Ocean impact on the intensification of cyclone Titli

Abstract

Tropical cyclones are the most devastating weather events which still needs to understand much due to the uniqueness in their paths and intensification locations. One such recent very severe cyclonic storm, Titli, is perfectly fit for the individual case study. The cyclone Titli originated from a low-pressure area formed over the southeast Bay of Bengal (BoB) and adjoining north of the Andaman Sea on 7th October 2018 and intensified into a very severe cyclonic storm on 10th over a region of low saline water pool in the western Bay of Bengal. The addition of low salinity water in this region is from the lower Mahanadi basin and surroundings that received excess rainfall in September 2018. The low saline waters developed high stratification and suppressed the upwelling at the cold-core eddy center and restricted to 50 m. Persistent high heat content and high internal energy are the primary sources of intensification of cyclone Titli. Generally, intense cyclones enrich biomass's enhancement in the ocean's surface layer after their passage. But in the case of Titli, biomass enrichment did not happen due to persistent high stratification, which is about 3-4. Even the 80 knots (150 km/h) winds cannot break up the upper layer stratification, suppressing the cyclone-induced upwelling. Observations show only a 0.2-0.4 mg/m3 rise in chlorophyll on the surface and it may be due to the land drove nutrients and lightning. Data analyzed from the high-resolution global NEMO model also shows the intrusion of low saline waters off India's east coast. Though the model is slightly overestimating the upwelling in the cold core eddy's surface layers, it represents the barrier caused by stratified waters. Both the observations and model datasets are well correlating, daily analyzed model data is well capturing the seasonal stratification caused by the low saline waters in the northern Bay of Bengal. These high-resolution global ocean model datasets are useful and essential for the accurate forecast of cyclones over the Bay of Bengal.