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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]

Recent investigations have shown a robust signature of poleward migration of the tropical cyclone latitudes using observations and climate model simulations. Most of these studies invoked the role of the Hadley circulation (HC) expansion in the poleward shifting of tropical cyclones. However, none of these studies focused on the dissection of the zonally asymmetric HC into ascending and descending regions at regional scales, which holds the key in establishing the association between these two phenomena. Here, we are reporting the poleward migration of tropical cyclones and their association with ascending region boundaries of the HC at regional scales for the first time. The results emphatically show that the tropical cyclone latitudes as well as latitudes of maximum lifetime intensity vary in tandem with boundaries of the ascending region of the HC as compared to its descending region thus providing a vital clue on processes governing poleward migration of tropical cyclones. [ABSTRACT FROM AUTHOR]

Recent investigations have shown a robust signature of poleward migration of the tropical cyclone latitudes using observations and climate model simulations. Most of these studies invoked the role of the Hadley circulation (HC) expansion in the poleward shifting of tropical cyclones. However, none of these studies focused on the dissection of the zonally asymmetric HC into ascending and descending regions at regional scales, which holds the key in establishing the association between these two phenomena. Here, we are reporting the poleward migration of tropical cyclones and their association with ascending region boundaries of the HC at regional scales for the first time. The results emphatically show that the tropical cyclone latitudes as well as latitudes of maximum lifetime intensity vary in tandem with boundaries of the ascending region of the HC as compared to its descending region thus providing a vital clue on processes governing poleward migration of tropical cyclones. [ABSTRACT FROM AUTHOR]

Recent investigations have shown a robust signature of poleward migration of the tropical cyclone latitudes using observations and climate model simulations. Most of these studies invoked the role of the Hadley circulation (HC) expansion in the poleward shifting of tropical cyclones. However, none of these studies focused on the dissection of the zonally asymmetric HC into ascending and descending regions at regional scales, which holds the key in establishing the association between these two phenomena. Here, we are reporting the poleward migration of tropical cyclones and their association with ascending region boundaries of the HC at regional scales for the first time. The results emphatically show that the tropical cyclone latitudes as well as latitudes of maximum lifetime intensity vary in tandem with boundaries of the ascending region of the HC as compared to its descending region thus providing a vital clue on processes governing poleward migration of tropical cyclones. [ABSTRACT FROM AUTHOR]

It is known that the Hadley circulation (HC) is responsible for the typical wet climate of the tropics and the dry climate of the subtropics. Previous studies have shown that the HC exhibits a poleward expansion of ~ 0.5–1° latitude per decade with significant regional and seasonal variability. Owing to its pivotal role in controlling the climate over tropics and subtropics, it is important to predict the evolution of HC in a future warming scenario from the perspective of formulation of adaptation strategies. In this regard, the current study employs the climate model simulations from the Indian Institute of Tropical Meteorology-Earth System Model (IITM-ESM) archived in the latest Coupled Model Inter-comparison Project 6 (CMIP6) to identify the long-term changes and future projections in the width of the ascending and descending branches of the HC, after validating it against the latest generation ERA5 reanalysis. Results show that the model is able to capture the observed changes in the total width of the HC and its ascending regions. Analysis of trends in the future projection of the width of the HC ascending and descending regions brings out results that are consistent with earlier reports using multi-model simulations archived in CMIP6. The future projections of HC intensity show weakening tendencies in both NH and SH. The trends in the model's future projection of zonal mean precipitation under two high forcing scenarios show hemispherical asymmetry with SH exhibiting relatively strong trends in both ascending and descending regions of the HC. The results are discussed in the light of the present understanding on HC dynamics. The significance of the present study lies in evaluating IITM-ESM, which is the first model from India to participate in CMIP, using ERA5 reanalysis and discussing the future projections of HC dynamics and its implications on long-term trends in precipitation under high forcing scenarios. [ABSTRACT FROM AUTHOR]

In the present communication, diurnal evolution of vertical structure of precipitating clouds over the southernmost part (7°–11°N) of the Western Ghats (WG) of Indian region during summer and winter monsoon periods is discussed using 17 years of Tropical Rainfall Measuring Mission (TRMM) precipitation radar measurements. This part of the WG experiences both summer and winter monsoons and provides a unique opportunity to study the orographical processes involved in the formation of precipitating clouds at diurnal scales during two contrasting background environments. During summer monsoon, the lower tropospheric winds are dominated by the presence of strong low‐level westerly jets, which interact with steep slopes of the WG whereas during winter monsoon, winds are very weak easterlies and encounter the WG from eastern side. The composite longitudinal distribution of vertical structure of precipitating clouds in terms of frequency of occurrence of radar reflectivities ≥23 dBZ is constructed at four local time intervals. The results are discussed in terms of bands of high frequency of occurrence of precipitating clouds and their longitudinal position with respect to the WG. A band of high frequency of occurrence of precipitation clouds is observed to be moving eastwards and their potential formation mechanism is attributed to the forced lifting over the upslope regions and to the upstream blocking over the offshore during the summer monsoon. During winter monsoon, a two band structure is observed one over the southern BOB, which is attributed to the persistent low‐pressure system observed over this region and another over the upslope of the WG from eastern side. Thus the present study for the first time brings out the diurnal evolution of the vertical structure of precipitating clouds during summer and winter monsoon over the southernmost part of the WG and discuss the potential physical processes involved in their formation. [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 time evolution of mesospheric quasi biennial oscillation (MQBO) in the 82–98 km altitude region using long‐term meteor radar observations over low and equatorial latitudes and TIMED Doppler Interferometer (TIDI) observations is discussed for the first time. The wavelet spectra of monthly mean zonal winds over Serpog (6.4°S, 106.7°E; 1993–1998), Koto Tabang (0.2°S, 100.3°E; 2003–2012) and Thumba (8.5°N, 76.9°E; 2006–2015) show the transient nature of the MQBO amplitudes, thus, questioning its perpetuity in the mesosphere‐lower thermosphere (MLT). The time period of the MQBO as well as its amplitude show variability with time. The latitude‐height structures of the MQBO at four time periods (24, 26, 28, and 30 months) are constructed using TIDI measurements, which show diverse latitudinal structure. The significance of the present study lies in bringing out the time evolution of the MQBO and addressing a few outstanding issues on its ephemerality and discrepancies in its amplitudes. Plain Language Summary: In the stratosphere and mesosphere of the earth's atmosphere over the equatorial region, there exists a periodic oscillation in the zonal winds with time period varying from 22 to 34 months. This periodic oscillation popularly known as the quasi biennial oscillation (QBO) is well characterized in the stratosphere. However, there have been contrasting observations of the QBO amplitudes and their latitudinal distribution in the mesosphere. Some of the recent studies also questioned about its intermittency as well as its seasonality. In the present study using long‐term observations of zonal winds in the 82–98 km altitude region over the three locations, Serpog (6.4°S, 106.7°E), Koto Tabang (0.2°S, 100.3°E), and Thumba (8.5°N, 76.9°E), the mesospheric QBO is characterized in terms their amplitude and time period. The observed discrepancies in the reported amplitudes and the variability in the time period of the mesospheric QBO are discussed. Using space‐based TIDI observations, the latitudinal distribution of the mesospheric QBO amplitudes at four time periods are also discussed. Key Points: The time evolution of the mesospheric quasi biennial oscillation (MQBO) is investigated using long‐term meteor radar observationsThe results show the intermittent nature of the MQBOLatitudinal distribution of the MQBO in the mesosphere‐lower thermosphere zonal winds is discussed [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 tropical Mesosphere‐Lower Thermosphere‐Ionosphere system is found to show significant variabilities during Sudden Stratospheric Warming (SSW) events. Recent studies have highlighted the possible role played by modified background wind conditions in communicating the SSW‐induced stratospheric perturbations to the Mesosphere‐Lower Thermosphere‐Ionosphere region. In the present study, changes in the background zonal winds at the tropical stratopause during major SSW events inferred from MERRA‐2 reanalysis data sets, rocket observations, and model simulations are reported for the first time. The tropical stratopause shows enhanced westward winds during the course of major SSW events. Rocketsonde observations from a low latitude station Thumba (8.5 ° N,76.9 ° E) also showed significant westward acceleration during three major SSW events. Further, Specified Dynamics version of the Whole Atmosphere Community Climate Model simulations for the 2008–2009 SSW replicate the observed features. Plain Language Summary: The winter time polar stratosphere undergoes sudden reversal of climatological eastward winds to westward winds accompanied by a large increase in temperature during dramatic events called Sudden Stratospheric Warmings. Previous studies have shown that the upper atmosphere (Thermosphere/Ionosphere) over low latitudes show strong signatures associated with these polar phenomena. Changes in the tropical middle atmospheric background winds in response to Sudden Stratospheric Warming events are thought to have a significant role in causing the observed changes in the upper atmosphere. In the current study, abrupt changes in stratopause winds over the low latitudes are reported using reanalysis, observations, and model simulations. Present results can contribute to understanding several features observed in the low latitude upper atmospheric altitudes in connection with these polar sudden warming episodes. Key Points: Enhanced westward winds at the tropical stratopause during major Sudden Stratospheric Warming (SSW) events in the Northern HemisphereWestward acceleration of stratospheric winds during both split and displacement type SSW eventsPoleward shift of the tropical zero wind line during the course of the warming [ABSTRACT FROM AUTHOR]

Atmospheric gravity waves over the Polar Regions are found to have myriad effects on the dynamics and chemistry of the middle atmosphere. Data collected from high vertical resolution radiosonde measurements carried out in campaign mode from the Indian research base in Antarctica, Bharati (69.4°S, 76.2°E) during the austral summer seasons of 2014–2015, 2015–2016 and 2016–2017 were used to characterize inertia gravity waves (IGWs). Wavelet analysis technique is employed to identify and isolate individual IGW packets. IGWs in the lower stratosphere region are characterized in terms of their vertical and horizontal wavelengths, intrinsic frequencies, directions of propagation, momentum fluxes, energy densities and ground based phase speeds. The observed gravity waves have short vertical wavelengths (~ 2 km) and low intrinsic frequencies (1f–2f). Zonal and meridional components of momentum fluxes are found to have comparable magnitudes. From the direction of propagation estimates, it is observed that the IGWs have a marginal predisposition towards eastward propagation during austral summers. It is found that the lower stratospheric region over Bharati during summertime is dominated by IGWs from non-orographic sources. Evidences for generation of IGWs from an upper tropospheric jet streak observed over Bharati station are provided. The jet streak is found to be associated with the intrusion of low potential vorticity air from middle latitudes and the accompanied development of an anti-cyclonic circulation. The observations suggest that low potential vorticity intrusion happened as a result of breaking of poleward propagating Rossby wave. Spontaneous adjustment of the unstable jet could be responsible for the IGW generation. The significance of the present results lie in characterizing the summer time IGW over the Bharati station for the first time using wavelet based approach and identifying the possible source mechanism. [ABSTRACT FROM AUTHOR]

The latent heat released in the clouds over the tropics plays a vital role in driving the Hadley circulation (HC). The present study discusses the influence of latent heating (LH) on the HC parameters viz., centre, strength and total width by using precipitation LH profiles derived from the space-borne observations of the Precipitation Radar (PR) onboard Tropical Rain Measuring Mission (TRMM) and meridional stream function (MSF) derived from ECMWF-Interim reanalysis. The latitude of peak latent heating, width of the latent heating distribution and the total LH released within the ascending limb of the HC are estimated and their influence on the HC centre, strength and width is quantified, for the first time. The present results show that the latitude of peak LH significantly influences the position of the HC centre with correlation coefficient of ~ 0.90. This high correlation between these two quantities seems to be due to their co-variability with the apparent motion of the Sun across the latitudes. The intensity of the HC in the NH as well as SH shows high correlation with the latitude of peak LH with coefficients − 0.85 and − 0.78, respectively. These results indicate that farther the latitude of peak LH from the equator in the summer hemisphere, stronger is the HC intensity in the winter hemisphere. The present analysis also reveals that the total LH released within the ascending limb of HC substantially influence the total width of the HC, with correlation coefficient ~ 0.52, as compared to the other two LH parameters. This observation can be attributed to the fact that the HC is sensitive to the latent heat release in the mid-tropospheric levels in the tropics. An attempt is also made to investigate the degree of variability of these parameters after deseasonalization and results are discussed in the light of present understanding. The significance of the present study lies in providing the observational evidence for the influence of latent heating on the HC strength/width variability, quantitatively, for the first time using TRMM observations of precipitation latent heating. [ABSTRACT FROM AUTHOR]

Tropical cloud clusters (TCC) play a vital role in Earth's climate by not only releasing a large amount of latent heat into the atmosphere but also by forming the basis for the development of tropical cyclones (TC). However, not all TCCs can develop into cyclones; only a few develop into TC selectively. There are large uncertainties in the current understanding of why only certain TCCs develop into TC while others don't. The present study employs global TCC observations generated by GridSat and IBTrACS datasets from 1980 to 2009 to investigate the TCC distributions over various Oceanic basins such as the North Atlantic (NA), South Atlantic (SA), East-West and South Pacific (EP, WP and SP), as well as the North Indian (NI) and South Indian (SI) basins. The central objective of the present study is to characterize the size spectrum of TCCs and investigate their potential transformation into TCs. The TCCs are identified based on different IR temperature thresholds in each basin. The present results suggest that ∼ 5.5 % of TCCs were developed into TCs annually globally, and their trends in each oceanic basin are discussed. The size spectrum of TCCs showed a dominant peak at 100–200 km2. About 48 % of TCCs transform into TCs within 24 hr of being identified. Furthermore, 85 % of TCCs develop into TCs within 84 hr of the first identification, while only 5 % of TCCs develop into TCs after 84 hr. Further, we have also analyzed the background environmental conditions such as low-level wind speed, vorticity, divergence, vertical shear, upper-level relative humidly and latent heating (LH) for developing and non-developing TCCs over the NI basin, which have not been explored in detail in earlier studies. It is noted that the relative humidity in the developing composite is around 10–20 % higher than that in non-developing TCCs, and LH in developing TCCs is 0.15 K/hr, larger than that in non-developing TCCs. The significance of the present study lies in investigating the developing TCCs as a function of their size and lifetime, including their long-term trends, and bringing out favourable environmental conditions for developing TCCs in the NI Ocean. • The present results found that overall ~ 5.5 % of TCCs were developed into TCs per year across the globe. • About 85 % of TCCs develop in to TCs within 84 hr of the first identification and only 5 % of TCCs develop into TCs after 84 hr. • The number of developing TCCs in the size range of 100–200 km2 over the various oceanic basin showed an increasing trend in the NA, WP, NI and SI basins. • It is noted that the Latent Heating in developing TCCs is 0.15 K/hr larger than that in non-developing TCCs. • The present study brought out the distribution of TCCs including their size spectrum, life time and long-term trends. [ABSTRACT FROM AUTHOR]

Highlights • Relative humidity, cloud fraction and precipitation trends within the Hadley Circulation boundaries are estimated. • Results show decreasing trends in the deep tropics and increasing trends at the edges of ascending region. • Results are in line with the expansion of Hadley Circulation and strengthening of the hydrological cycle. Abstract Climate model simulations and observations show that there is a poleward expansion of the Hadley Circulation (HC) as well as a strengthening of the hydrological cycle in a warming climate. However, to establish a relation between the two phenomena in present day climate, simultaneous investigations of the HC and hydrological cycle changes using observational/reanalysis data are necessary, which is limited as compared to model simulations. In this regard, the present study employs relative humidity (RH), cloud fraction (CF) and precipitation (RF) parameters of the hydrological cycle and analyse their long term changes within the HC ascending and descending regions, simultaneously. Long term RH and CF data (1979–2016) are obtained from ERA-I reanalysis, and RF from GPCP precipitation dataset. The boundaries of the HC are identified using the meridional Mass Stream Function (MSF) metric, a metric that can track the mass motion in the atmosphere in the meridional direction. The analysis brings out the spatial pattern of the distribution of trends in hydrological parameters within the HC boundaries. The trends are observed to be significantly positive at the edges of the HC ascending region and significantly negative in the regions near the HC edges, insignificant (and in some cases, negative) in the deep tropics. This pattern is more or less consistent in RH, CF, as well as RF parameters. Thus the study shows that there are regions of positive as well as negative trends within the both ascending and descending regions. The results are found to be in accordance with the poleward expansion of HC and strengthening of the hydrological cycle. Besides, a northward shift in the HC ascending regions are also indicated from the analysis of the annual cycle of trend in precipitation. The current investigation is thus envisaged to contribute to further exploration on the relation between the HC changes and the intensification of the hydrological cycle in a warmer climate. [ABSTRACT FROM AUTHOR]

Simultaneous observations of the mesosphere lower thermosphere (MLT) winds in the 80-100 km height region over a low-latitude station Thumba (8.5°N, 77°E) and an equatorial station Kototabang (0.2°S, 100.3°E) during 2006-2012 are used to study the climatology of mean winds and the quasi 2-day waves (QTDW). The 7 year mean annual cycle of the zonal and meridional winds and their interannual variability over both the observational sites are discussed in details. A remarkable agreement is noticed in the annual cycle of zonal winds over both the sites, whereas some discrepancies are observed in the meridional winds. The hourly meridional winds are analyzed to extract the day-to-day variability of the QTDW and their monthly mean. The climatology of the QTDW in the meridional winds over both the sites shows very good agreement, with three peaks in wave activity during austral summer, boreal summer and in the month of October. It is noted that the peak observed in the month of October is not very distant from the boreal summer peak. These three peaks are consistently observed in all years, with strong interannual variability. In general, the austral summer QTDW activity is the strongest among the three over both the observational sites. Apart from discussing the mean and interannual variability of the QTDW over both the sites, instantaneous occurrence of the QTDW over both the sites is further analyzed to infer their zonal wavenumbers. The wavelet analysis is employed to extract time evolution of the QTDW simultaneously over both the sites and the same is used to infer the zonal wavenumbers. The results from the case studies show that the observed QTDW during austral summer (January 2012), boreal summer (July-August 2008) and October month (October 2006) are westward propagating waves with zonal wavenumbers 3, 4 and 2, respectively. Further analysis using simultaneous space based observations are essential for generalizing the observed seasonal variations in the zonal wavenumbers. The significance of the present results lies in using the simultaneous observations of the MLT winds over the low and equatorial latitudes to bring out the climatology, interannual variability and the zonal wavenumbers of the QTDW. The result discussed in the present study adds to the current understanding of the QTDW, especially by inferring the zonal wavenumbers using ground based observations. [ABSTRACT FROM AUTHOR]

The changes in zonal mean circulation and meridional temperature gradient brought about by Sudden Stratospheric Warming (SSW) events in polar middle atmosphere are found to significantly affect the low latitude counterparts. Several studies have revealed the signatures of SSW events in the low latitude Mesosphere- Lower Thermosphere (MLT) region. Using meteor wind radar observations, the present study investigates the response of semidiurnal oscillations and quasi 2-day waves in the MLT region, simultaneously over low latitude and equatorial stations Thumba (8.5 o N, 76.5 o E) and Kototabang (0.2 o S, 100 o E). Unlike many case studies, the present analysis examines the response of low and equatorial latitude MLT region to typical polar stratospheric conditions viz., Quiet winter, Major SSW winter and Minor SSW winter. The present results show that (i) the amplitudes of semidiurnal oscillations and quasi 2-day waves in the equatorial and low latitude MLT region enhance in association with major SSW events, (ii) the semidiurnal oscillations show significant enhancement selectively in the zonal and meridional components over the Northern Hemispheric low latitude and the equatorial stations, respectively (iii) The minor SSW event of January 2012 resulted in anomalously large amplitudes of quasi 2- day waves without any notable increase in the amplitude of semidiurnal oscillations. The significance of the present study lies in comprehensively bringing out the signatures of SSW events in the semidiurnal oscillations and quasi 2-day waves in low latitude and equatorial MLT region, simultaneously for the first time over these latitudes. [ABSTRACT FROM AUTHOR]

In the present communication, a record breaking duration (23 months) of the eastward phase of the QBO at 20 hPa is reported and details of the tropical wave activity during the recent anomalous QBO event are discussed. Two-dimensional Fourier analysis revealed the presence of 30–40 and 10–15 day westward propagating wave number 1 structures at 40 hPa pressure level over the equator. A combination of the mid-latitude Rossby waves and the 30–40 day oscillations seems to be the most probable mechanism for the observed disruption of the QBO. [ABSTRACT FROM AUTHOR]

In the present communication, C-band polarimetric Doppler Weather Radar (C-DWR) observations are used to investigate the structure and evolution of organized precipitation bands during the Indian summer monsoon (ISM) of 2017, 2018 and 2019 over Thumba (8.50 N, 770 E), a coastal location in south India. The C-DWR observations show organized high radar reflectivity structures of ∼50 dBZ that organized into narrow bands of ∼200 km (North-South) in length and 10–20 km (East-West) in width with vertical extent of ∼6–8 km. These narrow bands of precipitation structures are observed to be formed over the Arabian Sea and subsequently propagating towards the radar site. The observed differential radar reflectivity (Z dr) and the correlation co-efficient values indicate the horizontally oriented droplets and non-uniform hydrometeors. The potential formation mechanisms of the precipitation bands are investigated using reanalysis winds. The results show that blocking effect induced by the Western Ghats around the radar site play a key role in the formation of organized precipitation bands. It is noted that the location of the blocking effect induced convergence (conducive for the formation of precipitating clouds) with respect to the orography is proportional to the intensity of the low-level winds. The significance of the present study lies in understating the structure and evolution of organized precipitation bands and discussing their potential formation mechanisms during the ISM using C-DWR observations. [Display omitted] • Structure and evolution of organized precipitation bands (OPB) are investigated using C-band polarimetric DWR at Thumba. • The study provides observational evidence for the upstream blocking mechanism in the formation of OPBs over the study region. • It is envisaged that the present results will help in modelling the physical processes responsible for the formation of OPBs. [ABSTRACT FROM AUTHOR]

The phase relation between convection and precipitation at diurnal scales is essential for convective parameterization in numerical weather prediction models. For the first time in a meteorological study, we quantified the phase relationship between convective available potential energy ( CAPE) and precipitation over the Indian summer monsoon region at diurnal scales using space-based precipitation and CAPE observations from 7 years (2006-2012) of GPS-RO measurements. Also, we quantified the phase relationship for the land and oceanic regions separately. On average, the peak in CAPE magnitudes leads precipitation peak by ∼2-4 h over the study region. [ABSTRACT FROM AUTHOR]

Abstract: The annular solar eclipse of 15th January 2010, which was the longest solar eclipse of the millennia, was visible at several parts of South India and China. A host of experiments were carried out at Thumba (8.5° N, 76.9°E) and Gadanki (13.51° N, 79.21° E) in India to study the effect of annular solar eclipse on various atmospheric processes taking place right from surface layer to Ionosphere as the maximum obscuration of the Sun took place during the peak noon hours. Many of the studies reported from these experiments focused on the effect of annular solar eclipse on the geophysical parameters and their variability during the maximum phase of the eclipse. However, there were no efforts to study the delayed effects of the annular solar eclipse on the geophysical parameters. In this regard, the present study discuss the delayed effect (~4hours after the maximum phase of the eclipse) of annular solar eclipse of 15th January 2010 on the troposphere and lower stratosphere winds over the eight geographical locations along the eclipse path [Thumba, Qingdao (36.06° N, 120.33°E), Zhengzhoes (34.71° N, 113.65°E), Enshi (30.28° N, 109.46°E), Chongqing (29.51° N, 106.48°E), Sheyang (33.76° N, 120.25°E), Fuyang (32.86° N, 115.73°E) and Weining (26.86° N, 104.28°E)]. The regular meteorological soundings over these eight locations at 12 UTC are utilized for the present study. The important difference between the observations over Thumba and other latitudes is the local time of occurrence of maximum phase of the eclipse. Over the Thumba the maximum phase of the annular eclipse observed in the mid-day whereas it is observed during the sunset hours over other latitudes. The analysis revealed that significant changes in zonal and meridional winds occurred only over Thumba, but not showed any significant changes over the other latitudes. The results are discussed in the light of present understanding of the eclipse induced atmospheric perturbations. [Copyright &y& Elsevier]

ABSTRACT For the first time, height profiles of meteor trail decay time due to the ambipolar diffusion process are estimated using temperature and pressure measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on-board Thermosphere Ionosphere Mesosphere Energetics and Dynamics ( TIMED) satellite. The comparison of the meteor trail decay time measured by a meteor radar over Thumba (85 N, 77°E) and SABER offered very valuable insights into the meteor trail decay processes and also provided much needed validation for assumption of ambipolar diffusion of meteor trails. It is observed that the assumption of ambipolar diffusion is valid in the height region of 90-96 km only where both SABER and radar measurements show excellent agreement in meteor trail decay time. The present analysis also shows that there are other processes which govern the meteor trail decay in the 80-90 km region, where large deviations are found between radar and SABER measurements. The differences between the SABER- and radar-observed decay times are quantified, and the processes responsible for the observed differences are also discussed extensively in the light of present understanding. The important outcome of the present study is the validation of assumption on ambipolar diffusivity of the meteor trails, which has significant implications in estimating the temperature using meteor trail decay time. [ABSTRACT FROM AUTHOR]

The All-Sky interferometric meteor (SKYiMET) radar (MR) derived winds in the vicinity of the equatorial electrojet (EEJ) are discussed. As Thumba (8.5° N, 77° E; dip lat. 0.5° N) is under the EEJ belt, there has been some debate on the reliability of the meteor radar derived winds near the EEJ height region. In this regard, the composite diurnal variations of zonal wind profiles in the mesosphere-lower thermosphere (MLT) region derived from TIMED Doppler Interferometer (TIDI) and ground based meteor radar at Thumba are compared. In this study, emphasis is given to verify the meteor radar observations at 98 km height region, especially during the EEJ peaking time (11:00 to 14:00 LT). The composite diurnal cycles of zonal winds over Thumba are constructed during four seasons of the year 2006 using TIDI and meteor radar observations, which showed good agreement especially during the peak EEJ hours, thus assuring the reliability of meteor radar measurements of neutral winds close to the EEJ height region. It is evident from the present study that on seasonal scales, the radar measurements are not biased by the EEJ. The day-time variations of HF radar measured E-region drifts at the EEJ region are also compared with MR measurements to show there are large differences between ionospheric drifts and MR measurements. The significance of the present study lies in validating the meteor radar technique over Thumba located at magnetic equator by comparing with other than the radio technique for the first time. [ABSTRACT FROM AUTHOR]

Using a unique set of satellite based observations of the vertical distribution of ozone during the recent annular solar eclipse of 15 January 2010, we demonstrate for the first time, a complete picture of the response of stratospheric ozone to abrupt changes in solar forcing. The stratospheric ozone decreased after the maximum obscuration of the Sun and then gradually increased with time. A dramatic increase in stratospheric ozone of up to 4 ppmv is observed 3 h after the maximum obscuration of the Sun. The present study also reports for the first time the mesosphere-lower thermospheric ozone response to solar eclipse. Thus it is envisaged that the present results will have important implications in understanding the ozone response to abrupt changes in solar forcing and time-scales involved in such response. [ABSTRACT FROM AUTHOR]

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]

A rare episode of minor circulation embedded in the Hadley circulation (HC) and processes responsible for its formation is discussed. Using 34 years (1979–2012) of HC climatology derived from reanalysis datasets, a minor circulation centered on ∼35°N and embedded within the northern hemispheric zonal mean HC is observed during the month of July 1993. A longitudinally resolved vertical velocity observations centered on 35°N latitudinal belt revealed that there is an anomalous upwelling over the North American sector possibly associated with "Great Floods of 1993" thus emphasizing the prominence of a regional feature and its impact on the zonally averaged circulation. • A rare episode of minor circulation embedded in the Northern Hemispheric Hadley Circulation is investigated. • The potential mechanism for the anomalous circulation is discussed. • The analysis reveals that the observed minor circulation is associated with the Great Floods of 1993. [ABSTRACT FROM AUTHOR]

Advance prediction of heavy rainfall days over a given location is of paramount importance as heavy rainfall impacts ecosystems, leads to floods, accounts largely for the total rainfall over the region and its prediction is highly desired for the efficient management of weather-dependent activities. Traditionally, Numerical Weather Prediction models serve the purpose of weather predictions, but they have their constraints and limitations. In this regard, artificial intelligence and machine learning tools have gained popularity in recent years. In the present study, we have employed the Gaussian Process Regression (GPR) approach, one of the machine learning methods, on a long time-series rainfall data for the determination of heavy and light rainfall days. Climatological data of daily rainfall for a period of 116 years from 1901 to 2016 over Sriharikota (13.66°N, 80.23°E), a coastal island location in India, is used for training the GPR model for the identification of the heavy and light category of rainy days. The performance of the GPR model is investigated by predicting the heavy and light rainfall days per year over Sriharikota. K-nearest neighbour, random forest, and decision tree models are also used and results are compared. The validation of GPR results shows that the performance of the proposed model is satisfying (root mean square error = 0.161; mean absolute error = 0.126; mean squared error = 0.026), especially for the heavy rainfall days. Furthermore, GPR model is extended to prediction of spatial distribution of monthly rainfall over the Indian region. Results obtained from the present study encourages the utilization of the GPR model as one of the promising machine learning tools for the prediction of heavy rainfall days over a given location. [ABSTRACT FROM AUTHOR]

The space-time variations in water vapor in the upper troposphere and lower stratosphere (UTLS) over the Asian summer monsoon (ASM) regions are investigated using six years of observations from the Aura-MLS to understand the ASM role in transporting water vapor to the tropical stratosphere. While some previous studies indicated that the ASM plays a role in dehydrating the lower stratosphere, the present investigations revealed that the ASM region plays an active role in hydrating rather than dehydrating the tropical lower stratosphere. The analysis also shows that only during the month of August (ASM) is moist air pumped into the lower stratosphere over the two key geographical locations (India and Western Pacific). The air parcel from the tropical tropopause takes approximately 10 - 12 months to reach the mid-stratosphere with an ascent rate of 2.8 x 10-4 m s-1. Thus it is envisaged that the present results will have important implications in understanding the exchange processes across the tropopause and its role in stratosphere chemistry. [ABSTRACT FROM AUTHOR]

Abstract: Based on the horizontal winds measured using SKiYMET meteor wind radar during the period of June 2004–May 2007, the seasonal and interannual variability of the diurnal and semidiurnal amplitudes and phases in the mesospheric and lower thermospheric (MLT) region over a low-latitude station Trivandrum (8.5°N) are investigated. The monthly values of amplitudes and phases are calculated using a composite day analysis. The zonal and meridional diurnal tidal amplitudes exhibit both annual and semiannual oscillations. The zonal and meridional components of semidiurnal tide show a significant annual oscillation. The phase values of both diurnal and semidiurnal tides exhibit annual oscillation above 90km. The effect of background wind in the lower atmosphere on the strength of diurnal tidal amplitudes in the MLT region is studied. The effect of diurnal tides on the background wind in the lower thermosphere is also discussed. [Copyright &y& Elsevier]