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

Abstract

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 Niña-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 troposphere 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.