半干旱区不同下垫面大气湍流通量比较分析

Analysis of Turbulent Flux on Different Underlying Surfaces over Semi-arid Area

为了更深入地认识不同条件下的陆-气相互作用,选取2007年1月至2008年12月兰州大学半干旱气候与环境观测站(Semi-Arid Climate and Environment Observatory of Lanzhou University,SACOL)与中科院吉林通榆观测站的湍流资料,并结合常规气象观测资料,利用Swinbank于1951年提出的涡动相关法分析三种下垫面上的湍流通量,从而定量地描述和认识陆-气相互作用,并比较分析半干旱区不同下垫面热通量和动量通量的日变化与季节变化特征。结果表明:(1)SACOL、草原站和农田站上感、潜热通量的日变化均表现为单峰型,其中感热通量Hs日峰值可分别达到140.3,157.3和144.8 W·m-2;潜热通量LvE日峰值为Hs的40%~75%。(2)夜间热通量主要集中于-22.6~24.2 W·m-2,夜间Hs一年四季均表现为负值,而LvE几乎保持正值。(3)各测站上动量通量τ具有明显日变化,但由于风向、风速差异,通榆地区τ的日峰值可达0.25 kg·m-1·s-2,而SACOL仅有0.08 kg·m-1·s-2。(4)通榆站上τ的日变化具有显著季节差异,春、秋季的日较差远大于其他季。(5)排除热力因子影响,黄土高原下垫面对湍流活动的削弱作用更强,在该下垫面上近地层大气更容易也更快趋于稳定。

In order to understand the land-atmosphere interaction between different conditions more deeply,we take eddy covariance technique proposed by Swinbank in 1951 primarily to analyse the turbulent flux which could describe the land-atmosphere interaction quantificationally on three types of underlying surfaces. We contrast the diurnal and seasonal variations of heat flux and momentum flux on loess plateau,grassland and cropland in semi-arid area by using turbulent data from January 2007 to December 2008,which comes from Semi-arid Climate and Environment Observatory of Lanzhou University（ SACOL）,the grassland and the cropland station in Tongyu. Combined with the conventional meteorological elements,the results showthat：（ 1） At the SACOL,grassland station and cropland station of Tongyu,the diurnal variations of sensible and latent heat flux both showa typical ＂singlepeak＂structure. The peak value of sensible heat flux（ Hs） in SACOL,grassland and cropland is 157. 3 W·m-2,144. 8 W·m-2 and 140. 3 W·m-2,which is the double of latent heat flux（ LvE）.（ 2） The heat flux mainly locate in-22. 6 - 24. 2 W·m-2 at night,and Hs is negative,LvE is positive.（ 3） The diurnal variation of the momentum flux（ τ） shows the same lawin the three station,the daily peak of τ in Tongyu is 0. 25 kg·m-1·s-2,which in SACOL is 0. 08 kg·m-1·s-2.（ 4） The diurnal variation of τ has an obvious difference in difference seasons,the daily range in spring and autumn is bigger than other seasons.（ 5） Except thermal factors,loess plateau has a stronger extinction effect on turbulent,atmosphere will be stable easier and quicker.