Interannual and Interdecadal Variability in the Storm Track, Cloudiness, and Sea Surface Temperature over the Summertime North Pacific

Abstract

Interannual and interdecadal variability in the summertime mean North Pacific storm track is examined in relation to summertime mean sea surface temperature (SST), nimbostratus, and marine stratiform cloudiness (MSC) (stratus, stratocumulus, fog). The storm track is diagnosed by root-mean-squared daily vertical velocity at 500 mb during the summer season (rms ?) obtained from the National Centers for Environmental Prediction?National Center for Atmospheric Research reanalysis. The cloud and SST data are obtained from surface observations. Year-to-year variations in the storm track exhibit significant coupling to variations in cloudiness and SST across the North Pacific. These correspond to coincident latitudinal shifts in the storm track, SST gradient, and MSC gradient. Moreover, both rms ? and nimbostratus show that the storm track moved equatorward and intensified between 1952 and 1995, consistent with the previously documented upward trend in MSC and downward trend in SST. Lead?lag relationships suggest variability in the storm track has a large role in forcing variability in SST. Boundary layer cloudiness responds to and adds a positive feedback to variability in SST. Weak relationships are observed with the summertime mean large-scale circulation, as diagnosed by sea level pressure. This suggests summertime North Pacific atmosphere?ocean interaction is dominated by local processes operating in the storm track and over the SST gradient, unlike the situation during winter.