Atmospheric and Sea-Ice Conditions in the Northwest Atlantic During the Decade, 1991-2000

Abstract

Atmospheric and sea ice conditions within the Northwest Atlantic during the decade 1991–2000 are described. The NAO index in the 1990s was the highest in the past 11 decades and there has been a general increase from the minimum of the 1960s. The high NAO in the 1990s was accompanied by an increase in southwesterly winds in the Labrador Sea region. With the exception of Nuuk, mean decadal air temperatures were above their long-term means at selected sites throughout the NAFO area, including record high decadal means in the Gulf of St. Lawrence and at Cape Hatteras. Air temperatures have generally been increasing since the 1960s from the Scotian Shelf northward. Sea-ice conditions off the Labrador and northern Newfoundland coast, in the Gulf of St. Lawrence and the Scotian Shelf indicate the least amount of ice in the 1960s. From Labrador to the Gulf of St. Lawrence there was little difference in ice severity between the 1970s, 1980s and 1990s; however, on the Scotian Shelf the ice area was less during the 1990s compared to the previous two decades. The decadal mean of the number of icebergs drifting southeastward along the Labrador and Newfoundland shelves was at a maximum during the 1990s. There has been large intra-decadal variability in all climate indices examined. The early years of the 1990s were characterized by high NAO indices, strong northwesterly winds, cold air temperatures from the Labrador Sea to the Gulf of Maine, and extensive ice cover. In 1996, the NAO index experienced its largest annual decline in the over 100-year record. During the remaining years of the 1990s decade, the NAO rose achieving values that even exceeded those of the early years of the 1990s. Of significance during the latter half of the decade was the eastward shift in the center of the atmospheric low-pressure system over the Northwest Atlantic. This shift contributed to weaker northwesterly winds, warmer temperatures in the Labrador Sea to the Gulf of Maine, and a reduction in sea-ice.