Inter‐decadal change of the middle‐upper tropospheric land–sea thermal contrast in the late 1990s and the associated Northern Hemisphere hydroclimate

Abstract

Although the middle‐upper tropospheric land–sea thermal contrasts play very important roles in modifying global monsoon, the inter‐decadal influences of the middle‐upper tropospheric land–sea thermal contrasts in the Northern Hemisphere on the global monsoon have not investigated specifically. In this study, it is found that the summer middle‐upper tropospheric zonal land–sea thermal contrast in the Eurasia–Pacific region changed from weak during the late 1980s and earlier and middle 1990s to strong after the late 1990s. This feature indicates a strengthened zonal land–sea thermal contrast during summer, which drives a stronger than normal Northern Hemisphere summer monsoon, with a hypothermal and wet climate over most of the subtropical East Asian and tropical African monsoon regions. In addition, the extensive anticyclonic circulation anomalies together with the less precipitation results in a warm and dry climate over the arid and semiarid regions to the west and north of the monsoon region, such as central Asia, Mongolia, and Northeast Asia. The inter‐decadal change of the middle‐upper tropospheric zonal thermal contrast is also closely associated with the warming trends of the extratropical North Pacific and North Atlantic during summer. However, this link possibly reflects a response of the warming oceans to the local atmospheric variability.