EXTENT AND DURATION OF ANTARCTIC SURFACE MELTING

The extent and duration of surface melting on the Antarctic ice shelve s and margins of the Antarctic ice sheet are derived from satellite pa ssive-microwave data for 1978-87. The occurrence of surface melting in daily maps of T-b is indicated by a marked increase in microwave brig htness temperature (T-b), which is caused by moisture in the near-surf ace firn. T-b increases of more than 30 deg above the annual-mean T-b are chosen to indicate melting. Most Antarctic surface melting occurs during December and January. The observed melting is correlated with r egional air temperatures, but some melt patterns also appear to be rel ated to katabatic-wind effects. The correlations suggest that the surf ace melting in Antarctica increases about 3.5 x 10(6) d km(2) per degr ee of summer temperature increase. The surface-melt index (duration ti mes area of melting) calculated for Antarctica is 24 x 10(6) d km(2), averaged over nine summers. The observed inter-annual and regional var iability is large. Surface melting was most extensive during the 1982/ 83 summer (36 x 10(6) d km(2)) and least extensive during the 1985/86 summer (15 x 10(6) d km(2)). The data indicate a decline in surface me lting over the 9 years, but meaningful inferences regarding trends in surface melting are precluded by the large inter-annual variability.