Deviation characteristics in intelligent grid forecast of flood season precipitation in Hedong area of Gansu based on CRA spatial forecast verification

doi:10.11755/j.issn.1006-7639-2024-06-0976

Abstract

Abstract:

It is of great significance to study the deviation characteristics in intelligent grid forecasting of precipitation during the flood season in Hedong area of Gansu for improving the accuracy level of regional precipitation forecasting and warning, and enhancing the ability of disaster prevention and reduction services. By using precipitation data in flood season from 1 766 automatic meteorological observation stations in Hedong area, 264 precipitation cases from 2018 to 2020 were selected. Based on the 3-hour interval intelligent grid precipitation forecasts issued by the Central Meteorological Observatory, the Contiguous Rain Area (CRA) of forecast field and the actual field are identified and matched, and classified according to hit, miss and false alarm, to further study the CRA deviation characteristics. The results show that, for the precipitation cases hit by the forecast, the falling area deviation of the intelligent grid forecast of the warm forcing precipitation is the largest, followed by precipitations of the oblique frontal generation and cold forcing categories. The intensity deviation of the cold forcing precipitation is the largest, followed by precipitations of the warm forcing and baroclinic frontogenetic categories. The maximum morphological deviation is found in baroclinic frontogenetic precipitation, followed by the cold forcing and warm forcing categories. The forecast area of the warm forcing and oblique frontal precipitations is biased towards the north and east, while the cold forcing precipitation is biased towards the south and east. The forecasted precipitation area of three types precipitation is larger for the beta scale and below, and smaller for the the alpha scale. Forecasters can establish localized model correction schemes based on the results of CRA spatial testing to improve the service capability of intelligent grid precipitation forecast.

Key words: weather situation, spatial verification, precipitation forecast, deviation analysis

摘要：

研究甘肃河东地区汛期降水智能网格预报偏差特征，对提升区域降水预报预警的精准化水平和防灾减灾服务能力具有重要意义。利用甘肃河东1 766个自动气象观测站的汛期降水资料，筛选出2018—2020年264个降水个例，基于中央气象台发布的3 h智能网格降水预报数据，对预报场和实况场的连续雨区（Contiguous Rain Area，CRA）进行识别和配对，并按照命中、假警报和未命中3种情况分类分析，进一步对预报命中的CRA偏差特征进行研究。结果表明：对于预报命中的降水个例，智能网格降水预报的落区偏差以暖强迫类最大，斜压锋生类和冷强迫类次之；强度偏差以冷强迫类最大，暖强迫类和斜压锋生类次之；形态偏差以斜压锋生类最大，冷强迫类和暖强迫类次之。暖强迫类和斜压锋生类降水的落区预报偏东偏北，冷强迫类偏东偏南。3类降水预报均表现为对β及以下尺度的降水落区面积偏大，而对α尺度降水落区面积偏小。基于CRA空间检验结果，预报员可建立本地化的模式订正方案，提高智能网格降水预报的服务能力。

关键词: 天气形势, 空间检验, 降水预报, 偏差分析

CLC Number:

P456.9

HAN Jing, JIAO Meiling, CAO Yanchao, WANG Juan, HE Tao, XU Geng, ZHOU Zhongwen, JIN Manhui. Deviation characteristics in intelligent grid forecast of flood season precipitation in Hedong area of Gansu based on CRA spatial forecast verification[J]. Journal of Arid Meteorology, 2024, 42(6): 976-986.

韩晶, 焦美玲, 曹彦超, 王娟, 贺涛, 徐耕, 周忠文, 金满慧. 基于CRA空间检验技术的甘肃河东汛期降水智能网格预报偏差特征分析[J]. 干旱气象, 2024, 42(6): 976-986.

Figures/Tables 11

Fig.1 Distribution of 1 766 automatic meteorological observation stations in Hedong area of Gansu Province

Fig.2 The CRA matching between forecast field and actual field （The blue area represents the forecast CRA， the surrounding light blue area represents the forecast extension area， the orange area represents the actual CRA， the surrounding light orange area represents the actual extension area， and the purple circle represents the intersection of the extension areas）

Fig.3 Weather system configuration for oblique frontal (a), warm forcing (b) and cold forcing (c) precipitation in Hedong area of Gansu Province （The green dashed lines indicate the 700 hPa isobaric humidity line, Unit: g·kg-1; the brown thin arrow represents a significant streamline at 700 hPa; the brown thick arrow represents the 700 hPa low-level jet stream; the red double solid line represents the 700 hPa shear line; the red solid lines represent temperature lines at 500 and 700 hPa, Unit: ℃; the blue solid line represents the 500 hPa trough line; the blue thick arrow represents the 200 hPa high-altitude jet stream; the blue sawtooth line represents a cold front; D represents a low-pressure system）

Fig.4 Changes in the average hit rate， miss rate， and false alarm rate of CRA of intelligent grid precipitation forecasts in Hedong area of Gansu Province from May to September during 2018-2020

Fig.5 Changes of the hit rate and false alarm rate with the number of CRA grid points in the forecast field (a), and hit rate and miss rate with the number of CRA grid points in the actual field (b) of intelligent grid precipitation forecast in Hedong area of Gansu Province during 2018-2020

Tab.1 The CRA grid distribution characteristics of precipitation in eastern and western parts of Hedong area of Gansu Province under different weather patterns 单位：个

天气形势类型	西部平均格点数	东部平均格点数
暖强迫	766	1 143
冷强迫	136	898
斜压锋生	490	1 243

Tab.2 Overall deviation of precipitation forecast

天气形势类型	平均值			中位数
天气形势类型	落区偏差占比/%	强度偏差占比/%	形态偏差占比/%	平均纬向偏差/（°）	平均经向偏差/（°）	平均面积偏差/%	平均强度偏差/%	最大降水量偏差/%
暖强迫	19.9	23.5	56.6	0.0	0.2	18.6	64.1	-24.0
冷强迫	8.1	33.3	58.6	0.0	0.0	62.3	0.0	-50.0
斜压锋生	15.7	21.2	63.1	0.0	0.0	12.8	63.9	-29.9

Fig.6 Box plots of proportion of precipitation zones, intensities, and morphological deviations for different types of precipitation

Fig.7 Deviation of centroid position between forecasts and actual conditions of three types precipitation

Fig.8 Scatter plot of precipitation forecast and actual precipitation grid points (a, c, e) and actual precipitotion grid distribution (b, d, f) of warm forcing type (a, b), cold forcing type (c, d) and oblique pressure frontogenesis type (e, f)

Fig.9 The scatter plots of average precipitation and forecasted rainfall intensity (a, e, i) and their proportions (b, f, j), and the scatter plots of maximum precipitation and forecasted rainfall intensity (c, g, k) and their proportions (d, h, l) of warm forcing type (a, b, c, d), cold forcing type (e, f, g, h), and oblique pressure frontogenesis type (i, j, k, l)

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