两种中尺度模式对甘肃河东暴雨日降水预报偏差精细化评估

Refined assessment of precipitation prediction deviation in stormy days using two mesoscale models in the Hedong Region,Gansu Province

利用2019—2021年暖季(5—9月)甘肃河东20个暴雨日的小时实况和模式数据,用降水强度、频率等要素进行研究,评估了CMA-SH9、CMA-MESO模式在4个子区(甘南高原、陇南、陇东和陇中)的降水日变化预报偏差。结果表明:(1)两种模式在陇南、陇东、甘南高原对≥2.5 mm·h^(-1)和≥5 mm·h^(-1)降水预报能力相当,但在陇中CMA-MESO对≥5 mm·h^(-1)的降水比CMA-SH9更易空报。(2)对≥2.5 mm·h^(-1)降水强度两种模式预报白天偏大,夜间偏小,夜间实况峰值时段偏差最大,陇中、陇东CMA-SH9降水强度预报在大多数时次优于CMA-MESO,陇南夜间CMA-SH9优于CMA-MESO,白天反之;陇南和陇东(甘南高原)CMA-SH9对≥5 mm·h^(-1)降水强度预报整体优于(劣于)CMA-MESO。(3)对≥2.5 mm·h^(-1)降水频率两种模式预报白天偏低,夜间偏高,夜间实况峰值时段偏差最大,CMA-SH9降水频率预报整体优于CMA-MESO;在陇南、陇中和陇东各时次对≥5 mm·h^(-1)降水频率预报偏低,实况峰值时段偏低更明显。(4)在4个子区内两种模式均以位相误差为主,振幅误差小。

In this study,we assess the characteristic bias in the diurnal precipitation forecasts from two models—CMA-SH9 and CMA-MESO—for hourly precipitation forecasts across four subregions in the Hedong Region of Gansu Province(the Gannan Plateau and the Longnan,Longdong,and Longzhong regions).These forecasts were assessed based on rainfall amount and frequency,using observed hourly precipitation data from 20 storm rainy days between May and September 2019-2021 in the same region.The results show the following:(1)Both mod-els have similar forecasting abilities for precipitation amounts of≥2.5 mm·h^(-1) and≥5 mm·h^(-1) in the Gannan Plateau and the Longnan and Longdong regions.However,the CMA-MESO model facilitates easier precipitation forecasts of≥5 mm·h^(-1) in the Longzhong region than the CMA-SH9 model.(2)For rainfall≥2.5 mm·h^(-1),both models overestimate intensity during the day and underestimate it at night compared to observations,with signifi-cant deviations mostly occurring around the peak time of observed rainfall at night.The CMA-SH9 model gener-ally outperforms the CMA-MESO model in predicting rainfall intensity in the Longzhong and Longdong regions most times of the day.In the Longnan region,the CMA-SH9 model performs better than the CMA-MESO model in predicting rainfall intensity at night but performs worse during the day.For rainfall≥5 mm·h^(-1),the CMA-SH9 model consistently predicts rainfall intensity better than the CMA-MESO model in the Longnan and Longdong re-gions,but worse in the Gannan Plateau,most of the time.(3)For rainfall≥2.5 mm·h^(-1),both models predict high-er rainfall frequency during the day and lower frequency at night compared to observations,with significant devi-ations mostly occurring around the peak time of observed rainfall at night.The CMA-SH9 model mostly outper-forms the CMA-MESO model in predicting rainfall frequency.For rainfall≥5 mm·h^(-1),both models underesti-mate rainfall frequency compared to observations in the Longnan,Longzhong,and Longdong regions,with the negative forecast deviation more pronounced around the peak time of observed rainfall at night.(4)Phase error are predominant across the four subregions for both models,while amplitude error was minimal.