雨滴谱的变化对降水估计的影响

针对雨滴谱的变化对降水估计的影响,提出根据激光雨滴谱仪上方雷达回波的结构特征将降水过程划分为对流云降水和层状云降水交替分布5个部分,通过基于2种降水类型的第Ⅰ种分类Z-R关系、基于5个部分的第Ⅱ种分类Z-R关系和基于整个降水过程的总体Z-R关系分析雨滴谱的变化对降水估计的影响。结果表明:当对流云降水向层状云降水过渡时,指数谱从无到有、多峰谱比例减小,Nw减小、μ增大、Dm变化不大;Nw与R变化相似,当Z增大时μ和Dm分别是递减和递增的;Z-R关系(Z=aRb)中a值变化范围较大、系数b在1~2波动且与层状云阶段相比,对流云阶段的a和b值较小;利用第Ⅱ种分类Z-R关系反演的雨强与基于雨滴谱仪观测数据计算的雨强最接近;雨滴谱仪在层状云阶段的反演效果明显强于对流云阶段,这与对流云降水中雨滴谱信息变化大且快等因素有关。     

风廓线雷达和雨滴谱仪资料在北京一次弱雨雪天气中的特征分析

利用北京市海淀区风廓线雷达、OTT Parsivel 2多功能激光雨滴谱仪和自动气象站观测资料,对2016年11月20日北京一次雨雪天气过程的演变特征进行了初步分析。结果表明:(1)风廓线(低模式)雷达反射率因子与雨滴谱仪反射率因子序列的变化趋势一致。当风廓线雷达反射率因子亮带消失后,雨滴谱反射率因子序列出现先降后升的小幅波动,降水相态转为降雪。(2)降水相态发生雨雪转换时,风廓线雷达谱宽600 m高度分散的大值区减弱并随高度降低后,雨滴谱仪数浓度出现先降后升的小幅度波动。(3)本次弱降水相态转换发生时,风廓线雷达所探测的垂直径向速度变化不明显,而雨滴谱仪降雨强度变化却有明显减弱特征,其雨强由5 mm·h^-1下降至1 mm·h^-1左右,这对临近降水相态变化的监测预报有一定指示意义。     

Microphysical Characteristics of Precipitation during Pre-monsoon,Monsoon, and Post-monsoon Periods over the South China Sea

Raindrop size distribution (RSD) characteristics over the South China Sea (SCS) are examined with onboard Parsivel disdrometer measurements collected during marine surveys from 2012 to 2016. The observed rainfall is divided into pre-monsoon, monsoon, and post-monsoon periods based on the different large-scale circumstances. In addition to disdrometer data, sounding observation, FY-2E satellite, SPRINTARS (Spectral Radiation-Transport Model for Aerosol Species), and NCEP reanalysis datasets are used to illustrate the dynamical and microphysical characteristics associated with the rainfall in different periods. Significant variations have been observed in respect of raindrops among the three periods. Intercomparison reveals that small drops (D < 1 mm) are prevalent during pre-monsoon precipitation, whereas medium drops (1?3 mm) are predominant in monsoon precipitation. Overall, the post-monsoon precipitation is characterized by the least concentration of raindrops among the three periods. But, several large raindrops could also occur due to severe convective precipitation events in this period. Classification of the precipitation into stratiform and convective regimes shows that the lg(N_w) value of convective rainfall is the largest (smallest) in the pre-monsoon (post-monsoon) period, whereas the D_m value is the smallest (largest) in the pre-monsoon (post-monsoon) period. An inversion relationship between the coefficient A and the exponential b of the Z?R relationships for precipitation during the three periods is found. Empirical relations between D_m and the radar reflectivity factors at Ku and Ka bands are also derived to improve the rainfall retrieval algorithms over the SCS. Furthermore, the possible causative mechanisms for the significant RSD variability in different periods are also discussed with respect to warm and cold rain processes, raindrop evaporation, convective activities, and other meteorological factors.     

广东两次飑线过程的微物理特征分析研究

基于中国气象局龙门云物理野外科学试验基地2DVD（Two-Dimensional Video Disdrometer）雨滴谱观测资料, 分析广东地区2017年5月4日（槽前型飑线）和2017年8月22日（东风型飑线）两次不同飑线系统不同降水类型的雨滴谱特征。根据雨强和雷达反射率随时间变化将降水分成对流降水和层云降水, 同时以20 mm/h为阈值将对流降水划分为对流前沿、对流中心和对流后沿。结果表明, 两次飑线系统在不同降水时期的微物理特征参数变化有所差异。槽前型飑线过程中, 对流降水的粒子分布较为分散, 中等粒径的粒子比重较高, 且对流区前半部分粒子尺寸大于“大陆性”对流特征, 后半部分粒子尺寸小于“海洋性”对流特征; 层云降水的粒子分布较为集中, 小粒径粒子居多。而东风型飑线整个降水时期基本上是由高浓度中小粒径粒子组成, 降水粒子粒径分布较为集中, 对流降水粒子介于“海洋性”和“大陆性”对流区之间。      

一次雨夹雪降水过程人工增水作业 的综合观测研究

2013年4月19日,河北省人工影响天气办公室在河北中南部地区对回流和西风槽复合天气系统云系进行人工增水作业,催化和探测部位在槽前上升气流云层和回流云层中,这次降水特点：(1) 降水系统呈“槽前云”和“回流云”两层结构,大粒子主要在上层槽前云中增长;(2) “槽前云”温度和云顶温度较高,“回流云”温度低,固态降水粒子在“回流云”粘连增长加大地面降雪;(3) 大云粒子和降水粒子很多;(4) 小云粒子丰富,全谱拟合曲线lgN=algD+b的截距b＞2,适合催化作业。在分析云微物理特征的基础上,结合实时天气、卫星、雷达、探空和雨量资料,从多角度分析了层状云增水作业实用技术和催化的宏微观响应,结果表明：作业后影响区雷达反射因子、卫星反演参量和云内微物理特征量都有明显变化;催化影响区地面降水的变异通过了显著性分析,但作业前后影响区内外这一差异是否是催化效果需要进一步验证。     

成都地区雨滴谱特征

选取成都信息工程学院气象观测场LNM激光雨滴谱仪获得的2009—2011年175次降水过程的观测资料,依据产生降水云的性质进行统计分类,基于微物理特征参量讨论了成都地区积云、积层混合云以及层状云降水雨滴谱的总体特征,同时结合3个典型个例的微结构参量进行对比分析。结果表明:成都地区积云降水和积层混合云降水的雨滴谱比层状云宽且雨滴数密度比层状云多,特别是在大雨滴和甚小雨滴部分;4种反映雨滴谱特性的特征直径从大到小依次为积云降水、积层混合云降水、层状云降水;成都地区层状云降水的雨强主要来自于小雨滴,而积云降水和积层混合云降水的雨强主要来自于大雨滴;雨强取决于大雨滴的数量,小雨滴贡献率与雨强呈负相关,中数体积直径对雨强变化有一定指示作用。对成都地区雨滴谱特征的研究,有利于进一步了解该地区降水的微物理特性及成雨机制,为降水数值预报工作积累资料和经验。     

Field and computer simulation experiments on the formation of desert pavement

A series of rainfall simulation experiments was carried out at the Walnut Gulch Experimental Watershed, Tombstone, Arizona (31° 43′N, 110° 41′W), to observe the speed at which desert pavement surfaces could be re-established following disturbance. The results of these experiments, which consisted of repeated, 5 min rainfall events, demonstrate that pavements can reform within 10 events, which is compatible with observations of the recovery of surfaces under natural rainfall on an annual cycle. A model for the development of pavements by raindrop erosion processes had previously shown the importance of these processes. The rainfall simulation experiments were used to test the general applicability of this model. The model was able to reproduce the general characteristics of the regenerated surfaces and the timing of their development. However, details of the particle size fractions produced were less well simulated by the model. Testing of the sensitivity of the model to the sediment transport parameters suggests that this problem is not related to the soil characteristics, but is more likely to be an indication of a poor understanding of all the feedbacks operating in the raindrop erosion processes. Copyright © 1999 John Wiley & Sons, Ltd.     

Rain properties controlling soil splash detachment

Laboratory experiments have been conducted to study the effects of various rain properties on sand detachment resulting from raindrop impact. Splash cups were exposed to simulated rainfall intensities ranging between 10 and 140 mm h⁻¹. The detached sand was collected and weighed whereas rain intensity, equivalent drop diameter and fall velocity of raindrops were measured with an optical spectro‐pluviometer (OSP). The properties of the simulated rain (i.e. median volume diameter and kinetic energy) were compared with those observed in natural conditions. Statistical analyses have been undertaken in order to evaluate which rain variable best predicts the mass of sand detached. Linear and non‐linear correlations between the mass of detached sediment and the product of drop size (d) by drop velocity (v), i.e. D^αV^β, with values of α varying between 1 and 6 and β between 0 and 3, have been computed. The results indicate that the coefficient of determination (R²) for α ranging between 3 and 5 and β lower or equal to 2 are satisfying. Although kinetic energy (D³V²) described splash detachment relatively well, the product of momentum by drop diameter (D⁴V) was slightly superior in describing splash detachment. Therefore, the momentum multiplied by the drop diameter is recommended as the best rain variable to describe splash detachment. Copyright © 2000 John Wiley & Sons, Ltd.     

Adaptability of rainfall simulators as a research tool on urban sealed surfaces – a review

Rainfall simulators can be a useful research tool for some purposes but are quite unsuitable for others. They have been useful in soil erosion and infiltration studies for over eight decades, but the possibility of using a rainfall simulator in urban nonpoint source pollution involving urban non-erodible surfaces has not been fully explored. In this review, the versatility of different rainfall simulators of varying sizes, configurations and styles used in the past two decades are appraised for possible adaptation to urban sealed surfaces. Recommended criteria for detailed rainfall simulator reporting are also outlined.

EDITOR M.C. Acreman

ASSOCIATE EDITOR not assigned     

气溶胶粒子的降水清除

讨论了雨滴在云下对气溶胶粒子的清除,考虑了气溶胶粒子和雨滴之间的碰并系数,雨滴谱以及气溶胶粒子谱对清除系数的影响。在０１＜ ｒ＜ １０ μｍ 范围内,利用不同的碰并系数表达式算得的降雨对该区间内气溶胶粒子的清除系数相差很大,但对总质量清除系数影响不大;雨滴谱的改变对总质量清除系数有很大影响;不同的气溶胶粒子谱对总质量清除也有一定影响。雨滴谱用Ｍａｒｓｈａｌｌ－ Ｐａｌｍ ｅｒ 分布;气溶胶粒子谱用Ｊｕｎｇｅ 分布ｎ（ｒ）＝ ａｒｂ 算得清除系数与雨强关系为Λ＝ ０５１Ｉ０７８,而气溶胶粒子谱改用三参数分布（ｒ）＝ ａｒｂｅ－ ｃｒ得到清除系数与雨强的关系为Λ＝ ０２５Ｉ０７７。