720 / 2024-09-19 10:14:36

Vigorous Forced Submesoscale Instability within an Anticyclonic Eddy during Tropical Cyclone "Haitang" from Glider Array Observations

South China Sea; weather events; submesoscale; tropical cyclone;

In this study, we examine intensive observational measurements from a 12-glider array in the South China Sea, and reveal that significant intensification of submesoscale frontal instabilities takes place within a mesoscale anticyclone eddy during the passage of TC "Haitang". The anticyclonic eddy shed from the Kuroshio loop current in the Luzon Strait. Fine-scale temperature and salinity observation from gliders captured the complex mesoscale frontal structure induced by mesoscale strain around anticyclone eddy. By defining the time and location of submesoscale instability occurrence, various submesoscale instabilities show significantly different spatial distributions as well as temporal evolution characteristics in AE. Measurements and analyses indicate the probability of submesoscale instabilities such as forced symmetric instability (SI) and gravitational instability (GI) occurrence during the TC period (~ 5 days) is found to be 2 times higher than that during the non-TC period (~25 days). Heat loss predominately leads to the occurrence of GI within the anticyclonic eddy and in the upper part of the negative potential vorticity (PV) layer. Strong wind stress induced by the TC promotes the injection of negative PV through cross-front Ekman buoyancy flux, leading to the occurrence of SI preferentially at the edge of the eddy and the lower part of the negative PV layer. These findings highlight the intensification of submesoscale instabilities corresponding to a tropical cyclone and provide insights for improving submesoscale parameterization in climate-scale ocean models.