Impact of tropical cyclones on the ocean heat budget in the Bay of Bengal during 1999: 1. Model configuration and evaluation

Abstract

The impacts of two consecutive, strong tropical cyclones (TCs) – 04B (10/15–10/19) and 05B (10/25–11/3) in 1999 (hereafter, TC1 and TC2) – on the upper ocean temperature and surface height of the Bay of Bengal (BoB) are examined using the Hybrid Coordinate Ocean Model (HYCOM). The HYCOM control run is driven by the Cross‐Calibrated MultiPlatform (CCMP) satellite winds, European Center for Medium‐Range Weather Forecasts Re‐analysis Interim (ERAI) surface reanalysis data, and Tropical Rainfall Measuring Mission precipitation. In order to investigate ocean response to high wind conditions, which are not well resolved by the CCMP or ERAI products, a modified Rankine vortex is adopted to reconstruct the TC winds in an experimental run. Wind stress is determined from wind speed when considering the level‐off and decline of drag coefficient at wind speed of 34 m/s and greater. The experimental run reproduces the strong SST reduction (∼−3°C) near the Orissa seashore along and on the right of the TC tracks. TC2 (category 5) cools the BoB SST less than TC1 (category 4) likely due to the initial SST depression by TC1. TC2 has higher winds and lingers over the ocean longer than TC1, and hence the onshore Ekman transport and mass convergence induced by TC2 wind is more prominent. The HYCOM mixed layer temperatures and depths to the south of the BoB generally agree with the observations very well. The simulations, however, have weaker vertical temperature gradient in the thermocline layer, suggesting that HYCOM produces a more diffusive thermocline than the observations.