A Heat Budget Analysis of the Polar Troposphere in and around Alaska during the Abnormal Winter of 1988/89

Abstract

In this study, we carried out a quantitative heat budget analysis of the polar troposphere in and around Alaska for the winter of 1988/89. The winter was characterized by drastic temperature variations. The surface minimum temperatures in the interior of Alaska were lower than ?40°C during two weeks in late January. This cold period was followed by extremely warm weather during February, especially in northern Alaska. The results of the heat budget analysis for the three-month average (December to February) show that the heat energy of the continental air mass in and around Alaska is maintained by a balance of warm advection, adiabatic warming, and radiative cooling. The analysis of the long-term variation during this period shows that the severe cold in late January was caused by an anomalous reduction in warm advection of sensible heat. The abnormally warm weather in February was caused by enhanced warm advection associated with a blocking formation over the North Pacific. We find that strong adiabatic warming due to large-scale descending motions occurs as a precursor to the blocking formation and the warm advection. It is suggested that the unusual temperature variation during this winter was caused by the enhanced, low-frequency variation of the 1arge-scale flow. The local radiative cooling acts to reduce the rapid temperature variation due to advection change.