Radar Echo Characteristics and Recognition of Warm-sector Torrential Rain in Sichuan Basin

Luo Hui; Xiao Dixiang; Kuang Qiuming; Qing Quan; Kang Lan

doi:10.11898/1001-7313.20200408

Vol.31, NO.4, 2020

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Luo Hui, Xiao Dixiang, Kuang Qiuming, et al. Radar echo characteristics and recognition of warm-sector torrential rain in Sichuan Basin. J Appl Meteor Sci, 2020, 31(4): 460-470. DOI: 10.11898/1001-7313.20200408.

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Luo Hui, Xiao Dixiang, Kuang Qiuming, et al. Radar echo characteristics and recognition of warm-sector torrential rain in Sichuan Basin. J Appl Meteor Sci, 2020, 31(4): 460-470. DOI: 10.11898/1001-7313.20200408.

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Radar Echo Characteristics and Recognition of Warm-sector Torrential Rain in Sichuan Basin

DOI: 10.11898/1001-7313.20200408

Luo Hui^1,2,
Xiao Dixiang^{1,2
,
,},
Kuang Qiuming³,
Qing Quan^1,2,
Kang Lan^1,2

1.
Sichuan Meteorological Observatory, Chengdu 610072
2.
Heavy Rain and Drought-Flood Disaster in Plateau and Basin Key Laboratory of Sichuan Province, Chengdu 610072
3.
CMA Public Meteorological Service Centre, Beijing 100081

Received Date: 2019-10-10
Rev Recd Date: 2020-03-11
Publish Date: 2020-07-31

Abstract

Abstract

Based on data of real-time precipitation and weather radar during 28 torrential rain events in warm regions of Sichuan Basin, radar echo characteristics of torrential rain in early and mature stages are analyzed. Feature vectors for identifying early and mature stages of torrential rain in warm regions are constructed and the selected samples are studied by random forest machine learning method. According to the influence range, duration, and cumulative amount of precipitation, the thunderstorm group is the main part of the rainstorm in the warm region, and its development can be divided into three types.According to the burst of short-term heavy precipitation, thunderstorm groups are divided into primary and mature stages. In the early stage of the thunderstorm to the mature stage, the "in situ development type" is dominant, the "individual development type" and the "in front side trigger type" are the second. With the evolution after the maturity, the "in situ development type" and the "front side trigger type" are the main types. Convective precipitation is the main type of heavy rain in the warm area. After the first type of thunderstorm group, the combination of mature thunderstorms is the main source of thunderstorms, which moves slowly and is conducive to the generation of heavy precipitation. In front of mature thunderstorms, new thunderstorm cells are continuously generated and merged to continue spreading northward, forming a large range of precipitation. Individual development thunderstorm groups have the longest duration and a large influencing range. They are accompanied by long-term merge when moving. Among 28 processes, a large proportion appears in the northwest and has the longest duration. Echoes of these processes are in the southwest-northeast direction, which is basically consistent with the trend of the Longmen mountains in the western part of the Basin. The uplift of the topography (generating easterly wind) plays a key role in the occurrence and development of warm rainstorms. In the primary stage, the average core height and average top height of "in situ development type" thunderstorm group has a bimodal structure. Similar structure is found for "front side trigger type" in the mature stage. Multiple parameters of three types of thunderstorm groups show a unimodal distribution in the nascent and mature stages. To identify heavy rains in the warm area, feature vector is constructed using multiple parameters of the thunderstorm group, and random forest machine learning is also applied, leading to satisfying results.
- warm-sector torrential rain;
- thunderstorm group;
- echo feature;
- random forest

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References(33)

Figures and Tables

Fig. 1 Station number of different level precipitation in different time periods

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Fig. 2 Combined reflectivity of three-type thunderstorm groups

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Fig. 3 Location of the strongest thunderstorm at 1 h interval

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Fig. 4 Probability density distribution of thunderstorm group in the height of the average core and the maximum core

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Fig. 5 Probability density distribution of thunderstorm group in the average top and the maximum top

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Fig. 6 Probability density distribution of thunderstorm group in the average and the maximum of maximum reflectivity factor

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Table 1 Characteristics of precipitation for different types

类型	降水持续时间	降水范围	过程累积降水	过程降水总体特征
Ⅰ型	较短	较小	强	降水移动缓慢导致累积降水大，范围小，持续时间较短
Ⅱ型	较长	较大	较强	降水相对集中，但范围不断扩大，导致影响范围大、持续时间长
Ⅲ型	最长	大	较小	降水分散，影响范围大，持续时间长

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Table 2 Environmental parameters of typical cases

类型	过程	对流有效位能/(J·kg^-1)	850 hPa假相当位温/℃	850 hPa 比湿/(g·kg^-1)	850 hPa 露点/℃	0~2 km垂直风切变/(m·s^-1)
	20140912	2190	83.5	16.3	19	2.0
Ⅰ型	20170818	2779	89.0	17.3	20	1.2
	20170821	3604	89.0	17.3	20	1.6
	20130725	3746	90.5	17.5	20	4.6
Ⅱ型	20170716	4126	92.6	18.4	21	4.4
	20170719	3178	90.5	17.6	20	2.6
Ⅲ型	20130619	2313	93.9	18.1	21	4.4
Ⅲ型	20170722	1993	92.7	18.5	21	7.6

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Table 3 Recognition result

试验序号	训练样本	测试样本	正确识别样本	初生误识别为成熟	成熟误识别为初生	分类识别正确率/%
试验1	475	153	140	6	7	91.5
试验2	474	154	145	2	7	94.2
试验3	475	153	138	7	8	90.2
试验4	448	180	166	3	11	92.2
试验5	473	155	141	5	9	90.9
试验6	459	169	158	3	8	93.5

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