An upper‐ocean general circulation model for the north pacific: Preliminary experiments

Abstract

A model with two active layers, a mixed layer and a pycnocline layer, over a semipassive deep ocean is described. The model is used to simulate a climatological seasonal cycle in the upper North Pacific. The formulation is similar to that in Cherniawsky et al. (1990). The model resolution is 1° latitude by 1.5° longitude, extending from 62°N to the equator. It is driven with monthly wind stress (Hellerman and Rosenstein, 1983) and with Newtonian heat and freshwater fluxes, which were inferred from climatological (Levitus, 1982) sea‐surface monthly temperatures and annual mean salinities. The monthly temperature anomalies (without the annual mean) are multiplied by a prescribed gain factor and advanced in time, compensating for time delay in the response of the mixed layer. No‐slip and no‐flux constraints are applied on north, east, west and land boundaries, while the following open boundary conditions are used at the equator: (a) free‐slip on zonal velocities in the two layers; (b) a prescribed meridional transport, due to local curl of the wind stress, in the mixed layer; (c) an antisymmetric meridional velocity plus a small flux‐balancing term in the second layer; and (d) across‐equator symmetry for layer depths, temperatures and salinities. Sensitivity to two aspects of parametrization is investigated: (1) the change to horizontal diffusion/viscosity coefficients that depend on the velocity deformation field (as in Smagorinsky, 1963), and (2) the use of idealized piecewise‐linear profiles for second‐layer temperatures and salinities for calculating mixed layer entrainment fluxes.     

A new mixed finite element method for poro‐elasticity

Development of robust numerical solutions for poro‐elasticity is an important and timely issue in modern computational geomechanics. Recently, research in this area has seen a surge in activity, not only because of increased interest in coupled problems relevant to the petroleum industry, but also due to emerging applications of poro‐elasticity for modelling problems in biomedical engineering and materials science. In this paper, an original mixed least‐squares method for solving Biot consolidation problems is developed. The solution is obtained via minimization of a least‐squares functional, based upon the equations of equilibrium, the equations of continuity and weak forms of the constitutive relationships for elasticity and Darcy flow. The formulation involves four separate categories of unknowns: displacements, stresses, fluid pressures and velocities. Each of these unknowns is approximated by linear continuous functions. The mathematical formulation is implemented in an original computer program, written from scratch and using object‐oriented logic. The performance of the method is tested on one‐ and two‐dimensional classical problems in poro‐elasticity. The numerical experiments suggest the same rates of convergence for all four types of variables, when the same interpolation spaces are used. The continuous linear triangles show the same rates of convergence for both compressible and entirely incompressible elastic solids. This mixed formulation results in non‐oscillating fluid pressures over entire domain for different moments of time. The method appears to be naturally stable, without any need of additional stabilization terms with mesh‐dependent parameters. Copyright © 2007 John Wiley & Sons, Ltd.     

Numerical Modeling and Observations of Tsunami Waves in Alberni Inlet and Barkley Sound, British Columbia

Alberni Inlet is a long and narrow fjord adjacent to Barkley Sound on the Pacific Coast of Vancouver Island, Canada. Port Alberni, at the head of the inlet, was affected in 1964 by the largest Pacific tsunami waves in Canadian history. We use observations and results from two numerical models to investigate the resonant characteristics of the region and amplification of tsunami waves in Barkley Sound and Alberni Inlet. The first model (A) was forced at its open boundary with a stationary autoregressive signal, similar to the observed background noise. The second model (B) used an initial sea-level deformation from a potential earthquake off California in the southern segment of the Cascadia Subduction Zone, producing transient tsunami waves. Spectral, cross-spectral and frequency-time (f-t) analyses of the observations were used to examine the resonant properties and topographic response of the local area. The respective results show large admittance functions over a wide 0.5–0.9 cph frequency band, implying a low Q factor but high amplification of arriving waves. This unusual behavior is a result of two effects: A quarter-wave resonance of the system for its fundamental Helmholtz mode and amplification due to the narrowing of the channel cross section from Barkley Sound to Alberni Inlet. The model A numerical results agree favorably with the observations, indicating an energetic resonant mode at frequency of ~0.53 cph (112 min), with its nodal line located near the entrance to Barkley Sound and amplification factor value close to 12. The results from the tsunami propagation model (B) yield spectral characteristics similar to those from the model A and from the observations. The maximum tsunami current speed for this scenario is 2.4 ms^?1 in Sproat Narrows, which divides Alberni Inlet into two parts, while the largest computed wave height is 1.6 m in the northern Alberni Inlet, in the area of Port Alberni.     

Effect of the radiative background flux in convection

Numerical simulations of turbulent stratified convection are used to study models with approximately the same convective flux, but different radiative fluxes. As the radiative flux is decreased, for constant convective flux: the entropy jump at the top of the convection zone becomes steeper, the temperature fluctuations increase and the velocity fluctuations decrease in magnitude, and the distance that low entropy fluid from the surface can penetrate increases. Velocity and temperature fluctuations follow mixing length scaling laws. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

从极化区的功能探讨长江三角洲的扩展范围

极化区作为一种具有全球意义的区域发展模式和空间组合形式,日益成为集聚经济要素和支配国家乃至全球经济命脉的巨大载体,承担着引领国家经济发展、参与世界竞争的功能.长江三角洲地区经过了近30年的高速发展,已经初具极化区的特征.但是,与其它世界级极化区相比,长江三角洲地区整体实力和带动能力仍然不足,国际竞争力还很有限.通过扩展极化区范围,可以扩大长江三角洲核心地区的腹地,缓解极化区资源环境瓶颈约束.关于长江三角洲地区的合理范围,各界意见纷纭,争论较多.基于"长三角"作为世界极化区的要求,从极化氏的科学概念、条件和以提高国际竞争力、完善极化区功能的目标出发,通过区域内城市之间的功能互补和经济联系分析,结合区域一体化的现实性,研究了扩大"长三角"的合理范围,得出了应把温州、金华、盐城、淮安、马鞍山、芜湖、铜陵、巢湖、合肥、滁州、宣城等城市作为扩展优先选择区,把宿迁、徐州、连云港、丽水、衢州、池州、安庆、蚌埠、黄山、宿州等城市作为扩展保留资格区,从而把长江三角洲地区从16个城市逐步扩大到37个城市的结论.     

2008年5月12日中国汶川M=7.9级地震预计增大了三条主要断裂系的破裂应力和地震发生率

龙门山断裂带上的汶川地震摧毁了四川的几座城市,夺去了69000多人的生命。计算结果显示,该地震可能使部分鲜水河断裂、东昆仑断裂大部以及部分岷江断裂应力增加了0．2～0．5bar,更加接近破裂状态。这3条位于青藏高原东部的活动断裂带均在离汶川发震带150-400km的库仑静应力影响范围内。由于部分受力断层上的应变累积至少已有一个世纪之久,最近的汶川地震有可能触发或加速这些断层带上新的7级以上强震的发生,从而可能造成从四川省康定至道孚、青海省玛沁至甘肃省洛大以及邻近区域的强烈震动。本文利用由计算得到的汶川地震引起的应力变化以及过去10年观测到的背景地震发生率,对该地区在未来10年内发生破坏性地震的概率以及可能的空间分布进行了预测。结果表明,研究区内在未来10年内发生M≥6级地震的概率为57％～71％,发生M≥7级地震的概率为8％～12％,是汶川地震前发震概率的2倍。     

Ecosystem response to regulatory and management actions: The southern California experience in long-term monitoring

Billions of dollars have been invested over the past 35 years in reducing pollutant emissions to coastal environments. Evaluation of the effectiveness of this investment is hampered by the lack of long-term consistent data. A rare opportunity exists in southern California to evaluate the effectiveness of management actions by analyzing long-term monitoring of effluent, sediment, benthos, and fish and comparing this trend data to periodic regional surveys of environmental condition. In this paper, we ask the question “have improvements in effluent quality in response to environmental regulation translated into improvements in the receiving environment?” Results indicate that management actions directed at reducing mass emissions from wastewater treatment plants (POTWs) have resulted in substantial improvement in aquatic communities. However, the magnitude and timing of response varies by indicator suggesting that use of multiple assessment endpoints is necessary to adequately interpret trends. Reductions in the effect of POTW effluent have allowed managers to shift resources to address other contaminant sources such as stormwater and resuspension of legacy pollutants.     

The Western Bohemia/Vogtland Region in the Light of the Webnet Network

The local network of digital seismic stations WEBNET monitors the seismic activitv of practically the whole region of Western Bohemia/Vogtland swarms. The network consists of ten short-period stations and one very broadband station. The paper describes the configuration of the network, instrumental equipment and the basic parameters of the stations. The method of and formula for computing the local magnitudes from the WEBNET and KRASLICE seismograms are also given. Based on continuous WEBNET observations in the period 1995-1999, we were able to improve the model of temporal and spatial energy release in the region, the principal characteristics of which are summarised in the paper. Apart from direct P and S waves, the WEBNET seismograms also contain other significant P- and S-type waves, provisionally interpreted as reflected PxP, SxS and SxP waves. The fundamental characteristics of these waves are given in the paper, and tentative mechanisms of their origination are discussed. The large residua in the travel times of the P and S waves, and the discrepancies in the seismograms recorded at stations located east of the principal focal zone are pointed out.     

Refined Locations of The Swarm Earthquakes In The Nový Kostel Focal Zone and Spatial Distribution of The January 1997 Swarm In Western Bohemia,Czech Republic

In order to improve the accuracy of the spatial distribution of earthquake foci in the principal Novy Kostel focal zone, refined focal locations of about 1500 micro-earthquakes of the 1991 – 1997 period were determined using the relative Master-Event location method. To estimate the reduction in the scatter of located hypocentres, the results were compared with those obtained by routinely used FASTHYPO method and cluster analysis (the nearest-neighbour method) was applied to the located foci to evaluate the spatial distribution of the foci. Based on the results of refined location and of the cluster analysis, a concept of seismic energy release in space and time in the main focal zone was developed. Especially the January 1997 earthquake swarm was studied in detail: 946 events were located with the Master-Event location method, and the dimensions and geometry of focal clusters were determined. Type analysis was applied to waveforms to divide approximately 800 located events into eight multiplet groups to each of which a characteristic source mechanism was assigned. The spatial distribution of the foci as well as of the eight types of source mechanisms was revealed in this way and also the planes fitting the clusters of foci with two predominant source mechanisms were determined fairly well.     

Homogeneous Velocity Models of The West Bohemian Swarm Region Obtained By Grid Search

West Bohemian earthquake swarms are used to determine the parameters of simple homogeneous velocity models of the individual subregions of the given area, based on a group of earthquakes that occurred in these subregions. The grid search method is used for location. Models yielding the minimum sum of squares of the travel-time residua in locating the whole group of earthquakes in the given subregion are considered suitable. Relocation obtained by grid search is compared with that obtained by the FASTHYPO method. The computations indicate that the subregions under consideration can be, from the point of view of earthquake location, sufficiently represented by homogeneous models, but the models differ for the data from different subregions. The velocities of these models are given. The models under consideration are compared with some of the previously published 1-D models of the broader region of Western Bohemia.