The characteristics of ultraviolet radiation in arid and semi-arid regions of China

Measurements of the broadband global solar radiation (R _S) and total ultraviolet radiation (the sum of UV-A and UV-B) were conducted from 2005 to 2010 at 9 sites in arid and semi-arid regions of China. These data were used to determine the temporal variability of UV and UV/R _S and their dependence on the water vapor content and clearness index. The dependence of UV/R _S on aerosol optical depth (AOD) and water vapor content was also investigated. In addition, a simple and efficient empirically model suited for all-weather conditions was developed to estimate UV from R _s. The annual average daily UV level in arid and semi-arid areas is 0.61 and 0.59 MJ m^?2 d^?1, respectively. The highest value (0.66?±?0.25 MJ m^?2 d^?1) was recorded at an arid area at Linze. The lowest value (0.53?±?0.22 MJ m^?2 d^?1) was recorded at a semi-arid area at Ansai. The highest daily value of UV radiation was measured in May, whereas the lowest value was measured in December. The monthly variation of the UV/R _s ratio ranged from 0.41 in Aksu to 0.35 in Qira. The monthly mean value of UV/R _s gradually increased from November and then decreased in August. A small decreasing trend of UV/R _s was observed in the arid and semi-arid regions due to recently increasing amounts of fine aerosol. A simple and efficient empirically model suit for all-weather condition was developed to estimate UV from R _s. The slope a and intercept b of the regression line between the estimated and measured values were close to 1 and zero, respectively. The relative error between the estimated and measured values was less than 11.5%. Application of the model to data collected from different locations in this region also resulted in reasonable estimates of UV.     

An indicator of sand storms in the south of the Tengger Desert

The Shagou section contains rich information about the formation and evolution of sand storms in the windward side of of the Tengger Desert (southern Tengger Desert, east of the Hexi Corridor). By investigating the grain size classes and the standard deviation of three sample groups in the Shagou section we discover that every group has four sensitive grain size components, and each sensitive grain size component has a tendency to be finest for the palaeosol stratum, coarsest for the sand stratum, and the loess intermediate between the two. The three sample groups have differences in their grain size distributions. Both S1 (average) and L1 (average) have two peaks. L1 (sand stratum) has three peaks and an additional coarse peak (275.4-550 µm) which is consistent with the grain size distribution pattern of the modern sand storm samples in the Tengger Desert. Moreover the additional peak of the palaeo-sand stratum correspondingly the interval of the grain size is exactly consistent with one of the four sensitive grain size components. Because the sand stratum in L1 of the Shagou section was the direct result of sand storm process of the Tengger Desert, the sand group percent of 275.4-550 µm in the Shagou section could be used as a sensitive indicator of sand storm in the south of the Tengger Desert (east of Hexi Corridor).     

基于城市交通脆弱性核算的大雾灾害风险评估

选用大雾观测资料测算城市地区的雾灾危险性指数,以规则网格作为评估单元,逐网格计算网格区域内的路网密度,以此作为雾灾的空间脆弱性指标,并针对重点设施的分布情况对脆弱性指数进行空间叠加订正;选用网格内的人口密度作为雾灾的易损性指标;危险性、脆弱性及易损性3项指标按5:2:1的分配比例综合测算雾灾的风险指数。实例研究选用北京地区1996年1月—2006年12月的大雾资料,按空间网格化方法对大雾灾害风险进行评估,结果表明:北京地区雾灾脆弱性指数的高值区域与高速路及环城路延伸方向一致,城市中心为人口集中分布地区,其综合风险指数高,与高速路段、环城路及机场等地段均为雾灾的高风险区域,北京东南部地区年平均雾日数相对较多,危险性指数值也较高,是雾灾较高风险区域。     

采用绘图法获取避雷针最小高度的方法

给定保护物高度和保护物高度处的保护半径,求取避雷针的最小高度通常只能通过国标中给出的计算式进行反算。以单支避雷针为例介绍了采用AutoCAD软件绘图获取避雷针最小高度的方法。     

内蒙古高等级公路道路结冰预报方法初探

利用1990—2007年内蒙古高等级公路包头—兴和段4个气象站监测的结冰和积雪资料,分析得出可能发生道路结冰的天气气候背景。并利用1990—2000年包头—兴和段可能发生道路结冰现象的降水天气过程的气象资料,总结出6种天气环流概念模型,为预报内蒙古高等级公路道路结冰提供参考。     

The Effects of Line-Wing Cutoff in LBL Integration on Radiation Calculations

There are three basic methods in radiative transfer calculations, i.e., line-by-line (LBL) integration, correlated k-distribution method, and band model. The LBL integration is the most accurate of all, in which, there are two quadrature algorithms named in this paper as integration by lines and by sampling "points when calculating atmospheric transmittance in the considered wavenumber region. Because the LBL integration is the most expensive of all, it is necessary and important to save calculation time but increase calculation speed when it is put into use in the daily operation in atmospheric remote sensing and atmospheric sounding. A simplified LBL method is given in this paper on the basis of integration by lines, which increases computational speed greatly with keeping the same accuracy. Then, we discuss the effects of different cutoff schemes on atmospheric absorption coefficient, transmittance, and cooling rate under both of accurate and simplified LBL methods in detail. There are four cutoff schemes described in this paper, i.e., CUTOFFs 1, 2, 3, and 4. It is shown by this numerical study that the way to cut off spectral line-wing has a great effect on the accuracy and speed of radiative calculations. The relative errors of the calculated absorption coefficients for CUTOFF 2 are the largest under different pressures, while for CUTOFF 1, they are less than 2% at most of sampling points and for CUTOFFs 3 or 4, they are ahnost less than 5% in the calculated spectral region, however, the calculation time is reduced greatly. We find in this study that the transmittance in the lower atmosphere is not sensitive to different LBL methods and different cutoff schemes. Whereas for the higher atmosphere, the differences of transmittance results between CUTOFF 2 and each of other three cutoff schemes are the biggest of all no matter for the accurate LBL or for the simplified LBL integrations. By comparison, the best and optimized cutoff scheme is given in this paper finally.     

北京市奥运期间气象灾害风险承受与控制能力分析

针对北京市奥运会期间的7种主要气象灾害(雷电、冰雹、大风、高温、暴雨、大雾和霾灾害),建立了气象灾害风险承受能力与风险控制能力评价的指标体系.经过专家评分,获取7种气象灾害的评价指标所对应的分值.利用层次分析法,计算评价指标的权重系数.最后得到7种气象灾害评价指标的加权平均值作为其风险承受能力与风险控制能力系数.利用灾害模数、经济易损模数、生命易损模数3个指标进行北京市奥运期间18个区县空间易损度区划分析.结果表明:北京市奥运会期间,高温灾害和暴雨灾害的风险承受能力与风险控制能力最弱;雷电灾害和大雾灾害的承受与控制能力中等;冰雹灾害和霾灾害较强;大风灾害最强.易损度空间差异分析表明,城区(东城区、西城区、崇文区和宣武区)、朝阳区和海淀区为高易损性区域;丰台区、石景山区、房山区、昌平区、顺义区和大兴区为中易损性区域;门头沟区、通州区、平谷区、怀柔区、密云县和延庆县为低易损性区域.     

北京自动气象站实时数据质量控制应用

自动气象站(AWS)观测资料是中尺度、短时效天气预报不可缺少的重要资料源之一.但由于AWS观测资料的特殊性,其质量问题不同程度地阻碍了它的使用.因此,AWS观测资料的质量控制越显重要.北京市气象局设计的自动气象站观测数据质量控制的方案主要是物理极值检查、历史极值检查、内部一致性检查、时间一致性检查、空间一致性检查等方法并把它应用于北京地区2007年奥运气象服务演练,取得了令人鼓舞的效果.结果表明:该质量控制方案的建立,能够实时反映北京市气象局自动站观测数据的可靠性,同时也反映出数据的缺测和及时性也存在一些问题.此系统的运行对2008年奥运气象服务,特别是对INFO2008和城市运行实时数据服务的可靠性将会发挥重要作用.     

沙澧河流域两场大暴雨过程的对比分析

利用常规观测资料、自动站资料和NCEP1°×1°再分析资料对2007年7月5日和14日沙澧河流域两场大暴雨过程进行了诊断对比分析.结果表明:不同影响系统下产生的大暴雨过程其动力机制有所差异.垂直螺旋度计算结果显示:两次过程700hPa等压面上正垂直螺旋度中心的移向和强度变化与降水落区及趋势变化有很好的对应关系,暴雨区出现在正垂直螺旋度中心移动的前方,对流域大暴雨的落区有一定的指示意义.5日呈现中低层正、高层负的垂直螺旋度配置,动力条件更有利于大暴雨的发生.湿位涡演变分析发现,5日中低层既存在对流不稳定,又存在对称不稳定,有利于垂直对流和倾斜对流发生,造成流域大暴雨.14日中低层大气处于对流稳定状态,但边界层和中层存在对流不稳定,同时中层还存在较强的对称不稳定,垂直涡度得到较大增长,导致上升运动的加强和水汽的垂直输送,有利于降水增幅.     

北京奥运演练精细化预报方法及其检验评估

2007年北京奥运演练期间精细化场馆客观预报方法,即支持向量机方法(SVM)和半周期函数拟合(HPFF)预报方法,为场馆精细化预报产品的制作提供了有力的技术支撑.利用2007年8月1-26日国家体育场、顺义水上中心等5个奥运场馆的5种地面气象要素(气温、相对湿度、风向、风速、和3小时累积降水量)观测资料,对SVM和HPFF客观预报方法以及预报员在客观方法基础上制作的3天逐3小时预报进行了检验评估.结果表明:(1)两种客观方法相比较,HPFF方法对于预报连续变化的气象要素(如气温、相对湿度和风速)的精细预报比SVM方法预报技巧高;而对不连续变化的变量(如:风向)的预报技巧低于SVM方法.(2)预报员制作精细要素预报在很大程度上依靠客观方法.预报员对于气温、相对湿度和风速的预报技巧略高于客观方法,对于降水和风向的预报技巧与客观方法相当.尽管预报员对客观方法的修正能力比较有限,但具有对两种客观方法结果做出择优选择的综合判别能力;(3)预报员0～63小时气温预报平均绝对误差约为1.8℃,气温预报误差≤1℃的准确率在43%左右,预报误差随预报时效变化不大;0～24小时相对湿度预报平均绝对误差约为10%,相对湿度预报误差≤10%的准确率是60%,误差随预报时效而有所增大;0～63小时风向预报准确率约20%,预报准确率随预报时效变化不大;0～63小时风速预报平均绝对误差在0.8～1.4m·s-1之间.