Effect of �spiciness� on the intensification of cyclones over Arabian Sea - A case study on Biparjoy

Abstract

In recent decades, there has been notable variability in the occurrence, frequency, and intensification of cyclones worldwide, and a significant trend has emerged in the northern Indian Ocean, notably the Arabian Sea. The recent cyclone, Biparjoy, occurred in June 2023 and stands out as a significant event among these occurrences. Through an extensive analysis utilizing available datasets (both in-situ and model-based) along the vertical trajectory of cyclone paths, it has been ascertained that the intensity of cyclones is influenced by the advection of warm saline (referred to as �Spicy�) water originating north of the cyclone�s track. This influx of high-saline waters occurs at various depths, inducing alterations in the vertical water column configuration. Notably, the diffusion of heat overtakes that of salt, resulting in the gradual dispersion of the saline water. These high salinity levels are prevalent at depths ranging from 0 to 300�m, with a pronounced concentration up to 100�m below the surface. The presence of these warm saline waters overlying the colder, fresher waters gives rise to a phenomenon known as �salt fingering� (45o < Tu < 90o), which establishes a stable surface layer predominantly controlled by temperature gradients. This stable surface layer, extending up to approximately 50�m in depth holding a substantial heat, fostering a positive feedback loop that amplifies cyclone intensity. As the spiciness of the Arabian Sea experiences an ascending trend in recent years, the continued extension of saline water advection bears intense implications for upper ocean heat content. This, in turn, creates a favorable environment for the formation and rapid intensification of cyclones.