BCC第二代气候预测模式系统对2015年一次寒潮过程的预报能力评估

利用BCC第二代气候预测模式系统(BCC_CSM2)的回报试验结果,评估了BCC_CSM2对2015年1月27—31日一次强寒潮过程的次季节预报能力,结果表明:(1)此次寒潮过程主要由新地岛以西的短波槽不断东移发展而形成的,模式能够提前10 d较好地预报过程期间降温以及高空环流形势,相关系数、距平符号一致率以及均方根误差都定量表明模式在10 d左右具有较好的预报能力,但是对降温程度的预报能力随起报时间的延长逐渐降低;(2)为了探讨随起报时间延长模式预报能力降低的原因,从位势倾向方程出发,分析相对涡度平流和温度平流随高度变化发现,在模式提前10 d之内的预报时段内,模式预报的相对涡度平流和温度平流随高度变化与再分析资料的诊断结果基本一致,能够合理预测短波槽的东移和槽脊的强度变化,当预报超过10 d后,模式中相对涡度平流的配置不利于短波槽的东移,模式预报的低层出现暖平流,并随高度增加而减小,不利于槽的加深,使模式预报的环流形势产生偏差,导致模式预报能力降低。

Evaluation of predicting a cold wave event in 2015 based on BCC_CSM2 model

Based on the re-forecast data of the BCC second-generation climate system model BCC_CSM2, the model''s subseasonal predictability of a cold wave event from January 27 to 31, 2015 was examined. Results indicate that the cold wave is developed from a short wave trough moving eastward in the west of the New Earth Island. The model is able to predict the temperature reduction and the evolution of upper air circulation during the cold wave event ahead of ten days. The correlation coefficient, anomaly sign consistency, and the RMSE all indicate that the model exhibit higher skills around ten days. But the forecasting capability for the degree of temperature reduction gradually decreases with the extension of the lead time. In order to explore the reasons for the decrease of forecasting capability of the model with the extension of the lead time, the vorticity advection and the temperature advection variation with height are analyzed using the geopotential height tendency equation. When the lead time is less than ten days, the model''s relative vorticity advection and the variation of temperature advection with height are consistent with those using the reanalysis data, which can reasonably reflect the eastward movement of the short-wave trough and the deepening of the rough ridge. However, when the lead time is over ten days, the model''s relative vorticity advection is not good for the eastward movement of the short-wave trough. Besides, the warm advection appears at the low level, and decreases with height, which is not beneficial for the deepening of the trough. The circulation features predicted by the model are greatly deviated from the observations, resulting in the decreasing forecasting capabilityof the model.