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1.
The aim of this paper is to show a climatology of Mesoscale Convective Systems (MCS) in the NE of the Iberian Peninsula, on the basis of meteorological radar observations. Special attention was paid to those cases that have produced heavy rainfalls during the period 1996–2000. Identification of the MCS was undertaken using two procedures. Firstly, the precipitation structures at the lowest level were recognised by means of a 2D algorithm that distinguishes between convective and non-convective contribution. Secondly, the convective cells were identified using a 3D procedure quite similar to the SCIT (Storm Cell Identification and Tracking) algorithm that looks for the reflectivity cores in each radar volume. Finally, the convective cells (3D) were associated with the 2D structures (convective rainfall areas), in order to characterize the complete MCS. Once this methodology was presented the paper offers a proposal for classifying the precipitation systems, and particularly the MCS. 57 MCS structures were classified: 49% of them were identified as linearly well-organised systems, called TS (39%), LS (18%) and NS (43%). In addition to the classification, the following items were analysed for each MCS found: duration, season, time of day, area affected and direction of movement, and main radar parameters related with convection. The average features of those MCS show an area of about 25000 km2, Zmax values of 47 dBz, an echotop of 12 km, the maximum frequency at 12 UTC and early afternoon and a displacement towards E-NE. The study was completed by analysing the field at surface, the presence of a mesoscale low near the system and the quasi-stationary features of three cases related with heavy rainfalls. Maximum rainfall (more then 200 mm in 6 h) was related with the presence of a cyclone in combination with the production of a convective train effect. 相似文献
2.
The remarkable wide range spatial scaling of TRMM precipitation 总被引：1，自引：0，他引：1
The advent of space borne precipitation radar has opened up the possibility of studying the variability of global precipitation over huge ranges of scale while avoiding many of the calibration and sparse network problems which plague ground based rain gage and radar networks. We studied 1176 consecutive orbits of attenuation-corrected near surface reflectivity measurements from the TRMM satellite PR instrument. We find that for well-measured statistical moments (orders 0 < q < 2) corresponding to radar reflectivities with dBZ < 57 and probabilities > 10− 6, that the residuals with respect to a pure scaling (power law) variability are remarkably low: ± 6.4% over the range 20,000 km down to 4.3 km. We argue that higher order moments are biased due to inadequately corrected attenuation effects. When a stochastic three — parameter universal multifractal cascade model is used to model both the reflectivity and the minimum detectable signal of the radar (which was about twice the mean), we find that we can explain the same statistics to within ± 4.6% over the same range. The effective outer scale of the variability was found to be 32,000 ± 2000 km. The fact that this is somewhat larger than the planetary scale (20,000 km) is a consequence of the residual variability of precipitation at the planetary scales. With the help of numerical simulations we were able to estimate the three fundamental parameters as α ≈ 1.5, C1 = 0.63 ± 0.02 and H = 0.00 ± 0.01 (the multifractal index, the codimension of the mean and the nonconservation parameter respectively). There was no error estimate on α since although α = 1.5 was roughly the optimum value, this conclusion depended on assumptions about the instrument at both low and high reflectivities. The value H = 0 means that the reflectivity can be modeled as a pure multiplicative process, i.e. that the reflectivity is conserved from scale to scale. We show that by extending the model down to the inner “relaxation scale” where the turbulence and rain decouple (in light rain, typically about 40 cm), that even without an explicit threshold, the model gives quite reasonable predictions about the frequency of occurrence of perceptible precipitation rates.While our basic findings (the scaling, outer scale) are almost exactly as predicted twenty years ago on the basis on ground based radar and the theory of anisotropic (stratified) cascades, they are incompatible with classical turbulence approaches which require at least two isotropic turbulence regimes separated by a meso-scale “gap”. They are also incompatible with classical meteorological phenomenology which identifies morphology with mechanism and breaks up the observed range 4 km–20 000 km into several subranges each dominated by different mechanisms. Finally, since the model specifies the variability over huge ranges, it shows promise for resolving long standing problems in rain measurement from both (typically sparse) rain gage networks and radars. 相似文献
3.
Four different mountainous locations were selected in the Valencia region, East coast of the Iberian Peninsula, for fog water collection studies. Data for 2004 were obtained by means of an instrument ensemble consisting essentially of a passive cylindrical fog water collector, a raingauge, a wind direction and velocity sensor and a temperature and humidity probe. An approximate data reduction technique was also found for this specific ensemble to eliminate the simultaneous rain water component from the fog water measurements. Main results indicate that fog water collection holds significant potential in this region, and especially for southern locations. Annual rates of fog water yield can be as high as 7.0 l/m2/day in the southern locations, in contrast to 2.0 l/m2/day collected at one site in a northern location. The highest summer fog water yield was 4.6 l/m2/day, a relatively large value. Except for the summer period, fog episodes delivering sizeable water volumes are inherently coupled to rainfall. Hourly frequencies of fog collection were also examined to show a distinct daily cycle in summer, denoting orographic fog formation during this period. Lastly, winds were analysed to resolve the most suitable directions for fog collector alignment. 相似文献
4.
梅雨锋云系内对流回波与层状回波的研究 总被引：4，自引：4，他引：4
本文利用1998年“淮河流域能量与水分循环试验（HUBEX）”所获得的大量雷达资料及遥测雨量计计资料，细致分析了淮河流域梅雨锋云系的结构，根据层状云和对流云在雷达回波图中的不同特征，本文提出用松散系数D（反映云系结构疏松程度）来区分大范围云带中的降水云类型，同529张PPI资料统计表明，若D＞0．17则说明该区结构松散，降水属于层状云降水，D≤0．17时，云区是对流性降水，由于梅雨锋水具有明显的不均匀结构特征，其中锋面对流云带和强下挂回波带是造成强降水的主要原因，在用地面雨量资料和雷达资料对地面降水进行短时（3小时以内）校正时，针对不同的降水类型采用不同的Z－R关系比用同一种Z－R关系的校正精度大约提高4％。 相似文献
5.
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 Ph 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 Zmax > 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. 相似文献
6.
Convective and Stratiform Cloud Rainfall Estimation from Geostationary Satellite Data 总被引：6，自引：0，他引：6
The Bayes Decision (BD) method was used to distinguish the corrective and stratiform components of cloud sys-tems from GMS-4 satellite data. A technique originally developed by Adler and Negri (1988, hereafter abbreviated AN) was improved for estimating the convective and stratiform cloud precipitation areas and rates of cloud systems from GMS satellite imagery. It has been applied to a tropical cyclonic cloud cluster observed over east coast area of China on September 23, 1992, which brought about flood disaster in that region. Overlaid 6-hour surface rainfall ob-servations show that the rainfall areas and amounts match with results from improved AN technique. The successful application of the Adler and Negri’s technique to convective and stratiform clouds provides encouragement for the use of this method over large region of mid-latitude China where radar data are not fully covered. 相似文献
7.
两个中尺度对流系统的降水结构和闪电特征 总被引：10，自引：3，他引：7
对两个处于不同发展阶段的中尺度对流系统(MCS)降水结构的分析结果表明,处于初生至发展阶段的MCS,对流降水和层云降水的面积比相对较大,处于成熟至消亡阶段的MCS的相对较小。本文进一步分析了这两个MCS个例在6km高度处的雷达回波特征及其和闪电的关系,结果表明处于初生至发展阶段的MCS的绝大部分事件(闪电资料的一种)集中发生在MCS中的强对流单体回波区,而对处于成熟至消亡阶段的MCS,事件集中发生在对流区和对流云向层云转化的回波区。 相似文献
8.
9.
浙江沿海登陆台风结构特性的多普勒雷达资料分析 总被引：1，自引：0，他引：1
利用浙江省新一代多普勒雷达组网资料,选取在浙江东南沿海近乎同一地点登陆的3个台风进行研究。从登陆前6 h到登陆后7 h,对比分析3个台风在登陆前后的雷达回波和降水结构时空变化特征。利用单多普勒雷达四维变分风场反演技术,对温州多普勒雷达探测资料进行了风场反演。结合利用雷达回波强度资料,对3个台风登陆前后1 h在云岩、昌禅等地造成特大暴雨的中尺度对流系统的三维结构及其演变特征进行了详细分析。结果表明,台风强度与其螺旋云带中的对流单体密切相关。台风强度愈强,其中低层环状平均回波强度就愈强,对流活动也就愈旺盛,降水强度也愈大。台风登陆前,回波(雨带)从眼墙向外围传播。台风登陆后,随着台风外围回波(雨带)明显减弱,台风眼墙回波(雨带)则明显增强,台风眼区逐渐被强回波所取代,使台风登陆后眼墙的平均雨强比登陆前增大。台风登陆后1 h,由于低(高)层水平辐合(散)增强,强对流回波中倾斜的上升(下沉)气流明显增大,使对流运动更加活跃,造成登陆后1 h的降雨量显著增强。台风强度与登陆后1 h降雨量的增强幅度成正比。台风强度越强,垂直风切变就越大,垂直切变风速大值区与最大降雨区有较好的对应关系。台风登陆后1 h,垂直切变风速的明显增加对登陆台风螺旋雨带中的中小尺度对流的加强和维持起到了非常重要的作用。 相似文献
10.
Preservation of rainfall properties in stochastic disaggregation by a simple random cascade model 总被引：3，自引：0，他引：3
We analyse properties of a simple discrete multiplicative random cascade model for rainfall disaggregation in urban hydrology. Two types of cascade models (canonical and microcanonical) are applied to the stochastic fine graining of rainfall observations into high resolution data. In particular, we analyse the disaggregation of 1280-min into 10-min data for a 20-year record period (Zurich raingauge, 1979–1998). Differences between the models and parameter estimation techniques are explored on simulated data with a special focus on three important properties of observed rainfall: distribution, intermittency, and extremes. The canonical models are overall better at preserving the distribution of rainfall at the 10-min scale. It is demonstrated that the growth of intermittency across scales is preserved well with all studied models. The ability of the models to reproduce rainfall extremes is a fundamental requirement in disaggregation. The studied models preserved annual rainfall maxima satisfactorily for short durations; however, the performance deteriorated for longer durations. The canonical models performed substantially better in capturing the variability in rainfall. The results are encouraging considering the parsimonious nature of the models and simple parameter estimation. 相似文献
11.
Dong-Kyun Kim Yeon-Hee Kim Dong-Eon Chang 《Asia-Pacific Journal of Atmospheric Sciences》2011,47(5):413-420
This study investigates microphysical properties from wind profiler Doppler spectra observed within a precipitation system that produced high rainfall rates up to 40 mm hr?1 near the southern coast of the Korean Peninsula on 25～26 June 2010. A 1290-MHz wind profiler located in the National Center for Intensive Observation of Severe Weather at Boseong, Korea, observed a widespread stratiform region and short-lived convective cells from 1850 UTC 25 to 0200 UTC 26 June 2010. By using a spectral model applied to observed profiler spectra, rainfall parameters and raindrop size distributions were retrieved below a melting layer during this period. Three representative periods during precipitation were selected based on intensities of bright band and characteristics in vertical profiles of radar reflectivity and Doppler velocity. During a brief convective period (～30 min), radar reflectivity tended to be proportional to vertical air motion (positive upward), suggesting that updrafts up to ～3 m s?1 over a large vertical extent through the melting layer probably contributed to increasing rainfall rates at the surface. In reflectivityrainfall rate distributions, large drop spectra (high reflectivity) were analyzed within downdrafts and small drop spectra (low reflectivity) within updrafts, similar to the large and small drop spectra but found in stratiform and convective regions, respectively, in previous studies. This indicates that the degree of spread between reflectivity and rainfall rate may be strongly dependent on positive and negative magnitudes of vertical air motion. For three categories of vertical air motion (i.e., updrafts, neutral, and downdrafts), physical relations between the retrieved rainfall parameters were examined. 相似文献
12.
J. Manuel Lpez 《Atmospheric Research》2007,83(2-4):272-283
At approximately 6:10 UTC in the morning of 17th August 2003, a squall line developed over south Catalonia (the northeast region of Spain). During the next 9 h, the squall moved rapidly northeast and crossed Catalonia and the French regions of Languedoc–Roussillon and Province, damaging and uprooting hundreds of trees and blocking trains in the region. Wind gusts reached were recoded up to 52 m/s with evidence of F2 intensity damage. This case study shows the characteristics of a derecho (widespread convectively induced windstorm).Radar observations of the evolving squall line show signatures often correlated with damaging surface winds, including:
- a. Bow echoes,
- b. Rear inflow notches,
- c. Rear inflow jets,
- d. Medium altitude radial convergence,
- e. Narrow gradient of very marked reflectivity,
- f. Development of isolated cells ahead of the convective line,
- g. A band of convection off the northern end of the line known as a “warm advection wing”.
13.
Serge Soula Oscar van der Velde Joan Montany Torsten Neubert Olivier Chanrion Michal Ganot 《Atmospheric Research》2009,91(2-4):514-528
During the summers of 2003 to 2006 sprites were observed over thunderstorms in France by cameras on mountain tops in Southern France. The observations were part of a larger coordinated effort, the EuroSprite campaigns, with data collected simultaneously from other sources including the French radar network for precipitation structure, Meteosat with images of cloud top temperature and the Météorage network for detection of cloud-to-ground (CG) flash activity. In this paper two storms are analyzed, each producing 27 sprite events. Both storms were identified as Mesoscale Convective Systems (MCS) with a trailing stratiform configuration (ST) and reaching a maximum cloud area of ~ 120,000 km2. Most of the sprites were produced while the stratiform area was clearly developed and during periods of substantial increase of rainfall in regions with radar reflectivity between 30 and 40 dBZ. The sprite-producing periods followed a maximum in the CG lightning activity and were characterized by a low CG flash rate with a high proportion of + CG flashes, typically around 50%. All sprites were associated with + CGs except one which was observed after a − CG as detected by the Météorage network. This − CG was estimated to have − 800 C km charge moment change. The peak current of sprite-producing + CG (SP + CG) flashes was twice the average value of + CGs and close to 60 kA with little variation between the periods of sprite activity. The SP + CG flashes were further characterized by short time intervals before a subsequent CG flash (median value < 0.5 s) and with clusters of several CG flashes which suggest that SP + CG flashes often are part of multi-CG flash processes. One case of a lightning process associated with a sprite consisted of 7 CG flashes. 相似文献
14.
The objective of this research was to acquire a raindrop size distribution (DSDs) retrieved from C-band polarimetric radar observations scheme for the first time in south China.An observation period of the precipitation process was selected,and the shape-slope (μ-Λ) relationship of this region was statistically analyzed using the raindrop sample observations from the two-dimensional video disdrometer (2DVD) at Xinfeng Station,Guangdong Province.Simulated data of the C-band polarimetric radar reflectivity Z_(HH)and differential reflectivity Z_(DR)were obtained through scattering simulation.The simulation data were combined with DSD fitting to determine the Z_(DR)-Λand log_(10)(Z_(HH)/N_0)-Λrelationships.Using Xinfeng C-band polarimetric radar observations Z_(DR)and Z_(HH),the raindrop Gamma size distribution parametersμ,Λ,and N_0were retrieved.A scheme for using C-band polarimetric radar to retrieve the DSDs was developed.This research revealed that during precipitation process,the DSDs obtained using the C-band polarimetric radar retrieval scheme are similar to the 2DVD observations,the precipitation characteristics of rainfall intensity (R),mass-weighted mean diameter (D_m) and intercept parameter (N_w) with time obtained by radar retrieval are basically consistent with the observational results of the 2DVD.This scheme establishes the relationship between the observations of the C-band polarimetric radar and the physical quantities of the numerical model.This method not only can test the prediction of the model data assimilation system on the convective scale and determine error sources,but also can improve the microphysical precipitation processes analysis and radar quantitative precipitation estimation.The present research will facilitate radar data assimilation in the future. 相似文献
15.
Influence of drizzle on Z–M relationships in warm clouds 总被引：1，自引：0，他引：1
This paper addresses the sensitivity of the relationships between radar reflectivity (Z) and liquid water content (M) for liquid water clouds to microphysical drizzle parameters by means of simulated radar observation at a frequency of 3 GHz of modeled cumulus clouds. A power law relationship for non drizzling clouds with water content as high as 3 gm− 3: Zc = 0.026 Mc1.61 is numerically derived and agreed with previous empirical relationships relative to cumulus and stratocumulus. This relationship is then used to explore the influence of drizzle on the correlation between radar reflectively and water content. Due to their large diameters with respect to cloud droplets, drizzle sized drops dominate radar reflectivity but do not carry the cloud water content so that reflectivity and liquid water content are expected to be not correlated in clouds containing drizzle. It is shown that for congestus or extreme congestus cumuli, microphysical conditions for which the Zc–Mc relationship can be used with a tolerance of 5 and 10% are provided whereas for humilis or mediocris cumuli, the presence of drizzle breaks down the Zc–Mc relationship whatever the situations. 相似文献
16.
A. A. Sin’kevich V. B. Popov I. A. Tarabukin E. V. Dorofeev Yu. A. Dovgalyuk N. E. Veremei Yu. P. Mikhailovskii V. S. Snegurov A. V. Snegurov 《Russian Meteorology and Hydrology》2018,43(8):506-515
The results of investigation of convective cloud merging observed near Saint Petersburg are presented. Data obtained with a set of remote sensing instruments (radar, radiometer, and lightning location system) were analyzed. Rain gage network data are used. Clouds simulation is performed using a 1.5-dimensional nonstationary model. A method to calibrate the radar measurements to obtain precipitation characteristics using rain gage network data is developed. According to radar data, a 2-km increase in the cloud top height was observed after Cu merging, the maximum reflectivity of clouds increased at 10 dBZ, maximum rain intensity and rain flux increased by about two times. The increase in rainfall intensity is also corroborated by rain gage observations and numerical simulations. An increase in the intensity of lightning discharges during the merging is registered. 相似文献
17.
This paper is focused on the study of rainfall yield characteristics of electrical storms observed over the Northern Iberian Peninsula during 1992–1996. To this aim Principal Components Analysis (PCA) and Self-Organizing Maps (SOM) method have been used. The SOM method is a group of artificial neural networks based on the topological properties of the human brain. Results clearly suggest that there exist three different meteorological patterns that are linked to the characteristics of electrical events found in the study area. In winter, most of the electrical events are formed under oceanic advection (NW air fluxes). On these cases, mean rainfall yield estimates reach values of 700 104 m3 per cloud to ground lightning flash (CG flash). During summer most frequent electrical storms are associated to local instability shooting by surface heating with advection of humidity coming from the Iberian Peninsula. Under these meteorological situations, rain is scarcer if compared with oceanic events but lightning CG counts reach the maximum values found in the area (about 10 CG counts per 20 × 20 km2 and day) giving this way the smallest rainfall yield with a mean value of 15 104 m3 per CG flash. Iberian air fluxes associated with cold air in upper parts of the atmosphere represent the third meteorological pattern found. This pattern is most common in spring and autumn but is not unusual in the rest of the seasons. In those cases mean rainfall yield in the area is about 150 104 m3 per CG flash. In all electrical episodes K instability index is greater than 15 °C but in the most lightning producing events, this index reaches in the area values greater than 24 °C. PCA results pointed out that there exists a relationship between rain and CG counts expressed by the first principal component computed from standardized data. However, we must notice that no event is solely linked to this axis, since a seasonal influence which decreases lightning production when rain increases is always present. Results found are of great interest for short term forecasting of flashfloods in mountainous areas like the Spanish Basque Country region. 相似文献
18.
19.
Qingwei ZENG Yun ZHANG Hengchi LEI Yanqiong XIE Taichang GAO Lifeng ZHANG Chunming WANG Yanbin HUANG 《大气科学进展》2019,36(10):1103-1120
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(Nw) value of convective rainfall is the largest (smallest) in the pre-monsoon (post-monsoon) period, whereas the Dm 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 Dm 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. 相似文献
20.
为避免直接同化时反射率非线性观测算子线性化带来的线性近似误差问题,目前许多研究和业务中还常采用间接同化方式来同化雷达反射率因子,其通过背景场温度判定水凝物类型及比例。基于一种实时天气背景依赖的雷达反射率因子间接同化方案,进行了4次暴雨过程（2次强对流,2次锋面）的循环同化及预报试验。结果表明:对于强对流暴雨个例,相对于传统温度判定方案,天气背景依赖方案的温度预报误差更小、降水预报评分更高,而对于锋面过程区别不明显;进一步机理分析表明,对于强对流暴雨个例,由于背景依赖方案在同化反射率因子时引入了实时天气背景信息,使得分析场水凝物结构能够更好表征实际对流特征且与其它模式变量更为协调,进而改善了模式预报的热、动力及水汽条件,从而改善了降雨预报效果;而锋面暴雨由浅对流过程占主导,水凝物以低层的雨水为主导,冰相水凝物对于该过程的影响较小,由于两种方案反演的雨水结构和量级均相似,因此降雨预报差异较小。 相似文献