Design of hail measurement networks*

Abstract

Hail and rain data collected in the National Hail Research Experiment's 1976 dense precipitation network have proved useful in defining the requirements of hail measuring networks. It is shown, at least for the hailstorm of 22 June 1976, that the primary maxima and minima of the spatial distribution of hail mass are revealed by a hailpad spacing of about 4 km, and that increasing detail obtains with smaller spacings until with spacings of 0.4 to 0.8 km finer scale features with dimensions of 1–3 km become defined. Monte‐Carlo and conventional statistical analysis show that the confidence limits on the errer in estimating the true hail mass for a storm increase approximately linearly with the mean spacing of hailpads. For the hailfall of 22 June 1976, there is 90% confidence that the true hail mass is estimated within ± 10% for a hailpad spacing of 1.7 km. Estimates of hail kinetic energy and number of hailstones of this accuracy require that hailpads be approximately 10–20% closer or farther apart, respectively. There is no simple numerical relation between the densities of hailpad and wedge raingauge networks covering the same area such that, if satisfied, the networks would then provide estimates of hail mass and total precipitation of the same accuracy for any storm. There is considerable daily variation in the size of hailswaths and in the spatial distribution of hail mass within them, pointing to the need for a climatological study of these aspects of hailfall to assess properly the requirements that a hail network must meet in a given region.     

雷达识别渭北地区冰雹云技术研究

通过对陕西渭北地区各雷达站观测的回波资料和地面降雹资料分析,得出了适合识别渭北地区冰雹云的7个指标。实际应用结果表明,识别效果良好,并可以做到提前识别,为防雹作业赢得非常宝贵的时间。     

冬小麦风雹灾害的等级划分与灾情评估

以冬小麦的风雹灾害为研究对象,从１９８１～１９９０年３３个冰雹个例中选取与冬小麦生长有关的１７个个例,以冰雹直径、降雹时间、降雹时阵风为因子,对冬小麦风雹灾害进行等级划分及灾情评估。应用证明,这些研究对提高农业灾害的管理水平具有重要意义。     

基于X波段双线偏振雷达的贵州威宁雹胚演变特征研究

为探究贵州省威宁地区雹暴过程中雹胚粒子的演变特征,本文在对X波段双线偏振雷达数据经过退折叠、滤波、自适应衰减订正后,运用Barnes插值方法对偏振参量进行插值,并结合模糊逻辑算法进行水成物粒子识别,然后对威宁县的两次典型雹暴过程进行了系统的分析,得到以下结论:(1)两次过程中高密度霰的来源均为冰晶聚合物和冻滴,低密度霰...     

Diurnal variations of upper winds in summer in Alberta

Abstract

Analysis of diurnal variations of upper winds in summer in Alberta reveals features consistent with the hypothesis of a thermally‐induced wind system resulting from the juxtaposition of the Rocky Mountains and the Prairies. These include diurnal variation of flow that is most pronounced at two levels, one near the surface and one near the level of the mountain tops. Attempts to find a connection between such a system and occurrence of hail were unsuccessful.     

Radar measurements of integral parameters of hailstorms used on hail suppression projects

The exact quantitative estimation of hailstorm precipitation intensity, allowing determining successfully the crop hail damage, is extremely necessary while carrying out of programs of experimental researches of the hail clouds as well as at realization of operative projects on hail suppression. On the other hand, the possibility of obtaining a trustworthy information about changes of hailfall intensity during cloud seeding operations enables to judge more objectively about seeding effect and to make a decision about its beginning and termination. Just because of such a parameter, the kinetic energy of hailfalls presents a great interest for the researchers. As it is known, measuring the kinetic energy of hailfalls is carried out both directly by ground network of hailpads, and by radar methods. The accuracy of the radar methods of the hail kinetic energy measurement strongly depends not only on the choice of an optimum formula for calculation but also on the algorithm used for separating hail and rain parts of radar echo and on the way it was used in the hail–rain mixture zone of precipitation.The method of calculating the kinetic energy of the hailfalls, based on empirical dependence of hail probability P_h on a height of a zone of a radar echo with a reflectivity of 45 dBZ above a level of zero isotherm ΔH₄₅, is offered in the given work. The algorithm of separating hail and rain parts of a radar echo and the way it was applied in a hail–rain mixture zone is described. The examples of hail streaks in contours of radar reflectivity and in isopleths of hail kinetic energy obtained using the given algorithm are shown.In Mendoza province (Argentina), a hail suppression project (1993–1997) for the analysis of the vertical structure of a radar echo with Z_max > 45 dBZ, such new parameter is an integral altitude, was used. This dimensionless parameter is most sensitive to such a condition of radar echo when all four contours of increased reflectivity Z₄₅, Z₅₅, Z₆₅, and Z₇₅ synchronously reach the maximal values. The analysis of time distributions of the main radar parameters of hailstorms on a background of values of integral altitude is resulted. It is shown that local hailfall maximum intensities on the ground are observed after the achievement of maximum integral altitude with a certain delay. It enables to predict zones of the greatest hail damage in a mode of radar observation.     

Radar measurement of rainfall by differential propagation phase: A pilot experiment

Abstract

A pilot project concerning the measurement of rainfall by polarization diversity radar, conducted jointly by the Alberta Research Council and the University of Essex in the summer of 1989, is described. The objective of the experiment was to test the theory that differential propagation phase shift can give a better estimate of rainfall with high rain rates (about 30 mm h^?1 and greater) than reflectivity measurements.

The project comprised a field experiment that was conducted in central Alberta during the period 20 July to 2 August 1989. The field experiment involved observing storms within about a 70‐km radius from Red Deer with the ARC S‐band polarization diversity radar and measuring rainfall at the ground through a network of fixed, volunteer observers and a mobile storm‐chase operation.

Theory describing how differential propagation phase may be extracted from the data recorded by the radar system is given.

Data collected on three days during the experiment (27 July, 29 July and 2 August) have been analysed and the results are presented. A total of 31 samples of total rainfall amount were collected on these days. All but three of the 31 radar rainfall amount predictions obtained from the differential propagation phase are within a factor of 2 of the rainfall observed at the ground. In fact, the average ratio of the total rainfall amount predicted from the differential propagation phase to the total rainfall amount measured at the ground is 1.16 for the 31 samples. This suggests that, on average, the total rainfall amount predicted from the differential propagation phase is only 16% higher than that measured at the ground. Of the 31 events, over a third involved some contamination of the differential propagation phase measurement through hail. Furthermore, because the K_DP technique does not rely on parameters dependent on precipitation characteristics or adjustment factors, the technique can be validated in a convenient location and then applied anywhere.

On the other hand, the radar rainfall amount estimates derived from Z‐R relations represent, in general, a large overestimation of the rainfall amount observed at the ground, especially when hail is present. No attempt was made to adjust or calibrate the radar rainfall estimates with raingauge data.     

Some Results from the Hailpad Network in León (Spain): Noteworthy Correlations among Hailfall Parameters

Summary  Since 1990 the Laboratory for Atmospheric Physics at the University of León has made use of a network of 250 hailpads spread over an area of 1000 km² in the province of León (north-western Spain). By the end of 1995, the network had detected 25 hailfalls of more than 15 km² in area, registered on 13 different days during the summer months. The 25 hailfalls were precipitated over more than 300 separate hailpads, leaving nearly 40 000 measurable prints. The size of each hailstone, whose mass and kinetic energy were taken simply as a function of the diameter of the stone was calculated using the hailpad network. In this way, an estimate has been made of the total quantity of ice which fell in each hailfall (circa 19 000 metric tons on average, although a figure ten times this was calculated for one particular hailstorm). The spatial evolution of the physical variables of the hail, determined from each pad, has also been graphically represented. In addition, the distribution of hailstone sizes has been analysed, and the characteristic distribution parameters calculated. Although exponential distribution is often used, the Kolmogorov-Smirnov test of goodness-of-fit shows a better fit for gamma distribution. The information provided by these parameters has been analysed for both distributions, in relation to some specific variables associated with hail. There is a good correlation between total energy and mass precipitated, but the quantity of hail per unit area correlates with the total energy or mass of the precipitation only through the area affected. The size distribution parameters only show good correlations with the maximum hailstone size recorded. Received October 1, 1998 Revised March 8, 1999     

庆阳2次强对流天气过程的新一代雷达资料对比分析

通过新一代天气雷达观测,利用基本数据产品和物理量产品,分析了庆阳市2005年5月30日强冰雹过程和7月1～2日连续暴雨过程中雷达回波强度、速度、云顶高度、垂直积分液态含水量的特征,并将2次过程的雷达产品特征进行了对比分析。结果表明:冰雹和连续性暴雨回波反射率因子差异大,冰雹回波发展移动快,达50 km/h,中心强度超过50 dBZ;回波移动前沿梯度大,速度图上出现速度模糊,雷达探测出中气旋,云顶高度超过12 km;降雹前VIL出现跃增,中心超过20 kg/m2都有降雹。而连续暴雨强度只有25～35 dBZ,移速慢,零速度线分布有规律,能反映低空急流和冷暖气团移动规律,云顶高度低,仅为5～8 km,降水过程中VIL变化小。     

The pseudospectral approximation applied to the shallow water equations on a sphere

Abstract

The Radar data Analysis, Processing and Interactive Display (RAPID) system, developed by McGill University researchers, synthesizes spherical coordinate radar data onto Cartesian maps displaying Constant Altitude Plan Position Indicator (CAPPI) reflectivity, Vertically Integrated Liquid water content (VIL), and other radar‐based parameters. In this study, Carvel radar (53.34°N, 114.09°W) data from July 2000 were processed using McGill's RAPID software. Specifically, we compared observations of severe convection, as identified by selected radar‐based reflectivity parameters, with surface severe weather reports and atmospheric sounding data. July 2000 was characterized by frequent severe thunderstorm activity over central Alberta; there were seven days with golfball‐sized hail, and two days with confirmed tornadoes. The VIL, upper level VIL (UVIL), and the maximum reflectivity at 7 km (Z7) were employed to quantify the strength and frequency of storms within a 120‐km radial distance of Carvel. For each day, the intensity of the convection was quantified by counting the total number of 1‐km² pixels in the study area that exceeded the severe thresholds for VIL, UVIL and Z7. The severe thunderstorm algorithms were found to be very effective at correctly identifying the observed severe thunderstorm events. All three radar parameters indicated a diurnal cycle, with severe convection starting after noon and peaking between 16:00 and 18:00 Local Daylight Time. A positive correlation was evident between the observed storm severity and the daily UVIL and Z7 pixel counts. The daily UVIL and Z7 pixel counts were also positively correlated with the Convective Available Potential Energy (CAPE) calculated from proximity soundings.     

The relation between the north pacific sea surface temperature anomaly during the sixties and hail damage in Alberta

Coincident with anomalously warm sea surface temperature in the North Pacific during the period 1962–67 was a period of low hail damage in the Province of Alberta. Investigation of thirty‐three years of hail insurance records reveals a reduction in hail damage during this period. Analysis of monthly mean upper air data indicates a significant change in the summer upper air circulation over Alberta. The mean jet stream is found to be farther south and much stronger than for the period 1950–61. Some evidence is found to support the claim that the hail damage shifted southward with the jet stream.     

德州降雹物理特征量的观测分析

根据山东德州１９８８．９．１７和１９９０．６．２３降雹过程的冰雹样品和雹谱资料，研究了降雹物理特征量与冰雹灾害的关系。     

2003 - 08 - 24 咸阳市大暴雨过程分析

利用高空、地面天气图、红外云图、多普勒雷达图等资料对临汾市2004年6月16日局地降雹的天气背景、形势演变、层结稳定度、云图和雷达回波等变化特征进行了综合分析，结合以往冰雹预报经验对新一代雷达的探测能力进行了初步检验。分析发现，这次降雹过程属典型的西北冷涡影响型，此类型降雹相对于西北气流型和西风槽型降雹具有其自身特征；从多普勒速度图上，可分析出降雹过程中飑线前后较明显的中尺度天气系统。     

1998-2008年阿克苏地区冰雹的时空分布特征及防御对策

统计分析了位于天山南麓的阿克苏地区1998--2008年的降雹资料,揭示了近年来地区降雹的时空分布特征以及冰雹云活动的主要路径,结果显示：该地区降雹分布为北部多、南部少,山区多、平原少;该地区降雹次数呈线性增加趋势,东部降雹次数多于西部、西部降雹次数增幅大于东部;由于冰雹云路径复杂多变,冰雹防御的重点在主要冰雹云路径和重点农作物区近年来新增的耕地面积成为防御的空白区,应增设作业点来填补空档区,达到“全覆盖”式作业体系     

A synoptic parameterization of the drag coefficient

Abstract

The problem areas affecting the evaluation of hail suppression experiments are reviewed. These include the hail sensors and networks, trop damage data, statistical analysis, the hail‐suppression hypothesis, and the technology of cloud seeding. General directions of needed research are proposed.     

三维对流云催化数值模式人工冰晶参数化方案的改进与个例模拟试验

在中国科学院大气物理研究所的三维全弹性对流风暴云催化数值模式(简称为IAP-CSM3D)的基础上,对模式中催化部分的参数化方案进行了改进,推导出人工冰晶与其它粒子之间相互作用的微物理过程的参数化方程。改进后的模式将催化产生的人工冰晶单独作为预报量进行处理,把人工冰晶与自然冰晶区分开,且考虑的人工冰晶谱型为双参数粒子谱,使模式更符合实际。利用改进后的模式模拟了2005年7月8日发生在辽宁省朝阳市的一次冰雹云天气过程,着重分析了催化云人工冰晶的微物理过程、空间分布和谱型,以及对冰相降水粒子的贡献。数值试验表明,自然雹云模拟结果与观测事实相吻合,说明改进后的模式对冰雹云具有较可靠的模拟能力。模拟分析表明,冻滴是该例自然雹云冰雹胚胎的主要来源,对该冰雹云进行AgI催化可明显地减少降雹量,特别是在云中冰雹形成初期进行催化防雹效果最好,既可产生最大的防雹作业效果又不至于过度减少降雨量。催化减雹的主要原因是催化显著地减少了云中冻滴向冰雹胚胎的转化总量。进一步研究发现,人工冰晶在云的不同阶段对各种冰相降水粒子的贡献是不同的。人工冰晶对雪花总质量的贡献较小,对霰总质量的贡献有所增大,而对冻滴总质量的贡献较大。模拟的冰晶粒子谱可较好地反映出人工冰晶谱型较窄,浓度较大,尺度较小的特征。     

A systematic hailpad calibration procedure for operational hail suppression in Greece

Summary Hailpads are used to provide quantitative hailfall measurements in several hail experiments and hail suppression operations around the world. The dented hailpads record the time-integrated size distribution and concentration of hailfall. In the five-year Greek National Hail Suppression Program (GNHSP) hailpad data have been used to estimate the global (impact) energy of hailswaths for the evaluation of the GNHSP.In this paper a systematic hailpad calibration procedure is developed applicable to operational programs. To meet this objective a calibration experiment has been conducted consisting of several tests to: consider differences between pad types; to examine the effects of ultra violet-light on hailpads for varying periods of time; to investigate the effect of painting and inking of the hailpad surfaces; to consider the effect of analyst's variability, loose hailpad stands, and bouneing; and to develop calibration eqqations. The concluded results seem to justify the design and performance of the hailpad calibration procedure.With 9 Figures     

一次强风暴三维结构的观测分析

2003年6月28日山东德州发生了一次降雹持续时间长、危害严重的强降雹天气过程。利用MICAPS、探空、NCEP资料,分析了降雹前的天气形势、能量场特征、含水量场。根据两部多普勒天气雷达资料,分析了雹云的演变过程及流场结构。研究表明,降雹前在降雹区上空西边低层存在高能舌,在中高层西边存在负能量平流或负能量平流中心。此次超级单体风暴过程由单个单体发展而来,具有强超级单体风暴的典型特征。该超级单体的移动方向在盛行风向右侧约20°左右,属于右移风暴。     

A Comparison of the Characteristics of Total and Cloud-to-Ground Lightning Activities in Hailstorms

The region of Beijing-Tianjin-Hebei is covered by two different lightning detection networks: SAFIR (Systeme d’Alerte Fondre par Interferometrie Radioelecctrique) for total lightning, including IntraCloud (IC) flashes and Cloud-to-Ground (CG) flashes, and the ADTD (ADvanced TOA and Direction system; TOA denotes time of arrival) network of China for CG lightning. Fourteen isolated hail-bearing thunderstorms in this region were examined in this study, using the data of SAFIR and ADTD. The peak of lightning frequency, for both total lightning and CG lightning, was often observed in advance of the occurrence of hailstones on the ground, with a trend of a rapid increase of lightning frequency before the hail was reported. The average lead times of the two types of lightning jump before hail events were obtained (total lightning: 32.2 min; CG: 25.4 min) through the 2σ lightning jump algorithm. Additionally, in hailstorms with a high ratio of positive CG flashes, the diameter of hail was larger and the duration of hail was longer; when negative CG flashes dominated, the diameter of hail was relatively small. The comparison of the characteristics of total lightning and CG flashes in hailstorms in this study is expected to serve as a supplementary tool for hail forecasting.