夏季绿洲生态环境对荒漠背景地表能量过程的扰动

利用观测试验资料,对比分析了夏季典型晴天敦煌绿洲与周围荒漠戈壁背景地表过程的差异,揭示了绿洲生态系统对干旱区荒漠背景地表过程的扰动特征。结果表明:绿洲地表净辐射日平均要高出周围荒漠戈壁背景60 W/m2以上,约占绿洲净辐射的1/4以上。对绿洲高出的净辐射贡献最大的是绿洲相对低的地表长波辐射,其次是较高的太阳总辐射。而绿洲相对较低的大气长波辐射对高出的净辐射有较大的负贡献,特别是地表反射辐射也有很小的负贡献。绿洲高出的地表净辐射主要贡献于加强潜热和地热流量,还有一部分被绿洲地表能量不平衡差额所占,它实际上可能由一般地表热量平衡所不考虑的垂直热量平流来输送。而绿洲明显低于荒漠背景的感热通量则节省了一部分净辐射能量。

The characteristics of spatial disturbance of surface processes in oasis on the background of desert

It is main character in arid area in north west China that desert and gobi are essential landscape and the oases are interspersed.Desert and Gobi effect oases, at the same time the desert and gobi also are effected by oases.Using the observational data in "the Field Experiment on Land-atmosphere Interaction over Arid Region of Northwest China" carried out in Dunhuang of Gansu Province,the differences between the surface energy processes in oasis and those in the near Gobi are analyzed,and the character of spatial disturbance of surface energy processes in Oasis eco-system on the Gobi Background were discovered.As a result,it is shown that the mean net radiation flux on oasis is 60 W/m~2 higher than that in near Gobi,and the margin value is one-fourth of mean net radiation flux on oasis.The peak value of effective long-wave radiation is lower 88W/m~2 and its average value is lower 35W/m~2 on a day.The most important contribution of the margin value is lower surface upward long-wave radiation flux on oasis,is 58.3%;the next is higher global solar radiation over oasis, is 42.7%;lower downward long-wave radiation flux on oasis is a opposite contribution to the margin value,and it is unexpected that the surface reflected radiation flux on oasis contribute a bit opposite to the margin value.The latent flux on oasis is ten times and the soil heat flux is three times as high as those on Gobi.But the sensible heat flux is about lower 50% than that in the near Gobi.In the surface heat budget on oasis,the margin value on oasis mainly distributes to enhancing the latent heat flux and ground heat flux in oasis,and its surplus,which includes what lower sensible heat flux over oasis than that on the near Gobi contributes,is occupied by the surface heat energy balance on oasis.The balance may be caused by the vertical heat advection flux,which is almost absent on its surroundings of Gobi and the common region.Now,we know that low albedo,low sensible heat and higher latent heat is character on oasis by contrast with that on Gobi background.These characteristics are important to maintain the oasis eco-system.But such high latent heat means too high evapotranspiration on the Dunhuang oasis and it is show from other side that the eco-system on the oasis is weak.It remind us we should protect our eco-system and environment.