Subseasonal And Interannual Variations Of Gap Wind Over The Eastern Pacific And Its Associated Air-sea Characteristics In Winter

Based on the high-resolution satellite observations and the NCEP-CFSR reanalysis,this study investigates the subseasonal and interannual variations of the winter gap wind over the Eastern Pacific and its associated air-sea characteristics.The main conclusions are follows.(1)It is found that gap wind displays a significant subseasonal cycle at 4-16 days.On the 4-16 days subseasonal time scales,the relationship between the gap wind anomaly and its underlying sea surface temperature(SST)anomaly experiences a significant transition when the gap wind reach its peak phase.Before the peak phase,their relationship is negative,indicating an atmospheric-to-oceanic forcing.In this period,the increasing northerly winds blow toward the Gulfs with dry and cold air flow,enhancing the surface net heat fluxes loss and leading to the SST decreased.After the peak phase,the relationship between gap wind anomaly and its underlying SST anomaly turns positive,corresponding to an oceanic-to-atmospheric forcing,especially the negative SST anomaly can last for 6 days.The associated cold SST anomaly in turn suppresses the turbulent mixing,causing sea surface wind speed decreased.In addition,the atmospheric circulation anomalies over the Eastern Pacific to North America may have an influence on the 4-16 days subseasonal variation of the gap wind.Positive sea level pressure(SLP)anomaly over the North Pacific move southeastward as the gap wind increasing and reach the Mexico Bay when the gap wind reaching its peak.The sea level pressure anomaly over the Mexico Bay enhance the North American High to enlarge the pressure differences between the north and south side of the Gulfs,contributing to the gap wind peak.(2)It is found that gap wind displays a significant subseasonal cycle at 20-90 days.On the 20-90 days subseasonal time scales,the relationship between the gap wind anomaly and its underlying SST anomaly also experiences a transition when the gap wind reach its peak phase.Before the peak phase,the relationship between gap wind anomaly and its underlying SST anomaly is positive,corresponding to an oceanic-to-atmospheric forcing.The associated warm SST anomaly in turn enhances the turbulent mixing,causing sea surface wind speed increased.After the peak phase,their relationship turns negative,indicating an atmospheric-to-oceanic forcing.(3)In addition,gap wind also displays a 2-4 years interannual cycle.On the interannual time scales,the variation of the Tehuantepec gap wind is primarily related to the North American high and the North Atlantic Oscillation(NAO).The Papagayo gap wind is primarily governed by the local North American high and low latitude circulation,while it is weakly associated with high latitude teleconnections such as NAO.Moreover,the variations of gap wind could affect the local subsurface structure of the ocean.