Variability and trends of near-surface wind speed over the Tibetan Plateau:The role played by the westerly and Asian monsoon

Near-surface wind speed exerts profound impacts on many environmental issues,while the long-term(≥60 years)trend and multidecadal variability in the wind speed and its underlying causes in global high-elevation and mountainous areas(e.g.,Tibetan Plateau)remain largely unknown.Here,by examining homogenized wind speed data from 104 meteorological stations over the Tibetan Plateau for 1961-2020 and ERA5 reanalysis datasets,we investigated the variability and long-term trend in the near-surface wind speed and revealed the role played by the westerly and Asian monsoon.The results show that the homogenized annual wind speed displays a decreasing trend(-0.091 m s^(−1)per decade,p<0.05),with the strongest in spring(-0.131 m s^(−1)per decade,p<0.05),and the weakest in autumn(-0.071 m s^(−1)per decade,p<0.05).There is a distinct multidecadal variability of wind speed,which manifested in an prominent increase in 1961-1970,a sustained decrease in 1970-2002,and a consistent increase in 2002-2020.The observed decadal variations are likely linked to large-scale atmospheric circulation,and the correlation analysis unveiled a more important role of westerly and East Asian winter monsoon in modulating near-surface wind changes over the Tibetan Plateau.The potential physical processes associated with westerly and Asian monsoon changes are in concordance with wind speed change,in terms of overall weakened horizontal air flow(i.e.,geostrophic wind speed),declined vertical thermal and dynamic momentum transfer(i.e.,atmospheric stratification thermal instability and vertical wind shear),and varied Tibetan Plateau vortices.This indicates that to varying degrees these processes may have contributed to the changes in near-surface wind speed over the Tibetan Plateau.This study has implications for wind power production and soil wind erosion prevention in the Tibetan Plateau.

Shifting of summertime weather extremes in Western Europe during 2012-2020

Over the past decades,droughts and heatwaves frequently appeared in Western Europe(45°-65°N,10°W-20°E)during boreal summer,causing huge impacts on human society and ecosystems.Although these extremes are projected to increase in both frequency and intensity under a warming climate,our knowledge of their interdecadal variations and causes is relatively limited.Here we show that the droughts and heatwaves in Western Europe have shifted in their trends in the last decade:for 1979-2012,wind speed and precipitation have both strengthened in Western Europe;for 2012-2020,however,Western Europe have experienced declined wind speed,decreased precipitation,and higher air temperature,leading to more frequent droughts and heatwaves there.Recent changes in the WE climate and extremes are related to the variations of the North Atlantic westerly jet stream.In 1979-2012(2012-2020),the westerly jet stream shifted equatorward(poleward),which enhanced(reduced)transportation of water vapor fluxes from the North Atlantic Ocean to the European land areas,resulting in wetter(drier)surface in Western Europe.Further analysis suggests that phase changes in the Pacific Decadal Oscillation could have played a key role in regulating the position of the jet stream,providing important implications for decadal predictions of the Western Europe summertime climate and weather extremes.