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This work investigates the spatial and temporal variability of the monsoon inversion (MI) over the Arabian Sea for the study of 37‐years period (1980–2016) using MERRA version2 (MERRA2) reanalysis and downscaled simulations generated with the Weather and Research Forecasting (WRF) model. After validating the downscaled products with the observations from four radiosonde stations (Salalah, Mumbai, Goa and Mangalore), we analysed the variability of MI from diurnal to seasonal scales. The diurnal evolution of the MI suggests that radiative cooling over the Arabian Peninsula at night, together with the onset of boundary layer jets along the coast of Oman, play an important role in amplifying the intensity and spatial extent of the MI during night and into the early morning hours. A seasonal analysis of the simulated winds and MI reveals that WRF reproduced the monsoon characteristics as observed in MERRA2 reanalysis, including the spatial and vertical orientations of the MI. The downscaled winds are slightly overestimated (by 1–2 m⋅s−1) over the Arabian Sea, which resulted in an increased simulated wind shear over the western Arabian Sea, ultimately manifested in the form of an enhanced MI. We further investigated the variability of the lower tropospheric wind speed and associated changes in MI over the 37‐year period. This reveals a significant decreasing trend during the summer monsoon over the western Arabian Sea. We argue that this led to a decreasing trend in the lower tropospheric wind shear and advection of temperature and hence, reduced the frequency of occurrence of the MI (shown in graphical abstract). [ABSTRACT FROM AUTHOR]

Vertically resolved Black Carbon (BC) measurements are obtained in situ up to 10 km during the summer monsoon season using a micro-aethalometer on-board balloon platform from Hyderabad (17.48oN, 78.40oE, 557 m msl), India. Simultaneous (on-board) aerosol size-segregated mass concentration measurements are made at particle sizes 0.5, 1.0, 2.5, 5.0 and 10.0 μm using a Particle plus Optical Particle Counter for estimating the fractions of BC in size segregated (SS) PM 2.5 and the fraction of SSPM 2.5 in SSPM 10. A prominent aerosol layer with large BC mass concentrations in the range of 10–25 μg/m3 is found below 4 km (above mean sea level) which matches well with the measured SSPM 2.5 concentrations showing consistency in the two independent measurements. Thin layers of BC are also detected at mid-tropospheric region at altitude ~7 km and another between 8 and 10 km. FLEXPART analysis for back trajectories suggests that these high concentrations of BC are transported from over the west Asian region of Somalia, Gulf of Aden and Oman. Meteorological parameters along with ozone concentrations obtained simultaneously using radiosonde and ozonesonde together with BC concentrations are used to estimate the actual BC heating rates for the first time. Shortwave BC heating rates as high as 4 K/day are observed in the lower thick layer. It is suggested that this strong heating rate can act as a feedback in weakening the stable layer and well mixing of pollutants up to 4–5 km altitude. Heating rates obtained using standard tropical atmosphere model is found to be overestimated in this case suggesting the use of real time atmospheric conditions for actual estimates. • BC profile up to 10 km is obtained for the first time during Indian Summer Monsoon season from southern part of India. • Simultaneous measurements of particulate matter obtained using P-OPC are used to estimate the BC mass fractions. • Realistic heating rates due to BC are estimated using measured BC concentrations along with background parameters. • FLEXPART Trajectory analysis is carried out to locate the sources for the observed BC and particulate matter. • Strong heating rates act as a feedback in weakening the stable layer and well mixing of pollutants up to 5km altitude. [ABSTRACT FROM AUTHOR]