Hsieh Cheng-I, Katul Gabriel
Department of Bioenvironmental Systems Engineering, National Taiwan University, Taipei, 10617, Taiwan.
Int J Biometeorol. 2009 Jan;53(1):87-100. doi: 10.1007/s00484-008-0193-0. Epub 2008 Nov 26.
This study investigated a two-dimensional Lagrangian stochastic dispersion model for estimating water vapor fluxes and footprint over homogeneous and inhomogeneous surfaces. Over the homogeneous surface, particle trajectories were computed from a 2-D Lagrangian model forced by Eulerian velocity statistics determined by Monin-Obukhov similarity theory (MOST). For an inhomogeneous surface, the velocity and atmospheric stability profiles were computed using a second-order Eulerian closure model, and these local profiles were then used to drive the Lagrangian model. The model simulations were compared with water vapor flux measurements carried out above an irrigated bare soil site and an irrigated potato site. The inhomogeneity involved a step change in surface roughness, humidity, and temperature. Good agreement between eddy-correlation-measured and Lagrangian-model-predicted water vapor fluxes was found for both sites. Hence, this analysis demonstrates the practical utility of second-order closure models in conjunction with Lagrangian analysis to estimate the scalar footprint in planar inhomogeneous flows.
本研究调查了一种二维拉格朗日随机扩散模型，用于估算均匀和非均匀表面上的水汽通量及足迹。在均匀表面上，粒子轨迹由二维拉格朗日模型计算得出，该模型由莫宁-奥布霍夫相似理论（MOST）确定的欧拉速度统计量驱动。对于非均匀表面，使用二阶欧拉闭合模型计算速度和大气稳定度剖面，然后将这些局部剖面用于驱动拉格朗日模型。将模型模拟结果与在灌溉裸土场地和灌溉马铃薯场地之上进行的水汽通量测量结果进行了比较。这种非均匀性涉及表面粗糙度、湿度和温度的阶跃变化。在两个场地均发现涡度相关测量的水汽通量与拉格朗日模型预测的水汽通量之间具有良好的一致性。因此，该分析证明了二阶闭合模型与拉格朗日分析相结合在估算平面非均匀流中标量足迹方面的实际效用。
