太行山复杂地形下华北暖季极端降水的时空分布特征

基于2012—2021年5—9月华北五省的逐日降水资料和台站地形高度数据,统计分析了华北全区及各子区域极端降水事件的降水量及其强度和频次的时空分布特征;并运用地理加权回归(GWR)模型分析得到极端降水事件的降水量、强度及频次与海拔高度之间的关系。结果表明:1)华北区域极端降水量的时间变化均呈多波动特征且区域差异性显著,太行山以西高原和以东平原降水频次多、波动明显且强度较弱,太行山南段以南平原降水频次少、变化平缓而强度明显偏强。2)极端降水量的空间分布呈现南北少、中间多的型态分布,降水量大值区分别位于燕山东南侧和太行山南段晋冀豫三省交界处;极端降水高频站点主要聚集在晋东南地区;日最大降水量超过300 mm的站点主要集中在太行山脉和燕山山脉与华北平原的过渡地带。3)华北区域38°N以北,极端降水量、降水频次、强度和日最大降水量均随海拔高度的升高而减小;38°N以南,山西南部临运地区降水量随海拔高度的升高而显著增加。由于降水频次和强度与地形均存在正相关而导致,太行山附近降水量随海拔高度的升高而减小的贡献主要在于降水强度而非降水频次。     

Short-term changes in the magnitude, frequency and temporal distribution of floods in the Eastern Mediterranean region during the last 45 years — Nahal Oren, Mt. Carmel, Israel

Short-term changes in Eastern Mediterranean precipitation affecting flow regime were documented in Nahal Oren, a 35 km² ephemeral stream in Mt. Carmel, a 500 m high mountain ridge located at the NW coast of Israel. The rainy winter of the Mediterranean type climate (Csa) in Mt. Carmel is characterized by average annual rainfall of 550 mm at the coastal plain to 750 mm at the highest elevation while the summer is hot and dry. Stream flow generates after accumulated rainfall of 120–150 mm while “large floods”, defined as flows with peak discharge of > 5 m³ s^− 1 and/or > 150,000 m³ in volume, are generated in response to rainfall of over 100 mm. Hence, large floods in Nahal Oren stream occur not earlier than December. Precipitation and flow data were divided into two sub-periods: 1957–1969 and 1991–2003 and compared to each other. The results indicate a clear increase in the frequency of large floods, their magnitudes and volumes during the second period with no parallel change in the annual precipitation. Similarly, an increase in storm rainfall–runoff ratio from < 5% to > 15% and a decrease in the threshold rainfall for channel flow by 16–25% were documented. These short-term variations in flooding behavior are explained by the clear decrease in the length of the rainy season and by the resulting significant shortening in the duration of the dry-spells. The increase in the number of large rainfall events and the large floods in each hydrological year together with the increasing number of years with no floods indicate strengthening of their uncertainty of behavior.     

华南前汛期的锋面降水和夏季风降水 II. 空间分布特征

利用中国730站降水资料和第I部分(郑彬等,2006)得到的华南前汛期锋面降水和季风降水的划分日期,计算出1958-2000年华南前汛期锋面降水量(强度)和季风降水量(强度)的序列,采用EOF和扩展EOF分析方法,得到华南前汛期降水的几个主要分布型,并探讨锋面降水与季风降水的可能联系。分析结果表明:华南前汛期的锋面降水和季风降水分布主要有三种类型——全区旱涝型、西南涝(旱)东北旱(涝)型、东南涝(旱)西北旱(涝)型。各分布型的时间系数与850 hPa风场的相关结果表明不同的分布对应着不同的低层环流形势。统计结果显示华南前汛期锋面降水的分布形式与季风降水的分布形式有一定的对应关系。     

广西季气温、降水量异常频次的时空分布特征

根据世界气象组织二倍标准差和降水量距平百分率±60%标准,统计分析了广西88站1960年以来春季(2~4月)、前汛期(4~6月)、夏季(6~8月)、秋季(9~12月)和冬季(12~2月)的平均气温和降水量表明,近二十多年来,异常气候增加了,从季节看,冬季,不仅是发生异常高温和异常低温最多的季节,也是发生异常多雨和异常少雨最多的季节,更是异常气候空间分布范围最大的季节。     

2004年9月川渝大暴雨期间西南低涡结构及其环境场的分析

采用NCEP再分析资料、常规观测资料、卫星云图资料及地面降水资料, 对2004年9月2日～8日发生在川东和重庆的大暴雨的影响系统及其环境场作了分析研究。结果表明, 此次暴雨分为三个阶段, 降水系统主要有两个:第一、三阶段的主要降水系统是低空切变线；第二阶段的主要降水系统是西南低涡, 而西南低涡影响期内的雨量最强、范围最大。西南低涡开始时为一β中尺度系统, 最后发展达α中尺度系统。其影响时间从4日00时到6日06时 (国际协调时）, 持续了54小时。本文对此次暴雨过程所做的研究表明, 川东地区的特殊地形, 500 hPa高空小槽以及700 hPa、 850 hPa低层鞍型流场均是西南低涡产生和维持的重要条件； 西南低涡上层为暖性结构； 在暴雨过程中有20个雨团接连发生, 中尺度系统是这次暴雨的直接影响系统；对水汽收支的计算表明, 水汽可能来自于低纬度热带地区。本文还对西南低涡与东北低涡的异同作了比较。     

海温对辽宁省主汛期降水异常影响的统计分析

在对辽宁省主汛期降水异常的时变特征进行分析的基础上，研究了前期海温场对辽宁主汛期(7—8月)降水影响的统计特征。结果表明：1)辽宁省汛期降水异常有明显的年际、年代际变化特征，近44a降水呈减少趋势。小波分析表明存在3～5a的年际周期和10～12a的年代际周期。2)存在2个影响辽宁汛期降水异常的海温关键区及相应的关键时段，它们分别是南大西洋(1—5月)和西太平洋(3—4月)，综合考虑2个关键区可更好地预示辽宁汛期降水的异常。     

A Short-Term Climate Prediction Model Based on a Modular Fuzzy Neural Network

In terms of the modular fuzzy neural network (MFNN) combining fuzzy c-mean (FCM) cluster and single-layer neural network, a short-term climate prediction model is developed. It is found from modeling results that the MFNN model for short-term climate prediction has advantages of simple structure, no hidden layer and stable network parameters because of the assembling of sound functions of the selfadaptive learning, association and fuzzy information processing of fuzzy mathematics and neural network methods. The case computational results of Guangxi flood season (JJA) rainfall show that the mean absolute error (MAE) and mean relative error (MRE) of the prediction during 1998 2002 are 68.8 mm and 9.78%, and in comparison with the regression method, under the conditions of the same predictors and period they are 97.8 mm and 12.28% respectively. Furthermore, it is also found from the stability analysis of the modular model that the change of the prediction results of independent samples with training times in the stably convergent interval of the model is less than 1.3 mm. The obvious oscillation phenomenon of prediction results with training times, such as in the common back-propagation neural network (BPNN) model, does not occur, indicating a better practical application potential of the MFNN model.     

三峡水库汛期分期的变点分析方法研究

介绍了变点分析理论，结合三峡水库汛期的分期，阐述了均值变点、概率变点的理论与分析方法。采用宜昌站1882-2001年实测日流量资料，用均值变点分析方法对汛期每日最大洪峰构成的时间序列进行分期；同时选择一定的阈值，在假定发生概率服从二项分布的条件下，应用概率变点分析方法进行分期，最后给出了三峡水库汛期的分期方式。经比较表明，变点分析理论应用于汛期分期中，能反映来水的基本规律，具有一定的应用价值；但从理论上以及防洪的角度来讲，概率变点分析方法较均值变点方法更适于水库汛期的分期计算。     

Temporal Variability of Iron Speciation in Coastal Rainwater

Iron occurs in rain as particulateand dissolved Fe and includes both Fe(II) and Fe(III)species. Model calculations and correlation analysisindicate Fe(II)(aq) occurs almost exclusively as thefree ion whereas Fe(III)(aq) occurs as both ironoxalate and Fe(OH)₂ ⁺(aq) with largevariations over the pH range from 4.0 to 5.0. Complexation with humic-like compounds may also beimportant for Fe(III)(aq); however, the concentrationand structural characteristics of these compounds haveyet to be determined. 112 rain samples were collectedfor iron analysis in Wilmington, North Carolina,between 1 July 1997, and 30 June 1999. Total iron,particulate iron and Fe(III)(aq) were higher inconcentration in summer and spring rain relative towinter and autumn rain. Fe(II)(aq) concentrations, incontrast, did not vary seasonally. Particulate iron,which was approximately half the total rainwater iron,was highest between noon and 6 p.m. (EST), probably dueto more intense regional convection including land-seabreezes during that time. The ratio ofFe(II)(aq)/Fe(III)(aq) was also highest in rainreceived between noon and 6 p.m., which most likelyreflects photochemical reduction of Fe(III)(aq)complexes to form Fe(II)(aq). A conceptual modeldepicting the interplay between iron species, lightintensity and organic ligands in rainwater ispresented.     

广西前汛期暴雨天气过程的特征分析

通过对1959-1999年4～6月发生在广西的暴雨天气过程特征作一较系统的分析,得出4～6月广西出现暴雨天气过程的年平均次数分别为0.98、2.39、2.78次;4～6月不出现暴雨天气过程的机率分别为0.34、0.07和0.07;4～6月出现的暴雨过程的年平均日数为1.02、2.73和4.05d。