Climate Dynamics: Unravelling the Characteristics of Monsoon Semipermanent Features

Abstract

The Indian summer monsoon (ISM) spans a crucial four-month period, unfolding from June to September (JJAS), inundating the Indian subcontinent with extensive rainfall. The stark contrast in land-sea heating stands as a key catalyst for the ISM phenomenon. Managing the ISM hinges on the orchestration of various monsoon semi-permanent features (MSF), encompassing entities like the Pakistan heat low, cross-equatorial low-level jet over the Arabian Sea, the tropical easterly jet over the Indian Ocean at 200 hPa, Mascarene High, and the seasonal anti-cyclone over Tibet. Fluctuations in these MSF wield significant influence over the Indian Summer Monsoon Rainfall (ISMR), making it crucial to scrutinize their structure and variability amidst evolving climate scenarios, foreseeing their impact on future monsoons. Additionally, the ISM displays internal variability, oscillating between deficit and surplus years. Understanding how MSF impacts this variability becomes pivotal. Therefore, the main focus of the study is to investigate the fluctuations in rainfall during JJAS across the Indian monsoon core region, as well as the unique features of the Monsoon Surge Frequency (MSF) in two divergent monsoon years. Prior research has underscored the pivotal role of the monsoon core zone in shaping ISM, hence focusing on this zone for the rainfall study. To achieve these objectives, datasets from reputable sources like the 5th generation European Centre for Medium-Range Weather Forecasts (ERA5), India Meteorological Department (IMD) rainfall records from 1981-2020, and Coupled Model Intercomparison Project Phase 6 (CMIP6) spanning 2015-2021 under four distinct SSP scenarios are employed. These datasets aid in deciphering alterations in MSF and their repercussions on ISM-induced rainfall. The assessment of rainfall percentage departure utilizes methodologies in line with Rajeevan et al.'s (2010) framework, ensuring comprehensive and comparable analyses across datasets. This comprehensive study amalgamates various datasets and analytical approaches to illuminate the complex interplay between MSF, rainfall variations, and the dynamics of the Indian summer monsoon, laying the groundwork for informed assessments of future climate scenarios and their potential implications on this critical meteorological phenomenon.