摘要
利用2017年1、4、7、10月“全球降水观测(global precipitation measurement,GPM)计划”每日08时(北京时)的24 h累计降水量和逐30 min降水量观测产品,从降水量和频率等角度,对同期GRAPES全球模式(GRAPES_GFS)第1(D1)、3(D3)、5天(D5)的全球降水预报性能和偏差特征进行细致评估与分析,且对低纬度暖池和北半球中纬度风暴路径区进行了重点观察,初步探讨了降水预报偏差特征在低纬度和中纬度明显不同的可能原因。结果显示:(1)GRAPES_GFS的D1—D5预报对全球日降水(量和频率)分布描述合理,能准确再现纬向平均降水(量和频率)的典型特征—降水“双峰”极大位于南北纬20°之间,次极大位于南北纬40°—50°地区的特征,以及关键区日降水时、空演变和降水日循环逐日演变的主要趋势特征。(2)低纬度的纬向平均湿日(≥0.1 mm/d)频率预报正偏差很小,但日降水量和强降水日(>25 mm/d)频率预报的正偏差明显、偏差极大值“双峰”位置恰是相应观测极大值所在处(南北纬5°—10°);中纬度的纬向平均日降水量预报基本无偏,但明显的湿日降水频率预报正偏差(20%—30%)和强降水日频率负偏差出现在南北纬40°—60°。降水偏差正、负分布特征随季节和预报时效基本保持不变,预报均方根误差数倍于平均误差,暗示模式降水预报偏差有系统性且性能表现波动较大。(3)日循环中,模式在暖池的降水量预报正偏差缘于降水强度预报偏强,降水频率预报的弱负偏差主要与降水落区预报偏小有关;而模式在北半球风暴路径区降水频率预报的正偏差则是降水落区预报偏大和空报弱降水事件两方面因素造成。(4)模式降水(量和频率)预报偏差特征在低纬度和中纬度的明显差异与模式次网格尺度和网格尺度降水比例失调有关,改进线索指向模式对流参数化方案中深对流的启动和深对流降水量的处理以及对流参数化方案
The performance of the operational global model system(GRAPES_GFS)for day 1(D1)to day 5(D5)precipitation forecasts is evaluated in terms of precipitation amount,frequency and diurnal cycle etc.against observational product of the Global Precipitation Measurement(GPM)data over four months(Jan,April,Jul and Oct)of 2017.Special attention is focused on areas of the Warm Pool(WP)in the Western Pacific and the Storm Track in the Northern Hemisphere(STNH).Results show that:(1)the D1—D5 forecasts reasonably capture global distribution pattern of precipitation.In particular,the model accurately reproduces the typical observed maximum feature of global zonal mean precipitation(amount and frequency)between 20°S—20°N and in latitudes of 40°—50°,and the simulated daily variation and diurnal cycle of precipitation well resemble observations over the WP and the STNH;(2)in the low-latitudes,the"double peaks"of positive forecast bias of daily precipitation amount and frequency of heavy rainfall days(>25 mm/d)occur in the same locations of observed precipitation maximums,while the positive forecast deviation of wet-day(≥0.1 mm/d)frequency is quite small.In the mid-latitudes,the forecast of daily precipitation amount is nearly unbiased,but positive deviation of wet-day frequency and negative bias of heavy rainfall day frequency are obvious in latitudes of 40°—60°.There is almost no change in the bias distribution pattern,and the deviation values vary a little in different seasons and increase from D1 to D5,while RMSE is several times of AME.The above results indicate that the model may have systematic errors in precipitation forecast and the model performance in daily forecast varies widely;(3)in terms of diurnal cycle,the positive bias of prediction amount is due to overprediction in precipitation intensity,and the slight negative deviation of precipitation frequency is attributed to under-prediction of the rainfall coverage in the WP.However,the positive bias of precipitation frequency is resulted from both factor
作者
刘帅
王建捷
陈起英
孙健
LIU Shuai;WANG Jianjie;CHEN Qiying;SUN Jian(Chinese Academy of Meteorological Sciences,Beijing 100081,China;National Meteorological Centre,Beijing 100081,China;Numerical Weather Prediction Center of the China Meteorological Administration,Beijing 100081,China)
出处
《气象学报》
CAS
CSCD
北大核心
2021年第2期255-281,共27页
Acta Meteorologica Sinica
基金
中国气象局GRAPES发展专项(GRAPES-FZZX-2018)。
