Magneto-gravity Waves Trapped in the Lower Solar Corona

The possibility of trapped magneto-gravity waves in the lower solar corona with an open magnetic field is discussed. Intensity variations and/or Doppler shifts of relevant UV, EUV and x-ray spectral lines in the chromosphere, transition region and lower corona may reveal the existence of such low-frequency modes (with periods longer than ∼ 1.5 hour). The spectrum may be either discrete or continuous depending on the reflection property of the narrow transition region. These modes can be utilized to probe the dynamics of the upper chromosphere, transition region and lower corona; they may also play an important role in coronal heating. This revised version was published online in June 2006 with corrections to the Cover Date.     

顶部间隙对超声速膨胀器流动特性的影响

隔板与机匣之间留有间隙,间隙的存在势必会对超声速膨胀器的内部流场和总体性能产生影响,为了获得超声速膨胀器内部间隙流动的流动细节,采用三维雷诺平均Navier-Stokes方程和标准k-ε湍流模型,就顶部间隙对超声速膨胀器流动特性的影响进行了数值研究。结果表明:膨胀流道出口斜激波导致吸力面压力高于压力面,隔板尾缘附近部分泄漏流体经间隙流回压力面侧;间隙的存在导致吸力面进口及中、后部近下端壁压力上升,而压力面前缘附近压力下降,对比同一隔板位置,间隙高度每增加1%喉部高度,超声速膨胀器隔板载荷系数最高下降2.6%;端壁损失和斜激波损失降低,但产生了泄漏损失,三维流道内总的流动损失增加,膨胀器效率降低,本文研究范围内效率最多下降8.8%;马蹄涡、泄漏涡及二者之间的相互作用是顶部区域的主要涡系结构;前缘附近气流经间隙流到吸力面侧和尾缘附近泄漏流体越过间隙重新流回压力面侧是间隙内气流的主要运动形式。     

极区中层惯性重力波临界层的VHF雷达观测

本文采用移动式ＳＯＵＳＹＶＨＦ雷达１９８７年６月在挪威Ａｎｄφｙａ（６９°Ｎ，１０°Ｅ）的观测数据，研究中层惯性重力波在临界层的传播特征．数据分析结果表明，在临界层附近波动会突然衰减，波能量被背景风所吸收，惯性重力波的水平传播方向和垂直传播方向在通过临界层后会迅速发生改变，说明临界层附近会产生向下传播的能量源．并且在临界层，回波强度达到峰值，表明临界层对产生雷达回波起着重要作用．     

色散和耗散对Alfven孤立波的影响

利用变数变换和解析积分的方法,分别找到了带色散项的DNLS方程和带耗散的MKdV方程的一类解析解,给出了存在孤立波的条件。     

Estimated errors in a global gravity wave climatology from GPS radio occultation temperature profiles

In a previous paper by Schmidt et al. (2008), from CHAllenging Minisatellite Payload (CHAMP) Global Positioning System (GPS) radio occultation data, a comparison was made between a Gaussian filter applied to the “complete” temperature profile and to its “separate” tropospheric and stratospheric height intervals, for gravity wave analyses. It was found that the separate filtering method considerably reduces a wave activity artificial enhancement near the tropopause, presumably due to the isolation process of the wave component. We now propose a simple approach to estimate the uncertainty in the calculation of the mean specific wave potential energy content, due exclusively to the filtering process of vertical temperature profiles, independently of the experimental origin of the data. The approach is developed through a statistical simulation, built up from the superposition of synthetic wave perturbations. These are adjusted by a recent gravity wave (GW) climatology and temperature profiles from reanalyses. A systematic overestimation of the mean specific wave potential energy content is detected and its variability with latitude, altitude, season and averaging height interval is highlighted.     

内重力波传播的3维传输函数模式研究

在考虑背景风场及大气耗散的条件下,建立了3维内重力波传输函数数值模式.分析了300 km高度3维传输函数在频率波数域的特性,并以近地面单位脉冲点源为激发源,得到了内重力波在3维空间中的时空分布.讨论了不同时空尺度地面方波源激发的内重力波在电离层高度的能量分布特征.结果表明,(1)对内重力波而言,背景大气相当于一个带通滤波器,只有波动周期和波长分别在15～30 min和200～400 km之间的重力波扰动最容易上传到300km高度;(2)在背景风场的作用下水平面上以同心圆扩散的波阵面以及垂直方向上成漏斗状的波阵面发生了变形,并且逆风方向比顺风方向更有利于声重力波由对流层向电离层高度传播;(3)300km高度对时间尺度和空间尺度分别在20～30 min和150～250 km之间的地面方波源响应的总能量最强.     

Alfven波在微电离大气中的衰减特性研究

利用简单的偶极子地磁场模型以及大气电子密度和电导率模式, 分析地面产生的磁扰动以Alfven波的模式传播到近地空间区域. 这种地面的磁扰动可能干扰近地空间卫星对空间磁扰动的观测. 通过对地面磁扰动Alfven波模式1000 km高度内的衰减情况进行模拟, 认为在近地空间采用地磁偶极子模型是合理的. 由于衰减随扰动频率的增大而急剧增强, 分析还得到了近地卫星能够探测到地面磁扰动的最大频率. 计算结果表明, Alfven波的衰减主要集中在高度50 km以下, 这个区域内的大气电导率极其微弱, 使Alfven波的传播受到极大衰减. 0.4 Hz以下的Alfven波沿磁力线传播到1000 km高度后衰减结为原来扰动幅度的千分之一, 因此频率在0.4 Hz以下的Alfven波可能会干扰低轨卫星探测磁场脉动.     

对流层雷暴源所产生的柱形重力波

已有充分的证据表明, 大气对流层的雷暴迹象是大气中间层重力波活动的显著代表源.在雷暴迹象的上方, 通过火箭已观测到大气中间层出现的热效应, 也已通过雷 达探测到大气平流层出现的上行重力波, 从地面和卫星平台上观察到夜间气辉有序而 成环状的重力波波形. 所有这些实验结果都与位于观测点下方的雷暴活动有紧密联系. 此类雷暴通常主要集中在中国东部沿海以及地球其他沿海海湾地域. 关于此类雷暴对大 气中间层的影响尚未被充分研究和了解. 为能有效地探究其成因, 利用所开发的一个二维计算机数值模型模拟和研究大气对流层的雷暴源所引发的上行重力波, 进而揭示 此类重力波产生的基本物理机理, 及其在大气中间层的能量耗散. 通过模拟研究发现, 雷暴源可以大面积高强度地聚集和释放积雨云的能量, 当这种周期性的对流变化引发大气对流层的不稳定性后, 就会有圆柱体重力波的产生和传播.     

An analytical model of prominence dynamics

Solar prominences are magnetic structures incarcerating cool and dense gas in an otherwise hot solar corona. Prominences can be categorized as quiescent and active. Their origin and the presence of cool gas ($～{10}^4$?K) within the hot ($～{10}^6\text{K}$) solar corona remains poorly understood. The structure and dynamics of solar prominences was investigated in a large number of observational and theoretical (both analytical and numerical) studies. In this paper, an analytic model of quiescent solar prominence is developed and used to demonstrate that the prominence velocity increases exponentially, which means that some gas falls downward towards the solar surface, and that Alfvén waves are naturally present in the solar prominences. These theoretical predictions are consistent with the current observational data of solar quiescent prominences.     

Nonlinear quantum ion acoustic shock wave dynamics with exchange-correlation effects

The dynamics of linear and nonlinear electrostatic shock excitations is studied in homogeneous, unmagnetized, unbounded and dissipative quantum plasma consisting of electrons and ions. The dissipation in the system is taken into account by incorporating the ion kinematic viscosity. The system is modelled using the quantum hydrodynamic equations in which the electrons are significantly affected by the quantum forces, viz., the quantum statistical pressure, the quantum Bohm potential and electron exchange-correlations due to electron spin. In the weakly nonlinear limit, using reductive perturbation method deformed Korteweg-de Vries Burgers’s (KdVB) equation, which elegantly combines the effects of nonlinearity, dispersion and dissipation is derived. It is found that the present model predicts the existence of both nonlinear oscillatory and monotonic shock structures. The temporal evolution, stability and phase-space dynamics of nonlinear ion acoustic shocks are investigated numerically to elucidate the effects of quantum diffraction, electron exchange correlation and ion kinematic viscosity.