共查询到20条相似文献，搜索用时 140 毫秒
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云系模式研究:云场的宏微观结构模拟 总被引：7，自引：4，他引：7
用计算物理方法设计构造了一个云系模式，并用一个实例作为初始场进行了模拟，模拟的云场宏观特征与实况观测比较一致，微观结构比较合理，配套的模式输出数据处理和绘图程序包能给出云系的点（粒子谱）、线（垂直廓线）、面（结构剖面）、体（云场，云型，云量，云系形状）的多维宏微观结构的云场图象。 相似文献
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投影追踪（ＰＰ）方法是处理高维非正态数据的一种新兴的统计方法．ＰＰ主成分则采用一种稳定的散布度量依次得到“感兴趣”的投影方向及投影指标,有效地克服了非正态要素线性组合中的一系列不稳定问题（如离群点导致虚假的主成分、主向量的不稳定等）,还使前几个成分的... 相似文献
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本文通过读取极轨气象卫星1B(1A5)资料和MODIS的HDF文件,实现了极轨图像的两种投影算法--后向映射法、抛点法.后向映射法通过粗扫描、精扫描两步,经计算循环数最小值得出最佳的粗扫描步长,同时也是精扫描的子窗口大小,从而得到原始极轨图像的投影变换算法;抛点法通过获取源始图像中每个像素值的地理位置,将其投影到新的投影图中,充分利用了源文件的所有像素信息,最后将投影图上由于变形而没有数据的位置进行插值,从而实现数据的投影变换,该方法最大的优点是速度快,算法简单,可以应用到各种极轨图像的投影中去. 相似文献
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混合多项式是以切比雪夫多项式与三角级数所组成的多项式。文中首先给出混合多项式展开系数及度量展开精度的相对指标的计算式；再通过实例，展开不规则空间点要素场及单站单要素和单站多要素场。计算结果表明，混合多项式展开，不仅可用于等距空间点要素场展开，而且可用于不规则空间点及时间序列场展开；最后，对混合多项式展开气象要素场的数理意义等问题做了讨论 相似文献
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球函数分析中经向数值积分的改进方案 总被引：4，自引：3，他引：1
在全球气候场的球函数分析中,定积分∫＾ｎｏｑ（θ）ｓｉｎθｄθ的近似计算是重要的。本文基于几何分析给出了它的一个改进方案,对标准化缔化勒让德函数Ｐ＾ｍ,ｎ的模和正交性计算表明,它可以明显提高气候场球函数分析的精度。 相似文献
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基于CMA全球模式（CMA-GFS）2019年10月至2020年12月逐日20:00（北京时）起报的数据,对东北半球高空气象要素预报进行检验评估,检验的要素包括500 hPa位势高度场和风场、 850 hPa温度场和700 hPa相对湿度场。结果表明：（1）从模式预报效果的时间变化来看,预报效果有明显的季节变化,500 hPa位势高度和850 hPa温度的预报场和分析场的相似度在夏季最低,700 hPa相对湿度场的相似度在冬季最低;随着预报时效的增加,各要素的误差幅度在夏季最小。（2）从模式预报效果的空间变化来看,500 hPa位势高度场在东北半球大部分地区预报场与分析场具有较高相似度,且中高纬地区相对低纬地区更相似,预报误差的幅度则在低纬地区相对较小高纬地区相对较大,且预报偏差以大范围负偏差为主。相比而言,模式对东亚地区的位势高度及其梯度具有更高预报技巧。850 hPa温度场预报相似度和误差幅度与500 hPa位势高度场分布相似,预报偏差则主要表现为中高纬地区温度预报整体偏低,中低纬地区偏高。在预报前期（24～48 h）, 20°N以北的中高纬地区温度预报场与分析场相似度较高,均方根... 相似文献
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中国气候资料站网均匀化订正的一种方案及应用 总被引：2，自引：0，他引：2
定义了中国160站站网不均匀性的两个度量参数—站域面积和站网密度。在给定球冠区面积S0=50×104km2下求得了它们的值,并论证了其合理性。用它们构造了第一类权重函数,将该权重函数应用于中国160站站网1、4、7、10月气温的全国气候平均值及均方差值的计算,得到了合理的结果。同时,构造了第二类权重函数,并应用于气温距平场时间序列的订正,对订正前、后的距平场序列进行EOF（empiricalorthogonalfunctions）分析,论证了订正后的结果优于订正前。 相似文献
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通过对大气流场在奇点处作速度场分解,确定雅可比矩阵特征值与大气运动形式之间的关系,以分析二维气旋、反气旋流场的特性,进一步了解实际二维大气的单个涡旋形态的动力学特性和形成机制。研究认为,任意水平速度场均可分解为线性的含有涡度场（与反对称矩阵对应）和变形场（与对称矩阵对应）的形式。高层地转平衡的高（低）压系统,奇点附近只有负（正）涡度场而无变形场,在天气图上表现为只有顺（逆）时针旋转的闭合涡旋。低层考虑摩擦的高（低）压系统,奇点附近不仅有负（正）涡度场,还有变形场。也就是说,在北半球高压不仅有顺时针旋转气流,还有向外的辐散气流;低压不仅有逆时针旋转气流,还有辐合气流。 相似文献
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为了研究全球大气位势高度场的气候变率, 利用NCEP/NCAR再分析资料, 按照距平高度场平均强度指数 (Ia) 分析发现, 半球距平高度场强度呈年单周振荡, 冬大夏小, 冬季随高度单调增大, 夏季有弱高、低值中心出现, 而北、南半球的差异明显表现在季节变化上; 进一步根据半球大气位势高度距平场球函数谱低维、低阶的基本特征, 将半球环流异常分为半球均匀异常 ( H ′00)、纬向均匀异常 ( H ′0)、超长波尺度异常 ( H ′ul) 和长波尺度异常 ( H ′l) 4种类型, 用波数域0≤m, k≤6上的球函数系数资料求得它们的方差贡献, 给出了4类异常的方差贡献随高度、季节变化的规律以及它们的半球际差异。由此得到异常环流球函数谱结构的总体特征为:对流、平流层之间存在明显变化。从对流层进入平流层, 一般由超长波异常为主转为纬向均匀异常为主 (冬半球) 或半球均匀为主 (夏半球); 半球均匀异常在对流层中不重要, 长波尺度异常在平流层中不重要, 它们拟合异常方差一般均小于10%; 北、南半球最大差异表现在冬季平流层R′00和冬、夏季对流层R′0南半球大于北半球, 冬、夏季对流层R′l北半球大于南半球。 相似文献
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利用WRF模式,对热带气旋“彩虹”（1522）登陆过程开展了高分辨率数值模拟,模拟验证表明:模式较成功地模拟出了“彩虹”的移动路径、强度变化和降水分布。利用高分辨率模拟资料,分析了“彩虹”登陆期间的大风分布以及热、动力结构特征,结合切向风动量方程开展了模拟诊断,结果表明:切向风动量方程各项在近地面层和边界层顶代表高度上的平面结构诊断分析显示,近地面（0.4 km）层上,VVOR（角动量径向平流项）和VPGF（切向气压梯度项）是切向风变化的最大贡献项;边界层顶（1.3 km）附近,VPGF和VVA（切向动量垂直平流项）对切向风起到正加速作用,而VVOR则根据入流（出流）特征,起到正（负）加速作用。切向风动量方程各项的轴对称平均结构诊断分析显示,“彩虹”登陆前,VVA和VVOR是决定切向风变化的主要贡献项。 相似文献
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采用地形坐标系下适合于复杂地形且满足地-气耦合的静力学三维中-β尺度气象预报模式,使用08时的实测流场经变分法初始化后得到的初始流场,模拟研究了上海地区的局地流场时空演变特征。模式较细致地考虑了湍流、长短波辐射、凝结、蒸发、地表热力平衡等因子,在此基础上,使用有限元法数值求解一阶闭合的三维欧拉平流扩散方程,模拟了上海地区的SO2浓度分布。结果表明:上海的局地流场具有明显的日变化特征,受海陆温差的影响明显,日间风速较夜间风速大,风向呈顺时针旋转;在不稳定层结情况下,高架点源排放的高空污染物对地面的污染物浓度有贡献,会造成地面污染物浓度升高。 相似文献
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Xiaoqiong ZHEN Shuqing MA Hongbin CHEN Guorong WANG Xiaoping XU Siteng LI 《大气科学进展》2022,39(3):386-402
A novel weather radar system with distributed phased-array front-ends was developed. The specifications and preliminary data synthesis of this system are presented, which comprises one back-end and three or more front-ends. Each front-end, which utilizes a phased-array digital beamforming technology, sequentially transmits four 22.5°-width beams to cover the 0°–90° elevational scan within about 0.05 s. The azimuthal detection is completed by one mechanical scan of0°–360° azimuths within about 12 s volume-scan update time. In the case of three front-ends, they are deployed according to an acute triangle to form a fine detection area(FDA). Because of the triangular deployment of multiple phased-array front-ends and a unique synchronized azimuthal scanning(SAS) rule, this new radar system is named Array Weather Radar(AWR). The back-end controls the front-ends to scan strictly in accordance with the SAS rule that assures the data time differences(DTD) among the three front-ends are less than 2 s for the same detection point in the FDA. The SAS can maintain DTD < 2 s for an expanded seven-front-end AWR. With the smallest DTD, gridded wind fields are derived from AWR data, by sampling of the interpolated grid, onto a rectangular grid of 100 m ×100 m ×100 m at a 12 s temporal resolution in the FDA. The first X-band single-polarized three-front-end AWR was deployed in field experiments in 2018 at Huanghua International Airport, China. Having completed the data synthesis and processing, the preliminary observation results of the first AWR are described herein. 相似文献
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Summary The dependence of the albedo on illumination direction is analyzed by constructing a canopy model in which the individual leaves are planar, Lambertian reflectors. Leaf transmission is treated separately, and is assumed to be proportional to the cosine of the zenith angle of the leaf normal. Effects of shading and obscuration are formulated assuming random distribution of the leaves with respect to the viewing and illumination directions. Variants of the model with different azimuthal leaf distributions are created and discussed as explicit expressions of the viewing/illumination geometry and the canopy characteristics.The canopy spectral single-scattering albedo factors, which are the conditional probabilities of a photon escaping from the canopy after a first reflection or a first transmission, are obtained by numerical integration over a hemisphere of the bidirectional reflectance and transmittance factors. Our analysis identifies the ratio of the projection of leaf area on the vertical plane perpendicular to the principal plane to that on a horizontal plane as the parameter that controls the dependence of the albedo on the solar zenith angle. The albedo factor due to the leaf transmittance generally increases with the zenith angle of illuminating beam more sharply than that due to the leaf reflectance.Model variants with various azimuthal distributions are compared with measured albedo of soybeans. Second and higher order scatterings are accounted for in a simplified way. The degree to which a model variant fits the measured albedo and its change with the solar zenith angle depends both on the leaf inclination angleand the azimuthal distribution of the leaf area.With 6 Figures 相似文献
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Summary Wet and dry spell properties of monthly rainfall series at five meteorology stations in Turkey are examined by plotting successive
wet and dry month duration versus their number of occurrences on the double-logarithmic paper. Straight line relationships
on such graphs show that power-laws govern the pattern of successive persistent wet and dry monthly spells. Functional power
law relationships between the number of dry and wet spells for a given monthly period are derived from the available monthly
precipitation data. The probability statements for wet and dry period spells are obtained from the power law expressions.
Comparison of power-law behaviours at five distinct sites in Turkey provides useful interpretation about the temporal and
spatial rainfall pattern. As in temperate areas such as Turkey the rainfall amounts change mostly due to one-month-long dry
or wet spells.
Received August 29, 1995 Revised November 9, 1995 相似文献
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闭合气压系统中心分布特征量及应用 总被引：5，自引：0，他引：5
用单位半径球面上闭合气压系统环流指数P（强度）、C（中心位置）的多年序列,构造了历年系统中心在C-周围分布的3个特征量：1）平均距离r,它定义为历年系统中心C偏离于气候中心C-（即中心位置异常C′）的权重几何平均距离,是系统中心分布区域大小的度量;2）压缩系数μ,它描述了历年系统中心分布区域偏离于圆形的程度,是历年系统中心位置分布各向异性的度量;3）极大异常方向β,它用系统中心极大异常偏离-C处正东方向的角度,给出了系统中心的主要异常方向。对1948—2007年6、7、8月100hPa南亚高压中心位置分布特征量的计算结果表明,它们能简要、精确地描述系统中心位置异常在球面上的分布特征。根据r、μ、β的定义,它们也适用于精确描述球面上其他要素场中闭合系统中心在球面上的分布特征。 相似文献
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气象要素场等值线图自动绘制 总被引：1，自引：0，他引：1
根据业务的特殊性研制的气象要素等值线图绘制软件,通过把离散站点自动连接成符合Delaunay特性的不规则三角形网格,自动生成的等值线符合人们手工绘制等值线规则,可以绘制气象要素和北太平洋海温等值线分布图,绘制海陆边界并填充颜色。通过自定义的坐标系,很好地解决了屏幕坐标与实际坐标之间的转换、地图投影的实现等问题。程序具有丰富的绘图功能,可以根据需要手工绘制各种矢量图形对象和插入图像对象,能修改对象属性,包括随意移动位置、改变大小等,可以设置各种对象的显示顺序,能设置对象为Alpha混合透明显示。图形对象实现矢量级别的无级缩放,实现精细打印功能,满足日益发展的业务需求。 相似文献
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Extensive turbulence measurements from the Limagne and Beauce experiments were used to compute a characteristic time scale of the turbulence field (Τ = second moment/dissipation rate) for turbulent kinetic energy, temperature and humidity variances, and temperature-humidity covariance. The height variations of these time scales were analysed. The characteristic half-time scale Τ/2 of the turbulent velocity field was found, as expected, to be of the same order of magnitude as the large-eddy time scale Τ L = Zi/w*, showing that the turbulence structure is controlled by large eddies in the bulk of the mixed layer. The increase of Τ/2 above z/Z i ～- 0.7 implies, however, that this time scale is no longer relevant to destruction of turbulent kinetic energy in the statically stable region with negative heat fluxes. An effective time scale Τeff, introduced by Zeman (1975), has been computed and its behaviour discussed. The scales for θ′ 2, q′2, and θ′q′ were found to be much shorter than Τ. Furthermore, a significant difference in behaviour was also revealed between the characteristic time scales of temperature and humidity fields in the stable layer. By using these experimental estimates, we tested some of the models for molecular dissipations, which are currently in use in higher order closure atmospheric boundary-layer models. The parameterized dissipation rates for θ′ 2, and q′ 2 agree well qualitatively with experimental estimates in the bulk of the mixed layer. In the stable layer, however, the parameterized dissipation rate ε θ tends to become larger than the experimental ones although the parameterized dissipation rate ε q still agrees with the experimental ones. For the molecular dissipation of θ′q′, this current model becomes physically inconsistent in the middle part of the mixed layer, because this term may become a production term for temperature-humidity covariance. 相似文献