Harmonious Inter-decadal Changes of July--August Upper Tropospheric Temperature Across the North Atlantic, Eurasian Continent, and North Pacific

The authors have developed an integral view of the inter-decadal variability of July--August (JA) tropospheric temperature across the entire subtropical Northern Hemisphere. Using reanalysis data and complementary balloon-borne measurements, the authors identify one major mode of variability for the period 1958--2001 which exhibits a significant cooling center over East Asia and warming centers over the North Atlantic and North Pacific. The cooling (warming) signals barotropically penetrate through the troposphere, with the strongest anomalies at 200--300 hPa. The amplitude of the cooling over East Asia is stronger than that of the warming over the North Atlantic (North Pacific) by a factor of 2 (3). This dominant mode exhibits a declining tendency for the entire period examined, particularly before 1980. After the mid-1980s, the tendency has leveled off. Variations of the harmonious change of JA upper tropospheric temperature represented by the principal component of Empirical Orthogonal Function analysis exhibit significant negative (positive) correlations with SST anomalies in the eastern tropical Pacific and the western tropical Indian Ocean (mid-latitude North Pacific). Possible mechanisms are discussed.