TRENDS IN DAILY WINTERTIME TEMPERATURES IN THE NORTHERN STRATOSPHERE

摘要

Long-term changes in the extrema reached in 31 years of daily northern stratospheric temperatures (T) are discussed. The lowest T reached at any location on any day (T-min) show trends of -1.90 and -1.85 K/decade at 50 hPa and 30 hPa. Increases in the maxima (T-min) are twice as large at 30 hPa as at 50 hPa. The trends are superimposed on a low-frequency variability of T-min with clear peaks between 1975/1976 and 1986/1987 and after 1991/1992. Before the middle 1970s no very low T-min were observed; this is very likely an observational constraint since T = 192 K this may be the lowest detectable value in the earliest years. A more robust measure of the coldness of the lower stratosphere is the area with T < 195 K at 50 hPa, which is relevant for PSC formation. It increased considerably over the 31 years owing largely to the persistence of cold days. [References: 9]