RESEARCH OF FACTORS OF INTERANNUAL AND INTRA-SEASONAL VARIABILITY OF THE MONSOON DEPRESSION IN THE INDIAN OCEAN

Abstract

Monsoon depressions (MDs) – areas of low pressure with cyclonic circulation that form over the Bay of Bengal - have a significant impact on weather conditions in the northern Indian Ocean during the summer monsoon. They are characterised by gale-force winds, high waves, intense cloud cover and heavy rainfall, posing a serious threat to maritime navigation and coastal infrastructure in the region. The recurrence and intensity of MDs are subject to significant fluctuations in time over a wide range of scales, from intra-seasonal to inter-decadal. Understanding the factors that control the variability of the MD regime is essential to reduce risks and losses in the maritime transport sector, which plays a key role in the global economy. In this paper, based on a comprehensive analysis of reanalysis data, observations, and numerical experiments, we investigate the large-scale dynamic and thermodynamic factors that determine the MD regime on interannual and intra-seasonal time scales. It is shown that changes in atmospheric circulation and ocean surface temperature in recent decades have contributed to a decrease in the number of MDs over the Bay of Bengal. At the same time, the results of regional model experiments indicate a possible increase in the frequency of the MDs in the context of the ongoing warming of the World Ocean. The analysis of intra-seasonal variations revealed statistically significant links between the MD activity and fluctuations in the intensity and position of the Intratropical Convergence Zone (ICZ). The quantitative estimates obtained in this work provide a basis for improving the quality of weather forecasts on sea lanes in the northern Indian Ocean and optimising strategies to minimise weather risks for the maritime industry.