Preliminary analysis of the intraseasonal air–sea interaction influenced by Xisha warm eddy

A study of the Xisha eddy is a good supplement to comprehend the local oceanic and atmospheric currents. Our work aims at analyzing the intraseasonal Air–Sea interaction process during the occurring of the Xisha warm eddy. Using a Complex Empirical Orthogonal Function statistical technique, we found an eddy that propagated southwestward along the continental slope of the northwestern South China Sea, at a similar phase speed to that of Rossby waves, at 0.12 m s⁻¹. Intraseasonal variability in spring is related to the ocean-to-atmosphere interaction, and involves the cloud-radiation effects on surface sea temperature, as well as its impact on lower-level convergence over the South China Sea. This process, induced by the warm eddy, results in abnormal surface sea temperature, downward shortwave/longwave radiation flux, surface latent heat flux, and wind changes. We used composite results and the Weather Research and Forecasting Model to explore how the observed surface sea temperature anomalies influence precipitation in the South China Sea. The results showed that the atmospheric transport of heat and moisture improved with respect to the surface sea temperature max and the air active events have caused lower atmosphere instability, along with the lower pressure and enhanced precipitation frequency in spring.