Meteorological Factors Affecting Interannual Variability of Summertime lce Extent in the Beaufort Sea

Abstract

The relationship between meteorological factors, measured at Barrow, Alaska, and summertime Beaufort Sea ice conditions along the shipping route between Pt. Barrow and Prudhoe Bay was investigated using data available from 1953?1975. Light-ice summers are associated with higher than normal sea level pressure (SLP) northeast of the Beaufort Sea (centered on 80°N, 120°W), lower than normal SLP over the east Siberian Sea and with more frequent surface winds primarily from the directions 135?195°. A reversal in this pressure and wind direction pattern occurs during heavy-ice summers. Air temperature, in the form of thawing degree days (TDD's), is the parameter most highly correlated with the summertime ice margin distance (r = 0.815) and it is highly correlated with SLP and wind direction. Correlation coefficients between these meteorological factors and ice margin distance increase during the summer suggesting their increasing importance to melt processes with time. The amount of open water by late summer and during autumn in the Beaufort Sea influences subsequent air temperatures, but has little or no influence upon subsequent local surface winds or the SLP distribution over the Northern Hemisphere. This interaction between ocean and overlying air, which encourages mild summers to be followed by mild autumns, accounts for the bimodal distribution in maximum accumulated TDD's noted at Borrow. Analysis of Landsat images of sea ice conditions and concurrent TDD's between 1972 and 1976 showed that at least 400 TDD's are needed to assure favorable ice conditions. Trends in SLP and TDD's since 1939 and 1921, respectively, suggest increasing severe ice-conditions as only 13 of 24 summers have accumulated 400 TDD's since 1953, while 28 of 32 had done so between 1921 and 1952. This was associated with a decline in Barrow mean summer temperature of 0.4°C from 1921?52 to 1963?75.