一次中小尺度强降水火箭增雨作业效果评估

分析了2003年7月23夜间至24日,衡水市受副热带高压外围强西南气流及弱冷空气共同作用下出现的一次小尺度强雷雨天气。介绍了实施火箭人工催化增雨作业情况,在作业同时进行了雨量、雨滴谱、雷达和闪电定位观测,利用常规天气图资料、雷达观测资料、闪电定位仪和雨滴谱、雨量等观测资料,对此次天气过程进行了分析,并采用作业区和非作业区对比的方法,就增雨效果从雨量、雨滴谱及秩和检验(Wilcoxon氏法)等方面进行了效果分析,结果显示:在局地强对流云系含水量丰沛,云顶高度高,云层温度低,过冷水区浓厚,同时垂直风切变有利于AgI粒子的结晶和扩散时,作业时机宜选择在降雨初期云中能量聚集尚未释放时,可进一步提高增雨作业效果。     

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.     

利用激光雨滴谱仪检验消（减）雨作业效果

为了有效地检验人工影响效果,设计了地面火箭和飞机催化作业方案,分析了2009年秋季的雨滴谱观测资料。计算了火箭作业点相对于激光雨滴谱仪的距离和方位,为了便于实际作业指挥中的灵活应用,将结果标注在多普勒雷达的地图上。分析了10次降水过程共5338min的雨滴浓度资料。结果显示,秋季积层混合云的雨滴浓度小于500个的占87.6%,而大于3000个的浓度出现几率很低,不同过程雨滴浓度分布有明显差别;2009年10月16日降水过程出现最大雨滴浓度6003个,部分原因可能与火箭消减雨催化作业有关。     

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。     

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.     

Dependence of shrub canopy water storage on raindrop size in revegetated desert

Abstract

The aim of this study was to evaluate canopy water storage (CWS) of the co-dominant shrubs in the revegetation of sand dunes in northwest China. Our results indicated that CWS differed among the xerophyte taxa studied. The average CWS increased exponentially with decreased raindrop size. The time course of CWS in terms of leaf area indicated that Artemisia ordosica attains its peak value of 0.48 mm within 170 min. The corresponding values for Caragana korshinskii and Hedysarum scoparium were 0.38 mm and 178 min, and 0.32 mm and 161 min, respectively, implying that A. ordosica had a higher CWS than C. korshinskii and H. scoparium. Dry biomass was a desirable predictor for estimation of CWS for C. korshinskii and H. scoparium, and shrub volume for A. ordosica. Our results show that the dependence of CWS on raindrop size varied in accordance with the shrub canopy structure.

Editor Z.W. Kundzewicz     

Precipitation Microphysical Characteristics of Typhoon Ewiniar (2018) before and after Its Final Landfall over Southern China

In this paper, the evolution of the microphysical characteristics in different regions(eyewall, inner core, and outer rainbands) and different quadrants [downshear left(DL), downshear right(DR), upshear left(UL), and upshear right(UR)]during the final landfall of Typhoon Ewiniar(2018) is analyzed using two-dimensional video disdrometer and S-band polarimetric radar data collected in Guangdong, China. Due to the different types of underlying surfaces, the periods before landfall(mainly dominated ...     

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。     

北上台风强降水形成机制及微物理特征

利用NCEP FNL分析资料、青岛降水现象仪和双偏振雷达观测资料, 对北上台风利奇马(1909)和巴威(2008)引发的局地对流性强降水微物理特征进行分析, 结果表明: 在台风外围的东南暖湿气流内, 受地形或边界层锋区触发形成的强对流单体后向传播或原地合并加强造成了局地强降水; 雨滴的质量加权平均直径(Dm)和对数归一化浓度(lgNw)分别为1.89 mm和3.86, 与典型台风降水相比平均直径更大、浓度更低, 形状参数μ和斜率Λ的μ-Λ关系也有明显不同; 随着雨强增强, 小雨滴占比下降而中到大雨滴比例明显上升, 直径1~4 mm雨滴对短时强降水的贡献超过90%;雨滴的碰并增长和对云水的聚集作用在对流性降水中占主导地位, 同时深厚的凇附过程对极端强降水的出现也起到了重要作用。     

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.