ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Ensemble-Based Analysis of Medium-Range Forecast Change and Uncertainty for the 20 July 2016 Severe Heavy Rainfall over North China
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Abstract:
Errors occur for mediumrange forecast of heavy rainfall over North China on 20 July 2016 by subjective forecast of National Meteorological Centre and numerical models. The mediumrange forecast performance of this heavy rainfall event is analyzed based on ECMWF ensemble forecast and T639 ensemble forecast data. The results reveal that: (1) there are obvious changes of location and intensity of rainfall of EC ensemble forecast which is caused by change of forecast for largescale weather system before and after 16 July. Compared to forecast initialized at 20:00 15 July, the ensemble mean circulation on 20 July initialized at 20:00 BT 16 July show that trough at 500 hPa over Hetao Region is deeper whereas downstream ridge is stronger, thus forming the pattern of slowly moving “high pressure to the east and low pressure to the west”. The Yellow River cyclone and midlower level southwest vortex move northward and become stronger. The forecast heavy rainfall is closer to the observed precipitation accordingly. (2) Ensemble sensitivity analysis shows that sensitivity areas are consistent with the spatial pattern of circulation difference before and after the forecast change. The largescale weather systems leading to the change of forecast of heavy rainfall are also sources of uncertainty of mediumrange rainfall forecast. (3) The most sensitive circulation system to precipitation forecast is the Yellow River cyclone. The Yellow River cyclone, the ensemble member is westward and northward and intensity is deeper, the corresponding forecast precipitation amount over BejingTianjinHebei Region is larger.
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Clc Number:
P456,P458
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