Observed Upper Ocean Variabilityduring Pre and Post-Monsoon Cyclones Viyaru and Lehar in the Bay of Bengal

We study multiple parameters during the pre-monsoon tropical cyclone (TC) Viyaru and the post-monsoon TC Lehar in the Bay of Bengal (BoB) to understand the differences in seasonal variability. The parameters included sea surface temperature (SST), sea surface salinity (SSS), mixed layer depth (MLD), Precipitation (PRE), sea level anomaly (SLA), ocean net heat flux (NHF), 20℃ isotherm depth (D ₂₀ ), sea surface winds, and sea level pressure (SLP). The in situ SST near the Viyaru tracks was 29.57 ^o C within 103.32 hours (cooled down ~ 3 ^o C) after the Viyaru’s landfall. The SST cooling near the Lehar track was sustained for 42 hours after the landfall. The SST observed before the formation of Viyaru was about 2–3 ^o C higher than that of Lehar. Near the TC track, the maximum decrease in SSS was 0.5 psu during Viyaru, while it was 0.3 psu during Lehar. The MLD during Lehar was about 5 m deeper than that during Viyaru. The increment of PRE for Viyaru was great, reaching a maximum of 500 mm per day, whereas that during Lehar remained lower than 450 mm. The heat loss during Viyaru was greater than that during Lehar. The depth of D ₂₀ for Viyaru increased from 127 m to 128 m, while that for Lehar remained 118 m. The SLP for Viyaru was lower than that for Lehar, dropping on the day after landfall. The distinct seasonal variabilities indicate that air-sea interactions and heat exchange mechanisms were markedly more intense during the pre-monsoon TC Viyaru.