Upper ocean response to tropical storm Biparjoy in the Arabian Sea based on moored buoy observations

Abstract

An Extremely Severe Cyclonic Storm (ESCS) ‘Biparjoy’ crossed very close to the moored buoys in the Arabian Sea (AS) during June 10-11, 2023 before its landfall on June 15 near Saurashtra and Kutch. The upper ocean response was examined, revealing significant changes in meteorological (wind, sea level pressure, and rainfall) and oceanic (waves, temperature, salinity profiles, and currents) parameters at AD06 and AD07, deployed by ocean observation systems group, National Institute of Ocean Technology (NIOT), Chennai. A spatial response study of Sea Surface Salinity (SSS) and Sea Surface Temperature (SST) was conducted to illustrate the pre- and post-cyclonic conditions.
On June 11, 2023, AD06 recorded Sea Level Pressure (SLP) drop to 965 hPa, 119.7 mm/day rainfall, and a maximum wind speed of 90 km/h (gustiness up to 153.7 km/h). At AD07, the wind peaked at 61.6 km/h on June 09, with SLP drop of 998.8 hPa on June 10, and 35.6 mm rainfall on June 11. SST dropped by ~4 °C at AD06 (June 12), and ~2 °C (June 10) at AD07. The Tropical Cyclone Heat Potential ~111 kJ/cm² and 135 kJ/cm² at AD06 and AD07, respectively favoured cyclone intensification. After June 11, the 26 °C isotherm (D26) shoaled significantly at AD06 (~24 m) with deepened mixed and isothermal layers, corresponding to enhanced cooling of SST at AD06 (~ 4 °C). Significant wave heights reached 8.9 m (AD06) and 7.29 m (AD07) with maximum wave heights of 14.6 m and 11.46 m, respectively, on 12^th and 10^th June. The spatial distribution of SST and SSS during the post-cyclone phase is marked by notable cooling (~ 27 °C) and an increase in salinity (~ 36 ppt) in the upper layers of the AS.