Polar amplification in a coupled climate model with locked albedo

In recent years, a substantial reduction of the sea ice in the Arctic has been observed. At the same time, the near-surface air in this region is warming at a rate almost twice as large as the global average—this phenomenon is known as the Arctic amplification. The role of the ice-albedo feedback for the Arctic amplification is still a matter of debate. Here the effect of the surface-albedo feedback (SAF) was studied using a coupled climate model CCSM3 from the National Center for Atmospheric Research. Experiments, where the SAF was suppressed by locking the surface albedo in the entire coupled model system, were conducted. The results reveal polar temperature amplification when this model, with suppressed albedo, is forced by a doubling of the atmospheric CO₂ content. Comparisons with variable albedo experiments show that SAF amplifies the surface-temperature response in the Arctic area by about 33%, whereas the corresponding value for the global-mean surface temperature is about 15%. Even though SAF is an important process underlying excessive warming at high latitudes, the Arctic amplification is only 15% larger in the variable than in the locked-albedo experiments. It is found that an increase of water vapour and total cloud cover lead to a greenhouse effect, which is larger in the Arctic than at lower latitudes. This is expected to explain a part of the Arctic surface–air-temperature amplification.     

Formation Mechanism of Soft X-Ray Transient Trans-Equatorial Loop System

The Soft X-ray Telescope (SXT) onboard Yohkoh often observed large-scale coronal loops connecting two active regions situated in opposite hemispheres. These are the trans-equatorial loop systems (TLSs). The formation mechanism of TLSs is not yet known. We analyzed a TLS observed simultaneously with Yohkoh/SXT and a coronagraph (SOHO/LASCO-C1). SOHO/LASCO-C1 observed loop expansion and eruption at the west solar limb. Yohkoh/SXT observed a rising motion (chromospheric evaporation) of hot and dense plasmas from the active regions located at the footpoints of the loop. Important results of our analyses are that (1) the loop eruption and the rising motion of the plasmas were simultaneous, (2) the TLS had a cusp-like appearance, and (3) the highest temperature region of the TLS was located above the bright loop seen in soft X rays. These observational results (loop expansion, eruption, and chromospheric evaporation) suggest that this bright (high-density) TLS was created by the same mechanism by which a solar flare occurs, namely, magnetic reconnection. In this paper, we propose a formation mechanism of the TLS that forms between two independent active regions.     

二根耦合振动弦的边界反馈稳定化问题(Ⅱ)

本文继续讨论二根耦合振动弦的边界反馈的数学模理;讨论了算子A的耗散性、予解式、半群e~(tA)及其指数稳定性。     

地震模拟振动台参数灵敏度分析

以地震模拟振动台（以下简称振动台）线性模型为基础，应用一阶灵敏度模型分析了振动台三状态反馈控制参数的灵敏度函数及其对系统动态特性的影响，用仿真的方法分析了三状态反馈参数的变化对系统输出特性的影响程度。     

Improved control algorithm for real‐time substructure testing

Real‐time substructure testing is a novel method of testing structures under dynamic loading. The complete structure is separated into two substructures, one of which is tested physically at large scale and in real time, so that time‐dependent non‐linear behaviour of the substructure is realistically represented. The second substructure represents the surrounding structure, which is modelled numerically. In the current formulation this numerical substructure is assumed to remain linear. The two substructures interact in real‐time so that the response of the complete structure, incorporating the non‐linear behaviour of the physical substructure, is accurately represented. This paper presents several improvements to the linear numerical modelling of substructures for use in explicit time‐stepping routines for real‐time substructure testing. An extrapolation of a first‐order‐hold discretization is used which increases the accuracy of the numerical model over more direct explicit methods. Additionally, an integral form of the equation of motion is used in order to reduce the effects of noise and to take into account variations of the input over a time‐step. In order to take advantage of this integral form, interpolation of the model output is performed in order to smooth the output. The improvements are demonstrated using a series of substructure tests on a simple portal frame. While the testing approach is suitable for cases in which the physical substructure behaves non‐linearly, the results presented here are for fully linear systems. This enables comparisons to be made with analytical solutions, as well as with the results of tests based on the central difference method. Copyright © 2001 John Wiley & Sons, Ltd.     

Placement of sensors/actuators on civil structures using genetic algorithms

The optimal design and placement of controllers at discrete locations is an important problem that will have impact on the control of civil engineering structures. Though algorithms exist for the placement of sensor/actuator systems on continuous structures, the placement of controllers on discrete civil structures is a very difficult problem. Because of the nature of civil structures, it is not possible to place sensors and actuators at any location in the structure. This usually creates a non‐linear constrained mixed integer problem that can be very difficult to solve. Using genetic algorithms in conjunction with gradient‐based optimization techniques will allow for the simultaneous placement and design of an effective structural control system. The introduction of algorithms based on genetic search procedures should increase the rate of convergence and thus reduce the computational time for solving the difficult control problem. The newly proposed method of simultaneously placing sensors/actuators will be compared to a commonly used method of sensors/actuators placement where sensors/actuators are placed sequentially. The savings in terms of energy requirements and cost will be discussed. Copyright © 2001 John Wiley & Sons, Ltd.     

The mechanism of the effects of the upwelling mean on the ENSO event mature phase locking

The mechanism of the effects of the upwelling mean on the ENSO event mature phase locking is ex-amined by using a mixed-mode model. The results show that the positive feedback process of the ef-fects of the seasonal variation of the upwelling mean on the Kelvin wave is the mechanism of the locking of the event mature phase to the end of the calendar year. The memory of the Rossby waves for the sign-shifting of the sea surface temperature anomaly from positive to negative 6 months before the cold peak time is the other mechanism of the locking of the La Nia event mature phase to the end of the calendar year. The results here are different from previous ones which suggest that the balance between cold and warm trends of sea surface temperature anomaly is the mechanism involved. The cold trend is caused by the upwelling Kelvin wave from upwelling Rossby wave reflected at the western boundary, excited by the westerly anomaly stress over the central Pacific and amplified by the seasonal variation of the coupled strength in its way propagating westward. The warm trend is caused by the Kelvin wave forced by the western wind stress over the middle and eastern equatorial Pacific. The cause of the differences is due to the opposite phase of the seasonal variation of the upwelling mean to that in the observation and an improper parameterization scheme for the effects of the seasonal varia-tion of the upwelling mean on the ENSO cycle in previous studies.     

Analysis of nonlinear site response using the LSST downhole accelerometer array data

Both linear and nonlinear behaviors of soil deposits were evaluated by strong and weak motion data observed on the surface and at depths of 6, 11, 17, 47 m at the Large Scale Seismic Test (LSST) array in Lotung, Taiwan. The soil properties measured by well logging and by the shear wave velocity profile measured by uphole and cross-hole methods are available. Both one-dimensional equivalent-linear method and nonlinear method are used for the evaluation have been used. The synthetic records at various depths are obtained by using the records at the bottom as input motion. These synthetic records are then compared with actual records at corresponding depths. Records of 13 earthquakes are used. We find that the synthetic records obtained from a linear model match well with actual records for small input motions, but the results obtained from a nonlinear model match poorly. On the other hand, the synthetic records using both the nonlinear model and equivalent-linear model are in good agreement with the observed records for large input motions. In these cases, the predicted response spectra using the linear model consistently overestimate the observed records. The threshold distinguishing the large and small input motions is 0.04 g at depth of 47 m for the LSST data. Thus, the nonlinearity started at 0.04 g and occurred unequivocally at 0.075 g. Furthermore, the dominant frequencies shift toward lower values when input motions become large. Clearly, the observed records at the LSST site manifest nonlinearity of soil response. The hysteresis loops evaluated by the nonlinear method show a permanent strain of about 0.01% in soil layers at higher ground motion input levels in this case.     

夯土墙在单调和反复水平荷载下的试验研究

通过对不同类型的夯土墙在单调荷载和反复荷载作用下的试验研究,分析了不同添加材料对夯土墙抗剪性能、抗震性能的影响,得到了夯土墙的裂缝开展规律、破坏特征、承载能力、延性及滞回性能。借用砌体结构的抗震承载力计算公式,给出了夯土墙抗剪、抗震计算的简化公式。     

时间域瞬变电磁法中心方式全程视电阻率的数值计算

给出了一种时间域瞬变电磁法视电阻率的数值计算方法，利用该方法可以容易地求出中心方式的全程视电阻率. 根据中心方式磁场垂直分量时间变化率Bz/T的核函数Y′(Z)的表现特征，以参数Z把整个瞬变过程分为早期阶段（Z>1.6）、早期到晚期的转折点（Z=1.6）和晚期阶段（Z<1.6）. 首先分别得到早期视电阻率和晚期视电阻率的精确值，然后通过转折点构成一条完整的全程视电阻率曲线. 虽然磁场垂直分量Bz的核函数Y(Z)是参数Z的单值函数，但同样存在一个从早期到晚期的转折点Z=1.6，转换点两边仍然可以得到一条早期曲线和一条晚期曲线. 在数值计算中，当迭代步长ΔZ<0.005Z时，视电阻率的相对误差小于0.5髎. 理论模型和实际数据计算表明，与早期和晚期近似值比较，全程视电阻率具有更高的精度和分辨率.