太原地区雨滴谱季节分布特征

Seasonal Distribution Characteristics of Raindrop Spectrum in Taiyuan

利用2017年12月-2022年11月太原雨滴谱数据,研究太原地区不同雨强和不同降水类型雨滴谱季节分布特征。结果表明:太原地区四季谱分布均呈单峰结构且均以雨滴直径D<1 mm的小雨滴为主,但对雨强R贡献最大的是D为1~2 mm的雨滴。各季节R<1 mm·h^(-1)的降雨均占比最大,但夏季超过50%雨量来自R≥5 mm·h^(-1)雨滴的贡献;R<2 mm·h^(-1)时,冬季大雨滴浓度更高,而小雨滴浓度相对较低;R≥5 mm·h^(-1)时,夏季雨滴浓度更高。四季均以层状云降水为主,标准化截距参数lgNw和质量加权直径D_(m)差异较小;对流云降水多发生在夏季且更接近海洋性对流,春、秋季既非大陆性也非海洋性对流。采用最小二乘法得到形状因子与斜率参数的μ-λ、降水动能以及反射率因子与雨强的Z-R关系曲线,其中μ-λ季节变化小,但地域性差异显著;幂函数和二项式函数分别对于降水动能参数关系E_(t)-R和E_(d)-D_(m)拟合效果更优;Z-R关系系数与指数成反比,对于层状云降水,春、秋季经典关系均高估降雨,冬、夏季存在经典关系由高估转为低估的情况;对于对流云降水,夏、秋季经典关系略高估降雨。

The raindrop size distribution(RSD)and parameter characteristics of different climate regions,rain types,topographies or weather systems have been extensively studied focusing on summer precipitation.However,even microphysical characteristics of precipitation in the same region can show significant seasonal differences.Seasonal distribution characteristics of RSD with different rain rates and rainfall types in Taiyuan are investigated and compared with conclusions from other regions based on observations of precipitation phenomenometer from December 2017 to November 2022.It can provide references for localized application of the parameterization of rainfall microphysics in numerical weather and climate prediction models,the rainfall kinetic energy flux estimation and the radar quantitative precipitation estimation.In addition,satellite measurements,ground observations,and reanalysis data are applied to explain the possible mechanism of seasonal differences in RSD.The RSD presents a unimodal structure with a peak of 0.562 mm and the decrease trend of concentration is more obvious in winter.Small raindrops with diameter less than 1.0 mm contribute more than 80%of the total number concentration,while the rain rate(R)is contributed primarily from mid-size raindrops with diameter of 1-2 mm during all seasons.The rainfall with R<1 mm·h^(-1) are most frequent in different seasons,but the rainfall with R≥5 mm·h^(-1) is predominant in summer.For the RSD of different rain rate,the highest(lowest)concentration of large(small)raindrops in winter is observed from the first two rain rate classes,while the concentration is higher in summer when the rain rate exceeds 5 mm·h^(-1).Rainfall at Taiyuan is dominated by stratiform rain throughout the year,lgNw or Dm has minor seasonal differences,and the distribution of lgNw and Dm is more similar to Nanjing.The convective rain occurs most often during summer and is close to the maritime-like cluster,the convective rain during spring and autumn is neither continental nor maritime,and there is no convective rain in winter.The stratiform rain has a wider spectrum width and higher concentration compared with the convective rain.μ-λ,E_(t)-R,E_(d)-D_(m),and Z-R relationships are derived by the least square method for different seasons.μ-λrelationships change little with seasons,but vary significantly compared with Florida in America.The power function and the binomial function has better fitting performance for E_(t)-R and E_(d)-D_(m),respectively.There is an inverse relationship between the coefficient and the exponent of the Z-R relationships.For stratiform rain,the classical relationship overestimates rainfall in spring and autumn,while the classical relationship turns from overestimated to underestimated as the rain rate increases.For convective rain,the classical relationship overestimates rainfall slightly in summer and autumn.