基于涡度相关的半干旱区沙丘-草甸水热通量对比分析

Heat and Water Vapor Fluxes of Dune-Meadow Landscape in Semiarid Area Based on Eddy Covariance Measurements

为了解科尔沁地区不同下垫面地-气界面的能量收支、水汽交换过程及其与气象要素的响应关系,利用涡度相关法开路系统、常规微气象观测系统等进行长期定位观测,选取流动半流动沙丘和草甸2种下垫面下的观测资料进行对比分析。结果表明:草甸与沙地潜热通量日变化差异明显,且春秋两季典型晴天更为显著,沙地约为草甸的26.2%和30.5%;夏季沙丘与草甸潜热极值大体持平,冬季2个站点差距缩小,互为上下波动;在冬、春、夏季3个典型晴天中,草甸与沙地感热通量差异显著的起始与终止时间不断提前,累积大于时长分别为19.5 h、16 h、6 h,秋季二者差异的时间不断推后,累积时长缩短;观测通量源区随风向改变而发生变化,风频比例越大,通量源区的贡献距离越长;草甸、沙地蒸散量与降雨呈负相关,雨后日蒸散值分别较晴天偏低14%和40%,晴天,沙地日蒸散量随风速波动呈规律性变化,而较大风速对草甸蒸散发不利。

Open loop system of eddy covariance method and conventional micro-meteorological system were employed in the study for the long-term positioning observation to investigate the energy budget,surface-atmosphere water vapor exchange process and the relationship with meteorological factors in the Horqin Sandy Land,a semiarid area. The primary objective was to compare and analyze the flux data of both sandy dune and meadow area. The results showed that the net radiation on four typical sunny days was low in the morning and evening,it reached the peak value around noon,and its curve was＂parabola-shaped＂. The average maximum appeared during the period of14： 00- 16： 00 pm at all sites in winter,spring,summer and fall. The latent heat flux over meadow was significantly higher than that on sand dune,and even it reached 4 times in spring and autumn. During crop growth season（ in August）,the accumulated latent heat flux reached the highest value in a year,and the extreme value of meadow area was basically equal with that of sand dune. In January,the latent heat flux difference between two sites tended to be smaller and fluctuated in a certain range. In general,the sensible heat flux over a meadow was lower than that over a dune. One thing to be concerned was that the negative sensible heat appeared after 18： 00 and 17： 00 pm in spring and summer over meadow site,respectively. In sunny days of winter,spring and summer,the starting and ending time when the different value between the meadow and sandy land was significant became earlier,but that in autumn was postponed. The source area was changed with the change of wind directions,the higher the proportion of wind frequency was,the longer the contribution distance of source area would be. There was a negative correlation between evapotranspiration of the two underlying surfaces and precipitation,the evapotranspiration values of the two underlying surfaces after rain were 14% and 40% lower than those on sunny day respectively,the daily evapotranspiration was regularly changed with wind speed fluctuation on sunny day,but the high wind speed was unfavorable for evapotranspiration of meadow.