Dynamical Ocean Responses to Typhoon Malakas (2016) in the Vicinity of Taiwan

Abstract

AbstractSaffir‐Simpson Category‐4 Typhoon Malakas crossed the Kuroshio, the Western Boundary Current of the North Pacific Ocean, and moved along the path of the Kuroshio for eight days between September 12 and 20, 2016. Malakas induced a 3–4°C sea surface cooling and an increase in sea surface Chlorophyll‐a concentration to 0.8 mg/m3. The total cooling area was approximately 18,000 km2. Satellite observations show that Malakas triggered two upwelling regions associated with two mesoscale eddies, both to the northeast of Taiwan. The Regional Oceanic Modeling System (ROMS) was employed to offer insights into the dynamical mechanisms on the ocean response to a typhoon. The numerical model results reveal that a coastal upwelling event was induced by southeasterly winds blowing prior to the arrival of Malakas' outer band, and caused a surface cooling near Taiwan's northeast coast. A branch of the Taiwan Warm Current interacted with the offshore Kuroshio current to form an eddy prior to the typhoon's arrival. Malakas then facilitated the development of the near‐coastal eddy. An open ocean eddy was triggered by inertial‐Ekman pumping under the forcing effect of Malakas. The interaction between the southward current caused by Malakas and the northeastward flowing Kuroshio maintained these two induced mesoscale eddies. Numerical results show a near‐inertial oscillation (IO) of about a 26‐h period with an e‐folding time scale of ∼5 days was magnified and modulated by Malakas. The typhoon‐induced oceanic phenomena were very well revealed in this combined observational and numerical modeling study.