Assessing aerosol interactions and re-distribution during very severe cyclonic storm Vardah (2016) in the Bay of Bengal

Abstract

Utilizing reanalysis and satellite observations, the present study investigates the interactions and redistribution of aerosols during a Very Severe Cyclonic Storm (VSCS) Vardah (6th to 13th December, 2016) in the Bay of Bengal (BoB). The detailed analysis focuses on the effects of aerosols on the tropical cyclone (TC) induced precipitation, including an examination of aerosol loading, changes in their distribution during the passage of the cyclone. As cyclone Vardah matured from a Severe Cyclonic Storm (SCS) to VSCS, a gradual reduction in the Precipitation Rate (PR) was observed, accompanied by an increasing trend of Lower Tropospheric Stability (LTS). Winds from the aerosol-rich north-eastern Himalayan region that were directed toward the cyclone resulted in a significant influx of aerosols into the cyclone.  Even more aerosol loading was recorded over the central and western BoB during the SCS and VSCS stages of TC Vardah, respectively. This could be due to the strong drag of winds from the north-eastern Himalayan region towards the cyclone as it approached the coastal region. Investigation of the spatial distribution of aerosols and precipitation rate during all three stages (i.e., Cyclonic Storm (CS), SCS, and VSCS) revealed that the presence of aerosols played a significant role in suppressing precipitation before cyclone Vardah made landfall. Additionally, spatio-temporal anomalies of AOD showed a sharp contrast, with anthropogenic aerosols depleted near the storm core due to wet scavenging, while natural aerosols such as sea salt were enhanced along the storm track, highlighting the cyclone’s dual role as both a cleanser and redistributor of aerosols. Further, our analysis revealed that TC Vardah deposited a significant amount of aerosols over Chennai, bringing it from the ocean. These results make an important contribution to understanding the redistribution of aerosols and their impact on precipitation induced by cyclones over the BoB.