High frequency wind-related seasonal mean latent heat flux changes

Surface latent heat flux (LHF) is an important component in the heat exchange between ocean and atmosphere. Seasonal mean LHF changes are often interpreted using seasonal mean wind changes. The present study analyzes the high-frequency wind-induced seasonal mean LHF changes. The changes in daily mean variables are decomposed into synoptic, intraseasonal, and low-frequency components and the respective contributions of the three components to seasonal mean LHF are estimated based on the bulk formula. It is shown that the high-frequency wind-induced LHF contributes an important part to climatological seasonal mean LHF and year-to-year variations of seasonal mean LHF in regions where low-frequency seasonal mean winds are weak, in particular, over the tropical Indian Ocean and western Pacific. A prominent feature is that the high-frequency and low-frequency wind-induced LHF anomalies tend to be opposite in those weak wind regions. In these regions, the reduced seasonal mean winds suppress seasonal mean wind-related LHF, but favors the accumulation of the high-frequency wind-induced LHF that increases in both active and inactive phases of high-frequency variations. Due to the shift of weak seasonal mean wind region with the low-frequency wind variations, the region of prominent high-frequency wind-induced seasonal mean LHF displaces with the season. The present results indicate an important upscale feedback of high-frequency wind variations to seasonal mean LHF.