到达地面的紫外辐射强度预报

紫外线指数一般用 0～ 1 5的数字来表示 ,通常规定 ,夜间的紫外线指数为 0 ,在热带高原地区 ,晴天无云时的紫外线指数为 1 5。世界气象组织规定了单位紫外线指数相当于 2 5 m W/m2 红斑加权剂量率。紫外线指数预报大致可分为统计预报方法和模式预报方法两种。统计预报方法主要依赖于高精密度、高准确性的紫外线实测资料和相关的气象要素观测 ;而模式预报方法则主要依赖于对平流层臭氧的预报和大气辐射传输模式的应用     

Water level and atmospheric humidity history of Lake Ichkeul (northern Tunisia) during the last 3000 years

Changes in paleoecology and climate of northern Tunisia during the last 3000 years were reconstructed based on the flood history interpreted from a 172-cm sediment core of Lake Ichkeul (NW Tunisia). Seven wet/dry episodes were identified based on biological (ostracods, foraminifera and mollusks) and biotic indices (H and E index, species richness and abundance). These proxy-based environmental changes were supported by correspondence analyses (CAs) and ecophenotypic responses of the brackish taxon Cyprideis torosa in addition to a grain-size study. Two dry episodes were identified in the lower (EP1) and upper (EP7) parts of the core. These were marked by the dominance of the brackish ostracod C. torosa. High water salinity was indicated by the presence of the brackish ostracod Loxoconcha elliptica, the foraminifer Ammonia sp. and lagoonal mollusks. The occurrence of the freshwater ostracods Ilyocypris sp., Herpetocypris sp., Dawinula stevensoni and Limnocythere inopinata was associated with high species richness and ecophenotypic changes of C. torosa valves indicating lower salinity during three major wet episodes (EP2, EP4, and EP6). The ecological and environmental changes, occurring between 3050 and 50 cal. year BP, are most likely linked to an increase of fluvial inputs which are also recognized in several other Mediterranean lakes. The humid episodes were interrupted by two saline periods (EP3 and EP5) during which freshwater ostracod assemblages declined, diversity indices dropped to the lowest values, and fine-grained sediments became dominant. The top of the core is characterized by the remarkable dominance of L. elliptica coupled with C. torosa, the absence of freshwater ostracods, and the changes in grain-size sediment parameters which are most likely the result of anthropogenic activities. The changes in hydrochemistry and sedimentology were attributed to the deepening of the Bizerte navigation canal, main wadis damming, and Tinja sluice construction which mostly occurred in the XX^th century.     

LONG-TERM VARIATIONS OF FOG AND MIST IN MAINLAND CHINA DURING 1951-2005

Fog is an important indicator of weather. Long-term variations of fog and mist were studied by analyzing the meteorological data from 743 surface weather stations in mainland China during 1951-2005. In climatology, there are more foggy days in the southeast than in the northwest China and more in the winter half of the year than in the summer half. The decadal change of foggy days shows regional variation. Southwest China is the region with the most foggy days, and more than 20 foggy days occur in Sichuan Basin in one year. Persistent heavy fog usually appears in winter and spring over the North China Plain and Northeast China Plain. Misty days are much more frequent in the provinces south of the Yangtze River than in the regions north of it, and there is an obvious increase of misty days after the 1980s. Southwest China is the area with the most number of misty days, and more than 100 misty days occur in Sichuan Basin in a year.     

广州市地面太阳紫外线辐射观测和初步分析

通过对广州市2000～2001年两年的地面紫外线辐射观测资料的分析表明广州市全年紫外线辐射强度84.3%出现在"中等"以上级别,"强"、"很强"级别占65.1%,尤其是第二、三季度分别有46.2%、62.1%的时间紫外线出现"很强"级别,分析表明广州市属于紫外线高辐射地区;各候(旬)的最小紫外线指数在夏秋季节的涨落脉动比冬春季节要大,尤其是秋季更加明显.另外,定义了每月云衰减因子(CAF),12～4月为明显的云衰减加强期;6～9月为明显的云衰减减弱期,分析期间最大云衰减因子仅为0.11.     

海口地区近地层流场与海陆风结构的研究

对海口市西郊观测的近地层流场与低空风、温探测资料进行了综合分析，讨论了位于我国北热带的海口市西郊近地层的流场特征，以及低层海陆风发生发展的观测实例及其规律。发现雨季海陆风出现频率达７５％，白天海风持续时间一般为１－４小时，最长可达１０小时。     

A STUDY ON LOW－LEVEL ATMOSPHERIC STRUCTURE ON THE SEASIDE BORDERS TO THE WEST OF HAIKOU

In this paper, the observed data of low-level wind and temperature collected from western outskirts of Haikou city, Hainan Island, are analysed. Mean boundary layer structure, generation and development of ground-level inversion and inner boundary layer on the coastal area of interest, which is in China,s northern tropical area, are analysed. It is found that an inner thermal boundary layer can be produced under intense insolation in both dry and rainy seasons, and the mixing layer on the coast is remarkably deeper than that of inland.     

南岭山地浓雾的宏微观物理特征综合分析

通过对南岭山地进行的雾野外观测资料以及数值试验的综合分析,得到了南岭山地浓雾和能见度的季节分布特征、雾滴谱微观特征与浓雾形成的物理概念图像。在秋末和冬春季节,南岭山地恶劣能见度出现的频率很高,能见度≤200 m浓雾过程的出现频率平均为24.7%,最高可达41.8%;冬春季节南岭山地出现的雾是复杂的微物理过程、局地地形、水汽输送与影响天气系统等宏微观相互作用的结果,属于平流雾、爬坡雾类型,与辐射雾明显不同,局地山地抬升冷却凝结对雾的形成起重要的作用,迎风坡对雾的形成有利,在海拔较低的迎风坡也可能出现浓雾,从而导致低能见度;南岭山地的雾以小滴谱为主,数密度比城市雾小,小粒子段谱型基本呈下降趋势;在多个微观变量中,含水量与能见度的反相关性最好;雾含水量等微结构特征量的起伏变化,与雾体本身的微物理过程有关外,雾体随环境风的平移过程中,不规则的爬坡、翻越山坡的运动是造成雾体微结构不均匀、振荡起伏变化的重要原因。     

广州地区汛期强降水的微物理特征

分析了广州地区从化测站１９９４年６月份的雨滴谱资料，发现造成华南特大洪涝灾害的６月份降水的特点是：降水时间长，雨强、雨滴浓度、尺度均较大，最大雨滴直径为６．５ｍｍ，最大雨强为１５５．０６ｍｍ／ｈ。另外，按天气系统、降水性质综合考虑分类，把降水分成５大类，提供了一组可供雷达定量测量降水时参考和应用的Ｚ－Ｉ关系。     

利用风廓线雷达资料对广州地区边界层日变化特征的分析研究

利用2010年11—12月亚运会期间设在广州五山站的车载式边界层风廓线雷达资料,对广州地区晴天条件下的边界层日变化特征进行分析。结论表明:（1） 折射率结构常数具有明显的日变化特征。夜间,受大气层结的抑制作用,湍流强度较弱,折射率结构常数的观测值约为10-17～10-18 m-2/3;白天,湍流在热力作用和动力作用的共同影响下,从底层大气向自由大气发展,观测值比夜间可增大两个量级,且在边界层顶部有较大阶跃。（2） 利用风廓线雷达谱宽资料可算出湍流耗散率,作为一种新的风廓线雷达二次产品,该参数对湍流的描述更为准确和细致。在晴天条件下,广州地区边界层顶从08时开始迅速上升,11时前后达到1 300 m左右,在日落前基本维持这个高度不变。