Spatiotemporal Variability Of Surface Wind Speed And Its Influencing Factors In The Middle And Lower Reaches Of The Yangtze River

Under the background of global warming,it is recognized that the temporal and spatial characteristics of surface wind speed variation and the intrinsic relationship between this characteristics and the related influencing factors in the middle and lower reaches of the Yangtze River,which is helpful to improve the analysis and prediction of surface wind speed and has theoretical and practical significance for exploitation of wind energy in this area.Based on the daily wind speed data of 72 meteorological stations,Landsat 8 images in this area and reanalysis data in different areas,the temporal and spatial characteristics of surface wind speed and its influencing factors from 1970 to 2015 are analyzed by using the linear regression estimation,modified Mann-Kendall(MMK)trend test,correlation analysis,multiple linear regression and ensemble empirical mode decomposition(EEMD).The main results are as follows:(1)The annual wind speed in the middle and lower reaches of the Yangtze River has a significant decline,and the downward trends of the seasonal mean wind speed and maximum wind speed or the seasonal lower wind days upward trend are larger in winter and the smallest in summer.Spatially,the annual mean wind speed and maximum wind speed of most stations present significant downward trends and the winter speed wind has download trend in most stations in this area.Moreover,the decreasing trends of annual mean wind speed and maximum windspeed or the increasing trend of the annual lower wind days have a spatial patterns that the trends increasing gradually from northwest to southeast over this area.(2)We choose the temperature data in the areas of low,medium and high latitude area with same longitude range of study area,in order to study the relationship between wind speed and temperature gradient,and we find that the annual temperature gradient decreasing rate are the largest in the low-high latitude area,and the least in the middle-high latitudes area,the seasonal temperature gradients weakening trends in both the two areas are the largest in autumn and the least in summer.In addition,the annual temperature gradient in the lower-middle latitude area have stronger correlation with the annual wind speed.When we study the skill of temperature gradient in explaining wind speed inter-annual variability,we find that annual maximum wind speed can be explained 28% by temperature gradient in the low-high attitude area,which indicates that the annual mean temperature gradient in the5low-high latitudes has a greater impact on the variability of wind speed(especially the annual maximum wind speed)over this area.(3)The relationship between wind speed and monsoon circulation on multiple scales are discussed by using EEMD,which decomposed the annual mean wind speed,maximum wind speed,lower wind days and Asian monsoon index,and a significant negative correlation betweenwind speed and the Asian monsoon is found on the component with a period of more than 30 years.The relationship between the annual monsoon and annual wind speed present a same spatial pattern that the correlation are gradually increasing from the northwest to the southeast.On the residue,area annual mean wind speed and lower wind days are significant correlated to the Asian monsoon,and the Asian winter monsoon have a larger impact on the wind speed variation over southeast part of this area(Poyang Lake Basin)than the Asian summer monsoon.(4)According to the underlying surface condition,we classified the meteorological stations in the study area.we find that trends of annual and seasonal mean wind speed,maximum wind speed and lower wind days of urban stations are larger than rural.Moreover,urbanization have major contribution to the annual mean wind speed and lower wind days over the middle and lower reaches of Yangtze River,it indicates that urbanization have a significant impact on the wind speed.