MIDTROPOSPHERIC 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 she et-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 performi ng cluster analysis on component scores of a principal components anal ysis 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 topo graphically defined regions of the ice sheet are compared with the nin e different synoptic patterns. Synoptic patterns that would produce on shore 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 ex tent. The strength and location of the North American trough and the B affin Bay low are highly related to the downstream flow over south Gre enland and consequently to the extent of surface melting on the Greenl and ice sheet. A westward displaced North American trough is associate d with increased melting whereas an eastward displaced trough is assoc iated with reduced melt. (C) 1998 Royal Meteorological Society.