Determination of ocean structure on response of sea surface temperature and chlorophyll to typhoon in NW Pacific Ocean

Typhoons in the northwestern Pacific induce strong oceanic responses. Using 17 years of satellite observations, the impacts of typhoons on sea surface temperature (SST) and chlorophyll-a (Chl-a) are investigated. The SST time series shows that the SST begins to decrease 2 days before the typhoon’s arrival and continues to decrease until 2 days following the typhoon’s passage. The Chl-a has a weak peak 2 days prior to the typhoon’s arrival, rapidly increases after the typhoon arrives, reaches the strongest response on the third day of the typhoon, and gradually decreases to a value slightly higher than the pre-typhoon level. Prominent responses are associated with typhoons that have stronger intensity and slower translation speed. The pre-typhoon upper ocean structure plays a dominant role in determining oceanic responses. Surface cooling is generally stronger where the pre-typhoon mixed layer depth (MLD) is shallow. However, the change in Chl-a shows a contrasting response in that the response prominently increases only when the depth of typhoon-induced mixing exceeds the pre-typhoon MLD. This study poses a quantitative approach to assess the influence of typhoons on the upper ocean from a statistical perspective with consideration of the upper ocean structure.