Is Cyclone JAL Stimulated Chlorophyll-A Enhancement Increased Over the Bay of Bengal?

Abstract

Cyclones pose a great havoc to coastal cities and its gale winds changes the upper ocean properties in the tropics. Previous studies reveal that strong cooling is observed along the cyclone track [1-3]. It also plays an important role in enhancing phytoplankton bloom and primary productivity in oligotrophic oceanic waters, especially in cyclone-dominated seas. The Bay of Bengal is the most vulnerable region to hazard of intense tropical cyclones during pre-monsoon (April-May) and post monsoon (October – December) seasons [4]. In recent years the bay experience more than 5 cyclones during the post monsoon season compared with the Arabian Sea. Tropical cyclones depend on the ocean for their energy supply. Observations have shown that the state of the ocean has a great influence on the intensities, structures, and even paths of tropical cyclones [5-9]. Upper ocean is greatly influenced by the cyclone gale winds. The wind stress and pressure drop associated with tropical cyclone generate turbulent mixing in the ocean, generate ocean currents, and alters the ocean’s thermal structure. Strong wind momentum helps to bring the subsurface water from a depth of 60 m, because of that the surface water shows strong cooling (1-7°C) also the very deep mixed layer during post cyclone stage [1013]. This cooling is mainly due to the vertical turbulent mixing induced by the strong momentum flux into ocean currents and accompanied entrainment of cooler thermocline water into the upper mixed layer. The magnitude of the surface cooling plays a vital role on reduction of the energy supply to cyclone for further intensification [13]. The main purpose of the study is to examine the physical and biological changes in the upper layers of the Bay water at different stages of Jal cyclone.