Surface Flux Variability over the North Pacific and North Atlantic Oceans

Abstract

Daily fields obtained from a 17-yr atmospheric GCM simulation are used to study the surface sensible and latent heat flux variability and its relationship to the sea level pressure (SLP) field. The fluxes are analyzed over the North Pacific and Atlantic Oceans during winter. The leading mode of interannual SLP variability consists of a single center associated with the Aleutian low in the Pacific, and a dipole pattern associated with the Icelandic low and Azores high in the Atlantic. The surface flux anomalies are organized by the low-level atmospheric circulation associated with these modes in agreement with previous observational studies. The surface flux variability on all of the timescales examined, including intraseasonal, interannual, 3?10 day, and 10?30 day, is maximized along the north and west edges of both oceans and between Japan and the date line at ?35°N in the Pacific. The intraseasonal variability is approximately 3?5 times larger than the interannual variability, with more than half of the total surface flux variability occuring on timescales of less than 1 month. Surface flux variability in the 3?10-day band is clearly associated with midlatitude synoptic storms. Composites indicate upward (downward) flux anomalies that exceed |30 W m?2| occur to the west (east) of storms, which move eastward across the oceans at 10°?15° per day. The SLP and surface flux anomalies are also strong and coherent in the 10?30-day band but are located farther north, are broader in scale, and propagate ?3?4 times more slowly eastward than the synoptic disturbances. The sensible and latent heat flux are proportional to the wind speed multiplied by the air?sea temperature and humidity difference, respectively. The anomalous wind speed has the greatest influence on surface flux anomalies in the subtropics and western Pacific, while the air temperature and moisture anomalies have the greatest impact in the northeast Pacific and north of 40°N in the Atlantic. The covariance between the wind speed and the air temperature or humidity anomalies, while generally small, is nonnegligible on synoptic timescales.