Retrieval of Air Vertical Velocity and Droplet Size Distribution in Squall Line Precipitation Using C-FMCW Radar

Chen Shaojie; Zheng Jiafeng; Yang Ji; Che Yuzhang; Ren Tao; Huang Xuan

doi:10.11898/1001-7313.20220404

Vol.33, NO.4, 2022

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Article Navigation > Journal of Applied Meteorological Science > 2022 > 33(4): 429-441

Chen Shaojie, Zheng Jiafeng, Yang Ji, et al. Retrieval of air vertical velocity and droplet size distribution in squall line precipitation using C-FMCW radar. J Appl Meteor Sci, 2022, 33(4): 429-441. DOI: 10.11898/1001-7313.20220404.

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Chen Shaojie, Zheng Jiafeng, Yang Ji, et al. Retrieval of air vertical velocity and droplet size distribution in squall line precipitation using C-FMCW radar. J Appl Meteor Sci, 2022, 33(4): 429-441. DOI: 10.11898/1001-7313.20220404.

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Retrieval of Air Vertical Velocity and Droplet Size Distribution in Squall Line Precipitation Using C-FMCW Radar

DOI: 10.11898/1001-7313.20220404

Chen Shaojie¹,
Zheng Jiafeng^{1, 2
,
,},
Yang Ji^{2, 3},
Che Yuzhang¹,
Ren Tao¹,
Huang Xuan¹

1.
School of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu 610225
2.
Key Laboratory of Transportation Meteorology, China Meteorological Administration, Nanjing 210008
3.
Nanjing Joint Institute for Atmospheric Sciences, Nanjing 210041

Received Date: 2022-03-28
Rev Recd Date: 2022-05-12
Publish Date: 2022-07-13

Abstract

Abstract

The zenith C-band frequency modulation continuous wave(C-FMCW) radar has good detection capability with high temporary-spatial resolution and large dynamic range. The Doppler spectral density data of two squall lines precipitation cases at Longmen of Guangdong are utilized to retrieve the air vertical velocity (V_a) in clouds and droplet size distribution (DSD). The empirical relation method (checking relationship between mean particle falling velocity (V_t) and reflectivity factor) and the small-particle-trace method are explored to retrieve the air vertical velocity in clouds. And then the droplet size distribution is retrieved from the translated Doppler spectral density by a velocity-diameter relation. The retrieved DSD of two squall lines are then compared and validated with the observation of K-band micro rain radar and second-generation Parsivel disdrometer. The retrieved V_a by the empirical relation method is slightly smaller for strong monomer than that by the small-particle-trace method and slightly larger for weak convective precipitation, but V_t is the opposite. The absolute value of V_t negative velocity by the empirical relation method and the small-particle-trace method corresponds to the moment of large particles and heavy rain observed by Parsivel disdrometer, indicating that V_a of two methods is basically reliable. The comparison in DSD retrieval show that the number of small droplets observed by radar is higher, but Parsivel disdrometer may underestimate it. The results of the empirical relation method are closer to micro rain radar and Parsivel disdrometer when rain rate is below 1 mm·h^-1. The medium droplets obtained by radar retrieval are consistent with Parsivel disdrometer measurements, but the concentration of large droplets is low when rain rate is stronger than 10 mm·h^-1. The retrieval results of both methods are close to Parsivel disdrometer and micro rain radar when rain rate is between 1 mm·h^-1 and 10 mm·h^-1. The strong convection makes droplets rupture severer in the peak area of heavy precipitation in the squall line, resulting in smaller mass-weighted mean diameter (D_m) and larger generalized intercept parameter N_w of the empirical relation method and the small-particle-trace method retrieval. For weak convective precipitation at the back of the squall line, the value of empirical relation method is quite close to Parsivel disdrometer. Under different rain rate, μ value of C-FMCW radar is less than 10 and the fluctuation is smaller, indicating that the results of C-FMCW radar is even more reliable than Parsivel disdrometer and micro rain radar.
- C-band frequency modulation continuous wave radar;
- spectral density;
- air vertical velocity;
- droplet size distribution

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References(26)

Figures and Tables

图 1 2016年5月15日飑线后部弱对流降水观测及反演结果

(a)C-FMCW雷达反射率因子Z_e, (b)经验关系法反演的大气垂直速度V_a, (c)示踪法反演的大气垂直速度V_a, (d)经验关系法反演的粒子群平均下落末速度V_t, (e)示踪法反演的粒子群平均下落末速度V_t, (f)雨滴谱仪观测的雨滴谱和雨强R

Fig. 1 Weak convective precipitation after the squall line passing on 15 May 2016

(a)C-FMCW reflectivity factor(Z_e), (b)air vertical velocity(V_a) retrieved by the empirical relation method, (c)air vertical velocity retrieved(V_a) by the small-particle-trace method, (d)mean particle falling velocity(V_t) retrieved by the empirical relation method, (e)mean particle falling velocity(V_t) retrieved by the small-particle-trace method, (f)droplet size distribution and rain rate(R) measured by disdrometer

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图 2 2016年5月15日不同雨强下的平均雨滴谱

(a)0<R≤0.2 mm·h^-1，(b)0.2<R≤1 mm·h^-1，(c)R>1 mm·h^-1

Fig. 2 Mean droplet size distribution under three rain rate conditions on 15 May 2016

(a)0<R≤0.2 mm·h^-1, (b)0.2<R≤1 mm·h^-1, (c)R>1 mm·h^-1

DownLoad: Full-Size Img PowerPoint

图 3 2016年5月15日19:43—21:20 3个设备物理量对比

Fig. 3 Comparison of physical parameters for three instruments from 1943 BT to 2120 BT on 15 May 2016

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图 4 2016年5月6日飑线过境强对流降水观测及反演结果

(a)C-FMCW雷达的反射率因子Z_e，(b)经验关系法反演的大气垂直速度V_a，(c)示踪法反演的大气垂直速度V_a，(d)经验关系法反演的粒子群平均下落末速度V_t，(e)示踪法反演的粒子群平均下落末速度V_t，(f)雨滴谱仪观测的雨滴谱和雨强R

Fig. 4 Strong convective precipitation of the squall line passing on 6 May 2016

(a)C-FMCW reflectivity factor(Z_e), (b)air vertical velocity(V_a) retrieved by the empirical relation method, (c)air vertical velocity(V_a) retrieved by the small-particle-trace method, (d)mean particle falling velocity(V_t) retrieved by the empirical relation method, (e)mean particle falling velocity(V_t) retrieved by the small-particle-trace method, (f)droplet size distribution and rain rate(R) measured by disdrometer

DownLoad: Full-Size Img PowerPoint

图 5 2016年5月6日不同雨强下的平均雨滴谱

(a)0<R≤1 mm·h^-1，(b)1<R≤10 mm·h^-1，(c)R>10 mm·h^-1

Fig. 5 Mean droplet size distribution under three rain rate conditions on 6 May 2016

(a)0<R≤1 mm·h^-1, (b)1<R≤10 mm·h^-1, (c)R>10 mm·h^-1

DownLoad: Full-Size Img PowerPoint

图 6 2016年5月6日18:00—21:41 3个设备物理量对比

Fig. 6 Comparison of physical parameters for three instruments from 1800 BT to 2141 BT on 6 May 2016

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