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1.
Abstract Triangulation from paired sferics (100 ± 50 kHz) received at stations 57 km apart gave 42 map locations of lightning flashes belonging to a thunderstorm well‐defined on weather radar. This storm was one of many in a long line along the leading edge of a band of light stratiform precipitation (snow above 3 km). The band was 9 km high and 60 km wide, and the storms were embedded in it. The convective region of the storm studied had a north‐south extent of 20 km, the east‐west extent averaging two‐thirds as much. Cumulus heights progressed from 3 km on the west to 7 ± 1 km on the east. Two‐thirds of the lightning flashes were in the convective region. The remaining third were in 160 km2 of the light stratiform precipitation immediately west of it. 相似文献
2.
G.W. Reuter 《大气与海洋》2013,51(2):216-229
Abstract Precipitation production is investigated for 9 intense thunderstorms that developed over the Lowveld in South Africa. A C‐band radar is used to observe the 3‐dimensional reflectivity pattern. Using an empirical relation between reflectivity factor and precipitation content and integrating over the storm volume provides an estimate of the total precipitation content aloft. Likewise, an area integration of the instantaneous rain rate at cloud base yields an estimate of the rate of total outflow. At their maturing stage, the storms had precipitation contents of 0.2 to 5.0 Tg and rainfall rates of about 0.3 to 2.0 Gg s?1. The total accumulation of rain at the ground ranged from 1 to 10 Tg. The characteristic storm updraft, defined as the ratio of the area‐averaged rainfall rate to the volume‐averaged precipitation content, was about 5 ms?1 for all storms. The time evolution of integral storm parameters is also presented and related to the overall storm development. The precipitation production values observed in the Lowveld storms compares well with previous estimates reported for large thunderstorms observed in Alberta and New England. 相似文献
3.
运用雷达反射率因子（Z）与降水强度（R）之间的关系定量估测降水,降水云体中的大气垂直运动（wa）不可忽视。PARSIVEL激光雨滴谱仪（简称PARSIVEL）在获取雨滴粒径分布的同时可以从测量的雨滴下降速度分布中提取wa,用于分析PARSIVEL高度上的大气垂直运动对雷达Z估测降水强度影响。使用2014年5-6月华南季风降水观测试验期间广东阳江5次层状云、6次对流性降水过程中PARSIVEL数据分析大气垂直运动对定量估测降水影响,wa对层状云和对流云降水强度影响范围分别为-0.18~1.05 mm·h-1和-5.44~24.81 mm·h-1,相对影响值分别为-13.61%~13.99%,-38.59%~25.92%。静止大气条件下,雷达估算降水Z-R关系式中系数A,b引起的层状云和对流云降水估测偏差平均分别为10.9%和25.5%。真实大气中雷达估测降水的偏差平均情况是层状云降水由于wa的对消作用降低为9.2%,对流云降水则增加到51.2%。对流性降水中大气垂直运动对雷达估测降水的影响较大。 相似文献
4.
Abstract A reflectivity‐rainfall rate (Z‐R) relationship is derived from Carvel radar and Edmonton rain gauge measurements. Our analysis indicates that the traditional point‐by‐point comparison method is not accurate for Alberta summertime precipitation due to timing errors in fast moving convective storms. The Window Probability Matching Method (WPMM) was superior and provided a robust Z‐R relationship in the form of Z = 32.5 R1.65. 相似文献
5.
Abstract Fourteen rain‐snow boundaries and freezing precipitation episodes within Canadian East Coast winter storms are examined. Radar, sounding, and surface observations are used to study the characteristics of these features. Rain‐snow boundaries and freezing precipitation episodes are coupled phenomena. The deepest radar echoes and the heaviest precipitation generally occur in the adjacent snow region, and surface wind shifts typically are associated with the transition to rain. 相似文献
6.
利用自动站实时降水资料、NCEP再分析资料和多普勒雷达资料,结合中尺度数值模式WRF对台风"利奇马"在浙东地区产生的极端降水过程进行分析,重点研究了浙东地形对极端降水的影响。结果表明,"利奇马"影响期间,浙东强降水过程出现2个雨量峰值,依次由台风外层螺旋云带和台风中心附近的多个中尺度对流云团持续影响所造成,浙东地形对这一系列对流云团有明显的加强作用。浙东地区西部山脉对"利奇马"有阻滞和辐合抬升两方面作用,前者通过地形阻挡拖曳,延长强降水时长,后者通过山前显著的动力抬升作用和水汽辐合加强造成降水增幅。根据估算可知,括苍山脉在强降水阶段对暴雨的增幅可达11 mm·h~(-1),接近此时段内总雨量的2.5成。通过敏感性试验降低地形高度后,浙东地区辐合及上升运动减弱,雨量也明显减少,进一步验证了浙东地形是造成此次极端降水事件的重要原因。 相似文献
7.
Winter precipitation isotope slopes of the contiguous USA and their relationship to the Pacific/North American (PNA) pattern 总被引：1，自引：0，他引：1
This study compares the synoptic-dynamic relationship between two phases of the Pacific/North American (PNA) pattern and winter precipitation isotopes at 73 sites across the contiguous USA. We use the spatial pattern of isotope slope—the rate of changes in precipitation isotope ratios with distance—to identify features in the seasonal precipitation isotope fields related to climatic patterns, PNA positive and PNA negative. Our results show relationships between zones of high isotope slopes and the spatial position of the polar jet stream and juxtaposition of air masses associated with the PNA pattern. During a positive PNA winter, zones of high isotope slope in the eastern USA shift southward. This change is coincident with a southward displacement of the polar jet stream in this region, which leads to a greater frequency of polar air masses and 18O-depleted isotope values of precipitation in the region. In the western USA, zones of high slope shift eastward during the positive PNA winter, associated with more frequent penetration of tropical air masses that bring 18O-enriched precipitation to the region. Differences in δ18O/temperature relationships between the PNA-positive and -negative winters and contrasting δ18O/temperature behaviors in the eastern and western USA provide support for the role of variation in moisture source and transport as a control on the isotopic patterns. These findings highlight the importance of synoptic climate driven by PNA pattern in determining the spatial patterns of precipitation isotopes and provide constraints on paleo-water isotope interpretation and modern isotope hydrological processes. 相似文献
8.
A variety of faulty radar echoes may cause serious problems with radar data applications,especially radar data assimilation and quantitative precipitation estimates.In this study,＂test pattern＂ caused by test signal or radar hardware failures in CINRAD （China New Generation Weather Radar） SA and SB radar operational observations are investigated.In order to distinguish the test pattern from other types of radar echoes,such as precipitation,clear air and other non-meteorological echoes,five feature parameters including the effective reflectivity data percentage （Rz）,velocity RF （range folding） data percentage （RRF）,missing velocity data percentage （RM）,averaged along-azimuth reflectivity fluctuation （RNr,z） and averaged along-beam reflectivity fluctuation （RNa,z） are proposed.Based on the fuzzy logic method,a test pattern identification algorithm is developed,and the statistical results from all the different kinds of radar echoes indicate the performance of the algorithm.Analysis of two typical cases with heavy precipitation echoes located inside the test pattern are performed.The statistical results show that the test pattern identification algorithm performs well,since the test pattern is recognized in most cases.Besides,the algorithm can effectively remove the test pattern signal and retain strong precipitation echoes in heavy rainfall events. 相似文献
9.
Abstract The precipitation chemistry stations operating in the Atlantic Provinces during the period 1980–1982 were assessed by comparing their siting characteristics and sampling procedures with the criteria recommended by the Canadian Federal‐Provincial Research and Monitoring Coordinating Committee (RMCC). The data collected at these stations were also evaluated according to standards recommended by the Unified Deposition Data Base Committee. Only one quarter of the 32 stations satisfied all of these criteria. In addition, there is evidence to suggest that some of the laboratories experienced problems analysing for nitrate or pH. Therefore, producing a coherent region‐wide data set for the major ions in precipitation was not feasible. However, the qualifying measurements were adequate to indicate an excess sulphate deposition of slightly less than 20 kg ha?1 a?1 to most of the region, with less than 10 kg ha?1 a?1 to Labrador. Although this analysis was restricted to the monitoring in Atlantic Canada, the results are of broader relevance in illustrating the potential problems inherent in merging data from several networks. 相似文献
10.
Abstract The Canadian Atlantic Storms Program (CASP) provided an opportunity for comparing two quite different remote‐sensing approaches to the detection of precipitation: radar backscatter and ambient ocean sound. Several of the gales passing the observation area during CASP produced substantial precipitation with the periods of radar backscatter showing close coincidence with simultaneous acoustic signals. The ambient sound record most readily yields an indication of precipitation from shifts in spectral slope. An important result of the experiment is the demonstration that an identifiable precipitation signal occurs even in strong wind conditions. The surface bubble layer formed during strong winds only partially attenuates the higher frequency acoustic components generated by precipitation. During rain‐free periods the attenuation can be interpreted in terms of the bubble size distribution. 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.
Zhongfang Liu Lide Tian Tandong Yao Wusheng Yu 《Theoretical and Applied Climatology》2010,99(1-2):95-104
The stable isotopic composition of precipitation in different regions reflects climatic factors such as temperature, precipitation, moisture sources, and transport process. However, the isotopic variation in the region is usually much complicated due to the combined influences of these factors. A good understanding of climatic controls on the isotopic composition of precipitation can contribute to the study on isotopic tracer for climate and hydrology. To investigate the isotopic variation of precipitation and its climatic controls in the middle of the Tibetan Plateau, a monitoring station for stable isotope in precipitation has been established in Nagqu region, central Tibetan Plateau. We obtained 79 daily samples at Nagqu Meteorological Station in 2000. The observed δ 18O in precipitation showed a distinctly seasonal pattern with higher values in spring and winter and lower values in summer, despite of individually low values in winter due to extremely low temperature. To further understand this pattern, we evaluated the influence of temperature, precipitation, moisture sources, and moisture transport process on precipitation δ 18O. A multiple linear regression model represents quantitatively the dependence of precipitation δ 18O on precipitation and temperature: δ 18Oppt?=??0.30P???0.11T???14.8 (R 2?=?0.13, n?=?79, P?=?0.005), which indicates δ 18O values in precipitation are more dependent on precipitation amount than on temperature. In contrast, when the temperature is low enough (<2°C), δ 18O values in precipitation are mainly dependent on temperature: δ 18Oppt?=?0.53T???10.2 (R 2?=?0.44, n?=?19, P?=?0.002). The variation of δ 18O in precipitation is also closely related to moisture origins and transport trajectories. A model is set up to trace the trajectories for air masses arriving in the observed region, and the results demonstrated that humid marine air masses from the Indian Ocean generally have significantly lower δ 18O values than dry continental air masses from the north or local re-evaporation. During monsoon precipitation, the distance and depth of moisture transport as well as convective precipitation all lead to the large variability of δ 18O in precipitation. 相似文献
13.
Norman R. Donaldson 《大气与海洋》2013,51(4):699-711
Abstract A case study of the degradation of weather radar data by the accretion of wet snow on a radar dome is presented as a precautionary example to radar users. During the ERICA field program in 1989, accumulated precipitation on the radome at Halifax, Nova Scotia, attenuated signal in a distinctive, pie‐shaped sector on the upwind side of the radar. 相似文献
14.
Abstract The thunderstorms of a June cold‐front passage have been observed by radar, on a constant‐altitude map at 6‐km height as “Larsen areas’ ‘ within which the precipitation intensity level exceeds 30 dBZ, and by two sferics receivers, frequency 100 ± 50 kHz, one at the radar and the other 57 km distant. From the sferics, a distribution of storms with angular extent was obtained. This yielded the distribution with azimuth of the sferics random observational errors: normal with standard deviation 2.1°. Combined with radar‐determined ranges (between 100 and 200 km), it also yielded the distribution with cross‐range linear extent of the sferics sources: log normal with median 9.2 km, standard deviation corresponding to a factor 1.6, for widths 6 to 15 km. No correlation was found between storm width and sferics rate. A power‐law relation has been found between sferics rate and the Larsen area A, sufficiently good that the sferics rate can be predicted within a factor 2 from the Larsen area, but different from that obtained for another day. For both days, the Larsen area A could be replaced by another precipitation parameter, P, in effect a weighted area taking into account the variation within A of the precipitation intensity. This more complex parameter was somewhat better than Aas a predictor of the sferics rate. 相似文献
15.
Analysis of the Microphysical Properties of a Stratiform Rain Event Using an L-Band Profiler Radar 总被引：2，自引：0，他引：2 
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下载免费PDF全文 This paper investigates spatial and temporal distributions of the microphysical properties of precipitating stratiform clouds based on Doppler spectra of rain particles observed by an L-band profiler radar.The retrieval of raindrop size distributions（RSDs） is accomplished through eliminating vertical air motion and isolating the terminal fall velocity of raindrops in the observed Doppler velocity spectrum.The microphysical properties of raindrops in a broad stratiform region with weak convective cells are studied using data collected from a 1320-MHz wind profiler radar in Huayin,Shaanxi Province on 14 May 2009.RSDs and gamma function parameters are retrieved at altitudes between 700 and 3000 m above the surface,below a melting layer.It is found that the altitude of the maximum number of raindrops was closely related to the surface rain rate.The maximum number of large drops was observed at lower altitudes earlier in the precipitation event but at higher altitudes in later periods,suggesting decreases in the numbers of large and medium size raindrops.These decreases may have been caused by the breakup of larger drops and evaporation of smaller drops as they fell.The number of medium size drops decreased with increasing altitude.The relationship between reflectivity and liquid water content during this precipitation event was Z = 1.69×10~4M~（1.5）,and the relationship between reflectivity and rain intensity was Z = 256I~（1.4）. 相似文献
16.
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 KDP 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. 相似文献
17.
Synoptic Pattern and Severe Weather Associated with the Wide Convection over Southeast China During the Summer Monsoon Period 下载免费PDF全文
下载免费PDF全文 Based on the Tropical Rainfall Measuring Mission (TRMM) precipitation radar observations, wide con-vection (WC) is defi ned as contiguous convective echoes over 40 dBZ, accompanied with a near surface ... 相似文献
18.
Abstract This paper presents the synoptic and meso‐scale aspects of the intense convective activity of 2 September 1974 in the Eastern Atlantic. Two main features were evident in the GATE B‐scale array: a broad convective band associated with the 700‐mb trough, and long and narrow lines of convection oriented SE‐NW. One of these lines, which moved across the B‐scale array and was penetrated by several aircraft, is described in detail. The structure of the cloud and precipitation fields, obtained from the analysis of satellite and radar data, indicates that intense precipitation occurred mainly at the leading edge of the line where new cells were continuously generating. Cross‐sections through the line (from boom, aircraft and tethered balloon data) show a gust front at the surface, a downdraft region associated with the rain area, and a wind shift in the lowest 300 m. The circulations around and within this line appear to be similar to a class of tropical squall‐lines studied at length by Zipser, (1977) and Houze (1977) with the important difference that the horizontal gradients of the dynamic and thermodynamic variables across the line were typically weaker. 相似文献
19.
梅雨锋上短时强降水系统的发展模态 总被引：4，自引：0，他引：4
利用2010、2011年5～7月我国东部地区梅雨锋盛行期的58次强降水个例,对产生短时强降水的中尺度对流系统回波演变模态及其系统特征进行了统计分析。本文中短时强降水特指小时降水超过30 mm。结果表明,与梅雨锋相伴的短时强降水系统回波演变模态主要为纬向型、经向型、转向型和合并型四类。纬向型、经向型和70%的转向型发展模态中中尺度对流系统（MCS）呈线状,合并型则主要为卵状。纬向型、转向型和合并型MCS以后向传播为主,但它们的生命史、移速和产生强降水持续时间有很大差别:纬向型生命史最长,强降水持续时间比转向型短;三类发展模态中转向型移速最快,生命史较纬向型短,但强降水持续时间最长;合并型移动最慢,生命史最短,强降水持续时间也最短。经向型MCS前向传播为主,移动最快,系统持续史短,约为纬向型的一半,30 mm h-1、50 mm h-1以上强降水持续时间约为转向型的1/3和1/5。纬向型MCS可向东或向南移动,经向型MCS通常向东或向西运动,合并型MCS可往任意方向移动,并且只有该发展模态中MCS会向北运动。虽然转向型MCS带来的短时强降水（尤其50 mm h-1以上）持续时间最长,经向型和合并型MCS产生短时强降水持续时间短,但四类发展模态中MCS的回波强度和回波高度的统计特征无明显区别。推测强降水持续时间可能与MCS的传播关系更加密切:经向型和合并型MCS前向传播占很大比重,生命史和产生的强降水更短;转向型和纬向型MCS的后向传播比重大,尤其转向型中不存在前向传播,对应短时强降水持续时间最长。 相似文献
20.
Abstract Remote measurements of wave spectra were made using MacLaren Plansearch's Marine Radar Wave Measuring System (Macrada©) for the duration of the ERS‐1 Grand Banks Experiment (10–27 November 1991). The system consists of a Furuno X‐band marine navigation radar and a personal computer. The system was installed and operated onboard the BIO Research vessel CSS Hudson during the experiment. The radar system provides fully directional wave spectra in real time (within minutes of image acquisition) as well as archiving of the raw images for future analysis. During each of the satellite overpasses, excellent data were collected, covering a variety of wave conditions. This paper describes the data analysis procedures and presents the results of the experiment. In addition, a sensitivity analysis is carried out to study: (1) sensitivity to the number of radar images processed on the resultant spectra, (2) effect of missing one or more images in a dataset, and (3) sensitivity to azimuth angle variation. Finally, the results are compared with corresponding directional wave spectra from other sensors (such as WAVEC Buoy and ERS‐1 SAR). 相似文献