SEARCH FOR CORRELATIVITY OF LIGHTNING(STROKE)WITH ATMOSPHERIC STRATIFICATION FACTORS

In this paper the statistical analysis is carried out on the correlation between lightning strokes andatmospheric stratification factors.It is shown that the total number of strokes in lightning process is mainlydecided by environmental temperature at altitude with the residual instability of 5℃(T_r).The instabilityshould also affect the total number of strokc in lightning process.A forecasting equation of stroke in light-ning process has been deduced and two interesting preliminary conclusions have been obtained.     

A swallow-tail type catastrophic model of earthquake process

（殷有泉）（杜静）Ａｓｗａｌｌｏｗ－ｔａｉｌｔｙｐｅｃａｔａｓｔｒｏｐｈｉｃｍｏｄｅｌｏｆｅａｒｔｈｑｕａｋｅｐｒｏｃｅｓｓ￥Ｙｏｕ－ＱｕａｎＹＩＮａｎｄＪｉｎｇＤＵ（ＰｅｋｉｎｇＵｎｉｖｅｒｓｄｙ，Ｂｅｉｊｉｎｇ１００８７１，Ｃｈｉｎａ）（Ｎｏｒｔ...     

中层大气Rossby波与惯性重力波的非线性相互作用（Ⅱ）波包之间的相互激发

进一步讨论了大中尺度Ｒｏｓｓｂｙ波与惯性重力波的非线性相互作用问题．从共振相互作用曲线来看，Ｒｏｓｓｂｙ波和惯性重力波可以在相当广泛的角谱范围内发生共振非线性相互作用．在一定条件下，一个大振幅波包可以激发两个小振幅波包不稳定增长而出现参量不稳定现象，这三个波包可以是同种类型或不同类型的波包．当两个大振幅波包发生相互作用时，非线性过程会产生另一个波包并使它增长，并且增长速度大于仅有一个大振幅波包时的增长速度．大尺度Ｒｏｓｓｂｙ波包税发两个较小尺度惯性重力波的过程是一种重要的能量串级（ｃａｓｃａｄｅ）过程．     

中层大气Rossby波与惯性重力波的非线性相互作用（Ⅱ）波包之间的相互激发

进一步讨论了大中尺度Ｒｏｓｓｂｙ波与惯性重力波的非线性相互作用问题．从共振相互作用曲线来看，Ｒｏｓｓｂｙ波和惯性重力波可以在相当广泛的角谱范围内发生共振非线性相互作用．在一定条件下，一个大振幅波包可以激发两个小振幅波包不稳定增长而出现参量不稳定现象，这三个波包可以是同种类型或不同类型的波包．当两个大振幅波包发生相互作用时，非线性过程会产生另一个波包并使它增长，并且增长速度大于仅有一个大振幅波包时的增长速度．大尺度Ｒｏｓｓｂｙ波包税发两个较小尺度惯性重力波的过程是一种重要的能量串级（ｃａｓｃａｄｅ）过程．     

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

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.     

多次透射公式的一种稳定实现措施

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。     

理查逊数和晴空颠簸的关系

对切变气流中重力内波的稳定性进行了数值计算，结果表明，判别晴空颠是否发生的临界Ｒｉ数随波长，层结稳定度和基本气流变强度的不同而有所变化，预报业务中用Ｒｉ〈０．２５作为预报晴空的指标易出现空报。     

Lagrangian meshfree particles method (SPH) for large deformation and failure flows of geomaterial using elastic–plastic soil constitutive model

Simulation of large deformation and post‐failure of geomaterial in the framework of smoothed particle hydrodynamics (SPH) are presented in this study. The Drucker–Prager model with associated and non‐associated plastic flow rules is implemented into the SPH code to describe elastic–plastic soil behavior. In contrast to previous work on SPH for solids, where the hydrostatic pressure is often estimated from density by an equation of state, this study proposes to calculate the hydrostatic pressure of soil directly from constitutive models. Results obtained in this paper show that the original SPH method, which has been successfully applied to a vast range of problems, is unable to directly solve elastic–plastic flows of soil because of the so‐called SPH tensile instability. This numerical instability may result in unrealistic fracture and particles clustering in SPH simulation. For non‐cohesive soil, the instability is not serious and can be completely removed by using a tension cracking treatment from soil constitutive model and thereby give realistic soil behavior. However, the serious tensile instability that is found in SPH application for cohesive soil requires a special treatment to overcome this problem. In this paper, an artificial stress method is applied to remove the SPH numerical instability in cohesive soil. A number of numerical tests are carried out to check the capability of SPH in the current application. Numerical results are then compared with experimental and finite element method solutions. The good agreement obtained from these comparisons suggests that SPH can be extended to general geotechnical problems. Copyright © 2008 John Wiley & Sons, Ltd.     

MHD instability due to non-homogeneity and non-uniformity of magnetic field in gravitating medium and its consequences in the central region of galaxies

The MHD wave instabilities due to non-uniform magnetic field and non-homogeneity of density have been studied. The reference (coordinate) system considered here is cylindrical type. The General Dispersion Relation (GDR) for the wave propagation in a gravitating but non-relativistic region has been derived. Similar to common knowledge, the said non-uniformities have been found to be responsible for the instability of the system. But interestingly many instability factors are produced due to presence of two types of non-uniformities simultaneously. This theory may add more clues for the event of instabilities, formation of hot plasma-bed in Galactic Central Region, and mass out-flow from there. Many conditions for instabilities could be obtained from GDR deduced here. However, a few conditions for critical wavelength of the MHD wave have been obtained in terms of system parameters (like gradient of magnetic field and rotation). This theory, in turn, may be helpful for the better understanding of the Explosion Theory of formation of outer structure of Galaxies like ours.