| Abstract: | Climate fluctuations, or modes, are largely manifested in terms of coherent, large-scale (3000 km) patterns of anomalous sea-level pressure or geopotential height at various altitudes. It is worthwhile to investigate how these modes relate to the specific processes associated with atmospheric forcing of the ocean, in this case for the southeast Bering Sea. This approach has been termed “downscaling.” Climate-scale patterns in this study are derived from covariance-based empirical orthogonal functions (EOFs) of low-pass filtered (10-day cut-off) 700-mb geopotential height fields for 1958–1999. By design, this EOF analysis elicits sets of patterns for characterizing the variability in the large-scale atmospheric circulation centered on the Bering Sea. Four modes are considered for each of three periods, January–March, April–May, and June–July. These modes are compared with atmospheric circulation patterns formed by compositing 700-mb height anomalies based on the individual elements constituting the local forcing, i.e. the surface heat and momentum fluxes.In general, different aspects of local forcing are associated with different climate modes. In winter, the modes dominating the forcing of sea-ice include considerable interannual variability, but no discernible long-term trends. A prominent shift did occur around 1977 in the sign of a winter mode resembling the Pacific North American pattern; this mode is most significantly related to the local wind-stress curl. In spring, forcing of currents and stratification are related to the two leading climate modes, one resembling the North Pacific (NP) pattern and one reflecting the strength of the Aleutian low; both exhibit long-term trends with implications for the Bering Sea. In summer, an NP-like mode and a mode featuring a center over the Bering Sea include long-term trends with impacts on surface heating and wind mixing, respectively. Rare events, such as a persistent period of strong high pressure or a major storm, also can dominate the summer Bering Sea forcing in particular years. |
