Mid‒tropospheric circulation and surface melt on the Greenland ice sheet. Part II: synoptic climatology

Daily values of the spatial extent of melting on the Greenland ice sheet—measured from satellite passive microwave sensors—are compared with a synoptic climatology of 700 hPa geopotential heights from May 1979 to June 1989. Nine common synoptic patterns were extracted by performing cluster analysis on component scores of a principal components analysis of daily 700 hPa heights. Discrete composite analysis is used to produce maps of the geopotential height and height departures for days classified as each synoptic type. The mean melt extent for eight topographically defined regions of the ice sheet are compared with the nine different synoptic patterns. Synoptic patterns that would produce onshore flow are associated with a greater spatial extent of melting in the north and east regions of the ice sheet. The south‒west regions of the ice sheet have greater melt extent during south‒westerly onshore flow, whereas north‒westerly onshore flow serves to reduce the melt extent. The strength and location of the North American trough and the Baffin Bay low are highly related to the downstream flow over south Greenland and consequently to the extent of surface melting on the Greenland ice sheet. A westward displaced North American trough is associated with increased melting whereas an eastward displaced trough is associated with reduced melt. © 1998 Royal Meteorological Society.