Impact of Soil Moisture Uncertainty on Summertime Short-range Ensemble Forecasts
To investigate the impact of soil moisture uncertainty on summertime short-range ensemble forecasts (SREFs), a fivemember SREF experiment with perturbed initial soil moisture (ISM) was performed over a northern China domain in summertime from July to August 2014. Five soil moisture analyses from three different operational/research centers were used as the ISM for the ensemble. The ISM perturbation produced notable ensemble spread in near-surface variables and atmospheric variables below 800 hPa, and produced skillful ensemble-mean 24-h accumulated precipitation (APCP24) forecasts that outperformed any single ensemble member. Compared with a second SREF experiment with mixed microphysics parameterization options, the ISM-perturbed ensemble produced comparable ensemble spread in APCP24 forecasts, and had better Brier scores and resolution in probabilistic APCP24 forecasts for 10-mm, 25-mm and 50-mm thresholds. The ISM-perturbed ensemble produced obviously larger ensemble spread in near-surface variables. It was, however, still under-dispersed, indicating that perturbing ISM alone may not be adequate in representing all the uncertainty at the near-surface level, indicating further SREF studies are needed to better represent the uncertainties in land surface processes and their coupling with the atmosphere.
Key wordsensemble forecast soil moisture perturbation probabilistic quantitative precipitation forecast.
为了研究土壤湿度不确定性对夏季短时集合预报的影响, 本研究通过扰动土壤湿度初值, 构建了一组5成员短时集合预报, 对我国北方区域进行了集合预报试验. 5个集合成员分别使用3个研究/业务中心的5套土壤湿度分析资料作为各自的土壤湿度初始场. 试验表明, 土壤湿度初值扰动在近地层至800 hPa大气中产生了较为明显的集合离散度. 24 h累计降水预报的集合平均预报优于每个集合成员. 通过与另一组混合微物理方案集合预报试验相比, 土壤扰动产生的24 h累计降水预报的集合离散度与混合微物理方案扰动相近但略低, 24 h累计降水概率预报的评分互有优劣. 尽管土壤湿度扰动在近地面大气产生了较为明显集合离散度, 但集合离散度仍然偏低, 说明单独扰动土壤湿度初值还不足以反应预报中近地面层的所有不确定性, 有必要进一步研究更加复杂精密的陆面扰动方法.
关键词集合预报 土壤湿度扰动 降水概率预报
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