Mesoscale physical processes and zooplankton transport-retention in the northern Norwegian shelf region

Northern Norwegian shelf regions are highly productive, supporting fisheries rich in commercially important species such as cod, herring and capelin. It has been long recognized that the mesoscale jets, meanders and eddies associated with interactions between the North Atlantic Current, Norwegian Coastal Current and regional bottom topographic features such as troughs, banks and shelfbreaks play important roles in transporting and retaining zooplankton. To investigate zooplankton distributions and their correspondence with the physical fields, three large-scale surveys with mesoscale resolutions on physical and biological fields were conducted in northern Norwegian shelf regions between latitudes 68°15′N and 70°15′N in springs of 2000–2002. Survey results provide insights into the relationships between zooplankton distributions and the physical features such as fronts, the Norwegian Coastal Current and eddies related to topographic features. The physical and biological data are integrated and analyzed focusing on water types, estimation of geostrophic currents from direct current measurements, along-shelf transport of zooplankton, and retention of zooplankton by the mesoscale meander–eddy over a typical bank area on the shelf. The estimated mean transport in the upper 100 m on the shelf in the survey region is approximately 6.4×10³ tonnes wet weight day⁻¹ northward. High zooplankton abundances were found over both Malangsgrunnen and Sveinsgrunnen banks. The specific accumulation rate from northward–southward transport in the upper 100 m over Malangsgrunnen was approximately 0.08 day⁻¹, while variable currents with an offshore gradient of zooplankton abundance over Sveinsgrunnen implies an offshore dispersion of coastal-originated zooplankton cohort.     

局部角度域波传播步进算法研究

本文从非均匀介质中波动方程出发,提出了基于一般标架的相空间（局部角度域）波传播的步进算法. 该方法在构造单程波的步进算法时,在选择标架或正交基等方面有更大的自由度. 我们以不随频率及深度变化且具有变尺度特性的Gabor_Daubechies紧标架为例,给出了单程波传输算子的具体形式及相应的波场步进算法;详细讨论了基于Gabor_Daubechies标架的传输算子的高频渐近展开问题,得出了在高频、小传输步长条件下传输算子的近似解析表达式,并给出使用条件. 通过模型算例,比较了精确传输算子与高频近似传输算子用于非均匀介质中波传播的结果,说明在一定条件下由两者得出的波场几乎是相同的.     

一种新的地球物理反演方法——模拟原子跃迁反演法

详细研究了一般地球物理反问题的迭代优化求解过程与物理学中原子跃迁过程的对应关系,建立了反演问题中模型空间、初始模型、局部极值模型、最优化模型等与原子的态空间、定态、激发态、基态等的对应关系. 在此基础上,模拟了物理学中原子从激发态向基态跃迁的物理过程,建立了一种与原子跃迁过程相对应的非线性随机跃迁数学模型和模型解跃迁搜索准则,导出了适用于一般地球物理资料的模拟原子跃迁的非线性反演算法. 用理论测试函数对这种新的反演方法进行了数值试验,结果表明该方法具有解不依赖于初始模型、收敛速度快等优点.     

局地云量变化气候效应的数值模拟

本文用统计得到的东半球夏季平均云量资料，利用改进的云－辐射计算模式，在三维有限区域模式中模拟局地云量变化的气候效应。模拟结果表明，高原地区和热带辐合带云量变化造成的气候效应都主要表现在青藏高原地区。在低反照率时，高原地区云量减少使该地区地表加热，引起高低空气压系统加强；高反照率时结果相反。热带辐合带云量减少会引起青藏高原地区降温和气压系统减弱。     

华南春季强风暴背景流场的若干特征

本文利用常规探测资料,分析了1983年3月25日发生在珠江三角洲地区的一次强对流天气过程背景流场的几个重要特征,如高空急流的结构与变化、辐散风场及与之相联系的背景次级环流、风场垂直切变和水平切变等.     

雷州半岛局部地热异常及其形成机制

雷州半岛地热场主要受基底构造格局的控制和地下水活动的影响,隐伏花岗岩体放射性元素生热对盖层地温的贡献不可忽视,第四纪更新世火山喷发活动的岩浆余热已几乎完全散失,岩浆体和围岩温度已趋于平衡。由火山喷发而形成的雷北螺岗岭和雷南石峁岭两个玄武岩台地,为半岛地下水的主要补给区,由于冷水流下渗的地温效应,新生界盖层浅部地温梯度<3℃/100m,呈现地热负异常。在以传导传热为主的区域,地热场特点与华北盆地相似,新生界盖层地温梯度与基底岩面的埋深密切相关。由于地壳深部较均一的热流在地壳表部再分配的结果,若干凸起区盖层地温梯度为4—5℃/100m,呈现地热正异常。某些控制凸起区的边界断裂,当深层热水沿其上涌,造成附加热源,和传导传热相叠加,盖层地温梯度可高达5—8℃/100m,形成更鲜明的地热正异常。     

Inversion of arrival-times in a region of dilatancy anisotropy

Shear-wave splitting has been identified in many three-component seismograms from two separate field experiments on a section of the North Anatolian Fault in North-West Turkey. These observations are consistent with shear-wave propagation through a zone of extensive-dilitancy anisotropy. A preliminary attempt has been made to confirm this interpretation by simultaneously inverting suites of arrival-times for hypocentral locations and for parameters describing an anisotropic halfspace. Although the inversion procedure is not globally convergent, it is possible to recognize the true solution by systematically varying the initial conditions. Applied to selected data sets, the inversion defines several anisotropic models that fit the data significantly better than a simple isotropic model, and display the anisotropy required by the shear-wave splitting. However, most of these anisotropic models are not superior when they are used to individually locate events in a much larger data set. However, for each experiment, there is a single model that produces clearly superior locations for the larger data sets than those of other anisotropic or simple isotropic models. Both models display similar velocity variations which are characteristic of propagation through distributions of biplanar cracks displaying orthorhombic symmetry. The principal axes of the two models are oriented in similar directions and are within 20° of the principal axis of regional stress derived from fault-plane solutions. The solutions indicate low velocities close to the tensional axis, as would be expected in extensive-dilatancy anisotropy.     

混沌系统的局域特征与可预报性

讨论了混沌系统的时间和空间的局域特征。首先分析了研究时间和空间局域特征的必要性。接着引进了有限时间不稳定和局域时间不稳定的概念，并对有关的计算问题进行了研究。对Ｌｏｒｅｎｚ系统的具体计算表明，随着轨线在混沌吸引子上的演变，局域不稳定特征有很大的变化，相应误差增长也有很大的变化。相应于误差迅速增长的轨线部分局限于很有限的相空间范围内，而且同误差增长缓慢的轨线部分占据的相空间区域截然可分。每一个例的可预报性依赖于轨线在相空间中所处的区域。混沌系统的这种局域特征可以是导致个例业务预报技巧之间有很大差别的主要原因。     

台风影响期间珠江三角洲局地强风暴和大暴雨发生的环境条件

采用１９７６－１９８３年６－８月珠江三角洲地区受台风影响期间区内各站逐日的强风暴和降水资料以及广泛站的探空资料，用相关对比度分析方法，对台风环流中的珠江三角洲局地强风暴和大暴雨发生的环境条件进行统计诊断，得出台风影响珠江三角洲时这两种强天气发生的有利的环境条件，并发现二者在气压、风速、层结稳定度和中下层位势不稳定等方面显著不同。