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991.
The main objective of the present paper is to show a methodology for undertaking rainfall regionalization of a region taking into account the convective features of the precipitation, and useful for establishing homogeneous zones for improving the alert system. This methodology has been applied to a hydrographic region located in northeast Spain, with an area of 16000 km2 and characterized by a highly contrasted topography. Information provided by meteorological radar and 5-min precipitation data for 126 automatic raingauges has been used for the period 1996–2002. The previous analysis done on the basis of the 1927–1981 rainfall rate series for the Jardí raingauge, located in Barcelona, has also been considered. To that end, the first step was to draw up a proposal for classification of the pluviometric episodes. Recourse was had for this purpose to definition of the β parameter, related with the greater or lesser convective character of the event and calculated on the basis of the rainfall intensity at the surface (Llasat, 2001) and, when data are available, on the basis of radar reflectivity. Results show that the threshold of 35 mm/h to characterize convective episodes from raingauge data can be corroborated from the radar point of view when convective precipitation is identified using 2-D algorithms with a reflectivity threshold of 43 dBZ. Once the soundness of the β parameter had been corroborated, it was applied to more than 2900 precipitation episodes recorded in the region, in order to discriminate the features of the different subregions and their time and space distribution throughout the entire series of the samples. Using this definition, 92% of the precipitation events recorded in this region, with accumulated rainfall above 35 mm, are classified as convective ones, representing 95% of the precipitation amount. Application of the β parameter combined with monthly rainfall data allows differentiation of 8 regions with different convective precipitation features. 相似文献
992.
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
993.
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
994.
本文利用太原多普勒雷达资料、卫星云图以及常规资料,分析了2005年8月16日引发太原市的城市内涝和山西省28个站的暴雨、大暴雨天气持续8h的时空分布特征,并进行了动力学分析和预报难点分析,提出了预报着眼点。 相似文献
995.
本文分析了2005年8月26日傍晚太原市尖草坪区降雹过程的急流、冷暖平流、形势背景,并通过对降雹过程的多普勒雷达资料的强度场、速度场及其它产品的分析,结合块状冰雹云出现特点,得出降雹过程不同阶段临近预报的较好预报和识别指标。 相似文献
996.
Monitoring Forest Fire Danger with Remote Sensing 总被引:2,自引:2,他引:0
Our paper presents a review of the use of remote sensing technologies for forest wildfire danger monitoring, with a particular emphasis on its applicability to fuel moisture monitoring. Remote sensing of fuel moisture was first done with NOAA-AVHRR NDVI images, but NDVI is more related to vegetation greenness rather than water stress. NOAA-AVHRR surface temperature images were also used, alone or in association with NDVI images. Both kinds of images have a limited image availability due to cloud cover. This is not the case for radar images, but their use in fuel moisture monitoring is still experimental, because of the noisy effects of several factors. Finally, the paper discusses the operational potentials and limitations of the use of each kind of satellite data for fire danger monitoring. 相似文献
997.
Episodic, large‐volume pulses of volcaniclastic sediment and coseismic subsidence of the coast have influenced the development of a late Holocene delta at southern Puget Sound. Multibeam bathymetry, ground‐penetrating radar (GPR) and vibracores were used to investigate the morphologic and stratigraphic evolution of the Nisqually River delta. Two fluvial–deltaic facies are recognized on the basis of GPR data and sedimentary characteristics in cores, which suggest partial emplacement from sediment‐rich floods that originated on Mount Rainier. Facies S consists of stacked, sheet‐like deposits of andesitic sand up to 4 m thick that are continuous across the entire width of the delta. Flat‐lying, highly reflective surfaces separate the sand sheets and comprise important facies boundaries. Beds of massive, pumice‐ and charcoal‐rich sand overlie one of the buried surfaces. Organic‐rich material from that surface, beneath the massive sand, yielded a radiocarbon age that is time‐correlative with a series of known eruptive events that generated lahars in the upper Nisqually River valley. Facies CF consists of linear sandbodies or palaeochannels incised into facies S on the lower delta plain. Radiocarbon ages of wood fragments in the sandy channel‐fill deposits also correlate in time to lahar deposits in upstream areas. Intrusive, sand‐filled dikes and sills indicate liquefaction caused by post‐depositional ground shaking related to earthquakes. Continued progradation of the delta into Puget Sound is currently balanced by tidal‐current reworking, which redistributes sediment into large fields of ebb‐ and flood‐oriented bedforms. 相似文献
998.
999.
多普勒雷达PPI资料在数值模式MM5中的应用 总被引:1,自引:2,他引:1
利用多普勒天气雷达观测的回波强度资料,估测大气的湿度值。假定回波强度大于4 0dBz的区域,相对湿度为1 0 0 % ,小于2 0dBz的区域相对湿度为90 % ,2 0~4 0dBz区域的相对湿度按线性变化求取。对应各点的温度值由MM5控制试验得出。然后通过迭代处理,求出对应各点的露点温度,通过以上步骤把雷达观测的回波强度值转换为模式中直接使用的物理变量,用于模式计算。为了验证该方法的可行性,进行了模拟试验,个例选用2 0 0 1年7月1 3日安徽全椒暴雨过程。背景场采用T2 1 3资料,加上常规探空,地面资料,通过分析形成控制试验的初始场。将安徽合肥新一代天气雷达观测的回波强度按上述方法加入到MM5中,形成敏感试验的初始场。水平网格为1 0 3×1 0 3,格距为1 0km ,垂直分33层,中心位置为31 0 0°N、1 1 7 6 6°E。试验结果表明,加入雷达资料后降水中心位置预报有明显改进。说明上述方法是可行的。 相似文献
1000.
利用K-邻域频数法对714SDN型多普勒天气雷达原始资料进行预处理,分析了参数的选取对处理结果的影响,得出了一些重要结论。根据应用中出现的问题,对该方法作了补充完善,使得补测效果更加有效。 相似文献