Observation of abnormal coastal cold-water outbreak in the Taiwan Strait and the cold event at Penghu waters in the beginning of 2008

Abstract

Abstract The Penghu archipelago locates near the Tropic of Cancer, guarding the southern entrance of the Taiwan Strait (TWS). Since the archipelago is usually surrounded by warm waters from the Kuroshio branch and the South China Sea, the marine ecosystem in the waters surrounding the archipelago is mainly tropical. However, this area may be invaded by cold water, which can cause serious ecological disasters. Among the few rare events ever documented, the cold event in early 2008 represented a typical case in this regard. In this paper, we investigated this event using in situ measurements and remote sensing data. Our analyses show that during the destructive snow and ice storm of early 2008, strong cold winds persisted for ~40 days over the TWS area, with a mean prevailing wind speed of about 15 m/s, and the water temperature in the strait dropped sharply, especially along the mainland coast. On the other side of the strait, the Penghu area experienced extremely low temperatures, leading to a cold event. Note that the time of temperature reduction in Penghu was earlier than the time of temperature reduction in the area farther north along the coast of Taiwan. This indicates that a cross-strait outbreak of the mainland coastal cold-water (MCCW) caused the cold event, and thus triggered the cold disaster. The outbreak resulted from the combined effect of favorable background hydrographic conditions, persistent strong northeasterly, strong mainland coastal current (MCC), and the interaction of current and waves with the bottom topography of the Taiwan Bank (TWB). Remotely generated coastal trapped waves (CTWs) may also play a role.