Impact of Tropical Cyclones on Geostrophic Velocity of the Western Boundary Current

Abstract

The tropical cyclone (TC) accompanied by tremendous winds is the most destructive atmospheric phenomenon on Earth. Recent studies have reported that the strength of TCs will increase under conditions of global warming (Mei et al., 2015;Walsh et al., 2016;Webster et al., 2005). Under these circumstances, it is all the more important to expand and advance knowledge about the TC not only for its improved prediction and prevention of damage from them, but also for a better understanding of its influence on the climate with respect to its interactions with the ocean.The western boundary current (WBC) is one of the strongest ocean current systems on Earth. This poleward current of geostrophic nature, with a strong thermal gradient (i.e., thick warm layer of water on the ocean side and strongly stratified water on the shelf side), also carries heat into the middle latitudes and contributes toward global heat balance (Hu et al., 2015). The existence of warm water in the basins not only becomes a source of the WBC, but also leads to the generation of a large number of cyclones in the tropics, many of which pass through the WBC in the northwestern part of the Pacific and Atlantic oceans. What happens when these two strong natural processes interact?Many studies on the thermal response of the ocean to TCs have been carried out. The wind stress associated with a TC transfers its momentum onto the upper layer of the ocean; this creates vertical current shear, resulting in vigorous vertical mixing accompanied by sea surface cooling, especially on the right side of the TC passage (D'Asaro et al., 2007;Park et al., 2019;Price, 1981). Also, within the radius of maximum wind of the TC, the strong cyclonic wind stress induces horizontal divergence in the ocean surface Ekman layer, and consequent temperature decrease (or density increase) in the water column is caused by upwelling (i.e., ba-