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Monsoon Inversion (MI) plays a key role and is one of the semi-permanent features of Asian Summer Monsoon. MI is defined as a sustained temperature inversion (TI) that is observed in the lower troposphere, during summer monsoon (June to September) over the Western AS (WAS) with its peak between July and August. A comprehensive analysis of formation, evolution, and dissipation of MI is made using long-term observations from satellites and ERA-5 reanalysis of 15 years (2008–2022). The climatological day-to-day and monthly variations of MI over the Arabian Sea are studied. The occurrence of inversion (TI) during pre-monsoon, i.e., during April and May, is at a lower altitude and is strengthened by subsidence. The MI is found to occur strongly over the WAS, while it is seen occasionally with lesser strength over the Eastern Arabian Sea (EAS) during July–August. The advection is nearly five times stronger than subsidence. The reasons for the existence and strength of MI are investigated using the data of dust from the CALIPSO. There is a ~ 15% difference in the occurrence of dust over WAS compared to EAS. Also, MI occurrence has shown significant differences in temperature profiles during dust and non-dust cases. The analysis of MI reveals that strong MI is due to more advection of warm dry and dust laden air from desert regions (west, north and northwest directions). The present study has significance to the understanding of interannual monsoon variability. [ABSTRACT FROM AUTHOR]

Since March 2020, the COVID‐19 pandemic has significantly reduced the availability of global aircraft‐based observations (ABOs), which has been restored later in 2021. This study focuses on the impact of ABOs on a regional reanalysis. Indian Monsoon Data Assimilation and Analysis (IMDAA) is a regional reanalysis for a period from 1979 to 2020 (originally up to 2018) over India and surrounding regions produced at the National Centre for Medium Range Weather Forecasting (NCMRWF), India, in collaboration with the UK Met Office. A comparison of the impact of ABOs on other conventional and satellite observations assimilated in the NCMRWF global model and IMDAA during 2019 and 2020 revealed the importance of ABOs, particularly in IMDAA, since it did not assimilate the latest satellite data as the IMDAA system was frozen in October 2016. A data denial experiment that removes all the ABOs from the IMDAA assimilation system for a period from March to November 2019 is designed. The results from the IMDAA reanalysis run, which assimilates ABOs during the same period, are compared with the data denial experiment. Assimilation of ABOs strengthened the upper tropospheric circulation, the Tropical Easterly Jet (TEJ), during the Indian summer monsoon compared to the data denial experiment. Analysis of the features of two cyclones that developed over the North Indian Ocean during the study period revealed that ABO assimilation played a key role in simulating the track and intensity of these cyclones when they were in the 'severe' category. Since the sample is small, more cyclone cases need to be analysed to consolidate the result. [ABSTRACT FROM AUTHOR]