Eddy heat transport across the Luzon Strait derived from current- and pressure-recording inverted echo sounder observations

Abstract

The heat transport across the Luzon Strait has crucial impact on the heat budget of the South China Sea. However, the quantum of heat transported is uncertain owing to the scarcity of observations. In this study, the zonal eddy heat transport (ZEHT) across the Luzon Strait was investigated using a mooring array of current- and pressure-recording inverted echo sounders. The ZEHT is generally westward and downgradient. The downgradient ZEHT is related to the positive baroclinic energy conversion. A new method was proposed to empirically determine the long-term (1993–2022) ZEHT from the sea surface height (ZEHTSSH). The long-term ZEHTSSH had a mean value of 3.8 TW (1 TW = 1012 W) directed westward. The seasonal mean ZEHTSSH was the largest in winter (4.5 TW) and smallest in summer (2.7 TW). The largest ZEHTSSH during winter may be caused by enhanced baroclinic instability facilitated by smaller stratification and higher vertical velocity shear. The long-term mean ZEHT is estimated as 2.6 TW if the gaps of the Luzon Strait not covered by the mooring section are considered. This study has proposed a new method to derive a long-term ZEHT time series based on observations, which will be meaningful for the study on the oceanic heat budget around the SCS and related climate study.