夏季中国中东部不同历时降水时空分布特征   总被引：7，自引：2，他引：5  

金炜昕  李维京  孙丞虎  左金清 《气候与环境研究》2015,20(4):465-476

利用1961~2012年台站逐时降水资料,分析了夏季中国中东部不同历时降水的主要气候分布和长期变化特征,为深入认识其时空变化规律和形成机理奠定基础。分析结果表明,降水事件的平均历时由南向北呈"短—长—短"分布型,华南和北方地区以6 h以下的短历时降水为主;而中部地区(28°N~37°N)6 h以上长历时降水占总降水量60%以上。随着降水历时的增加,小雨事件(0.1~1.0 mm/h)的发生概率降低,中雨事件(1.1~10.0 mm/h)的发生概率升高;大雨、暴雨事件(10.0 mm/h)更易出现在35°N以南历时偏短的降水事件中。1961~2012年,中国中东部总降水量呈"南升北降"的趋势分布,夏季南方大部分地区降水强度、时数和事件数均呈上升趋势;而北方地区降水时数和事件数显著减少,不过降水强度呈增强趋势。中东部降水历时总体呈上升趋势,尤其以我国长江与黄河之间的中部地区变化最为显著。同时,该地区短历时(1~6 h)降水无显著的年代际转折,长历时(6 h)降水的年代际增加是20世纪70年代末至20世纪90年代初降水增多的主要原因。20世纪90年代初期以来,南方地区降水的年代际增多则是长、短降水共同作用的结果,但超过6 h降水的影响范围更广,且影响中心较短历时降水偏北。  相似文献   

Laboratory light-scattering measurements with Titan's aerosols analogues produced by a dusty plasma     

E. Hadamcik  J.-B. Renard  G. Cernogora  C. Szopa 《Planetary and Space Science》2009,57(13):1631-1641

The chemistry leading to the formation of solid aerosols (tholins) in Titan's atmosphere is simulated by a capacitively coupled plasma in a N₂-CH₄ gas mixture. The solid grains are produced in volume directly in the gas phase and studied ex-situ by SEM imaging and by light scattering on clouds of particles. The scattered light properties depend on the physical properties of the particles (morphologies, size distribution), as well as on the phase angle and the wavelength of the light. The particles may be aggregated or agglomerated grains. The grains size distribution is studied as a function of plasma parameters such as initial methane concentration introduced into the discharge, gas flow, absorbed RF power and plasma duration. The average grain size increases when the amount of CH₄ increases, when the gas flow decreases, and when the plasma duration increases up to a limit for each production condition.For all the samples, the absorption decreases with increasing wavelength in the visible domain. As usually found for irregular particles, the polarization phase curves have a bell-shaped positive branch and a shallow negative branch. The maximum of polarization (P_max) increases when the average grain size decreases (sub-μm-sized grains). To obtain P_max values within the range of those measured in Titan's atmosphere; the average grains diameter has to be smaller than 100 nm, in agreement with the space observations results. In the light-scattering experiment, the size of the agglomerates in the clouds is in the 40-80 μm range in equivalent diameter. As a consequence P_max increases with decreasing wavelength due to the increasing absorption, in agreement with observations of Titan from outside the atmosphere.  相似文献   

模拟水—岩作用的新方法     

郑西来 《地球科学与环境学报》1990,(3)

本文在详尽研究了山东铝厂碴场区地质、水文地质条件和水文地球化学环境的基础上,将地下水含水介质概化为一组矿物的集合体,把地下水和含水介质间的作用用一系列物理化学反应来加以描述。然后,根据“能量最低”和“物质守恒”原理建立线性规划数学模型,用单纯形法计算出了地下水和含水介质间的物流量。  相似文献   

瞬变电磁法中两种关断电流对响应函数的影响及其应对策略   总被引：26，自引：1，他引：26       下载免费PDF全文

白登海  Maxwell Meju 《地震地质》2001,23(2):245-251

关断时间是影响瞬变电磁资料处理和解释质量的一个重要因素 ,也是衡量TEM仪器性能的一个关键参数。提出了一种直接数值校正方案 ,并通过对线性和指数关断电流的校正描述了该方案的实施过程。根据文中提出的方案 ,只要仪器记录了一次场的衰减曲线 ,就可以进行较为精确的校正 ,并不必要假设线性衰减或指数衰减 ,这一结论无论是对TEM的仪器设计还是数据处理都具有重要意义  相似文献   

Sediment non-linearity and attenuation of seismic waves: a study of accelerograms from Lefkas, western Greece     

P. Dimitriu  N. Theodulidis  P. Hatzidimitriou  A. Anastasiadis 《Soil Dynamics and Earthquake Engineering》2001,21(1)

We investigate the dependence of the S-wave high-frequency spectral-decay parameter, κ (“kappa”) — a measure of wave attenuation — on ground-motion amplitude. 21 three-component accelerograms from two adjacent sediment sites in the town of Lefkas, western Greece, are used, representing 17 earthquakes with magnitudes M_w 4.7–7.0 and hypocentral distances 12–93 km. Recorded peak horizontal ground accelerations (PGA) and velocities (PGV) are 22–540 cm/s² and 1.3–54.5 cm/s.Fourier amplitude spectra are computed for S-wave windows, and the frequency range is visually determined where the high-frequency spectral decay can be approximated by a straight line on the linear-log plot; its slope (and hence κ) is computed by linear regression. κ is found to depend on hypocentral distance as κ=0.108+0.058R (r=0.518).As PGV increases from 1.3 to 54.5 cm/s, κ₀ (κ at 0 km, characterising inelastic attenuation in the site's subsurface geology) varies between 0.060 and 0.160 s. κ₀ is found to correlate very strongly with log MGA (r=0.645) (MGA — mean horizontal acceleration in the S-wave window) but also with log PGA (r=0.447) and log PGV (r=0.627). We attribute this behaviour to sediment non-linearity (shear-modulus degradation), resulting in the decrease of the site's dominant-resonance frequency (from about 3.5 to 2.4 Hz) and leading to the increase of κ₀. Our results imply that at sediment sites, an important contribution to κ comes from wave attenuation (damping) in the softest sediments and show that κ₀ is amplitude dependent, thus being a measure of sediment non-linearity.  相似文献   

无约束最优化的一个算法     

吴炳荣 《测绘学院学报》1996,(3)

无约束最优化是最优化的重要组成部分，一方面它可以用来直接解一些实际问题，另一方面它又是解决其它一些数学问题的工具。本文给出求解无约束最优化的一个算法，该算法简便，且具有二次终结性。证明了算法的全局收敛性，数值结果表明有较快的收敛速度。  相似文献   

中强地震前地震频次－震级关系式拟合优度变化的研究   总被引：3，自引：0，他引：3  

李志雄  张国民  傅征祥  张永仙 《中国地震》1996,(3)

根据著名的Ｇｕｔｅｎｂｅｒｇ－Ｒｉｃｈｔｅｒ（以下简写成Ｇ－Ｒ）地震频次－震级统计关系式研究了我国东部地区（１０８°Ｅ以东）部分Ｍｓ≥５．０中强地震前一定时空尺度内中小地震频次与震级线性拟合优度（线性相关系数ｒ）随时间变化的特征。结果表明，利用中强地震前震中区一定范围内的中小地震进行Ｇ－Ｒ关系式拟合时，其线性拟合优度在地震前出现不同程度的异常现象。其变化特点是：在中强地震发生前期，震源区及其附近中小地震的发生在能级上分配均匀，线性拟合优度接近１；随着中强地震的临近，该区中小地震在能级上的分配存在着较显著的不均匀现象，表现为线性拟合优度明显下降。这种拟合优度的异常变化具有中期异常性质，有可能为中强地震的中期判定提供依据。  相似文献   

论塔吉克斯坦杜尚别－瓦赫什地区地震活动性的地质标志问题     

Ａ．Ｐ．伊索克 《内陆地震》1996,(3)

据航、卫片解译，杜尚别－瓦赫什地区有１１条线性构造。由它们构成的努涅克和科摩索姆洛巴德构造结为晚更新世－全新世活动构造，未来可能发生强震及灾难性地震。  相似文献   

非线性最优化问题的一个算法及其收敛性     

朱建青 《测绘学院学报》1997,(3)

讨论了具有广泛应用的线性等式、线性不等式及非负约束的非线性最优化问题。以极方向的特殊组合加上修正向量为搜索方向，给出一个具有超线性收敛速度的算法。较以往的算法有明显的优点，具有较好的稳定性和实用性。  相似文献   

A NOTE ON THE APPLICATION OF LINEAR WAVE THEORY AT A CRITICAL LEVEL     

Andreas Dörnbrack  Carmen J. Nappo 《Boundary-Layer Meteorology》1997,82(3):399-416

The purpose of this note is to estimate the accuracy and practical limitations of applying linear theory at a critical level over a realistic range of atmospheric stabilities for an idealized surface terrain. These estimates are made by comparing the results of a linear model with a nonlinear numerical model at a critical level. Essentially similar results are obtained from each model for wave stress, wave breaking height and wave dissipation through the critical level. Because gravity waves can be either evanescent or internal depending on the relative sizes of the Scorer parameter and the wavenumber of the ground surface disturbance, the somewhat paradoxical result develops that wave breaking and non-linearity increase with increasing bulk Richardson number. It is recommended that steady linear wave theory be used in gravity wave drag parameterizations provided near real time profiles of background velocity and temperature are available.  相似文献