Exceptionally cold water days in the southern Taiwan Strait: Their predictability and relation to la Niña

Abstract

The objectives of this study were to assess the predictability of exceptionally cold water in the Taiwan Strait (TS) and to develop a warning system on the basis of the scientific mechanism, which is a component of the information technology system currently under development in Taiwan to protect aquaculture against extreme hazards. Optimum interpolation sea surface temperature (SST) data were used to find exceptionally cold water days from January 1995 to May 2017. We found that the SST and wind speed over the TS are low and strong in La Niña winters, respectively. According to tests conducted using relative operating characteristic curves, predictions based on the Oceanic Niño Index and integrated wind speed can be employed at lead times of 60-120 and 0-25 days, respectively. This study utilized these two proxies to develop a possible warning mechanism and concluded four colors of warning light: (1) blue, meaning normal (0% occurrence probability); (2) cyan, meaning warning (∼ 50% occurrence probability); (3) yellow, meaning moderate risk (∼ 60% occurrence probability); and (4) red, meaning high risk (∼ 75% occurrence probability). Hindcasting winters over the period 1995-2017 successfully predicted the cold water hazards in the winters of 2000, 2008, and 2011 prior to the coldest day by ∼ 20 days.