Page 30 - 《高原气象》2022年第5期

5 期 孔祥伟等：西北地区东部强降水大尺度数值模式预报空间误差分析 1123

Spatial Deviation Analysis of Heavy Precipitation Forcast of Large Scale

Numerical Weather Prediction in Eastern Northwest China

1
1，2
KONG Xiangwei ，ZHANG Junxia ，YANG Xiaojun ，FU Jiaolan 3
1
（1. Lanzhou Central Meteorological observatory，Lanzhou 730020，Gansu，China；
2. College of Atmospheric Sciences，Lanzhou University/Joint Center of Research and Training for
Weather and Climate Prediction，Lanzhou 730000，Gansu，China；
3. National Meteorological Centre，Beijing 100081，China）

Abstract：Quantitatively examining the spatial deviation of precipitation forecast in numerical models is impor‐
tant to improve the model forecast performance and enhance the ability of forecasters correcting the model fore‐
cast products subjectively. Based on encrypted precipitation observations and 24-hour precipitation data forecast‐
ed by the ECMWF，GRAPES-GFS large-scale numerical models with 36-hour limit from May to September of
2019-2020 over the eastern Northwest China，51 heavy precipitation targets are identified by using the Contigu‐
ous Rain Area technique. According to the features of 500 hPa circulation system，these targets are classified into
low trough type，southwest flow type，and two high shear type. The spatial deviation，including displacement，
intensity，and pattern deviation，of heavy precipitation forecast in the two models are analyzed quantitatively.
The results are as follows：（1）The pattern deviation of precipitation forecast in ECMWF and GRAPES-GFS ac‐
count for the largest proportion of the total deviation，which reach 65. 99% and 63. 72%，respectively，corre‐
sponding with 21. 55% and 20. 31% displacement deviation，and 12. 47% and 15. 97% intensity deviation. Pat‐
tern deviation are mainly related to the activities of the small-and medium-scale convective systems in the warm
zone.（2）The heavy precipitation areas in two models shift more northwestward compared with observations.
Forecast deviation largely depend on the scales of precipitation areas. The precipitation forecast of medium- β
scale heavy precipitation areas in ECMWF is better than GRAPES-GFS，and the medium-α scale rainfall areas
are overestimated in two models. The deviation of maximum precipitation and mean rainfall intensity forecasted
by ECMWF are less than 6%，while are more than 33% in GRAPES-GFS.（3）The maximum precipitation in
low trough type is underestimated by ECMWF，and the area and mean rainfall intensity vary with the precipita‐
tion scale. For southwest flow type，ECMWF's forecast indicates that the area and mean rainfall intensity are
slightly larger，while the maximum precipitation is weaker than observations. The rainfall area in two high shear
type forecasted by ECMWF is most easy to underestimated and even missed，but reasonable results can be seen
in mean rainfall intensity and maximum precipitation. The area，average rainfall intensity，and maximum precipi‐
tation in the two high shear type and southwest flow type are underestimated by GRAPES-GFS.（4）For the dis‐
placement deviation in ECMWF，these are northwestward shift for low trough type and southwest flow type and
northward shift for high shear type. However，in GRAPES-GFS，there are northwestward shift for low trough
type and westward shift for southwest flow type. The displacement deviation are not obvious in two high shear
type.
Key words：The eastern Northwest China；contiguous rain area；spatial deviation；heavy precipitation；large-
scale numerical weather prediction