Typhoon-induced ocean subsurface variations from glider data in the Kuroshio region adjacent to Taiwan

Abstract

Underwater gliders are used to investigate the variations on the ocean surface and subsurface during the 14 typhoons that passed over the Kuroshio region near Taiwan in 2010-2013. Typhoon-induced subsurface layer warming, which was formed on the basis of the heat pump effect of the vertical mixing process, is observed in this study. In addition, the gliders observe the variations in salinity during the passage of the typhoons. Typhoons, accompanied by heavy rainfall, introduce a considerable amount of fresh water into the upper ocean, diluting the surface salinity. The diluted salinity accompanied deepening of the mixed layer which moved downward to the subsurface by vertical mixing, supplying fresh water to both the surface and subsurface layers. Additionally, because of vertical mixing, maximum temperature variations occur at the bottom of the mixed layer or at a level deeper than the mixed layer. Changes of the heat content show that a series of vertical mixing events occurs in the upper ocean. Pairs of salinity profiles indicate comprehensive vertical mixing in the upper ocean and yield schematics to compare typhoons with or without heavy rainfall. Higher sustained wind speeds may contribute to a considerable drop in sea surface temperature, but possibly not to the magnitude of the subsurface warming. The upper ocean thermocline gradient before a typhoon is an important factor to determine the magnitude of subsurface warming. This study concludes a glider observational result that typhoons cause subsurface layer warming and freshening in the Kuroshio region near Taiwan.