Characteristics of Raindrop Size Distribution for a Squall Line at Chuzhou of Anhui During Summer

Jin Qi; Yuan Ye; Ji Lei; Lu Dejin; Feng Jingyi

doi:10.11898/1001-7313.20150609

Vol.26, NO.6, 2015

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Jin Qi, Yuan Ye, Ji Lei, et al. Characteristics of raindrop size distribution for a squall line at Chuzhou of Anhui during summer. J Appl Meteor Sci, 2015, 26(6): 725-734. DOI: 10.11898/1001-7313.20150609.

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Jin Qi, Yuan Ye, Ji Lei, et al. Characteristics of raindrop size distribution for a squall line at Chuzhou of Anhui during summer. J Appl Meteor Sci, 2015, 26(6): 725-734. DOI: 10.11898/1001-7313.20150609.

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Characteristics of Raindrop Size Distribution for a Squall Line at Chuzhou of Anhui During Summer

DOI: 10.11898/1001-7313.20150609

Jin Qi¹,
Yuan Ye^{1
,
,},
Ji Lei¹,
Lu Dejin^1,2,
Feng Jingyi¹

1.
Anhui Weather Modification Office, Hefei 210031
2.
Nanjing University of Information Science & Technology, Nanjing 210044

Received Date: 2015-01-16
Rev Recd Date: 2015-06-23
Publish Date: 2015-11-30

Abstract

Abstract

Characteristics of raindrop size distribution are analyzed using a ground-based disdrometer for a mid-latitude squall line at Chuzhou of Anhui on 31 Jul 2014. The observational precipitation are classified into convective rain, transition rain and stratiform rain based on the radar reflectivity and rain rate at surface. The convective rain is divided into leading edge, convective center and trailing edge according to a threshold rain rate 10 mm·h^-1. The raindrop spectrum characteristics in different precipitation regions are studied. Results show that the mass-weighted diameter for convective center, transition region, stratiform region are stable with mean values of 1.8 mm, 1.0 mm and 1.7 mm, respectively. The generalized intercepting parameter N_w of convective precipitation is larger compared with stratiform precipitation, indicating a larger number concentration of drops. The μ value is the largest for transition precipitation but the smallest for convective precipitation. The raindrop spectrums are different for varied rain type. For convective precipitation, it shows a highest concentration of raindrop within each size range, especially for small size of raindrops, which results in a smaller raindrop size than tropic region. For stratiform precipitation consists of a lower number concentration of small drops and less large raindrops, therefore, the spectrum curve is flat. For transition precipitation, the number concentration of small drops is close to stratiform precipitation without large drops, results in a steep spectrum. The mass-weighted diameter for leading edge is large probably caused by gravity separation at the early stage of precipitation. The rainwater content of stratiform precipitation is smaller compared with convective precipitation. The mass-weighted diameter of stratiform precipitation is larger compared with convective precipitation, and it increases more rapidly compared with convective precipitation as the rain water content increasing. The reflectivity is larger for stratiform precipitation compared with convective center precipitation at the same rain rate. The Z-I relationship of stratiform precipitation is Z=409I^1.48 when partitioning the rain into convective rain, transition rain and stratiform rain, but Z=395I^1.51 when the partitioning is blurred. The Z-I relationship is improved and the accuracy of radar rainfall estimates is enhanced by dividing the rain type more exactly. In summary, although the raindrop size distribution for a squall line at ground is discussed, the knowledge on microphysical process of mid-latitude squall line is still insufficient. Dual polarization radar can be applied to further investigate the microphysical process in different types of internal cloud precipitation in the future.
- squall line;
- raindrop size distribution;
- microphysical process;
- precipitation classification

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References(26)

Figures and Tables

图 1 合肥雷达2014年7月31日0.5°仰角的PPI图像

(三角形为雨滴谱仪所在位置)

Fig. 1 PPI images of Hefei radar with a elevation of 0.5° on 31 Jul 2014

(the black triangle is the location of disdrometer)

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Fig. 2 Changes of rain rate from 2330 BT 30 Jul to 0250 BT 31 Jul in 2014

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Fig. 3 Time change of raindrop distribution and microphysical parameters from 2330 BT 30 Jul to 0250 BT 31 Jul in 2014 (a) spectral distribution (the shaded denotes number concentration, the black solid line denotes D_m), (b)R, (c) lgN_w, (d) lgN₀, (e)μ

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Fig. 4 Raindrop spectra of different precipitation type on 31 Jul 2014(solid lines represent fitting curve of Gamma)

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图 5 2014年7月30日23:58—31日02:27 μ-Λ关系，

(黑色实线对应D_m=(4+μ)/Λ中D_m为1.0，1.5，2.0 mm)

Fig. 5 μ-Λ relationship from 2358 BT Jul 30 to 0227 BT Jul 31 in 2014

(black solid lines correspond to the relationship D_m=(4+μ)/Λ given D_m of 1.0, 1.5, 2.0 mm)

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图 6 沿图 1b中线AB的反射率因子剖面

(三角形代表雨滴谱仪所在位置)

Fig. 6 Vertical cross section of Z along AB in Fig. 1b

(the triangle denotes the location of disdrometer)

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Fig. 7 Relationship of D_m-W from 2358 BT 30 Jul to 0227 31 Jul in 2014(the solid line denotes the fitting curve of convective center and trailing edge, the dashed line denotes the fitting curve of stratiform)

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Fig. 8 Relationship between Z and I from 2358 BT Jul 30 to 0227 BT 31 Jul in 2014 (a) stratiform precipitation, (b) convective precipitation

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Table 1 Mean values and standard deviations of parameters from 2358 BT 30 Jul to 0227 BT 31 Jul in 2014

参数	对流前沿降水 (4个样本)		对流中心降水 (42个样本)		对流后沿降水 (13个样本)		过渡性降水 (33个样本)		层云降水 (54个样本)
参数	平均值	标准差	平均值	标准差	平均值	标准差	平均值	标准差	平均值	标准差
I/(mm·h^-1)	6.8		54.0		5.0		0.4		2.3
N_t/m^-3	351	103	2524	1294	411	75	92	44	104	22
W/(g·m³)	0.29	0.12	2.40	1.37	0.29	0.11	0.03	0.01	0.11	0.03
D_m/mm	2.0	0.07	1.8	0.15	1.4	0.16	1.0	0.13	1.7	0.14
lgN_w/(mm^-1·m^-3)	3.1	0.19	4.2	0.21	3.8	0.06	3.3	0.27	3.0	0.13
lgN₀/(mm^-1-μ·m^-3)	3.5	0.50	4.7	0.31	5.9	0.88	7.5	1.72	4.4	0.72
μ	1.7	1.78	2.6	0.86	6.4	1.66	9.2	3.43	5.2	1.84
Λ/mm^-1	2.9	0.98	3.6	0.77	7.7	2.07	13.2	3.87	5.6	1.58
注：N_t为雨滴总数浓度。

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