Closed families of periodic solutions of a restricted three-body problem     

A. D. Bruno  V. P. Varin 《Solar System Research》2009,43(3):253-276

The planar restricted three-body problem has an infinite number of families of symmetric periodic solutions (SPSs). The natural SPS families include certain families which are self-closed with respect to small variations in a parameter. These families remain closed for any admissible variations in the mass parameter μ. However, there are closed SRS families of another type, which exist only in bounded intervals of μ and are formed via self-bifurcations of some SPS families. This type of SPS families is poorly understude. This work describes the initial stage (4 bifurcations) of a bifurcation cascade of the natural family i and points out other closed SPS families known to date.  相似文献   

Numerical Simulations of Sheltering in Valleys: The Formation of Nighttime Cold-Air Pools     

S. B. Vosper  A. R. Brown 《Boundary-Layer Meteorology》2008,127(3):429-448

Numerical simulations of flow over two-dimensional valleys are conducted in order to study the occurrence of pools of cold air that form at the bottom of valleys during stable nighttime conditions. The results show that during strong surface radiative cooling and light-wind events, the near-surface potential temperatures that occur at the bottom of valleys can be several kelvin below the environmental mean. This is true for quite shallow valleys with depths and widths of 50 m and 1 km, respectively, and is a result of in situ sheltering at the valley bottom. For windier conditions or less rapid cooling, the cold-pool temperature contrasts are reduced. For shallow valleys the magnitude of the difference between the potential temperature at the bottom of the valley and the mean value increases with increasing valley depth. However there is a critical valley depth, beyond which the valley flow becomes decoupled from that aloft and there are no further increases in the potential temperature difference. This critical valley depth depends on the wind speed and radiative cooling rate and the results indicate it is a function of a non-dimensional valley depth (or inverse Froude number), which is itself a property of the undisturbed profiles of wind and stability.  相似文献   

夏季南海台风移动路径的一种客观预报方法   总被引：1，自引：0，他引：1  

黄小燕  金龙  姚才  黄明策 《南京气象学院学报》2008,31(2):287-292

以1960—2003年共44a夏季的7月、8月、9月西行进入南海海域的台风样本为基础,综合考虑南海台风移动路径的气候持续因子和数值预报产品物理量因子,运用条件数方法选取因子并建立回归方程,进行台风路径预报模型的预报建模研究。通过对比分析发现,基于条件数方法的南海台风移动路径模型具有较好的预报效果,7月、8月、9月3个月24h台风路径预报的平均距离误差为153．9km,预报能力明显高于目前国内外的其他一些台风路径客观预报方法。该方法的预报精度相对于逐步回归方法有了很大的提高,相对于气候持续法也为正的预报技巧水平。  相似文献   

Street Versus Rooftop Level Concentrations of Fine Particles in a Cambridge Street Canyon     

Prashant Kumar  Paul S. Fennell  Allan N. Hayhurst  Rex E. Britter 《Boundary-Layer Meteorology》2009,131(1):3-18

Dispersion of particles, as evidenced by changes in their number distributions (PNDs) and concentrations (PNCs), in urban street canyons, is still not well understood. This study compares measurements by a fast-response particle spectrometer (DMS500) of the PNDs and the PNCs (5–1000 nm, sampled at 1 Hz) at street and rooftop levels in a Cambridge UK street canyon, and examines mixing, physical and chemical conversion processes, and the competing influences of traffic volume and rooftop wind speed on the PNDs and the PNCs in various size ranges. PNCs at street level were ≈6.5 times higher than at rooftop. Street-level PNCs followed the traffic volume and decreased with increasing wind speed, showing a larger influence of wind speed on 30–300 nm particles than on 5–30 nm particles. Conversely, rooftop PNCs in the 5–30 nm size range increased with wind speed, whereas those for particles between 30 and 300 nm did not vary with wind speed.  相似文献   

On the Parameterization of Convective Entrainment： Inherent Relationships among Entrainment Parameters in Bulk Models     

孙鉴泞 《大气科学进展》2009,26(5):1005-1014

  相似文献   

地形对超强台风罗莎降水影响的初步分析   总被引：5，自引：3，他引：2  

黄奕武  端义宏  余晖 《气象》2009,35(9):3-10

为了进一步加深地形对台风降水影响的细节了解,用变分法合成的高分辨率降水资料和地形资料,结合日本再分析资料,对0716号台风罗莎登陆期间地形对降水的影响作了初步分析.过程降水量与地形相关分析表明,沿海地形对降水的影响较大.强降水区主要分布在沿海山体的迎风坡上.分析1小时降水量在不同强度区间的频次分布,发现在山体地形的影响下,山脉区域降水加强.浙江东南沿岸的山体引起的降水增益相对东北沿岸区域的山体偏大.利用日本再分析资料和地形资料计算了气流过沿海山体时的无量纲数Fr值.由于气流Fr较小,气流过浙江沿海地形时更容易翻越山体.抬升位置发生在迎风坡上,因而强降水区也落在迎风坡上.东南沿岸区域的地形对迎风气流的强迫垂直运动在垂直方向上的渗透比东北沿岸区域更深厚,这是导致东南沿岸区域地形对降水增益比东北沿岸区域偏大的原因.  相似文献   

一次梅雨锋暴雨过程的中尺度特征分析   总被引：2，自引：2，他引：0  

易军  寿绍文  高守亭  李启泰 《气象科学》2009,29(6):761-767

利用中尺度非静力平衡模式WRF-V2.1对2007年7月7-8日江淮地区一次梅雨锋暴雨过程进行数值模拟,分析其中的中尺度重力波(MGW)特征,并运用拉格朗日Rossby数(Ro)来诊断非平衡流特征.研究表明:这次暴雨过程中的中尺度重力波波长约为56～75 km,相速约12～19 m·s~(-1);在有利的大尺度环流形势下,地转调整机制是MGW产生的首要机制,Wave-CISK和地转调整为波动传播提供了充足的能量,使MGW在具有波导结构的大气中维持了相当长的时间;满足舶指标的不平衡运动区与重力波活动区十分接近,它对波动产生的时间和区域方面有一定的指示作用.  相似文献   

Beginning of the super‐soft phase of the classical nova V2491 Cygni     

D. Takei  J.‐U. Ness 《Astronomische Nachrichten》2010,331(2):183-186

We present the results of soft X‐ray studies of the classical nova V2491 Cygni using the Suzaku observatory. On day 29 after outburst, a soft X‐ray component with a peak at ∼0.5 keV has appeared, which is tantalising evidence for the beginning of the super‐soft X‐ray emission phase. We show that an absorbed blackbody model can describe the observed spectra, yielding a temperature of 57 eV, neutral hydrogen column density of 2 × 10²¹ cm^–2, and a bolometric luminosity of ∼10³⁶ erg s^–1. However, at the same time, we also found a good fit with an absorbed thin‐thermal plasma model, yielding a temperature of 0.1 keV, neutral hydrogen column density of 4 × 10²¹ cm^–2, and a volume emission measure of ∼10⁵⁸ cm^–3. Owing to low spectral resolution and low signal‐to‐noise ratio below 0.6 keV, the statistical parameter uncertainties are large, but the ambiguity of the two very different models demonstrates that the systematic errors are the main point of concern. The thin‐thermal plasma model implies that the soft emission originates from optically thin ejecta, while the blackbody model suggests that we are seeing optically thick emission from the white dwarf (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

郑州市大气气溶胶数浓度和质量浓度时空变化研究   总被引：1，自引：1，他引：0  

李尉卿  崔娟 《气象与环境科学》2010,33(2):7-13

利用激光粒子计数器和颗粒物自动测定仪测量的郑州市大气气溶胶粒子的数浓度和质量浓度,分析了局地气溶胶的干沉降和湿沉降以及郑州市大气气溶胶数浓度和质量浓度的时空变化,结果表明:郑州市局地区域大气气溶胶中粒径≥2μm的粒子,沉降速度随粒径的增大而增大,而粒径≤0.3μm的粒子,沉降速度变化不大;湿沉降率大于干沉降率。气溶胶浓度有明显的日变化特征,17:00-19:00为最高峰,6:00-9:00为次高峰,这是早晨及下午上下班汽车运行高峰期向大气排放的尾气和汽车扬尘所致。在垂直分布上,45-80 m处的粒子数多于1.5 m处的粒子数;在水平分布上,交通建筑区内的浓度高于其他功能区的浓度。  相似文献   

基于熵权的五元联系数法在郑州市水资源丰富程度评价中的应用     

徐栋  吴泽宁 《气象与环境科学》2010,33(3):86-89

针对水资源丰富程度评价中的不确定性及水资源分布特点,将集对分析中的五元联系数法应用于水资源丰富程度评价。在确定各评价指标的权重时,将信息论中的熵值理论引入该模型,运用信息熵所反映实测数据的效用值计算各评价指标的权重。通过对郑州市的实例应用表明基于熵权的五元联系数法计算简便,评价结果合理,为水资源丰富程度评价提供了一种简单而实用的评价方法。  相似文献