Comparison of different land-surface perturbation methods in short-range ensemble forecasts

Abstract

In order to compare the sensitivity of short-range ensemble forecasts to different land-surface parameters in the South China region, three perturbation experiments related to the land surface model (LSM), initial soil moisture (ISM), and land–atmosphere coupling coefficient (LCC) were designed, and another control experiment driven by the Global Ensemble Forecast System (GEFS) was also performed. All ensemble members were initiated at 0000 UTC each day, and integrated for 24 h for a total of 40 days from the period 1 April to 10 May 2019 based on the Weather Research and Forecasting model. The results showed that the perturbation experiment of the LSM (LSMPE) had the largest ensemble spread, as well as the lowest ensemble-mean root-mean-square error among the three sets of land-surface perturbed experiments, which indicated that it could represent more uncertainty and less error. The ensemble spread of the perturbation experiment of the ISM (ISMPE) was generally less than that of LSMPE but greater than that of LCCPE (the perturbation experiment of the LCC). In particular, although the perturbation of the LCC could not produce greater spread, it had an effective influence on the intensity of precipitation. However, the ensemble spread of all the land-surface perturbed experiments was smaller than that of GEFSPE (the control experiment). Therefore, in future, land-surface perturbations and atmospheric perturbations should be combined in the design of ensemble forecasting systems to make the model represent more uncertainties.摘要为了比较不同陆面扰动方法对短时集合预报的影响, 本研究设计了陆面模式扰动实验 (LSMPE), 初始土壤湿度扰动实验 (ISMPE), 陆面-大气耦合系数扰动实验 (LCCPE) 以及大气扰动对照实验 (GEFSPE). 结果表明, 在三组陆面扰动实验中, LSMPE能代表最大的不确定性且误差最小;ISMPE的离散度要比LCCPE稍大, 但是耦合系数的减弱能有效降低区域平均降水量.然而, 所有陆面扰动实验产生的离散度均小于GEFSPE, 这表明未来有必要将陆面扰动与大气扰动相结合, 以使得模式能代表更多的不确定性.