Air-sea Characteristics In Association With Mesoscale Oceanic Eddies Over North Pacific In Summer

A series of high-resolution satellite and reanalysis data is used to investigate the coupling relationships between oceanic eddies and atmosphere over the subtropical North Pacific and Kuroshio Extension in summer,where two large bands of Eddy Kinetic Energy lie in,by means of eddy detection scheme,filtering,composite analysis and numerical simulation.The main conclusions are follows.(1)Results show that there are both positive and negative correlations between sea surface temperature(SST)and wind speed at 10-m over eddies on a daily time scale over the subtropical North Pacific in summer,indicating not only oceanic but also atmospheric forcing exist in mesoscale oceanic eddies.(2)When SST is in phase with sea surface wind speed for warm(cold)eddies over the subtropical North Pacific in summer,upward(downward)net heat flux is enhanced,together with increased(decreased)total cloud cover and precipitation,negative(positive)anomalies of geopotential height,positive(negative)anomalies of relative humidity and upward(downward)movement.The sea water temperature anomalies and current curl are enhanced,so warm(cold)eddies are relatively stronger.All of these changes indicate ocean-to-atmosphere forcing to a certain extent.In addition,when SST is in opposite phase with sea surface wind speed for warm(cold)eddies over the subtropical North Pacific in summer,downward(upward)net heat flux is enhanced,total cloud cover and precipitation are decreased(increased)with positive(negative)anomalies of geopotential height,air temperature at low-middle layer and negative(positive)anomalies of relative humidity.Moreover,the sea water temperature anomalies and current curl are weakened,so warm(cold)eddies are relatively weaker.All of these are conducive to the maintenance of warm(cold)eddies under clear(rainy)sky,indicating atmosphere-to-ocean forcing to a certain extent.(3)There are both positive and negative correlations between sea surface temperature(SST)and wind speed at 10-m over eddies on a daily time scale over Kuroshio Extension in summer.Distributions of positive and negative anomalies of atmospheric variables over eddies in this area are almost similar to that in the subtropical North Pacific.But the proportion of eddies with positive correlations between S ST and wind speed at 10-m compared to total eddies in Kuroshio Extension is higher than that in the subtropical North Pacific.What's more,the results of observation and WRF numerical simulation show that among eddies that force atmosphere in Kuroshio Extension,magnitudes of precipitation,latent heat,planetary boundary layer height and friction speed positive anomalies over warm eddies are larger than that over cold eddies,which makes to some degree clear that warm eddy's forcing on the atmosphere is stronger than cold eddies.