Synergistic regulation of the interdecadal variability in summer precipitation over the Tianshan mountains by sea surface temperature anomalies in the high-latitude Northwest Atlantic Ocean and the Mediterranean Sea

摘要

We explored the interdecadal variability in summer precipitation over the Tianshan mountains and the associated background of atmospheric circulation anomalies. There was a clear interdecadal increase in summer precipitation over the Tianshan mountains during the time period 1961-2016, with lower precipitation from 1961 to 1990 and higher precipitation from 1993 to 2016. The sea surface temperature anomalies in the high-latitude northwest Atlantic and the Mediterranean Sea are partly responsible for the interdecadal variability of precipitation in the Tianshan mountains. The warmer sea surface temperature anomalies in these two regions excite a positive anomaly of geopotential height over the northwest Atlantic and to the north of the Mediterranean Sea, respectively, synergistically modulating the downstream atmospheric circulation near Lake Baikal via the eastward dispersion of Rossby wave energy originating from the northwest Atlantic via the Black Sea. As a result, an interdecadal increase in geopotential height has occurred near Lake Baikal since the 1990s. Corresponding to this interdecadal increase in geopotential height, an anomalous anticyclone appeared near Lake Baikal during 1993-2016, inducing an anomalous easterly flow over the Tianshan mountains. This anomalous easterly flow caused an interdecadal decrease in the eastward export of water vapor on the eastern boundary of the Tianshan mountain region, resulting in an interdecadal increase in the total water vapor budget over the mountains. This has facilitated the interdecadal increase in summer precipitation over the Tianshan mountains since the 1990s.