青海省最高、最低气温不对称性变化的诊断分析

利用青海省１３个站逐月最高、最低气温资料,分析了月、季、年平均最高、最低气温的变化。结果表明最高、最低气温存在明显不对称变化趋势,尤其是３、４月存在明显的反向变化趋势。同时分析了西宁城市效应对最高、最低气温的影响。     

Effects of supplemental viscous damping on seismic response of asymmetric-plan systems

Coupling between lateral and torsional motions may lead to much larger edge deformations in asymmetric-plan systems compared to systems with a symmetric plan. Supplemental viscous damping has been found to be effective in reducing deformations in the symmetric-plan system. This investigation examined how supplemental damping affects the edge deformations in asymmetric-plan systems. First, the parameters that characterize supplemental viscous damping and its plan-wise distribution were identified, and then the effects of these parameters on edge deformations were investigated. It was found that supplemental damping reduces edge deformations and that reductions by a factor of up three are feasible with proper selection of system parameters. Furthermore, viscous damping may be used to reduce edge deformations in asymmetric-plan systems to levels equal to or smaller than those in the corresponding symmetric-plan system. © 1998 John Wiley & Sons, Ltd.     

The Asymmetry of Subsurface Temperature Anomalies Associated with ENSO in the Equatorial Western Pacific

The phenomenon of ENSO asymmetry has been recognized for many years, but most studies have focused on the asymmetry of surface temperature anomalies in the equatorial eastern Pacific. Here, the authors investigate the temperature asymmetry associated with ENSO in the subsurface of the western Pacific through analysis of observations and numerical experiments with an ocean GCM. Both the observation and simulation exhibit significant ENSO asymmetry, characterized by negative temperature skewness in the equatorial western Pacific and positive skewness in the eastern Pacific. Heat budget analysis reveals that nonlinear dynamical heating results in the positive temperature asymmetry in the equatorial eastern Pacific, but tends to weaken the negative temperature asymmetry in the equatorial western Pacific. The climatological meridional current transports the temperature anomalies and corresponding negative asymmetry from the off-equator region to the equator in the subsurface of the western Pacific. Through a sensitivity experiment with reversed wind stress forcing, the authors suggest that the skewness of the wind stress anomalies does not contribute to the negative temperature asymmetry in the western Pacific in the first-order approximation, while the internal nonlinear dynamics does play a key role. The study suggests that, as a result of nonlinear processes, the oceanic responses to anomalous wind stress are nonlinear and asymmetric in the tropical Pacific.     

小入射角下海浪后向散射系数不对称性和各向异性分析验证

基于北京遥测技术研究所机载波谱仪实测数据以及ECMWF提供的风场数据,分析了不同风速条件下小入射角海浪平均后向散射系数不对称性与各向异性随入射角的变化特性,并对导致这一现象的原因进行了初步分析。结果表明:小入射角下,海浪平均后向散射系数随入射角增大呈现递减趋势并在18°时达到某一稳定值,之后基本维持不变;海浪后向散射系数不对称性与各向异性均随入射角增大呈现递增趋势,同样在18°增大至某一稳定值,之后基本维持不变;低风速条件下,海浪不对称性和各向异性与风速有关,且风速越大不对称性与各向异性越明显。     

线性准地转模型中副热带环流对潜热加热的定常响应I.基本性质及特征分析

利用线性理论模型进行解析和模拟是大气科学的重要基础研究方法之一, 其简单明了, 解释了如Rossby波形成等重要的环流现象。近年, 有研究 (Chen et al., 2001) 运用定常线性准地转模型研究副热带高压的形成, 在相似加热强迫下, 其结果与理论研究和GCM的研究不同。本文运用该模型系统研究了由季风降水产生的潜热加热所激发的副热带定常波的结构特征, 以理解其结果与GCM不一致的原因。研究表明基本流对热强迫的定常波的结构有重要的影响: (1) 当基本流为东风或为零时, 定常波在垂直方向上表现为第一斜压结构, 波动振幅随东风的增大而减小; (2) 当基本流为西风时, 呈现向上的传播特征, 振幅随高度的升高而增大。而且存在一个临界风速Uc(约3 m/s), 此时, 波动振幅最强; 基本流的平流作用具有非对称性, 西风时平流作用远远强于东风。由此揭示了该线性模型解的本质: 加热在热源区所激发的经向地转涡度输送必须能够平衡加热的位涡制造和纬向位涡平流; 基本流的经向和垂直方向的变化使得气旋和反气旋中心偏向热源中心北侧, 并进一步发现当基本流为夏季亚洲季风区纬向平均的纬向风场时, 线性模型的解中位于中低层的反气旋中心显著抬升, 而不出现在地面上, 与完整的大气环流模式的结果接近。说明即使在线性模式中, 洋面副高的形成也不能完全用季风潜热加热来解释; 另外, 静力稳定度对热强迫的副热带环流的影响也很重要, 使热源的强迫作用放大。     

黄河三角洲桩西101站潮沟地貌形态及其水动力学研究

在潮沟下游，横跨且生趣与潮沟的横断面设了５个观测站，进行了２４ｈ的水动力测量。结果表明，涨落潮流速流向不对称，在潮沟内，涨落潮流流速差别很大，涨潮流流速最大为９ｃｍ／２，而落潮流流速最大可达３８ｃｍ／ｓ。据推测，潮沟内之所以落潮流流速明显大于涨潮流流速，可能是由于潮沟与岸线斜交有关。     

双节点有限元模拟直立走滑断裂地震位移场

结合位错理论和有限单元法，对介质横向不均匀性引起的直立走滑断裂地震水平位移场不对称性进行了数值模拟研究。结果表明，断层两侧介质泊松比和弹性模量的横向不均匀性，均可以引起直立走滑断层同震破裂及地震位移场的不对称性，其中，断层两侧介质的剪切模量比(刚度比)对直立走滑断裂地震位移场不对称性起主要作用。     

谱模式SAMIL对南亚季风区大气季节内振荡向北传播的模拟

基于与NCEP资料结果的比较,研究了中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室发展的大气环流模式SAMIL对夏季南亚季风区季节内振荡（ISO）向北传播特征的模拟,并结合目前对ISO北传机制的理解对模拟结果进行了分析讨论。SAMIL在夏季南亚地区模拟出相当强度的季节内振荡的活动,并且模拟的ISO也表现出与NCEP资料相似的从赤道向北传播的特征,但传播的速度要慢于NCEP资料的结果。模拟的北传ISO具有与NCEP资料相似的结构特征,涡度和水汽场明显的呈经向不对称,涡度和水汽的正异常位于ISO对流的北面,最大的上升运动和最强的行星边界层辐合也位于ISO对流的北面。ISO 结构的经向不对称性正是模式模拟的ISO具有向北传播特征的原因;而模式对夏季南亚季风区高低层风场和行星边界层水汽的合理模拟起了关键的作用。同时,根据关于ISO北传机理的已有研究,模式的结果也表明南亚地区夏季风场的垂直结构是那里ISO向北传播的重要机制。     

Early formed regional antiforms and synforms that fold younger matrix schistosities: their effect on sites of mineral growth

In the metamorphic cores of many orogenic belts, large macroscopic folds in compositional layering also appear to fold one or more pervasive matrix foliations. The latter geometry suggests the folds formed relatively late in the tectonic history, after foliation development. However, microstructural analysis of four examples of such folds suggests this is not the case. The folds formed relatively early in the orogenic history and are the end product of multiple, near orthogonal, overprinting bulk shortening events. Once large macroscopic folds initiate, they may tighten further during successive periods of sub-parallel shortening, folding or reactivation of foliations that develop during intervening periods of near orthogonal shortening. Reactivation of the compositional layering defining the fold limbs causes foliation to be rotated into parallelism with the limbs.Multiple periods of porphyroblast growth accompanied the multiple phases of deformation that postdated the initial development of these folds. Some of these phases of deformation were attended by the development of large numbers of same asymmetry spiral-shaped inclusion trails in porphyroblasts on one limb of the fold and not the other, or larger numbers of opposite asymmetry spirals on the other limb, or similar numbers of the same asymmetry spirals on both limbs. Significantly, the largest disparity in numbers from limb to limb occurred for the first of these cases. For all four regional folds examined, the structural relationships that accompanied these large disparities were identical. In each case the shear sense operating on steeply dipping foliations was opposite to that required to originally develop the fold. Reactivation of the folded compositional layering was not possible for this shear sense. This favoured the development of sites of approximately coaxial shortening early during the deformation history, enhancing microfracture and promoting the growth of porphyroblasts on this limb in comparision to the other. These distributions of inclusion trail geometries from limb to limb cannot be explained by porphyroblast rotation, or folding of pre-existing rotated porphyroblasts within a shear zone, but can be explained by development of the inclusion trails synchronous with successive sub-vertical and sub-horizontal foliations.     

Seasonal evolution of the transverse thermohaline asymmetry in the Ria de Pontevedra (northwestern Spain)

A quasi-permanent transverse asymmetry in the thermohaline properties of the Ria de Pontevedra (northwestern Spain) was measured from October 1997 to October 1998 during 23 cruises. On average, the density increased form north to south. This asymmetry was maintained by salinity during the wet season, and by salinity and temperature during the dry season. The density difference between coasts (Δσ_t = σ_tsouth − σ_tnorth) and the river discharge were positively correlated (correlation coefficient, approximately 0.6) throughout the year. The density difference was negatively correlated with the upwelling index during the wet season (correlation coefficient, approximately −0.45) and positively correlated during the dry season (correlation coefficient, approximately 0.55).