Upper Ocean Structure Determines the Contrasting Typhoon-Induced Chlorophyll-a Responses in the Northwest Pacific

Abstract

The frequent typhoons in the northwest Pacific drive oceanic responses, for example, changes in sea surface temperature (SST) and chlorophyll-a (Chl-a). A composite analysis shows that SST (Chl-a) around the typhoon center decreases (increases). The SST begins to decrease 3 days before the typhoon’s arrival and further decreases until 2 days following the typhoon’s passage. The Chl-a increases rapidly after the typhoon’s arrival, and the maximum value is reached 3 days after the typhoon. Large oceanic responses are often associated with typhoons that have high wind speeds and slow translation speeds. From the perspective of the upper ocean structure, increasing changes in SST are identified with a shallower pre-typhoon mixed layer depth (MLD). However, a significant dependence of the Chl-a response on the pre-typhoon MLD emerges only when the depth of typhoon-induced mixing is greater than the pre-typhoon MLD. This study helps to quantitatively describe typhoon-induced changes with consideration of the determinant oceanic environment.