower thermosphere (MLT) region obtained by taking hourly mean values of horizontal wind velocities for 4 years (August 2013 July 2017) through continuous measurements using a medium-frequency (MF) radar (operating frequency - 1.98 MHz) located at the low-latitude Indian station Kolhapur (16.8 degrees N; 74.2 degrees E). The MF radar located at Kolhapur was upgraded in 2013, and these results of Q2DW have been reported for the first time after upgrading. The present study investigated variability in seasonal, annual, interannual, and solar indices of Q2DWs traveling in zonal (EW) and meridional (NS) components in the MLT region. The Q2DW activity is observed to be stronger during austral summer (January-February) (EW = similar to 5 m/s and NS = similar to 8-10 m/s) than during boreal summer (June-July) (EW = similar to 5 m/s and NS = similar to 6-8 m/s). The Q2DW amplitudes are larger in the meridional component than in the zonal one. A strong semiannual oscillation (SAO) has been observed in Q2DWs, with peak during January-February and June-July. In addition, small enhancement is seen in meridional Q2DW in October (similar to 5-6 m/s). It is observed that the entire spectrum (40-60 h) measured between 86 and 94 km contributes to the SAO amplitudes during January-February and June-July, whereas the waves measured between 42 h and 52 h contribute to enhancement in October similar to that reported elsewhere. In general, the Q2DW amplitude shows large interannual variability. The easterlies developed in the global circulation model in Northern hemisphere during May intensify up to around summer solstice. Q2DW activity peaks during westerly shear zone and intensifies with time at a lower thermospheric altitude (above 90 km). Small positive correlations (r = 0.2 for sunspot number and r = 0.1 for 10.7 cm solar flux) have been observed between Q2DW amplitudes and solar activity. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.

The present study describes L-hydroxy proline catalyzed unpredicted formation of 4,5-dihydro-1H-pyrazolo[3,4-b]pyridines instead of expected 4,7-dihydro-1H-pyrazolo[3,4-b]pyridines in aqueous ethanol at ambient temperature through one-pot three-component reaction. Furthermore, this protocol was evaluated using green chemistry metrics indicating green relevance of the present synthetic methodology. Most of the synthesized compounds were evaluated for their antitubercular activity against Mycobacterium tuberculosis H37RV strain, showing excellent results based on minimum inhibitory concentrations (MIC). Among the screened derivatives 4f, 4i, and 4j exhibited antitubercular activity with promising MIC value of 1.6g/mL. [GRAPHICS] .

The nightglow observations of OI 630.0 nm emission carried out from low latitude station Kolhapur using All Sky Imager (ASI) with \(140^{\circ}\) field of view (FOV) for the month of April 2011 are used. The images were processed to study the field aligned irregularities often called as equatorial plasma bubbles (EPBs). The present study focuses on the occurrence of scintillation during the traversal of EPBs over ionospheric pierce point (IPP). Here we dealt with the depletion level (depth) of the EPB structures and its effect on VHF signals. We compared VHF scintillation data with airglow intensities at Ionospheric pierce point (IPP) from the same location and found that the largely depleted EPBs make stronger scintillation. From previous literature, it is believed that the small scale structures are present near the steeper walls of EPBs which often degrades the communication, the analysis presented in this paper confirms this belief.

The optical observations of ionospheric and mesospheric CH 630.0 nm, OI 557.7 nm along with OH emission carried out from low latitude Indian station, Kolhapur (16.8 degrees N, 74.2 degrees E) using CCD based all-sky camera system. The features of night airglow variations observed during the period of a strong geomagnetic storm, which commenced on March 17, 2015, at similar to 04:30 UT (10:00 IST (Indian Standard Time = UT + 5.5 h)). Dst of similar to-222 nT was seen in this storm suggest that this is among the strongest. The 0! 630.0 nm images on 16, 17 and 18 March show the development of Equatorial Plasma Bubbles (EPBs) and bright intensity regions in OI 630.0 nm emission. Generally, EPBs move from west to east direction but it moved in reverse direction on the strong magnetically disturbed night. The EPBs drift velocity was less by similar to 100 m/s than the velocity measured on magnetically quite night 16-17 March 2015. The bright intensity regions are also observed in 01 557.7 nm airglow, but there is no intensity enhancement seen in OH emission. It is also observed that the CH 630.0 nm intensity variation well matches with the GPS VTEC variation for PRN-2. The reversal in EPBs drift velocity and the nightglow intensity variations due to the strong magnetic storm are discussed. (C) 2018 Published by Elsevier Ltd on behalf of COSPAR.

This paper reports the statistical analysis of zonal drift velocity of equatorial plasma bubbles (EPBs) inferred from advanced optical technique (all‐sky imager) with OI 630.0‐nm airglow emission from January to April of 2011 to 2013. Over 143 nights of observations have been carried out using all‐sky imager over low‐latitude station Kolhapur (16.8°N, 74.2°E; 10.6°N dip latitude), out of which 58 nights showed signatures of EPBs. We study the hourly, monthly, and seasonal variation in zonal drift velocity of EPBs. Also, the magnetically disturbed nights (Ap > 18) are separately studied. It is observed that (a) the daily peak zonal drift velocity is seen to be positively correlated to corresponding daily averaged 10.7‐cm solar flux. (b) The zonal drift velocity is found to be larger in the equinox months than that of winter months. (c) During the disturbed nights the zonal drift velocity gets slower and one of the disturbed nights showed the latitudinal variation in zonal drift velocity during the development phase of EPBs before midnight hours. We suggest that this variation might be occurred due to the disturbance dynamo electric fields at low latitude, which reduces the EPBs' eastward velocity. (d) The zonal drift velocity of EPBs presented in this paper is in good agreement with the previous studies as well as the HWM‐07 model values.

The amplitude scintillation data, recorded at 251 MHz by two spaced receivers at low latitude station Kolhapur [16.42oN, 74.2oE] are used. We have considered data of magnetically disturbed days (Ap > 20) to investigate the effect of magnetic activity on the ionospheric irregularities by observing the coherence scales of the scintillation pattern produced by the irregularities. The coherence scales are calculated using the method introduced by Bhattacharyya et al. (2003). Coherence scale lengths on magnetically disturbed days are higher than that of on quiet days. During magnetically disturbed period the coherence scales in the post midnight period are greater than that of in the pre midnight period. This suggests that magnetospheric electric field generated in storm time causes increase in coherence scales but shows large increase after midnight.

All-sky imaging observations of OI 630.0nm airglow were carried out in campaign mode from Panhala (16.8°N, 74.1°E geographic; 11.1°N dip latitude), India, during January to March 2008. On 14 of 37 nights, equatorial plasma bubbles were observed. The drift speeds were observed to decrease with time in concurrence with the previous results. The tilts were mostly westward while on rare occasions the plasma bubbles tilted eastwards. The drifts were found to be relatively lesser on disturbed nights while the tilts appear to be marginally larger. The interdepletion distances (or bubble spacings) also showed a decreasing trend with time till midnight indicating that the bubbles approach each other with the passage of time. Such a behavior is not reported earlier and it seems to have important implications for understanding the time evolution of plasma bubbles. On occasions, the bubbles occurred in groups. An ionosonde operating over Indian dip equatorial site Tirunelveli (1.1°N dip latitude) was used to study the variations in the base height of the ionosphere during the plasma bubble observations. The ionosonde measurements indicate lack of significant pre-reversal enhancement (PRE) during geomagnetic quiet days in which the bubbles were observed.

The paper reports night time observations of ionospheric irregularities made through amplitude scintillation of 251 MHz signal at Kolhapur (16.4 degrees N, 74.2 degrees E), an equatorial Appleton anomaly region using spaced antenna system. Monthly and night time percentage of occurrence of scintillations, during increasing solar cycle from January 2011 to August 2015, is discussed. The parameters such as-maximum cross-correlation function (C-I), Fade Rate are also studied. The percentage occurrence is observed to be higher in post sunset period and during equinoctial months than in winter and summer months. Scintillation occurrence is observed to be suppressed during increasing solar activity. C-I shows seasonal changes. Percentage of occurrence of C-I >= 0.5 decreases with increase in solar activity and fade rate also shows solar activity dependence.

All Sky Imager (ASI) data of over 351 nights with OI 630.0nm emission recorded during 2011 to 2015 (increasing phase of 24th solar cycle) are analyzed to study the percentage occurrence of EPBs. The ASI is installed at low latitude station Kolhapur (16.8°N, 74.2°E, 10.6° dip. Lat.) which has 140° field of view (FOV). In this paper we have studied hourly, daily, seasonal and yearly percentage of occurrence of EPBs and their variation with solar and magnetic activity. The EPBs onset occurs at around 20:00 IST and extends towards dawn with a peak around midnight. We analyzed all the disturbed nights (Ap>18) from the period of 2011 to 2015 and observed that the magnetic activity suppresses the occurrence of EPBs. Also the EPBs are fairly correlated with solar activity (10.7cm solar flux).

In this work, we have studied the characteristics of equatorial plasma bubbles (EPBs), such as their zonal drift and tilt, from the low‐latitude and dip equatorial region in the Indian longitude sector during the main phase of the 17 March 2015 storm. All‐sky airglow imaging observations from Tirunelveli (8.7°N, 77.8°E geographic, 1.7°N dip latitude) and Kolhapur (16.7°N, 74.3°E geographic, 11.5°N dip latitude) are utilized here. On 17 March 2015, EPBs were observed to drift eastward during 14:30–16:30 UT between 3°S and 15°N dip latitudes. A westward drift presumably under the influence of the disturbance dynamo electric field initially appeared at higher dip latitudes almost 10 h after the storm onset, and subsequently, the same was observed at lower dip latitudes. The EPBs attained a peak westward drift at ~17:00 UT followed by a gradual decrease in their speed till ~18:30 UT. After regaining their westward speed, the EPBs continued to drift westward till 22:00 UT. Moreover, a latitudinal gradient in the drift motion of the EPBs was also observed on this night. Another interesting observation made from the images obtained from Tirunelveli was the presence of a large westward tilt of the EPBs. The most intriguing finding of this study, however, was the asymmetry in the tilt of the EPBs at conjugate points during the premidnight hours on 17 March 2015. In this study, the possible mechanisms that can explain these observations are discussed in light of the current understanding of the equatorial electrodynamics and EPBs.

The photometric measurements of mesospheric OH and O( 1 S) emission, carried out from Kolhapur (16.8°N, 74.2°E), Maharashtra during January-April 2005 are used to study the wave characteristics. The nocturnal variability reveals the dominant long-period wave signatures with significant amplitudes of embedded short-period waves. We carry out a sensitivity study on the vertical wavelength (VW) derived with the help of Krassovsky parameters (η = |η|e iΦ ) of the OH data, which reveals VW to vary from 38.9 to 110.2 km. This was compared with the VW estimates using the phase difference of the simultaneously observed waves in both OH and O( 1 S) emission intensities. Results reveal that in the absence of attitudinally resolved measurements, the VW estimated using Krassovsky method can be used.

the various phenomenon and structures observed in night airglow all-sky imager (ASI) images (such as, drift motions of gravity waves and plasma bubbles) these are accurately measured only after the spatial calibration of the images. While spatial calibration is a process of computing pixel to real-world unit transformations although accounting for many errors inherent to the imaging setup. Calibration of image is important when accurate measurements required in real-world units. In this paper spatial calibration includes the alignment to true north and measurement of field of view (FOV) of captured ASI images. For the spatial calibration the stars in the (ASI) image are used as a reference points which is then compared and calibrated with star catalogue image to find true north and FOV of ASI image. The spatial calibration and FOV measurement of an image is useful when the imaging setup is not stationary. This paper presents developed simple but accurate methodology for spatial calibration and FOV measurement of ASI image. The software is developed for the FOV measurement and spatial calibration by using Mat Lab 7.0.