A high resolution nonhydrostatic tropical atmospheric model and its performance

A high resolution nonhydrostatic tropical atmospheric model is developed by using a ready-made regional atmospheric modeling system. The motivation is to investigate the convective activities associated with the tropical intraseasonal oscillation (ISO) through a cloud resolving calculation. Due to limitations in computing resources, a 2000 kmx2000 km region covering the forefront of an ISO-related westerly is selected as the model domain, in which a cloud-resolving integration with a 5-km horizontal resolution is conducted. The results indicate the importance of stratus-cumulus interactions in the organization of the cloud clusters embedded in the ISO. In addition, comparative integrations with 2-km and 5-km grid sizes are conducted, which suggest no distinctive differences between the two cases although some finer structures of convections are discernible in the 2-km case. The significance of this study resides in supplying a powerful tool for investigating tropical cloud activities without the controversy of cloud parameterizations. The parallel computing method applied in this model allows sufficient usage of computer memory, which is different from the usual method used when parallelizing regional model. Further simulation for the global tropics with a resolution around 5 km is being prepared.     

27.3-day and 13.6-day atmospheric tide and lunar forcing on atmospheric circulation

An analysis of time variations of the earth‘s length of day (LOD) versus atmospheric geopotential height fields and lunar phase is presented. A strong correlation is found between LOD and geopotential height from which a close relationship is inferred and found between atmospheric circulation and the lunar cycle around the earth. It is found that there is a 27.3-day and 13.6-day east-west oscillation in the atmospheric circulation following the lunar phase change. The lunar revolution around the earth strongly influences the atmospheric circulation. During each lunar cycle around the earth there is, on average, an alternating change of 6.8-day-decrease, 6.8-day-increase, 6.8-day-deerease and 6.8-day-increase in atmospheric zonal wind, atmospheric angular momentum and LOD. The dominant factor producing such an oscillation in atmospheric circulation is the periodic change of lunar declination during the lunar revolution around the earth. The 27.3- day and 13.6-day atmospheric oscillatory phenomenon is akin to a strong atmospheric tide, which is different from the weak atmospheric tides, diurnal and semidiurnal, previously documented in the literature. Also it is different from the tides in the ocean in accordance with their frequency and date of occurrence. Estimation shows that the 27.3-day lunar forcing produces a 1-2 m s^-1 change in atmospheric zonal wind. Therefore, it should be considered in models of atmospheric circulation and short and middle term weather forecasting. The physical mechanism and dynamic processes in lunar forcing on atmospheric circulation are discussed.     

Accelerated vortices in compressible media

A class of exact vortical solutions of the hydrodynamic equations for compressible media (single component or two-phase) is examined, taking viscosity and a gravitational field into account. Velocity profiles that have the structure of a vortex with a uniformly rotating, low-pressure, low-density trunk and a converging radial flow of matter are analyzed. These flows have low energy dissipation and can easily occur under natural conditions. Translated from Astrofizika, Vol. 51, No. 4, pp. 617–632 (November 2008).     

南海北部坡折带溶解氧分布特征及理化环境因子影响

依据2010年1月南海北部坡折带冬季航次资料,发现150~1 000 m层溶解氧表现出东北高、西南低的分布特征,在垂向上溶解氧整体上呈由表至底逐渐降低趋势。在强烈的水交换作用下溶解氧浓度大于8 mg/dm3等值线占据50 m以浅海域。中尺度暖涡在很大程度上改变了中下层海水中溶解氧空间分布,150~1 000 m层暖涡中心附近海域的溶解氧含量显著高于周边未受或受暖涡影响较小的海域,此外,溶解氧与营养盐、温度、盐度、pH之间在不同层次上存在明显的相关性,表明该海域冬季溶解氧的分布受物理过程和生化过程的影响。     

东南印度洋沿岸海温年代际振荡及经向传播探讨

用SODA资料分析了热带西南印度洋上升区温度距平与整个南印度洋温度距平的时滞相关, 发现热带西南印度洋上升区温度距平与65°S, 105°E附近200 m深度的温度距平存在滞后10 a的相关振荡, 同时探讨了其可能的机制为温跃层内的斜压内波驱动, 即65°S, 105°E附近200 m深度的温度距平沿着温跃层上层在东南印度洋沿岸从高纬度向低纬的传播, 传播时间大约为10 a左右, 这种信号在传播过程中表现得较弱, 而在起点和终点的两端振荡比较强。波动的传播相比振荡本身要显得弱。     

Long-term changes of (polar) mesosphere summer echoes

Strong VHF radar echoes have been observed not only during summer months at polar latitudes (polar mesosphere summer echoes, PMSE) but also at middle latitudes (mesosphere summer echoes, MSE). These echoes are closely connected with small ice particles, thus containing information about mesospheric temperature and water vapour content. But the (P)MSE also depend on the ionisation due to solar wave radiation and precipitating high energetic particles. Observations with VHF radars at Andenes (69.3°N; 16.0°E) since 1994 and at Kühlungsborn (54.6°N; 11.8°E) since 1998 are used for investigations of the solar and geomagnetic control of the (P)MSE as well as of possible long-term changes. The (P)MSE are positively correlated with the solar Lyman α radiation and the geomagnetic activity and have slightly positive trends. Due to the limited measuring period, the significance levels of the detected (P)MSE trends are small. Positive trends in noctilucent clouds (NLC) and polar mesospheric clouds (PMC) are in general agreement with (P)MSE trends.     

Chaotic dynamics analysis and control of iterative procedure of capacity spectrum method

The capacity spectrum method (CSM), capable of predicting the demands of forces and deformations of the inelastic system, has been applied in the ATC and FEMA guidelines. The deformation of an inelastic system is solved iteratively by using the equivalent linearization for CSM, which actually forms a nonlinear map or discrete dynamical system. However, the iterative procedure of CSM did not converge for some inelastic systems, and the complicated dynamical phenomena for the solutions such as the periodic oscillation, period-doubling bifurcation and chaos may occur, which were shown in the bifurcation plots of iterative map of the simplified CSM in ATC40 and FEMA440. This paper presents a novel method to analyze and control the non-convergence of the iterative procedure of CSM from the perspective of chaotic dynamics. The Lyapunov exponent of the dynamical system is employed to identify the evolutional state and stability of solutions. Finally, the stability transformation method as a simple, versatile and effective chaos feedback control approach is applied to control the convergent failure of CSM in ATC40 and FEMA440. The numerical results illustrate that the stability transformation method can capture the desired fixed points of the dynamical system and obtain the stable convergent solutions of CSM.     

核幔边界的速度结构对PKPab波形的影响

用地球的自由振荡研究地球内部结构、速度间断面、密度分布等具有射线理论不可替代的优点。而地球的自由振荡可以用简正振型来表示,用简正振型叠加方法合成的PKP波理论地震图,其PKPab波震相和PKPdf波震相的走时与射线理论计算的理论走时基本一致,并且研究了在地幔底部至核幔边界上方300km处,压缩波的速度梯度的变化对PKPab波振幅的影响,从而证明当波以接近掠射角或者大于掠射角入射时,会有漏能现象的发生,或者可称之为隧道效应。发现用3个不同模型合成的地震图,在震中距相同的情况下,核幔边界上P波速度梯度大的,其PKPab波的振幅较小一些。这也进一步说明核幔边界上方P波速度梯度的变化对漏能现象有一定程度的影响。     

单跨简支梁竖向振动的磁悬浮半主动控制

由于传统的隔振器需要足够的竖向刚度来支撑上部结构,因而不能隔离竖向振动。为了解决这一问题,本文提出一种新的隔振策略,即磁浮式半主动控制方法,并将这一方法应用于弹性梁弯曲振动的半主动控制。将均质弹性梁简化为一带集中质量的简支梁,导出了控制系统的运动方程,讨论了系统在平衡点的稳定性,应用推广的Runge-Kutta方法,得到了系统在随机地面输入下的加速度响应。结果表明：杆件的初始悬浮位置是磁浮式半主动控制系统的平衡点,且平衡点是L稳定的;磁浮式半主动隔振系统具有类似于软弹簧的性质,与普通的弹性简支梁相比,磁浮式半主动振动控制系统的振动频率较低,加速度响应明显减小,系统具有良好的竖向隔振性能。     

一次西南涡暴雨的等熵位涡特征分析

应用常规资料和0.5°×0.5°的GFS再分析资料,对2010年7月19日发生在河北山东的一次西南涡暴雨过程产生的条件及其等熵位涡演变特征进行了分析。结果表明：西南涡、高、低空急流、地面低压是这次暴雨过程的主要影响系统;等熵位涡的演变和形态对冷空气活动有很好的示踪作用;等熵位涡中心两侧气流辐合,利于地面低压发展;高位涡下传,导致了大暴雨产生;等熵位涡大值区及移动方向与降水落区有很好的对应关系。