Varied spatiotemporal changes in wind speed over the Tibetan Plateau and its surroundings in the past decades

The means and changes of annual and monthly wind speed and their extremes over the Tibetan Plateau and its surroundings (TPS) in 1970-1999, 2000-2005 and 2006-2015 are investigated. The correlations between eight atmospheric circulation indices and wind speed variables are also investigated for possible mechanisms of wind speed change over the region. The study shows that the strongest wind appears during February-June, whereas the weakest wind appears in October-January. Weak annual extreme wind concentrates in the southern Gansu, the central Sichuan, the western Yunnan, and near the boarders of Qinghai, Tibetan Autonomous Region and Sichuan. Strong annual extreme wind occurs in the western and central Xinjiang, the central Tibetan Autonomous Region, and the western Qinghai and Gansu. Above 3,600 m, mean and extreme wind speed increases significantly with elevation. Monthly and annual mean wind speed show negative trends over the TPS in 1970-1999 as well as in 2006-2015 but to a lesser extent while 2000-2005 witnesses increasing wind speed. During 1970-1999, Tibetan Plateau High and westerlies respectively show the strongest negative and positive effects on wind speed changes but their influences weaken in 2000-2015 for which Western Pacific Subtropical High and Indian Summer Monsoon appear to play a more important role. The observed decreasing wind speed in 1970-1999 and 2006-2015 is largely due to decreasing zonal and meridional wind speed while for 2000-2005, the observed increasing wind speed is related to the increasing meridional wind speed.