Characteristics and causes of surface wind speed variations in Northwest China from 1979 to 2019

摘要

New characteristics of surface wind speed variations in Northwest China and the possible explanations for them have remained undetermined over the recent decades. This study presents the characteristics and possible mechanisms of surface wind speed variations in Northwest China from 1979 to 2019. The results show that the surface wind speed in Northwest China underwent a two-stage change rather than a persistent decline from 1979 to 2019; specifically, it declined significantly before the early 2000s and then increased gradually thereafter. The meridional pressure gradient decrease caused by the meridional temperature gradient reduction corresponded to a decrease in the winter surface wind speed in Northwest China during 1979-2002. The meridional pressure gradient increase caused by the meridional temperature gradient increase was consistent with an increase in the winter surface wind speed in Northwest China during 2003-2019. This suggests that the spatially inhomogeneous variations in surface air temperature in Eurasia's mid-high latitudes may be the main reason for the surface wind speed variations in Northwest China. Furthermore, the decadal strengthening of the East Asian winter monsoon (EAWM) may have resulted in an upward trend of the surface wind speed in Northwest China after the early 2000s by strengthening the Siberian High (SH). Although the variations in the surface wind speed in Northwest China are inconsistent with those in the winter Arctic Oscillation (AO) index, there is a significant negative correlation between them on the interannual timescale. With a negative (positive) AO phase, the surface wind speed in Northwest China increases (decreases) in winter.