陇中黄土高原垂直感热平流输送对LAS和EC观测感热通量差异的影响

利用"黄土高原陆面过程试验研究(LOPEX)"2010年6月定西站的陆面过程综合观测资料,以造成大孔径闪烁仪(LAS)和涡动相关仪(EC)测量感热通量的差异为切入点,从中尺度垂直感热平流输送过程入手,将垂直感热平流输送的贡献作为地表有效能量的一部分引入EC直接观测的感热通量,对比引入前后LAS和EC测量感热通量的差异大小.结果表明:黄土高原定西观测站近地层大气垂直方向主要表现为向上运动,峰值达到0.074 m·s^-1,为垂直感热平流输送提供了必要的动力条件.尤其该地区处在半干旱区,地表受太阳辐射加热比较显著,近地层温度梯度最大可达0.39 K·m^-1,为产生垂直感热平流提供了能量基础.加入垂直感热平流输送的贡献后,EC地表能量不闭合度的日均值由直接观测的0.30缩小到0.24.修正后,LAS和EC测量的感热通量拟合的线性趋势系数由直接观测时的1.258缩小到1.186,两者差异得以缩小.

Impact of Vertical Sensible Heat Advection on Differences between LAS and EC Measured Sensible Heat Flux over the Loess Plateau in Central Gansu,China

Using the observation data of Experimental Study of Land Surface Processes in Chinese Loess Plateau (LOPEX) for the period of June, 2010 at Dingxi observation station, this article compared the differences between LAS and EC observed sensible heat flux by introducing the vertical sensible heat advection as an effective surface energy to sensible heat flux of EC observation. The results suggested that the mainly air movement at Dingxi observation station is upward with the max value of 0.074 m·s^-1, providing the necessary dynamic conditions for vertical advection. Furthermore, for the site locating at semi-arid areas, the surface is well heated by solar radiation, and that causes a large temperature gradient near surface with a max value of 0.39 K·m^-1, which provides the energy basis for generating vertical advection. When the contribution of vertical sensible heat advection is taken into consideration, the daily average surface energy unclosure of EC reduced from 0.30 to 0.24, and the linear fitting coefficient between LAS and EC measured sensible heat flux reduced from 1.258 to 1.186, which indicates that the differences between LAS and EC measured sensible heat flux could be reduced after the correction.