淮北地区不同类型暴雨雨滴谱特征及其Z-R关系研究

Raindrop spectral characteristics and Z-R relationship of different rainstorm types in Huaibei region

  • 摘要: 选取2017—2020年淮北地区夏季雨滴谱观测资料对低槽型、副热带高压边缘型、冷涡影响型和台风型4种类型暴雨的雨滴谱进行分析。研究表明淮北地区降水主要以层状云为主,而对总降水贡献率大的却是对流云降水。不同类型暴雨微物理量同样存在差异,低槽型、台风型暴雨的粒子数浓度较大,副热带高压边缘型和冷涡影响型各种特征直径比其他两类大。分析不同尺度雨滴粒子与雨强的关系,小雨滴数浓度占比超过60%,但对雨强起主要贡献的是中粒子,不同类型暴雨的差异主要是由小雨滴和大雨滴对雨强贡献率的差异造成的;并且随着雨强的增大,小雨滴的贡献率逐渐降低,大雨滴增大。不同雨强档下的雨滴谱分布基本呈单峰型,随着雨强增大各尺度档粒子数浓度升高,谱宽增大,斜率逐渐减小;当雨强增大时质量平均直径(Dm)-标准化参数(lgNW)分布趋于集中,Dm和lgNW的平均值分别为1.15 mm和3.79 mm−1m−3;通过Γ分布拟合发现,低槽型和台风型暴雨谱分布参数的平均值和标准差大于另外两类;除标准化参数的偏度为负值外,其余各参数的偏度均为正值;不同类型暴雨谱型-斜率(µ-Λ)及反射率因子-雨强(Z-R)略有差异。研究得出的淮北地区暴雨Z-R关系为Z=164.4R1.42,相比之下,目前雷达系统采用的标准关系式低估了淮北地区暴雨降水量,尤其在评估低槽型和台风型暴雨时误差较大。

     

    Abstract: Based on observations of summer raindrop spectra in Huaibei region from 2017 to 2020, the raindrop spectrum distributions of four rainstorm types, i.e., the trough type, the subtropical high edge type, the cold vortex type and the typhoon type, are analyzed. Results show that the occurrence frequency of precipitation in Huaibei area is dominated by stratiform precipitation, while convective precipitation is the main contributor to total precipitation. The microphysical parameters of different types of rainstorms are also different. The number concentration of low trough type and typhoon type is larger than that of other types, and the characteristic diameters of subtropical high edge type and cold vortex type are larger than those of the other two types. The relationship between raindrop particles and rain intensity at different scales is analyzed. It is found that small raindrops account for more than 60% of the number concentration, yet medium raindrops make a major contribution to rain intensity. The differences between different types of rainstorm are mainly caused by differences in the contribution rates of small raindrops and heavy raindrops to rainfall intensity. And with the increase of precipitation intensity, the contribution rate of small raindrops decreases, while that of large raindrops increases. The distribution of raindrop spectrum under different rain intensity classes is basically unimodal. With the increase of rain intensity, the number concentrations of various particles increase, the spectral width increases and the slope decreases. When the rain intensity increases, the mass-weighted mean diameter (Dm)-normalized intercept parameter (lgNW) distribution tends to be concentrated, and the mean values of Dm and lgNW are 1.15 mm and 3.79 mm−1m−3, respectively. Through Gamma distribution fitting, it is found that the mean values and standard deviations of spectral distribution parameters of low trough type and typhoon type are greater than those of the other two types. The skewness of all parameters is positive except that of the parameters (lgNW), which is negative. The shape parameter-slope parameter (µ-Λ) and radar reflectivity factor-radar reflectivity factor (Z-R) are slightly different between different types of rainstorm. In this paper, total precipitation in Huaibei area is calculated by Z=164.4R1.42. In contrast, the standard relationship adopted by radar system at present underestimates rainstorm precipitation in Huaibei area, especially for low trough type rainstorms and typhoon type rainstorms.

     

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