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Upper mesospheric wind data acquired by the medium frequency radar at Kolhapur (16.7°N, 74.2°E) 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. [ABSTRACT FROM AUTHOR]

The vertical profiles of specific humidity in the troposphere measured by the millimetre-wave humidity sounder (MHS) onboard of the Earth Observation Satellite (EOS)-07 (Microsoft 2B) are validated using ground-based radiosonde observations during July-August 2023. MHS onboard EOS-07 (hereafter referred as EOS-07/MHS) is a 6-channel cross-track scanning radiometer operating in the 183.31 ± 16.25 GHz band. The EOS-07 observations are used to retrieve three-dimensional specific humidity profiling from 1000 hPa (surface) to 100 hPa (16 km) atmospheric pressure levels with a spatial resolution of 10 km at nadir. The EOS-07/MHS measurements over India have a high correlation coefficient of 0.98 with the radiosonde observations. The mean relative bias is found to be 0.44 ± 0.55 g kg−1 below 350hPa and 2.8 ± 2.3 g kg−1 above 350 hPa. It is also found that above the 350 hPa level, MHS seems to be systematically overestimating the radiosonde measurements. After that, the EOS-07/MHS measurements are used to construct the diurnal variation of humidity during the active phases of the Indian summer monsoon. The observations are consistent with the present understanding of the Indian summer monsoon system. The present results are very encouraging and demonstrate the great potential of EOS-07/MHS observations of humidity for meteorological application, especially in understanding the hydrological cycle. [ABSTRACT FROM AUTHOR]

In the present communication, first results from an experiment to measure intrinsic frequency spectrum of atmospheric gravity waves using balloon-borne quasi- Lagrangian frame of reference observations in the mid-stratosphere over a tropical station, Hyderabad (17.4°N, 78.2°E) are discussed. A zero-pressure polyethylene balloon with GPS-sonde payload was drifted at ~31 km altitude for a horizontal distance of ~100 km for measuring pressure, wind and temperature at 1 sec temporal resolution. The measured altitude of the balloon showed variability within ±100 m, thus ensuring a near horizontal drift. These observations are used to estimate the intrinsic frequency spectrum of gravity waves in the mid-stratosphere over an Indian observational site. The successful experiment has opened up a new avenue for studying not only the stratospheric gravity wave dynamics, but also for exploring the horizontal mapping of stratospheric trace gases. [ABSTRACT FROM AUTHOR]

The characteristics of convective systems over the Indian summer monsoon (ISM) region derived by using a unique combination of four satellites METEOSAT, TRMM, COSMIC and CloudSat comprising of both active and passive remote sensing sensors are discussed for the first time. Six years of observations during ISM brought out the preferential geographical regions and time for formation of shallow, deep, and very deep convective systems. It has been observed that shallow, deep, and very deep convective clouds are abundant over ISM region and their distributions show a relatively high frequency of occurrence over the Head Bay of Bengal as compared to other regions. The mean vertical structure of clouds are also been studied using CloudSat observations over several latitudinal belts. The time of maximum occurrence of convective type cloud systems are also quantified using the present observations. The analysis suggests that the deep and very deep convective cloud systems peak during late afternoon hours over many parts of the Indian landmass with few exceptions such as over foothills of the Himalayas, where it peaks during the early morning hours. The three-dimensional structures of convective systems are also discussed. The significance of the present results lie in providing new insights into the characteristics of convective systems by investigating CAPE, clouds, and precipitation, which in turn play a vital role in understanding the internal dynamics of ISM. [ABSTRACT FROM AUTHOR]

The characteristics of convective systems over the Indian summer monsoon (ISM) region derived by using a unique combination of four satellites METEOSAT, TRMM, COSMIC and CloudSat comprising of both active and passive remote sensing sensors are discussed for the first time. Six years of observations during ISM brought out the preferential geographical regions and time for formation of shallow, deep, and very deep convective systems. It has been observed that shallow, deep, and very deep convective clouds are abundant over ISM region and their distributions show a relatively high frequency of occurrence over the Head Bay of Bengal as compared to other regions. The mean vertical structure of clouds are also been studied using CloudSat observations over several latitudinal belts. The time of maximum occurrence of convective type cloud systems are also quantified using the present observations. The analysis suggests that the deep and very deep convective cloud systems peak during late afternoon hours over many parts of the Indian landmass with few exceptions such as over foothills of the Himalayas, where it peaks during the early morning hours. The three-dimensional structures of convective systems are also discussed. The significance of the present results lie in providing new insights into the characteristics of convective systems by investigating CAPE, clouds, and precipitation, which in turn play a vital role in understanding the internal dynamics of ISM. [ABSTRACT FROM AUTHOR]