The 1.5–5-day eastward waves in the upper stratosphere–mesosphere as observed by the Esrange meteor radar and the SABER instrument     

E.G. Merzlyakov  D.V. Pancheva 《Journal of Atmospheric and Solar》2007,69(17-18):2102

Data of neutral meridional wind obtained by the meteor radar at Esrange and data of temperature and pressure measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics (TIMED) spacecraft were studied with respect to a day-to-day atmospheric variability with periods ranging from 1.5 to 5 days. The detailed analysis was carried out for February 2004. Perturbations of the atmospheric parameters at the examined periods appeared mainly as eastward-propagating waves of zonal wavenumbers 1 and 2. We suggested that these waves excited by the jet instability on both flanks of the polar-night jet in the upper stratosphere and mesosphere interact nonlinearly with each other, and this interaction generates secondary waves. The radar observed both primary and secondary waves at mesospheric heights. The data analysis supports this suggestion. Under conditions of weaker instability observed in February 2003 the perturbations of atmospheric parameters of periods ranging from 1.5 to 5 days had smaller amplitudes at heights of the mesosphere than those in February 2004. It was found that the Eliassen-Palm fluxes calculated for the waves generated by the jet instability were mainly downward directed. This result suggests a possible dynamical influence of the mesospheric layers on the lower atmospheric levels.  相似文献   

Stability and accuracy analysis of outer loop dynamics in real‐time pseudodynamic testing of SDOF systems     

Oya Mercan  James M. Ricles 《地震工程与结构动力学》2007,36(11):1523-1543

Real‐time pseudodynamic (PSD) testing is an experimental technique for evaluating the dynamic behaviour of a complex structure. During the test, when the targeted command displacements are not achieved by the test structure, or a delay in the measured restoring forces from the test structure exists, the reliability of the testing method is impaired. The stability and accuracy of real‐time PSD testing in the presence of amplitude error and a time delay in the restoring force is presented. Systems consisting of an elastic single degree of freedom (SDOF) structure with load‐rate independent and dependent restoring forces are considered. Bode plots are used to assess the effects of amplitude error and a time delay on the steady‐state accuracy of the system. A method called the pseudodelay technique is used to derive the exact solution to the delay differential equation for the critical time delay that causes instability of the system. The solution is expressed in terms of the test structure parameters (mass, damping, stiffness). An error in the restoring force amplitude is shown to degrade the accuracy of a real‐time PSD test but not destabilize the system, while a time delay can lead to instability. Example calculations are performed for determining the critical time delay, and numerical simulations with both a constant delay and variable delay in the restoring force are shown to agree well with the stability limit for the system based on the critical time delay solution. The simulation models are also used to investigate the effects of a time delay in the PSD test of an inelastic SDOF system. The effect of energy dissipation in an inelastic structure increases the limit for the critical time delay, due to the energy removed from the system by the energy dissipation. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

大气中对称不稳定机制的动力学分析及暴雨的分析与预报   总被引：1，自引：0，他引：1  

景丽  陆汉城 《气象》2002,28(6):23-27

用气块法从力学角度对对称不稳定机制及在对称不稳定条件下产生的环流进行分析，更全面地定义了对称不稳定及它的产生机制和中尺度环流形成的过程。对暴雨个例诊断分析表明，有些强降水区在降水前和降水过程中存在着不对称不稳定，说明对称不稳定条件下形成的环流对暴雨有引发和加强作用。在以往研究原基础上，总结出了利用常规观测资料分析对称不是否存在，及其能量大小的方法，用它来预报是否降水及降水的强度，从而提高降水预报准确率。  相似文献   

WAVE-CISK对称不稳定谱点分布的半圆定理     

张铭 《大气科学》2001,25(4):559-566

采用滞弹性近似研究了WAVE-CISK下对称性扰动的谱点分布,得到了WAVE-CISK下对称不稳定扰动谱点分布的半圆定理,用其可估计该对称不稳定增长率的上界.发现存在WAVE-CISK时加热反馈和层结参数对该不稳定的增长率均有重要影响.WAVE-CISK加热反馈越强、基流的垂直切变越大,扰动的垂直结构越简单则该不稳定增长率的上界就越大.存在WAVE-CISK时滞弹性近似下的对称不稳定发生的条件也较Boussinesq近似下的更苛刻.  相似文献   

青岛气旋类暴雨预报方法   总被引：4，自引：0，他引：4       下载免费PDF全文

耿敏  韩春深  林滋新 《气象》2001,27(12):26-28

使用天气动力学和统计学相结合的方法，以地面影响系统为依据、700hPa西南急流为条件对1983－1999年6－8月青岛地区40次暴雨进行了分型，划分为气旋、台风和冷锋三类。以气旋类暴雨为例，根据预报经验，选取相应的预报因子，建立0、1权重回归方程，用以预报青岛地区6－8月未来24小时的暴雨。气旋类方程准确率为78.0%。用此方法对2000年6－8月进行试报，效果较满意。  相似文献   

镍锗尖晶石位错域的高温蠕变实验研究   总被引：9，自引：1，他引：9       下载免费PDF全文

赵永红  J.D.Lawlis  S.Karato 《地球物理学报》2001,44(5):696-703

利用人工合成的多晶材料研究了镍锗尖晶石在位错域的高温蠕变性质.多晶材料的颗粒尺寸约8μm.单轴压缩试件为圆柱状,使用气体介质围压筒.常压蠕变试验过程中,围压为300MPa,温度为1373-1523K,应力在55-330MPa范围内.从实验结果得出了镍锗尖晶石在位错域的流动律,应力指数n=29±01,表明流动的微观机制为位错蠕变.与其他尖晶石进行对比可以发现一个力学同构群,虽然在正尖晶石和反尖晶石之间存在一定的差异.在位错蠕变域,尖晶石与橄榄石归一化的强度类似.由于尖晶石的剪切模量比橄榄石高50%,其实际强度也比橄榄石高.将橄榄石和尖晶石的蠕变数据外推到地球内部条件时,由于其高应力指数,橄榄石则有可能比尖晶石的强度高.  相似文献   

多次透射公式的一种稳定实现措施   总被引：3，自引：2，他引：3  

周正华  廖振鹏 《地震工程与工程振动》2001,21(1):9-14

基于对双曲偏微分议程数值解稳定性的GKS（Gustafsson,Kreiss and Sundstrom）准则的物理解释，本文提出了在波动模拟中多次透射公式飘移失稳的一个简单措施，并用波源问题和散射问题的数值试验检验了建议的稳定措施的有效性。  相似文献   

粘弹性介质中的地震波   总被引：1，自引：0，他引：1  

范家参 《地震研究》2001,24(4):358-362

给出了三元件的标准线性粘弹性固体在半平面内传播的地震波的解析解，它是由已知的弹性半平面内的解析解迭粘滞性解而得，从而克服了视地壳为二元件粘弹性体的Voigt模型或Maxell模型的缺点。  相似文献   

Effect of frictional heating on pre-seismic sliding: a numerical simulation using a rate-, state- and temperature-dependent friction law   总被引：1，自引：0，他引：1  

Naoyuki Kato 《Geophysical Journal International》2001,147(1):183-188

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Transition To Geostrophic Turbulence In The Laboratory, And As A Paradigm In Atmospheres And Oceans     

Peter L. Read 《Surveys in Geophysics》2001,22(3):265-317

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