ANOMALOUS WARMING OF THE STRATOSPHERE OVER NORTH AMERICA IN EARLY 1957

Abstract

The anomalous stratospheric warming of January and February 1957 is studied in detail by means of constant pressure charts, time sections, and cross sections. The warming occurred as the meandering Arctic stratospheric jet stream of wave number two developed into a pair of vortices extending to above the 10-mb. surface. It is concluded that development of stratospheric waves in the Northern Hemisphere is facilitated by autumnal growth of a forced perturbation locked in place by a warm ridge over the Aleutian area. The baroclinicity and rate of development were in agreement with Fleagle's criteria for the growth of disturbances. Interaction between the tropospheric jet stream and Arctic stratospheric jet stream during the period of development is believed responsible for the great intensity of the 1957 warming.