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.

Decadal changes of the wintertime tropical tropospheric temperature and their influences on the extratropical climate

A decadal change of the tropical tropospheric temperature （TT） was identified to occur in the winter of 1997. Compared with that in the former period （1979-1996）, the wintertime TT was significantly high over most of the tropical regions except over the tropical eastern Pacific during the latter period （1997-2014） because the sea surface temperature （SST） exhibited a decadal La Nifia-like pattern after 1997. The warm SST anomalies over the tropical western Pacific facilitated enhanced precipitation and increased heat release to the tropical atmosphere, leading to a warmer tropical tropo- sphere in the latter period. In addition to the mean TT values, the interannual variability of the tropical TT changed in 1997. The leading mode of the tropical TT explained 72.9 % of the total variance in the former period. It led to significant warming over midlatitude North America via a Pacific-North America （PNA）-like wave train and off the coast of East Asia via an anomalous lower-tropospheric anticyclone around the Philippines. The mode remained a similar pattern but explained 85.4 % of the total variance in the latter period, and its location was slightly westward-shifted compared with that in the former period. As a result, the structure of the PNA-like wave train changed, leading to anomalous warming over northwestern North America and enhanced precipitation over the southern North America. Meanwhile, the anomalous lower- tropospheric anticyclone around the Philippines shifted westward, leading to increased precipitation and regional warming over East Asia. The decadal changes of the leading mode of the tropical TT and its influences on the extratropical climate can be attributed to the changes of the tropical SST variability.

Weakening of Indian Summer Monsoon in Recent Decades

The analysis of 43 years of NCEP-NCAR reanalysis data and station observations reveals the connections between tropospheric temperature variations and the weakening of the Indian summer monsoon circulation. The Indian summer monsoon variation is strongly linked to tropospheric temperature over East Asia, showing significant positive correlations of mean tropospheric temperature with all-Indian summer rainfall and the monsoon circulation