Impacts of the binary typhoons on upper ocean environments in November 2007

Using multiple satellite observations, Argo floats profiles, and one-dimensional (1-D) ocean mixed layer model, this study systematically investigated the impacts of the binary typhoons Hagibis and Mitag [which coexisted respectively in the South China Sea (SCS) and western North Pacific (WNP) during November, 22 to 26, 2007] on upper ocean environments. It was observed that intense Ekman pumping and two mesoscale cold, cyclonic eddies, which, induced by long forcing time of strong wind stress curls, appeared respectively in two certain areas instead of after the binary typhoons' trails. Both cyclonic eddies retained for similar to 39 days, accompanied with maximum sea surface height anomaly (SSHA) reduction of similar to 25 cm induced by Hagibis and of similar to 44 cm induced by Mitag, respectively. The largest sea surface temperature (SST) drop of 7 degrees C and 2 degrees C, the maximum chlorophyll a (Chl-a) enhancement respectively was >20 times and similar to 3 times in these two eddies' regions induced by Typhoon Hagibis and Mitag, respectively. The results of the 1-D ocean mixed layer model showed that, given its 84 h forcing time, the simulated MLT cooling and mixed layer deepening induced by Hagibis were similar to-2.8 degrees C and 45 m, respectively, similar to-0.5 degrees C and 25 m for Mitag at its 66 h forcing time. This work provides convincing evidences that typhoons, which appear frequently in the SCS and the WNP, play a notable role in the activities of mesoscale eddies in these areas.