卫星遥感结合气象资料计算的中国干旱区夏季地面感热特征

Characteristics of the surface sensible heat flux calculated with the aid of satellite remote sensing and field observations over the arid region of northwest China in summer

选用美国国家海洋和大气局(NOAA)系列卫星观测的1982-2006年历年夏季每半月合成的归一化差值植被指数(NDVI)数据资料和针对我国西北干旱区不同下垫面的Ch-INDV参数化关系式,计算了我国110°E以西/35°N以北区域内84个气象站历年夏季各月的地表热力输送系数Ch值和地面感热通量序列,并将其与ERA-40再分析感热资料进行了比较分析。随后,通过数理统计和经验正交函数(EOF)分析方法,研究其时空分布的基本特征和异常变化的演变规律及其东、西部地面感热年际变化的差异。主要结论为:(1)我国西北干旱区夏季地面感热通量实际计算值与ERA-40再分析感热资料相比,两者在值的大小、分布形势和年际变化趋势上均较一致,但感热实际计算值的空间分布更加明显地突出了各气象站所在区域的局地特征。(2)对西北干旱区夏季地面感热EOF分析表明,第一模态反映了全场一致的空间变化,第二和第三模态在干旱区东部和西部区具有不同的南北反向或东西反向的空间变化。第一和第二主分量有较明显的年代际或更长时间尺度的周期变化,第三主分量的年际变化较明显。(3)西北干旱区东部和西部夏季地面感热输送具有相反的年际变化趋势,干旱区东部呈逐年增加的趋势,而西部表现出显著的逐年减弱的趋势,气候倾向率分别为0.34和-2.08 W.m-2.(10 a)-1。(4)西北干旱区夏季地面感热输送具有较明显的年代际变化特征。20世纪80年代,地面风速比气候平均值偏大使得地面感热输送整体偏强;90年代,地面风速和地气温差比气候平均值均偏小使这一时期的地面感热输送整体偏弱;21世纪初几年,西北地区中部的感热输送偏弱,东、西两边除个别站外均偏强,这主要由新疆西部和内蒙古部分地区的地气温差迅速拉大而成。

The monthly surface thermal transfer coefficients and sensible heat fluxes of 84 meteorological stations in the arid region of northwest China in summer are calculated with the aid of the normalized difference vegetation index(NDVI)data from 1981 to 2006 observed by National Oceanic and Atmospheric Administration(NOAA)remote sensing satellites,Ch-INDV parametric relational expressions and conventional observations of meteorological stations.Then,the calculated values of the surface sensible heat flux in summer are compared with ERA-40 reanalysis data.Finally,the basic climatic features of the surface sensible heat flux in summer are analyzed and the differences in the changes of the surface sensible heat fluxes between eastern and western parts of the arid region of northwest China are studied using mathematical statistics and empirical orthogonal function(EOF) methods.The main conclusions are as follows:(1)The surface sensible heat fluxes calculated by the observations of conventional meteorological stations and ERA-40 reanalysis data are uniform on magnitude and in both distribution situations and the interannual change tendencies.But the spatial distribution of the calculated values can obviously reveal the local climate characteristics of the surface sensible heat flux in the regions where the weather stations are located.This Paper has a big improvement compared with reanalysis data and the past studies,because in the process of the surface sensible heat fluxes computation not only has considered the scientific question of surface thermal transfer coefficient Ch value in the arid region of northwest China,but also selected more conventional observations of meteorological stations.(2)The empirical orthogonal function(EOF)analysis of the surface sensible heat flux in summer shows that the first eigenvector of EOF displays unanimous space variation and the second and third eigenvectors have opposite space variation from east to west or from north to south.Furthermore,the first and second models have obvious interdecadal variation periods and the interannual variation of the third model is more obvious.(3)Taking 97.5°E as the boundary,the eastern and western parts of northwest arid region have different interannual variation trends in summer.The surface sensible heat transfer of arid region's eastern part increases gradually year by year.But,western part is contrary to eastern part and both climate tendency rates are 0.34 and-2.08 W·m-2·(10a)-1.(4)The surface sensible heat transfer in arid region of northwest China has an obvious interdecadal change in summer.All field is strong(weak)in 1980s(1990s),which is because the ground wind speed is bigger than that of the climate average value in 1980s and the ground wind speed and the ground and air temperature difference are smaller than that of the climate average value in 1990s.After 2000,the surface sensible heat transfer in middle part of arid region of northwest China became weak,but that was strong in eastern and western parts except individual stations.This is mainly because the ground and air temperature difference in the western part of Xinjiang Autonomous Region and in parts of Inner Mongolia Autonomous Region increased quickly.