Using the Adjoint-Based Forecast Sensitivity Method to Evaluate the Observations of Wind Profile Radar and Microwave Radiometer Impacts on a Model Forecast
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摘要: 同化大量观测资料可以有效地改进模式预报结果,但不同观测对预报的影响有着显著差异,合理评估观测对预报的贡献是数值模式中最具挑战性的诊断之一。本文采用基于伴随的预报对观测的敏感性(Forecast Sensitivity to Observation,简称FSO)方法,构建WRFDA(Weather Research and Forecasting model’s Data Assimilation)框架下的WRFDA-FSO系统。基于2019年9月超大城市项目在北京地区获取的风廓线雷达(Wind Profile Radar,简称WPR)和地基微波辐射计(Microwave Radiometer,简称MWR)观测数据,利用WRFDA-FSO系统,开展观测对WRF模式12 h预报的影响试验,并分析风温湿观测对预报的贡献。结果表明:(1)同化的观测资料(MWR、WPR、Sound、Synop和Geoamv)均减小了WRF模式12 h预报误差,对预报为正贡献,其中MWR观测对预报的影响最大,WPR风场观测对预报的改进效果优于Sound的风场观测。(2)WPR的U、V观测和MWR的T、Q观测中,V观测和T观测对预报的正贡献值更高,对预报的改进效果更优。(3)WPR和MWR多数高度层的观测均减小了预报误差,对预报为正贡献,其中MWR的T观测对预报的正贡献主要位于近地面800 hPa以下。Abstract: Many assimilated observations can effectively improve the results of a model forecast. However, there are significant differences in the effects of various observations on the forecast. It is one of the most challenging diagnostics in numerical models to reasonably evaluate the observation contribution to the forecast. In this paper, the weather research and forecasting model’s data assimilation (WRFDA) and forecast sensitivity to observation (FSO) system was constructed in WRFDA by the method of adjoint-based FSO. Based on wind profile radar (WPR) and ground-based microwave radiometer (MWR) data obtained by the mega city project in Beijing in September 2019, the experiments on the impact of observations on the 12 h forecast of the WRF model are carried out using the WRFDA-FSO system. The contribution of wind, temperature, and humidity observations to the forecast is analyzed. The results show the following: (1) In general, the assimilated observations (MWR, WPR, Sound, Synop, and Geoamv) reduce the 12 h forecast error of the WRF model and make a positive contribution to the forecast. Among these, MWR observations have the greatest impact on the forecast, and the improvement of WPR observations on the forecast is better than that of wind field observations of sound. (2) Among the U and V observations of WPR and temperature and specific humidity observations of MWR, the positive contribution value of V observations and temperature observations to the forecast is higher, and the effect of improving the forecast is better. (3) The WPR and MWR observations, at most levels, reduce the forecast error and are a positive contribution to the forecast. The positive contribution of temperature observations is mainly below 800 hPa near the ground.
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图 1 2019年9月(a)00时(协调世界时,下同)和(b)12时观测对预报的影响(
$ \Delta e $ ,单位:103 J kg−1)及其近似估计($ \delta e $ ,单位:103 J kg−1)的时间序列Figure 1. Time series of the impact of observation on the forecast (
$ \Delta e $ , units: 103 J kg−1) and its approximate estimation ($ \delta e $ , units: 103 J kg−1) at (a) 0000 UTC and (b) 1200 UTC in September 2019图 2 2019年9月(a)00时和(b)12时不同观测的站点观测对预报的贡献及其位置分布(红色表示该站点观测对预报负贡献,蓝色表示该站点观测对预报正贡献;图例中“/”前后的数字分别表示该观测的正贡献站点数和总站点数)
Figure 2. Contribution of the station observation with various observations to the forecast and its location distribution at (a) 0000 UTC and (b) 1200 UTC in September 2019 (red indicates a negative contribution of the station observation to the forecast, and the blue indicates a positive contribution of the station observation to the forecast; the numbers before and after “/” in the legend represent the number of positive contribution stations and total stations of the observation respectively)
图 4 2019年9月00时和12时北京地区7站点(HD、YQ、HR、MY、PG、DX和XYL)的(a)WPR观测和(b)MWR观测对预报误差的平均贡献(单位:102 J kg−1)。HD:海淀,YQ:延庆,HR:怀柔,MY:密云,PG:平谷,DX:大兴,XYL:霞云岭
Figure 4. Average contribution (units: 102 J kg−1) of (a) WPR observations and (b) MWR observations to the forecast error at seven stations, which are Haidian (HD), Yanqing (YQ), Huairou (HR), Miyun (MY), Pinggu (PG), Daxing (DX), and Xiayunling (XYL) in Beijing at 0000 UTC and 1200 UTC in September 2019
图 5 2019年9月00时观测误差σ≤3且新息增量|δy|>4的WPR(a)U观测和(b)V观测对应的对预报误差的贡献(单位:102 J kg−1)与新息增量(单位:m s−1)的散点图(黑色表示该观测对预报负贡献,灰色表示该观测对预报正贡献)
Figure 5. Scatter plot of forecast error contribution (units: 102 J kg−1) and innovation increment (units: m s−1) corresponding to (a) U observations and (b) V observations of WPR with observation error less than or equal to 3 and innovation increment greater than 4 (σ≤ 3 and |δy|>4) at 0000 UTC in September 2019 (black indicates a negative contribution of the observation to the forecast, and gray indicates a positive contribution of the observation to the forecast)
图 6 2019年9月00时MWR的T观测对应的(a)对预报误差的贡献(单位:103 J kg−1)、(b)分析增量(单位:K)、(c)新息增量(单位:K)以及(d)观测误差(单位:K)随高度的分布
Figure 6. The distribution of (a) a forecast error contribution (units: 103 J kg−1), (b) an analysis increment (units: K), (c) an innovation increment (units: K), and (d) an observation error (units: K) with a height corresponding to temperature observations of MWR at 0000 UTC in September 2019
表 1 剔除近似结果不准确的时次前后各观测资料对预报误差的贡献统计(单位:104 J kg−1)
Table 1. Statistics of contributing various observations to the forecast error before and after eliminating inaccurate approximate results (units: 104 J kg−1)
观测资料 00时对预报误差的贡献 12时对预报误差的贡献 剔除前 剔除后 剔除前 剔除后 MWR −117.06 −128.38 11.89 −62.56 WPR 5.88 −12.75 −125.16 −26.30 Sound −26.07 −45.37 −82.87 −25.41 Synop −14.90 −23.14 −26.71 −42.30 Geoamv −0.77 −0.58 0.27 −0.30 表 2 2019年9月00时和12时廓线观测对预报误差的平均贡献(单位:J kg−1)统计
Table 2. Statistics of the average contribution of profile observations to the forecast error (units: J kg−1) at 0000 UTC and 1200 UTC in September 2019
观测 时次 观测对预报误差平均贡献/J kg−1 U V T Q WPR 00时 15.09 −80.49 − − 12时 −94.35 −127.96 − − MWR 00时 − − −468.49 −72.34 12时 − − −286.58 −17.00 Sound 00时 −8.73 −38.06 −75.78 −88.89 12时 −30.75 −44.42 −30.36 −8.55 表 3 2019年9月00时和12时不同高度层WPR观测对预报误差的平均贡献(单位:J kg−1)统计
Table 3. Statistics of the average contribution of WPR observations at various altitudes to the forecast error (units: J kg−1) at 0000 UTC and 1200 UTC in September 2019
高度层 00时对预报误差的
平均贡献/J kg−112时对预报误差的
平均贡献/J kg−1U V U V <500 m −129.32 −289.43 105.27 −497.88 500~1000 m 23.99 −60.47 −248.26 −300.04 1000~1500 m 216.62 −37.83 −80.44 −188.43 1500~2000 m 180.83 −135.84 −153.71 −144.17 2000~3000 m −49.26 −103.49 −99.29 −102.72 3000~4000 m −156.17 −38.77 −64.03 −20.35 ≥4000 m −61.11 −21.52 −33.31 12.6 表 4 2019年9月00时和12时不同高度层MWR观测对预报误差的平均贡献(单位:J kg−1)统计
Table 4. Statistics of the average contribution of MWR observations at various altitudes to the forecast error (units: J kg−1) at 0000 UTC and 1200 UTC in September 2019
高度层 00时对预报误差的
平均贡献/J kg−112时对预报误差的
平均贡献/J kg−1T Q T Q >900 hPa −1949.85 −77.67 −919.90 −51.68 800~900 hPa −580.04 −132.18 −419.22 23.19 700~800 hPa 356.33 −1.47 −163.18 −90.48 600~700 hPa 144.00 −41.48 28.37 90.92 500~600 hPa −5.21 55.16 10.35 −13.02 400~500 hPa −7.08 −97.08 2.40 −21.19 ≤400 hPa 6.33 −130.80 4.46 −39.21 表 5 2019年9月00时WPR观测对预报误差的贡献(单位:J kg−1)分类统计
Table 5. Classified statistics of the contribution of WPR observations to the forecast error (units: J kg−1) at 0000 UTC in September 2019
U观测 负贡献(×103J/kg) / 观测数 正贡献(×103J/kg) / 观测数 |δy|>4 |δy|≤4 |δy|>4 |δy|≤4 σ≤3 148.75 / 37 157.99 / 730 −76.35 / 74 −195.55 / 969 σ>3 0.12 / 4 0.92 / 36 −3.16 / 17 −2.43 / 80 V观测 负贡献(×103J/kg) / 观测数 正贡献(×103J/kg) / 观测数 |δy|>4 |δy|≤4 |δy|>4 |δy|≤4 σ≤3 61.40 / 28 100.50 / 697 −35.13 / 46 −281.52 / 1039 σ>3 0.14 / 3 0.87 / 49 −1.89 / 10 −1.98 / 75 表 6 2019年9月00时 MWR观测对预报误差的贡献(单位:J kg−1)分类统计
Table 6. Classified statistics of the contribution of MWR observations to the forecast error (units: J kg−1) at 0000 UTC in September 2019
T观测 负贡献(×103J/kg) / 观测数 正贡献(×103J/kg) / 观测数 |δy|>2 |δy|≤2 |δy|>2 |δy|≤2 σ≤1 50.81 / 39 309.20 / 197 −308.19/ 41 −932.91 / 285 σ>1 101.56 / 418 71.54 / 558 −287.15/ 305 −121.72 / 541 Q观测 负贡献(×103J/kg) / 观测数 正贡献(×103J/kg) / 观测数 |δy|>2 |δy|≤2 |δy|>2 |δy|≤2 σ≤1 19.76 / 10 89.65 / 474 −4.79 / 2 −235.19 / 788 σ>1 73.84 / 45 55.41 / 384 −49.06 / 85 −116.53 / 516 -
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