Spatio-temporal Changes Of Terrestrial Near-surface Wind Speed Over Globe In The Last 44 Years And Its Relationship With The Pressure-gradient Force

The investigation of terrestrial near-surface wind speed(SWS)is beneficial to strengthen the understanding of climate change,is beneficial to the development and evaluation of wind energy sources.Consequently,the investigation of terrestrial SWS has important theoretical significance,as well as practical value.Based on the shortcomings of the existing research on wind speed change,this study use the observed terrestrial SWS datasets,reanalysis wind speed datasets to investigate the spatio-temporal characteristics of terrestrial SWS and the potential causes of changes in terrestrial SWS over globe.The correlation analysis,composite analysis,principle component analysis,and dynamical diagnostic analysis etc.,were used to these analysis.The conclusions were shown as follows:The terrestrial SWS mainly showed slowdown over the globe,with the decreasing trend of-0.092 m/(s·10yr).The most significant reduction in terrestrial SWS was located in Eurasia,offshore regions in America,with the decreasing trend can reach-0.3 m/(s·10yr).The explain variance of the first mode in terrestrial SWS can reach 65.11%;meanwhile the spatial pattern of first mode mainly showed positive over globe.The explain variance of the second mode in terrestrial SWS was 18.12%;at the same time,the time series of second mode showed increase during the period 1977-1993 and showed decrease during the period 1993-2016.Moreover,the contribution of zonal wind and meridional wind to the changes of total terrestrial SWS was different.In the middle and high latitude areas of the northern Hemisphere,the trend of wind decline is more pronounced,with some areas reaching-0.2 m/(s·10yr).In Central Europe,Southeast Asia,Central Asia,wind speed changes near the coastline of South America are mainly dominated by wind change,and the contribution of wind speed changes to the change of total wind speed is more than 70%.Wind speed changes in northern and southern Europe,at the junction of Eurasia and on the southeast coast of China are mainly dominated by weft winds,and the contribution of weft wind speed changes to the change of total wind speed is more than 65%.During the study period,the global average annual air pressure gradient force showed a significant downward trend,and the fastest decline in 1990-2005.The most obvious areas of the decline in air pressure gradient force are located on the west coast of North America,northern North America,Central Europe and northern Asia.The first modal variance explain variance of pneumatic gradient force is 14%,and the explain variance of the second modal variance is 10%.The explain variance of the first to second modal variance of the ground-to-wind and the first to second modal variance of the air pressure gradient force are identical,and the two are identical spatial and temporal field distributions,and the linear regression correlation coefficients between them reach 0.98.On the global average,there was a significant positive correlation between the wind and the measured continental winds near the ground,the correlation coefficient reached 0.6,and for each enhancement of 1 m/s,the measured wind speed increased by 0.37/s.The contributions of different regions vary,in the northernmost part of Asia and parts of central South Africa,where the wind winds increase by approximately 0.6/s per 1 m/s.In addition,the measured wind speed on the near ground fluctuates greatly,which means that the measured wind speed will be affected by other factors in addition to the measured wind speed affected by the ground turn wind.The changes of PGF could be attributed to the changes of temperature gradient.The increasing trend of annual mean temperature was 0.256 0C/yr.The increase in temperature induced the decrease of temperature gradient.The annual mean temperature gradient exhibited decreasing trend,every 100km,with the trend coefficient of-0.033?/yr.,which passed the 99%confidence level test.The most significant reduction in temperature was found in mid and high latitudes over the northern Hemisphere,which can reach-0.1 ?/yr in some regions.In addition,there is a positive correlation between temperature gradients and pneumatic gradient forces in most parts of the world,and areas that are significantly positively correlated are mainly in Central Asia,East Asia,North America,parts of Africa and parts of South America.On the global average,the correlation coefficient between temperature gradient and pneumatic gradient force reaches 0.72,and the fluctuation of temperature gradient and pneumatic gradient force with time is basically the same,and there is no significant difference between the two.