三类降水云雨滴谱特征研究

利用GBPP-100型地面雨滴谱仪在沈阳夏季测得的积云、层状云和积层混合云的降水资料，分析了三类云降水雨滴谱的谱型、微结构参量及其短时变化特征。     

坡面降雨溅蚀及其模拟

对雨滴的溅蚀过程及影响因素作了全面的分析。在揭示黄土地区梁峁上部雨蚀规律的基础上,运用牛顿第二运动定律,推导出雨滴对土粒撞击力的表达式。在假定雨滴溅蚀率与雨滴侵蚀力成线性关系情况下,推导出雨滴溅蚀量表达式,经桥沟流域径流场上应用,效果令人满意。     

雨滴微波辐射特征量之间关系的探讨

通过对一次特定降水过程雨滴谱资料的分析，建立了Z－M、M－I和k-M的统计模式。在与理论模式和国内外有关资料的对比中，得到了一些有意义的结果。这些结果，无论对进一步的理论探讨或气象台站的实际工作，都具有一定的参考价值。     

Physically based modelling of sediment generation and transport under a large rainfall simulator

A series of large rainfall simulator experiments was conducted in 2002 and 2003 on a small plot located in an experimental catchment in the North Island of New Zealand. These experiments measured both runoff and sediment transport under carefully controlled conditions. A physically based hydrological modelling system (SHETRAN) was then applied to reproduce the observed hydrographs and sedigraphs. SHETRAN uses physically based equations to represent flow and sediment transport, and two erodibility coefficients to model detachment of soil particles by raindrop erosion and overland flow erosion. The rate of raindrop erosion also depended on the amount of bare ground under the simulator; this was estimated before each experiment. These erodibility coefficients were calibrated systematically for summer and winter experiments separately, and lower values were obtained for the summer experiments. Earlier studies using small rainfall simulators in the vicinity of the plot also found the soil to be less erodible in summer and autumn. Limited validation of model parameters was carried out using results from a series of autumn experiments. The modelled suspended sediment load was also sensitive to parameters controlling the generation of runoff from the rainfall simulator plot; therefore, we found that accurate runoff predictions were important for the sediment predictions, especially from the experiments where the pasture cover was good and overland flow erosion was the dominant mechanism. The rainfall simulator experiments showed that the mass of suspended sediment increased post‐grazing, and according to the model this was due to raindrop detachment. The results indicated that grazing cattle or sheep on steeply sloping hill‐country paddocks should be carefully managed, especially in winter, to limit the transport of suspended sediment into watercourses. Copyright © 2006 John Wiley & Sons, Ltd.     

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。     

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。     

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.