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201.
雷击地闪密度与雷暴日数的关系分析 总被引:13,自引:4,他引:9
根据美国卫星观测得到的我国各省区年平均总闪电资料并计算出各省区的年平均地闪密度(以下简称地闪密度);根据全国各省区220个站点的年平均雷暴日资料,按照<建筑物防雷设计规范>GB50057-94(2000年版)(以下简称<规范>)公式计算出全国各省区的地闪密度.比较两种方法得出的地闪密度,发现存在较大的差异,且不同区域差异变化很大.用单位雷暴日地闪密度概念,分析了我国各地单位雷暴日地闪密度的差异及其原因,指出单位雷暴日地闪密度能粗略反映与我国气候特征相适应的地闪密度的分布状况.进一步分析湖州市2007年人工观测和闪电定位仪观测的闪电资料,得到相同的结论.从而提出<规范>规定的地闪密度计算公式存在较大误差,应对其进行进一步的修订和完善. 相似文献
202.
Mesoscale Analysis of a Heavy Rainfall Event Along the Huaihe River Valley During 8-9 July 2007 下载免费PDF全文
During 8-9 July 2007,several successively developed rainstorms along the Meiyu front produced heavy rainfall in the Huaihe River Valley,which led to the most catastrophic flooding in this region since 1954.Through mesoscale analysis of both conventional and intensive observations from upper air and surface stations,automatic weather stations,Doppler radars,and the FY-2C satellite,the current study examines the developing style and environmental conditions of the mesoscale convective systems(MCSs)that led to the development of the rainstorms.Our analysis showed that this event went through three phases.The first phase of the heavy rainfall(Phase Ⅰ)was caused by a meso-α-scale wind shear in the lower troposphere during 0200-1700 BT(Beijing Time)8 July.Phase Ⅱ was characterized by a reduction in rain rate and the formation of a low-level vortex between 1700 BT 8 and 0200 BT 9 July.In Phase Ⅲ,the well-organized mature meso-α-scale low-level vortex brought about intensified rains during 0200-0800 BT 9 July.Satellite and raclar observations showed a backward development of MCSs(new convective cells were generated at the back of the system)in PhaseⅡ,a forward development in Phase Ⅲ,and a spiral organization of the convective lines in Phase Ⅱ.The heavy rainstorm systems were initiated continuously along a surface mesoscale dew-point front with a horizontal scale of~300 km(as part of the Meiyu front)in the upper reaches of the Huaihe River Valley near Fuyang City,Anhui Province and then gradually decayed in the middle and lower reaches.It is hypothesized that lifting by strong low-level convergence is sufficient to trigger convection in the high CAPE(convective available potential energy)environment. 相似文献
203.
The relationship between dust weather frequency (DWF), which denotes the
number of days of dust weather events, over Beijing and the East Asian
Monsoon (EAM) was studied using DWF data for Beijing during the period
1951--2006. Results show that, during this period, the blowing-dust weather
frequency (BDWF), as well as the indices of East Asian winter monsoon (EAWM)
and East Asian summer monsoon (EASM), all decreased considerably, with a
t-test confidence level of 99%. The correlation coefficients between the
chosen EAWM index and BDWF over Beijing in winter and the following spring
were 0.34 and 0.33, respectively, with significance levels of 0.01 and 0.02,
respectively. For the chosen EASM index and BDWF, these correlation
coefficients were 0.51 and 0.45, respectively, with both at a confidence
level exceeding 99.9%. With the linear trends removed, the values (in the
same order as above) were 0.14, 0.14, -0.12, and -0.09, all not significant
at the 95% confidence level. Clearly, the EAM relates mainly to DWF over
long timescales. To a certain extent, the EAM might have some impact on DWF
by affecting the associated surface air temperature and precipitation during
the corresponding time period in sand-dust source regions at the interannual
scale. A stronger (weaker) EAWM might advance (suppress) the occurrence of
DWF, and the opposite for the EASM. 相似文献
204.
Continuous Measurement of Number Concentrations and
Elemental Composition of Aerosol Particles
for a Dust Storm Event in Beijing 总被引:1,自引:0,他引:1
A continuous measurement of number size distributions and chemical composition of aerosol particles was conducted in Beijing in a dust storm event during 21-26 March 2001. The number concentration of coarse particles ( 〉2μm) increased more significantly than fine particles ( 〈2μm) during the dust storm due to dust weather, while the anthropogenic aerosols collected during the non-dust-storm period tended to be associated with fine particles. Elemental compositions were analyzed by using proton-induced X-ray emission (PIXE). The results show that 20 elements in the dust storm were much higher than in the non-dust-storm period. The calculated soil dust concentration during the dust storm was, on average, 251.8μg m^-3, while it was only 52.1μg m^-3 on non-dust-storm days. The enrichment factors for Mg, A1, P, K, Ca, Ti, Mn, Fe, C1, Cu, Pb, and Zn show small variations between the dust storm and the non-dust-storm period, while those for Ca, Ni and Cr in the dust storm were much lower than those in the non-dust-storm period due to significant local emission sources. A high concentration and enrichment factor for S were observed during the dust storm, which implies that the dust particles were contaminated by aerosol particles from anthropogenic emissions during the long-range transport. A statistical analysis shows that the elemental composition of particles collected during the dust storm in Beijing were better correlated with those of desert soil colleted from desert regions in Inner Mongolia. Air mass back-trajectory analysis further confirmed that this dust storm event could be identified as streaks of dust plumes originating from Inner Mongolia. 相似文献
205.
206.
基于单站短弧段光学观测的低轨卫星轨道预报算法 总被引:1,自引:0,他引:1
基于单站短弧段的目标跟踪预报技术是保证高精度光电经纬仪在非常规环境下正常跟踪捕获目标的重要途径.构建了基于非线性滤波器的跟踪预报算法,能够在正常情况下为闭环跟踪提供引导数据,同时构建了基于非线性变换的目标预报算法,可以在无有效观测数据情况下为经纬仪提供轨迹引导,保证目标不丢失.证明了非线性滤波在单站短弧段跟踪预报算法中比常规扩展卡尔曼滤波(Extended Kalman Filter,EKF)更有效.计算表明,本文设计的非线性滤波器可以作为光学跟踪设备的引导算法,引导精度同经纬仪的随机测量精度等量级,在设备系统误差达到50"时,预报60 s的精度可达到20",仍然满足跟踪设备的视场要求. 相似文献
207.
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209.
横切潍北-莱州湾凹陷郯庐断裂带的地震反射剖面和断裂带内的凹陷断层、沉积相和油气特征,直接或间接显示了郯庐断裂带的延伸、运动性质和活动时限。郯庐断裂带在海域和陆上的几何形态及其组合基本一致,根据切过断裂带的剖面和平面上断层的组合特征,判断其为兼具垂直位移的走滑运动断层系。走滑断裂带的活动控制着凹陷内同构造沉积以及构造样式,表明郯庐断裂带的活动时限具分段性,相当于渤海湾盆地孔店组(E1?2k)-沙四段(E2?3s4)沉积期(古新世-早始新世)-孔店组-沙二段(E2?3s2)沉积期(古新世-始新世)-孔店组-沙一段(E2?3s1)(古新世-渐新世)沉积时期,走滑拉分活动由南向北迁移; 活动方式也由古新世-早始新世的左旋走滑活动,被早始新世之后的右旋走滑活动所替代。 相似文献
210.