Seasonal variations in atmospheric responses to oceanic eddies in the Kuroshio Extension

Abstract

Analyses using high-resolution satellite observations reveal distinct seasonal variations in atmospheric responses to oceanic eddies in the Kuroshio Extension (KE) region, characterised by much stronger surface wind speed and heat flux responses in the cold seasons (winter and spring) than in the warm seasons (summer and autumn). Cloud liquid water and rain rate also display seasonally dependent characteristics, with more deficit (surplus) in winter than in summer over the cold (warm) oceanic eddies. CFSR (Climate Forecast System Reanalysis) data can well reproduce these seasonal variations in surface atmospheric responses to the eddies in the KE region, albeit with much weaker responses in surface wind speed and with stronger responses in latent heat flux in comparison with the results based on satellite observations. In addition, the CFSR data also reveal remarkable seasonal variations in tropospheric responses, with eddy-induced wind speed (vertical velocity) anomalies reaching as high as 900 hPa (800 hPa) in winter, while they only occur near the sea surface in summer. The Weather Research and Forecast (WRF) model is applied to study the seasonal variations in atmospheric responses to idealised oceanic eddies. The model successfully simulates the seasonal variations in atmospheric responses to an idealised warm eddy in terms of wind speed, heat flux, marine atmospheric boundary layer (MABL) height and vertical velocity in both seasons. Both the CFSR data and the model simulations indicate that the seasonal variations in atmospheric responses to oceanic eddies can be attributed to the variations in background atmospheric stability during different seasons.