基于WRF/CALMET的近地面精细化风场的动力模拟试验研究

Dynamic Modeling Study of Highly Resolved Near-Surface Wind Based on WRF/CALMET

本文利用中尺度动力模式WRF和诊断模式CALMET对琼州海峡的两次冷空气过程的近地层风场进行模拟和诊断,所用的资料是美国NCEP再分析FNL资料。WRF模式第一至第四层网格的水平距离分别是27、9、3和1 km,并用WRF-1 km场以单向嵌套模拟方式降至200 m,同时以WRF-1 km预报场作为CALMET初猜场降尺度诊断至200 m。分别用CALMET-200 m风场、WRF-1 km风场和WRF-200 m风场,3个风场的风速、风向与沿琼海海峡分布的21个测站(其中6个测风塔)观测资料进行检验比较分析。主要结论是:(1)CALMET-200 m的风速RMSE明显小于另外两组试验,风向RMSE总体上差异不大;在60~80 m高度上也没有明显差异。(2)在0~8 m·s^(-1)风速,10 m高度上CALMET-200 m风场诊断结果最好,风速平均偏差值从4~0 m·s^(-1),WRF的两组试验平均偏差值比CALMET-200 m结果大约2 m·s^(-1),风向上表现为偏差的分布更加集中;60~80 m高度上,CALMET-200 m诊断效果与WRF-1 km模拟效果相当,但是冷空气时段内WRF-200 m的风速要远远差于另外两组试验;而3组试验的风向并无大的差异。(3)WRF/CALMET模式系统在非冷空气活动时段内的风速风向模拟诊断偏差更小,说明其在层结相对较稳定时模拟诊断的准确度更高。

Two cold air events that happened in Qiongzhou Channel were modeled by mesoscale dynamic model WRF and diagnostic model CALMET,and the research focuses on the near-surface wind.Horizontal grid spaces of four nests in WRF model are 27 km,9 km,3 km and 1 km respectively.The fourth nest with 1 km grid space of CALMET and the fifth nest in WRF is set as model initial field for down grid space to 200 m,so as to get the final field which is able to fulfill the resolution required.Wind speed and direction of CALMET-200 m,WRF-1 km and WRF-200 m are contrasted with the observed winds at 21 observing stations(including 6 anemometer towers) distributed in the two sides of the Qiongzhou Channel.The main conclusions are as follows:(1) CALMET-200 m speed RMSE is much less than the two other experiments with time going,but there is not any notable difference in wind direction RMSE.In the height of 60— 80 m,RMSE can not show any difference in wind direction,either.(2) At 10 m height,CALMET-200 m wind is diagnosed to be the best with the average error varing from 4 m · s^(-1) to 0 m · s^(-1).The average errors of the other two experiments are about 2 m · s^(-1) bigger than CALMET-200 m.The distribution of errors is more concentrated in direction.In 60 — 80 m height,the three experiments have almost the same results.But the result of WRF-200 m wind speed shows worse than the results of the other two experiments,while not differences in wind direction are found in the three experiments.(3) Smaller wind speed and direction average errors of WRF/CALMET system in non-cold air condition show that the system can perform better when the atmospheric stratification is relatively stable.