Roles of tropical cyclones with varying intensities in the re-distribution of aerosols

Abstract

The study analyzes three tropical cyclones (TC) with varying intensities, namely BOB02, a deep depression in the Bay of Bengal; Tauktae, an extremely severe cyclone in the Arabian Sea (AS); and Amphan, a supercyclone in the Bay of Bengal, which developed on October 11, 2020, May 13, 2021, and May 16, 2020, respectively. The analysis focuses on studying the re-distribution of the aerosols over the Indian region using these distinct datasets: Modern-Era Retrospective Analysis for Research and Application, version 2 (MERRA2), Integrated Multi-Satellite Retrievals for GPM (IMERG), and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). Throughout the cyclonic period, which includes the period from the inception of the low-pressure area to its dissipation as well as the pre-cyclonic and post-cyclonic periods (one week prior to and after the cyclonic period, respectively), various parameters related to aerosols and background meteorological conditions were collected. The primary parameter of interest was the aerosol optical depth (AOD). The analysis revealed significant variations in meteorological parameters such as wind speed, temperature, relative humidity, and rainfall along the cyclone track during both the cyclonic and post-cyclonic conditions compared to the pre-cyclonic conditions of these TCs. The AOD surrounding the cyclone track decreases during cyclonic and post-cyclonic conditions compared to pre-cyclonic conditions. This is due to the scavenging of both anthropogenic and natural (dust) aerosols. Conversely, AOD increases along the cyclone track, mainly due to an increase in natural (sea salt) aerosols. During pre-cyclonic conditions, both natural (dust) and anthropogenic (black carbon, organic carbon, and sulfate) aerosols contribute significantly to the total AOD, whereas during pre-cyclonic conditions, the main contributors are natural (sea-salt) aerosols. The coarse-mode particles are more dominant during cyclonic and post-cyclonic conditions than pre-cyclonic ones. Furthermore, our observations indicate that the atmospheric boundary layer (ABL) height increases by ∼0.1–0.6 km along the cyclone track during cyclonic conditions compared to pre-cyclonic conditions. While AOD from the free troposphere (FT) contributes more to the total AOD, contributions from ABL increase, while those from the FT decrease during cyclonic and post-cyclonic conditions.