Abstract:

Wind fields over the Loess Plateau are very complex due to the complex underlying surface. This paper investigated the effect of subgrid-scale terrain parameterization on near surface wind fields simulated by the WRF over the Loess Plateau. Results indicated that the subgrid-scale terrain standard deviation (σsso) was larger over complex terrain, and the elevation differences between observation sites and the nearest model grids increased with σsso. In summer of 2012, wind speed in the designated region was small. When the influence of subgrid-scale terrain was ignored, the WRF over-estimated wind speed when the observation value was higher, but under-estimated wind speed when the observation value was smaller. The RMSE between the simulated and observed wind speed was small over relatively flat area, while it was larger over complex terrain area. Simulated wind speed was much closer to observations when subgrid-scale terrain parameterization scheme was included in the WRF. Statistics indicated obvious improvement in the accuracy of simulated wind speed. Although simulated wind speed was higher than observations, the diurnal variations were well captured by all the simulations and the lowest bias was achieved when Jimenez’s parameterization scheme was used. Simulations with Jimenez’s parameterization scheme could precisely capture the spatial distribution feature of wind speed, but simulations with Mass’s parameterization scheme had medium improvements at all stations.

Key words: WRF, loess plateau, subgrid-scale terrain, wind field

摘要：

黄土高原特殊的地形导致该地区风场特征复杂，本文以黄土高原为研究对象，通过3组数值模拟试验，探讨次网格地形参数化对WRF模式模拟近地面风场的影响。结果表明：地形越复杂，次网格地形标准差越大，WRF模式中离站点最近格点的海拔高度与站点实际海拔高度差异越大；研究时段内，若不考虑次网格地形影响，观测风速较小时，WRF会高估风速，而观测风速较大时，WRF则低估风速。在相对平坦的地区，模拟风速与观测风速之间的均方根误差较小，地形越复杂时，均方根误差越大。采用次网格参数化方案后，模式对风速的模拟有明显改进，认同指数、准确率、相关性等都有明显提高，模拟误差明显降低。3组试验均能模拟出风速的日变化，但不考虑次网格地形影响时，模拟的风速几乎是观测值的2倍，考虑次网格地形影响后，模拟的风速明显降低，其中Jimenez方案模拟的风速与观测值之间的偏差最小，能更好地描述风速的空间分布特征，而Mass方案仅降低了平原和山谷地区的风速却没有突出山区的高风速，对风速空间变化的模拟不如Jimenez方案。

关键词: WRF, 黄土高原, 次网格地形, 风场