The Stratospheric Evolution of Sudden Warmings in 1969–74 Determined from Measured infrared Radiation Fields

Abstract

Radiance measurements made by the Satellite Infrared Spectrometers (SIRS A and B) and Vertical Temperature Profile Radiometers (VTPR) in 1969?74 comprise a basically uniform observational data source, in view of the similarity of the transmittance weighting functions for the stratospheric channels of these instruments. Hemispheric radiance maps of measurements in the 669 and 678 cm?1 channels are used to depict the evolution of major stratospheric warmings in the 1969?70, 1970?71 and 1972?73 winters. These warnings are indicated to have arisen from the interaction of eastward-travelling thermal waves with a standing wave in eastern Siberia. Sudden warming in the Arctic was related to the poleward migration of the resultant thermal systems. In these events the arctic mean stratospheric temperature increased by about 30°C in 8 days, but local increases were at least twice as great in the upper (196?70 and 1970?71) or middle (1972?73) stratosphere. The polar vortex breakdown is illustrated with the aid of conventional 10-mb map analyses and 2-mb data based on isobaric layer thicknesses derived from the radiance maps. A preliminary description of a late winter warming in 1973?74 is also given. Radiance patterns associated with minor and major events are distinguished, and during the 1973?74 winter both types are described within the context of repeating oscillations in the thermal structure. In all cases observed, major warmings were associated with the occurrence of horizontal radiance gradients of 15 mW (m2sr cm?1) (10°lat)?1 in both radiation channels.