Climatic relationships to Chesapeake Bay salinity during southern oscillation extremes

Monthly cool-season salinity over the 1958 to 1991 period is analyzed for t he Chesapeake Bay (CB), and the salinity variations are associated with low -frequency 500 hPa flow variations and with extremes of the Southern Oscill ation (SO). Results identify a significant decrease in mean CB surface sali nity, which is supported by similar trends in individual salinity subbasins occupying the northern extremes of the bay. Zonal (meridional) flow associ ated with the North Atlantic Oscillation (NAO) seems to be linked to below- (above-) normal CB salinity, while the Southern Oscillation Index (SOI) see ms to be negatively correlated with CB salinity. Principal components analy sis (PCA) reveals that the Pacific/North American (PNA) pattern is related to CB salinity, even though the PNA index is not. Within extreme El Nino mo nths, the strongest association between CB salinity and PCA-derived circula tion suggests that 500 hPa height features over the Great Plains may be lin ked to surface salinity in CB. By contrast, during La Nina months, height f eatures over the Desert Southwest appear to be linked more directly to surf ace CB salinity. The results also suggest that 500 hPa flow patterns conduc ive to extreme precipitation in the northeastern United States are related to salinity variations in the northern bay. However, for the bay as a whole , and especially the southern portions of the bay, flow patterns favoring m ean advective processes of CB and oceanic surface waters may be more import ant than those patterns relating to precipitation in contributing drainage basin areas. Results may be useful to environmental planners in the CB regi on.