近共振地形强迫Rossby孤立波

利用扰动展开和时空伸长变换导得了包括地形强迫的非齐次ＫｄＶ方程，讨论了近共振地形强迫Ｒｏｓｓｂｙｙ孤立波的产生，及其与自由孤立波的相互作用，得到了一些有意义的结果，显示出地形对扰动具有明显的增幅作用，在某种程度上可以解释局地地形在阻塞高压形成中的作用。     

有地形坡度的非线性Kelvin行波

提出了一个考虑地形坡度的非线性Kelvin行波解的模型，在假定了地形坡度沿山脉走向不变而仅在垂直于山脉走向的方向有改变的情况下，求得了该模型的解析解，这有助于加深对沿海山地捕获波的认识。文中还将该解与经典情形(即侧边界取为垂直刚壁而底面为水平)的解作了比较，发现前者的波速与扰动振幅均较后者要小，这与我国东南沿海武夷山区的沿海山地捕获波的情况相一致。     

National height datum,the Gauss–Listing geoid level value w0 and its time variation 0 (Baltic Sea Level Project: epochs 1990.8, 1993.8, 1997.4)

 A methodology for precise determination of the fundamental geodetic parameter w ₀, the potential value of the Gauss–Listing geoid, as well as its time derivative ₀, is presented. The method is based on: (1) ellipsoidal harmonic expansion of the external gravitational field of the Earth to degree/order 360/360 (130 321 coefficients; http://www.uni-stuttgard.de/gi/research/ index.html projects) with respect to the International Reference Ellipsoid WGD2000, at the GPS positioned stations; and (2) ellipsoidal free-air gravity reduction of degree/order 360/360, based on orthometric heights of the GPS-positioned stations. The method has been numerically tested for the data of three GPS campaigns of the Baltic Sea Level project (epochs 1990.8,1993.4 and 1997.4). New w ₀ and ₀ values (w ₀=62 636 855.75 ± 0.21 m²/s², ₀=−0.0099±0.00079 m²/s² per year, w ₀/&γmacr;=6 379 781.502 m,₀/&γmacr;=1.0 mm/year, and &γmacr;= −9.81802523 m²/s²) for the test region (Baltic Sea) were obtained. As by-products of the main study, the following were also determined: (1) the high-resolution sea surface topography map for the Baltic Sea; (2) the most accurate regional geoid amongst four different regional Gauss–Listing geoids currently proposed for the Baltic Sea; and (3) the difference between the national height datums of countries around the Baltic Sea. Received: 14 August 2000 / Accepted: 19 June 2001     

Vortex–ridge interaction in a rotating fluid

The evolution of barotropic vortices interacting with a topographic ridge on a f-plane is studied by means of laboratory experiments in a rotating tank and numerical simulations. The initial condition in all experiments is a cyclonic vortex created at a certain distance from the ridge. The results are presented in two main scenarios: (a) weak interactions, which occur at early stages of the experiments, when the vortex is far from the ridge, and thus weakly experiences the influence of the topography. In these situations, the vortex slowly drifts towards the ridge with a leftward inclination due to the ascending slope of the topography. Such a behaviour is similar to the “northwestern” motion of cyclones over a weak sloping bottom. The circular shape of the monopolar vortex is preserved. (b) Strong interactions, in which the vortex core reaches the ridge and presents a more complicated evolution. The cyclone “climbs” to the top of the topography and crosses to the other side. Once the vortex experiences the opposite slope, it moves backwards trying to return to the original side of the ridge. For strong enough vortices, this process may be repeated a number of times until the vortex is dissipated by viscous effects. During these interactions the shape of the vortex is strongly deformed and several filaments are produced. In some cases the vortex is cleaved in two parts when crossing the ridge, one at each side of it and moving in opposite directions.Weak and strong interactions are numerically simulated by using a quasi-two-dimensional model. The results confirm that the vortex behaviour is governed by stretching and squeezing effects associated with changes in depth over the ridge and, at latter stages, by Ekman damping due to the solid bottom. The main results observed during strong interactions on a f-plane are also found on preliminar topographic β-plane experiments.     

北方一次强降雪过程的中尺度数值模拟

利用中尺度数值模式MM5对2003年3月14~16日发生在内蒙古中部偏南地区的一次强降雪过程进行了二重嵌套的48 h数值模拟研究。结果表明:模式较好地模拟了本次过程强降雪中心的强度、位置以及强降雪的时间变化。导致本次过程降雪产生的主要影响系统是地面倒槽和700 hPa中α尺度低涡,其影响时间相对持久。强降雪的出现则是由于高空短波槽产生的高层强辐散强迫与低层增强的辐合相互耦合所致。高低层系统这一适宜配置的维持时间相对短暂,却导致了本次过程降雪强度的两个峰值的出现。同时,中α尺度低涡的形成和加强及其与低空暖湿急流的适宜配置也是强降雪产生的一个有利因素。阴山山脉对本次过程强降雪的强度和位置具有重要影响:山脉使降雪在其南麓增强,北麓减弱。山地强迫抬升是导致这一结果的直接原因。另外,山地在其迎风坡使上升运动增强的同时也使正涡度减小和低层辐散增强。     

Effects of surface topography on seismic ground response in the Egion (Greece) 15 June 1995 earthquake

The Greek coastal town of Egion on 15 June 1995 was shaken by a strong, small epicentral distance, earthquake that caused heavy damages to buildings and loss of life. The damages were concentrated in the central elevated part of the town whereas the flat coastal region remained almost intact. This non-uniform distribution of damage is studied in this article in terms of surface topography effects by conducting seismic response analyses of a simplified 2-D profile of the town. A dynamic finite element code implementing the equivalent-linear soil behavior (FLUSHPLUS) was used for the analyses and it was found that the step-like topography amplified greatly the intensity of motion without affecting its frequency content. The analyses showed that the motion recorded by an accelerograph installed at the center of the town is in agreement with the computed values; they also indicated a particularly intense amplification close to the crest of the steep slope, where a multi-story RC residential building partially collapsed. In contrast, the level of motion was found to be low at the flat coastal zone of the town where the earthquake damages were insignificant. It is concluded that the characteristic surface topography of the town played an important role in modifying the intensity of base motion.     

格莱尼改正及其在地球物理数据处理中的意义

格莱尼改正是重力改正的一种,是对球面半径约166.7 km以外地形和均衡造成的重力综合效应的改正,改正后所得格莱尼异常可对应研究区范围内地壳结构特征,具有重要的研究意义.但近年来国内的重力研究中,对格莱尼改正的认识和重要性还不是十分透彻,特别是在大区域研究中,忽略这一远区重力效应可能会对研究结果的解释造成误导.针对这一问题,本文介绍了格莱尼改正的含义、由来与研究历史,指出了在大区域研究中需要考虑格莱尼效应的重要性,以“扇形球壳块”法为例给出了格莱尼改正的计算原理,列举了格莱尼异常在地球物理中的常见应用,并通过重力改正与莫霍面深度反演实例,通过对反演结果的控制点检测与精度评价,指出格莱尼异常反演所得莫霍面埋深更接近地震方法结果,从而表明了格莱尼改正在地球物理研究中的不可忽视性,并指出完全布格改正与格莱尼改正在计算方法上可实现统一.     

Effects of topography on lofting gravity flows: Implications for the deposition of deep-water massive sands

Hyperpycnal flows are generated in the marine environment by sediment-laden fresh water discharge into the ocean. They frequently form at river mouths and are also generated in proximal ice-melting settings and are thought to be responsible for transporting a large proportion of suspended river sediment onto and off the continental shelf. Hyperpycnal flows are an example of gravity currents that display reversing buoyancy. This phenomenon is generated by the fresh water interstitial fluid being less dense than that of the ambient seawater. Thus after sufficient particles are sedimented the flow can become positively buoyant and loft, forming a rising plume. Here we present results from physical scale-modelling experiments of lofting gravity currents upon interaction with topography. Topography, in the form of a vertical obstacle, triggered a localised lofting zone on its upstream side. This lofting zone was maintained in a fixed position until the bulk density of the flow had reduced enough to allow lofting along its entire length. The obstructed lofting zone is associated with a sharp increase in deposit thickness. By inference these experimentally established lofting dynamics are applied to improve understanding of the potential for hyperpycnal flows to deposit deep-water massive sands. This study provides a depositional mechanism by which large volumes of sand can be deposited in the absence of traction and the fines removed, leaving thick deposits of structureless sand with a low percentage of mud. This conceptual model for the first time provides a framework by which the geometries of certain deep-water massive sands may be predicted within specific depositional and basinal settings. This is crucial to our understanding of massive sand deposits in modern and ancient turbiditic systems and in the commercial evaluation of hydrocarbon potential of such sedimentary successions.     

Comparison of USGS and DLR topographic models of Comet Borrelly and photometric applications

Stereo analysis of images obtained during the 2001 flyby of Comet Borrelly by NASA's Deep Space 1 (DS1) probe allows us to quantify the shape and photometric behavior of the nucleus. The shape is complex, with planar facets corresponding to the dark, mottled regions of the surface whereas the bright, smooth regions are convexly curved. The photometric as well as textural differences between these regions can be explained in terms of topography (roughness) at and below the image resolution, without invoking significant variations in single-particle properties; the material on Borrelly's surface could be quite uniform. A statistical comparison of the digital elevation models (DEMs) produced from the three highest-resolution images independently at the USGS and DLR shows that their difference standard deviation is 120 m, consistent with a matching error of 0.20 pixel (similar to reported matching accuracies for many other stereo datasets). The DEMs also show some systematic differences attributable to manual versus automatic matching. Disk-resolved photometric modeling of the nucleus using the DEM shows that bright, smooth terrains on Borrelly are similar in roughness (Hapke roughness θ=20°) to C-type asteroid Mathilde but slightly brighter and more backscattering (single-scattering albedo w=0.056, Henyey-Greenstein phase parameter g=−0.32). The dark, mottled terrain is photometrically consistent with the same particles but with roughnesses as large as 60°. Intrinsically darker material is inconsistent with the phase behavior of these regions. Many local radiance variations are clearly related to topography, and others are consistent with a topographic explanation; one need not invoke albedo variations greater than a few tens of percent to explain the appearance of Borrelly.     

Recent changes in flood risk in the Gran La Plata,Buenos Aires province,Argentina: causes and management strategy

The paper analyses the causes of flood occurrence in the Gran La Plata, Buenos Aires Province, Argentina, and the changes that have occurred since the 1970s. The area is characterized by serious deficiencies in the use and management of water resources. The main factors are: (1) flood risk information is not updated; (2) urban building organization does not consider the flood risk; (3) the topography and other physical features are not taken into account in urban development. This research considers some specific problems, especially in data availability, and suggests ways to solve them, including improved analytical methodology. One of the main objectives is to analyse flood risk in social terms, producing a map of flood risk from the “human social vulnerability” point of view. The results suggest that flood risk has increased since the 1980s and that this is associated with changes in precipitation patterns that have also been aggravated by lack of controls on urban development. The poorer areas with the lowest level of infrastructure and public services, many of them developed over the last quarter-century, are especially vulnerable.