THE DISTURBED CIRCULATION OF THE ARCTIC STRATOSPHERE

Abstract

The annual cycle of disturbed circulation in the arctic stratosphere (i.e., areas north of the main jet-core of the Ferrel westerlies) is discussed in the light of climatological and synoptic evidence. In summer, the Ferrel westerlies and their wave-trains choke off with height to a zero-level near 50 mb. Because of the warmth of the arctic stratosphere, easterly anticyclonic flow is continuous at higher levels. In August, cooling begins, and by September a barotropic westerly vortex, continuous with the Ferrel vortex, is established. In October and November, this vortex becomes baroclinic and appears distinct from the Ferrel westerlies. Winter circulation has two aspects: (1) warm, barotropic, anticyclonic flow associated with a strengthening and extension of the Alaskan warm ridge, which extends to above 25 mb; and (2) cold-low development near the pole, with a marked tendency for the development of a cold trough over eastern Canada. Polar-night jet-streams and travelling baroclinic waves characterize the outer parts of the cold-lows. The thermal waves associated with these disturbances often have large amplitudes and normally affect the entire stratosphere. The apparent independence of stratospheric disturbances centered above 50 mb is examined, and the probable physical and dynamical processes involved are tentatively discussed.