Inter-station correlation and estimation errors of areal average rain rate

In this study an equation for estimating the error involved in the areal average rain rate considering the inter-station correlation was derived and applied for two cases: the first compared two storm events with different inter-station correlations, and the second evaluated the seasonal variation of estimation error of monthly rainfall. Similar cases, but without considering the rainfall seasonality, were also investigated for the comparison. This study was applied to the Geum River Basin with 28 rain gauge measurements, each having more than 30 years of rainfall data. A summary of the application results follows: (1) When considering the inter-station correlation, the estimation error involved in the areal average rain rate became significantly decreased proportional to the inter-station correlation. (2) The estimation error of monthly areal average rainfall showed strong seasonality with high ones during the wet season and lower ones during the dry season. (3) The estimation error was well proportional to the areal average rain rate as well as to its standard deviation. The ratio of estimation error to the areal average rain rate itself was estimated to be about 0.1 for the case of assuming no inter-station correlations, but decreased to 0.06 for the case of considering the inter-station correlations between measurements. (4) The relation between the standard deviation of areal average rain rate and the estimation error became much stronger than that between the areal average rain rate itself and the estimation error. The ratio of estimation error to the standard deviations of rain rate amount was estimated to be about 0.2 for the case of assuming no inter-station correlations, but decreased to 0.1 for the case of considering the inter-station correlations. This relation was found to be valid for any case of accumulation time such as in daily, monthly, or annual rainfall data.     

Identifying individual rain events from pluviograph records: a review with analysis of data from an Australian dryland site

Rainfall is routinely reported as falling in ‘events’ or ‘storms’ whose beginning and end are defined by rainless intervals of a nominated duration (minimum inter‐event time, MIT). Rain events commonly exhibit fluctuations in rain rate as well as periods when rain ceases altogether. Event characteristics such as depth, mean rain rate, and the surface runoff volume generated, are defined in relation to the length of the rain event. These derived properties are dependent upon the value of MIT adopted to define the event, and the literature reveals a wide range of MIT criteria. Surprisingly little attention has been paid to this dependency, which limits the inter‐comparison of results in published work. The diversity in criteria also diminishes the usefulness of historical data on event durations, rain rates, etc., in attempts to document changes in the rainfall climate. This paper reviews the range of approaches used in the recognition of rain events, and a 5 year pluviograph record from an arid location is analysed. Changing MIT from 15 min to 24 h (lying within the range of published criteria) alters the number of rain events from 550 to 118. The mean rain rate declines from 2·04 mm h^?1 to 0·94 mm h^?1, and the geometric mean event duration rises from 0·66 h to 3·98 h. This wide variation in the properties of rain events indicates that more attention needs to be paid to the selection and reporting of event criteria in studies that adopt event‐based data analysis. The selection of a MIT criterion is shown to involve a compromise between the independence of widely‐spaced events and their increasingly variable intra‐event characteristics. Copyright © 2008 John Wiley & Sons, Ltd.     

黄河某水电站顺层岩质滑坡形成机理与演化过程

黄河上某水电站坝后存在一大型顺层岩质滑坡.钻探、平硐、槽探和现场勘查勘察资料表明该滑坡具有平面分区和剖面分层的显著特征.运用地质环境系统全过程动态演化的观点,采用力学理论、物理模型、数值模拟等方法,分析了滑坡的形成机理和演化机制:该滑坡是在河流冲刷和地震活动等内外综合作用下因层状岩质斜坡岩体层间错动和溃屈基而形成,其演化具有明显时间和空间差异性的多次滑动.在此基础上采用多种极限平衡计算方法综合评价滑坡各区、各级在天然状态下的稳定状态,并结合滑坡所处的地质环境及其演化特征预测滑坡在雾雨、地震以及二者耦合作用下的演化趋势.     

义乌市降水变化特征分析

根据历史和实测资料的统计分析,得到义乌市的降水变化特征。结果表明:丰水期义乌市的涝年偏多,旱年偏少,而枯水期则旱年偏多,涝年偏少。厄尔尼诺事件的当年或翌年,义乌市的降水显著偏多,而拉尼娜事件的当年或翌年,义乌市的降水则显著偏少。丰水期平均入梅日偏早,平均出梅日偏晚,平均梅雨日数偏长,平均梅雨量偏多,而在枯水期则反之。义乌市6月6—15日入梅的可能性最大,出梅日期的时间分布相对比较分散,其集中期的发生规律不如入梅集中期明显。厄尔尼诺事件的当年或翌年,义乌市的出梅日偏晚,而拉尼娜事件的当年或翌年,义乌市的出梅日偏早。研究结果可为水库源区雨季的人工增雨作业提供科学依据。     

Relationships Between Rainwater Composition and Synoptic Weather Systems Deduced from Measurement and Analysis of Hong Kong Daily Rainwater Data

The composition of Hong Kong rainwater has been studied in the context of seven types of prevailing synoptic weather system. These represent different precipitating airmass origins in terms of continental, maritime, local or mixed sources. Replicate sampling was performed on a daily basis from 1994–1995 for both bulk deposition (n = 60) and simultaneous wet deposition (n = 27) collectors. Reliable analytical data were obtained for the concentrations of the soluble components H+, Na+, Ca2+, K+, Mg2+, Cl-, NO3- and SO42-. The acidity of rainwater was found to be greater when Hong Kong was under the influence of an approaching cyclone (type AC), northeasterly monsoon (type NE) or cold front (type CF) than for prevailing easterly anticyclones (type E), southerly/southwesterly monsoon systems (type S), or cyclonic flows (type C). A common characteristic of occasions of acid rain in Hong Kong was the build-up of local pollutants under conditions of low windspeed, as shown by the significant correlation between rainwater pH and lognormal surface windspeed, but not windvector. The acidity of Hong Kong rainwater was thus largely determined by local sources, although the participation of a continental airmass was evident for some systems. The daily bulk deposition flux of H+ on rainy days varied by more than an order of magnitude from type C (0.2 meq m-2 d-1) to types AC, trough (T) and NE (>2 meq m-2 d-1).     

Study on Moist Potential Vorticity and Symmetric Instabilityduring a Heavy Rain Event Occurred inthe Jiang-Huai Valleys

1.IntroductionSubsequenttothe1970s,manynativemeteorologicalresearchersdiscoveredthatmesoaiscalesymmetricinstabilitydisturbanceislikelytoplayanimportantroleintriggeringandorganizingbandedconvectionandresponsibledirectlyformultiplerain--bands.Asahighly...     

Flood simulation in the coastal lowlands of northern Jiangsu, China

The coastal lowlands in northern Jiangsu Province, China, is characterized by low relief and low water surface gradient in streams. The flooding stages are commonly lower than the high-tide level and the tidal range is relatively small. All these factors prohibit rapid discharge of floodwater and make the flood regimes here extremely sensitive to the sea level rise. The 1991 Plum Rain was examined, when precipitation was significantly higher than normal. The one-dimensional open-channel non-conservative flow model was used to simulate the stream flow in the channel network of studied area. GIS technology was used to delineate the maximum in undated area by analyzing the DEMs.     

2017年5月大气环流和天气分析

2017年5月大气环流的主要特征是极涡偏强且呈单极型分布,中高纬环流呈多波型,西太平洋副热带高压强度较常年偏强,南支槽强度较常年偏弱。5月全国平均气温17.1℃,较常年同期偏高0.9℃,为1961年以来第4高;全国平均降水量59.4 mm,比常年同期（69.5 mm）偏少14.5%,但5月7日广州出现破历史极值的极端强降水。月内我国南方地区有5次区域性暴雨天气过程;北方出现极端高温过程;东北西部、华北等地发生严重气象干旱;北方地区有2次沙尘天气过程。     

融安县汛期暴雨气候特征及单站短期预报方法

通过对融安县４２ａ雨量资料及近１０ａ６６ 场暴雨个例的分析,得出该县的暴雨气候特征和影响系统分型,并结合当地近年暴雨预报实践经验, 总结出适合于当地Ⅰ、Ⅱ、Ⅲ型暴雨短期预报方法。实践证明, 该方法切实有效, 可为县站预报专家系统的建立提供依据。     

长江流域近50年降水变化及其对干流洪水的影响

根据我国长江流域气象观测站近42年的资料,分析了整个流域年和季节平均面雨量、暴雨日数和暴雨量的变化特征,以及降水对流域径流和洪水的影响.长江流域年和夏季平均面雨量存在明显的年际和年代变化特征,也表现出比较显著的趋势变化特点.大部分测站年平均面雨量呈增加趋势,夏季和冬季平均面雨量的增加趋势尤其明显;秋季平均面雨量呈显著下降趋势.同时,年和夏季暴雨日数和暴雨量也在较大范围内呈显著增加趋势.长江流域的降水对干流平均流量具有重要影响.1973年、1983年和1998年的洪水主要是由明显高于平均的流域面雨量引起的;长江下游平均流量变化趋势也同流域年平均面雨量、夏季平均面雨量变化趋势基本一致,特别是70年代末以来,下游平均流量和流域面雨量的上升趋势更加明显,并同时在1998年达到最高值.长江流域大的丰水年一般对应El Nino年或El Nino次年,表明E1 Nino对长江较大洪水可能具有一定影响.