Influence of Indian ocean on structure and variability of monsoon low level jet in the present and future climate perspectives

Abstract

The Monsoon Low-Level Jet (MLLJ) is a crucial synoptic feature of the Indian summer monsoon, responsible for a significant portion of moisture transport to the Indian subcontinent. The present study focuses on analyzing the variability and vertical structure of the Monsoon Low-Level Jet (MLLJ) during the Southwest Monsoon season from 1979 to 2022. To conduct in-depth analysis, the total MLLJ path was divided into five regions: the Southern Indian Ocean, Equatorial Indian Ocean, Arabian Sea, Indian subcontinent, and the Bay of Bengal. The mean jet core height for these selected regions was found to be 588.84 ± 37.81, 874 ± 16.9, 849.62 ± 24.11, 830 ±39.85, 832 ± 41.25 and mean jet speed were found to be 2.96 ± 2.78, 10.49 ± 1.07, 15.79 ± 3.1, 11.43 ± 3.4 and 9.857 ± 3.09 respectively. Monthly variation in the jet properties were also analysed. To consider the impact of global warming on MLLJ characteristics, the analysis was conducted by dividing the study period into two epochs: pre-20 (1979 – 2000) and post-20 (2001 – 2022). The properties of the jet exhibit remarkable differences between these two epochs. Trend analysis also indicates a significant change between these epochs. Jet properties show robust interconnections with sub-seasonal ocean processes, including Somali, Oman, and South Eastern Arabian Sea upwellings in the Indian Ocean. The Arabian Sea Mini Warm Pool exhibits a significant correlation with jet properties, especially Arabian Sea core height.Extensive research was conducted to deeply investigate the pivotal influence of MLLJ characteristics on cloud and precipitation processes. The association of Convective Available Potential Energy (CAPE) and convective precipitation with core height exhibited similarities in the Arabian Sea (AS) and Indian subcontinent (IS) regions, while the Bay of Bengal (BB) region displayed notable differences. The Jet speed exhibits same pattern. In the study, MLLJ characteristics were examined in relation to ocean-atmospheric processes, including the IOD, ENSO, and SIOD indices, with a focus on notable variations in the SIOD index. The MLLJ characteristics also correlate with Indian summer rainfall, showing significant relationships. To assess future prospects, historical (1850-2014) and projection (2015-2096) data from IITM ESM were analyzed in conjunction with jet properties.