The seasonal cycle of midlatitude static stability over land and ocean in global reanalyses

Abstract

[1] Using a new reanalysis data set, the seasonal cycle of the midlatitude tropospheric static stability is examined. Dry and moist static stability measures are analyzed as a function of latitude, longitude, and season. It is shown that in both the Northern (NH) and Southern Hemispheres (SH), dry and moist static stability averaged over the midlatitudes maximizes in December–February. Examining the spatial structure of the stability changes indicates that the difference in the seasonal cycle between hemispheres is due to the behavior over land, which maximizes its stability in winter. Ocean surfaces have qualitatively similar cycles in both hemispheres. It is clear that moist processes are important in determining the static stability in both hemispheres. Although a previously derived moist scaling theory works fairly well to explain the seasonal changes in both hemispheres, it is argued that the large differences in seasonal cycles between land and ocean may indicate different mechanisms at play between the largely ocean-covered SH and the land-dominated NH.