Gravity Wave Mixing and Effective Diffusivity for Minor Chemical Constituents in the Mesosphere/Lower Thermosphere

The influence of gravity waves (GWs) on the distributions of minor chemical constituents in the mesosphere-lower thermosphere (MLT) is studied on the basis of the effective diffusivity concept. The mixing ratios of chemical species used for calculations of the effective diffusivity are obtained from numerical experiments with an off-line coupled model of the dynamics and chemistry abbreviated as KMCM-MECTM (Kuehlungsborn Mechanistic general Circulation Model—MEsospheric Chemistry-Transport Model). In our control simulation the MECTM is driven with the full dynamical fields from an annual cycle simulation with the KMCM, where mid-frequency GWs down to horizontal wavelengths of 350 km are resolved and their wave-mean flow interaction is self-consistently induced by an advanced turbulence model. A?perturbation simulation with the MECTM is defined by eliminating all meso-scale variations with horizontal wavelengths shorter than 1000 km from the dynamical fields by means of spectral filtering before running the MECTM. The response of the MECTM to GWs perturbations reveals strong effects on the minor chemical constituents. We show by theoretical arguments and numerical diagnostics that GWs have direct, down-gradient mixing effects on all long-lived minor chemical species that possess a mean vertical gradient in the MLT. Introducing the term wave diffusion (WD) and showing that wave mixing yields approximately the same WD coefficient for different chemical constituents, we argue that it is a useful tool for diagnostic irreversible transport processes. We also present a detailed discussion of the gravity-wave mixing effects on the photochemistry and highlight the consequences for the general circulation of the MLT.     

Numerical simulations of spicule driving mechanisms

Spicules are known as one of the most prevalent small-scale dynamic phenomena on the sun, which are likely to give considerable contribution to coronal heating and mass supply. We discuss a model of the spicules driven by a train of slow MHD shock waves propagating along a vertical expanding magnetic flux tube. The shocks are initiated due to compression of the tube by the increasing external pressure in the lower chromosphere. Downflow of spicular material depends on radiative cooling and other dissipative processes.     

Transverse Oscillations of Coronal Loops

On 14 July 1998 TRACE observed transverse oscillations of a coronal loop generated by an external disturbance most probably caused by a solar flare. These oscillations were interpreted as standing fast kink waves in a magnetic flux tube. Firstly, in this review we embark on the discussion of the theory of waves and oscillations in a homogeneous straight magnetic cylinder with the particular emphasis on fast kink waves. Next, we consider the effects of stratification, loop expansion, loop curvature, non-circular cross-section, loop shape and magnetic twist. An important property of observed transverse coronal loop oscillations is their fast damping. We briefly review the different mechanisms suggested for explaining the rapid damping phenomenon. After that we concentrate on damping due to resonant absorption. We describe the latest analytical results obtained with the use of thin transition layer approximation, and then compare these results with numerical findings obtained for arbitrary density variation inside the flux tube. Very often collective oscillations of an array of coronal magnetic loops are observed. It is natural to start studying this phenomenon from the system of two coronal loops. We describe very recent analytical and numerical results of studying collective oscillations of two parallel homogeneous coronal loops. The implication of the theoretical results for coronal seismology is briefly discussed. We describe the estimates of magnetic field magnitude obtained from the observed fundamental frequency of oscillations, and the estimates of the coronal scale height obtained using the simultaneous observations of the fundamental frequency and the frequency of the first overtone of kink oscillations. In the last part of the review we summarise the most outstanding and acute problems in the theory of the coronal loop transverse oscillations.     

7. Dynamics,winds, circulation and turbulence in the atmosphere of venus

With the possible exception of the lowest one or two scale heights, the dominant mode of circulation of Venus' atmosphere is a rapid, zonal, retrograde motion. Global albedo variations in the ultraviolet may reflect planetary scale waves propagating relative to the zonal winds. Other special phenomena such as cellular convection in the subsolar region and internal gravity waves generated in the interaction of the zonal circulation with the subsolar disturbance may also be revealed in ultraviolet imagery of the atmosphere. We discuss the contributions of experiments on the Orbiter and Entry Probes of Pioneer Venus toward unravelling the mystery of the planet's global circulation and the role played by waves, instabilities and convection therein.     

基于HLLC格式的理想MHD方程数值模拟

针对理想MHD(magnetohydrodynamics)方程数值求解困难的问题,基于原始的HLLC (Harten-Lax-Van Leer Contact wave)近似黎曼解方法,发展出一种新的适用于理想MHD问题的通量计算格式。控制方程采用有限体积法离散,时间推进采用隐式的LU-SGS（lower-upper symmetric Gauss-Seidel）格式,并且采用双曲型散度清除技术来抑制磁场散度的累积。通过一维激波管问题的数值模拟表明,HLLC-MHD格式能准确的分辨并捕捉复杂的磁流体力学波系结构,保证数值计算的精度,最大的数值计算误差不超过10%;通过二维的Rotor问题的数值模拟研究表明,HLLC-MHD格式能够应用于多维理想MHD问题的数值模拟,并且能够准确捕捉多维情况下磁流场中的阿尔文波;通过对比有、无散度清除的Rotor问题计算结果表明,双曲型散度清除技术可以将磁场散度峰值从50降低到2,有效抑制高磁场散度区域的散度累积,同时也会将误差传播到低散度区域,并且引起边界处散度的累积,影响计算的稳定性。      

Microphysics of Cosmic Plasmas: Hierarchies of Plasma Instabilities from MHD to Kinetic

In this article, we discuss the idea of a hierarchy of instabilities that can rapidly couple the disparate scales of a turbulent plasma system. First, at the largest scale of the system, L, current carrying flux ropes can undergo a kink instability. Second, a kink instability in adjacent flux ropes can rapidly bring together bundles of magnetic flux and drive reconnection, introducing a new scale of the current sheet width, ?, perhaps several ion inertial lengths (δ _i ) across. Finally, intense current sheets driven by reconnection electric fields can destabilize kinetic waves such as ion cyclotron waves as long as the drift speed of the electrons is large compared to the ion thermal speed, v _D ?v _i . Instabilities such as these can couple MHD scales to kinetic scales, as small as the proton Larmor radius, ρ _i .     

Coupling at the Atmosphere-Ionosphere-Magnetosphere Interface and Resonant Phenomena in the ULF Range

We discuss the electromagnetic processes in the ULF range which are important for the coupling between the atmosphere, ionosphere, and magnetosphere (AIM). The main attention is given to the Pc1–2 frequency ranges (f≈0.1–10 Hz) where some natural resonances in the AIM system are located. In particular, we consider the resonant structures in the spectra of the magnetic background noise related to the Alfvén resonances in the ionosphere as a possible diagnostic tool for studies of the ionospheric parameters. We also discuss the self-excitation of Alfvén waves in the ionosphere due to the AIM coupling and the role of such waves in the acceleration of electrons in the upper ionosphere and magnetosphere. Precipitation of magnetospheric ions due to their interaction with the ion-cyclotron waves is analyzed in relation to the ionospheric current systems, formation of partial ring current, and the influence of the ionosphere-magnetosphere feedback on the generation of such waves.     

Magnetopause stability threshold for patchy reconnection

This review is devoted to the problem of the internal fine structure of the Earth's magnetopause. A number of theoretical and experimental papers dealing with this subject is discussed from a unified viewpoint. The Vlasov kinetic approach is used to study the stability of magnetopause magnetic surfaces that can be destructed by the growth and overlapping of magnetic islands. The stochastic wandering of magnetic field lines between the destructed surfaces can result in magnetic percolation, i.e. the appearance of a topological connection of interplanetary and geomagnetic field lines. Such a process may be considered as a mechanism of the macroscopic (but spatially localized) reconnection. We discuss this in relation with the phenomena of spontaneous patchy reconnection, recently observed at ISEE satellites and now known as flux transfer events.Drift tearing mode, which is responsible for the growth of magnetic islands can be stabilized due to its coupling with ion sound waves, and the process of percolation will be interrupted if even a thin region with smooth stable magnetic surfaces exists within the magnetopause. Accordingly, we obtain a magnetopause stability threshold for localized reconnection. It is represented in the form of dependence of marginal dimensionless thickness of the magnetopause on the angle of magnetic field rotation within it.Further, we discuss the possible role of lower hybrid turbulence permanently observed within the. magnetopause and speeding up the process of reconnection. Nonlinear calculations supporting the developed model are given in the appendices. We consider briefly the motion of reconnecting flux tubes and evaluate the time necessary for the accomplishment of percolation. The calculations show that the appearance of reconnection patchies at the dayside magnetopause cannot occur too far from the stagnation region. The latter agrees with experimental indications on the most probable site of the formation of flux transfer events. In the concluding part of the review we discuss the necessary limitations on the theory, possible lines of its future advance and comparison with the experimental data.     

Sprite-Producing Lightning-Ionosphere Coupling and Associated Low-Frequency Phenomena

Theoretical and experimental evidence is collected for additional ionization regions in the mesosphere above lightning discharges and their connection with transient luminous events (TLE). New insights are reported into the different appearances in the Very Low Frequency (VLF) link traces as affected by the mesospheric ionization regions. Based on these findings, physical processes going on in the ionization regions and their coupling to the primary lightning discharge process are conceptualized. Thereafter, some diagnostic potential is outlined. Finally, the ionization regions are considered as a transmitter of secondary low-frequency waves. The distinction is made between the primary electromagnetic waves emitted by the lightning and the secondary waves. As a consequence the Extremely Low Frequency (ELF) and Ultra Low Frequency (ULF) transient signatures observed on the ground are understood as a composite of both wave types. In addition a novel method is introduced to extract the charge moment change of a sprite producing lightning discharge.     

Influence of the Solar Cycle on the General Circulation of the Stratosphere and Upper Troposphere

The record of dynamical structure reveals a systematic variation that operates coherently with the 11-yr variation of UV irradiance. Involving periods shorter than 5 years, the systematic variation reflects the influence of the QBO on the polar-night vortex. It has the same basic structure as interannual changes associated with the residual mean circulation of the stratosphere. A signature of the solar cycle also appears in the direct correlation to solar flux, as recovered through regression of the entire monthly record. That signature, however, is sharply enhanced around solstice, when the residual circulation is active, and during extremal phases of the QBO. In the tropics, the solar signature follows, throughout the year, from a decadal modulation in the frequency of the QBO. The modulation is manifested to either side of the QBO’s mean frequency, in two spectral peaks where the QBO dwells: one at (24 months)⁻¹, reflecting a Biennial Oscillation (BO), and another at (36 months)^-1. Intrinsic to the QBO, those peaks are separated from its mean frequency by ∼11 years⁻¹.Through the QBO’s residual circulation, the decadal modulation introduces anomalies in the subtropics, with symmetry about the equator. Accompanying anomalous temperature in the subtropics is a stronger signature over the winter pole. Discovered by Labitzke and van Loon 1988, that solar signature reflects anomalous downwelling of the Brewer-Dobson circulation. It is shown to follow through the BO, which is intrinsic to the QBO and its modulation of the polar-night vortex.     

Physics of Electric Discharges in Atmospheric Gases: An Informal Introduction

A short account of the physics of electrical discharges in gases is given from the viewpoint of its historical evolution and application to planetary atmospheres. As such it serves as an introduction to the papers on particular aspects of electric discharges contained in this issue, in particular in the chapters on lightning and the discharges which in the last two decades have been observed to take place in Earth’s upper atmosphere. In addition to briefly reviewing the early history of gas discharge physics we discuss the main parameters affecting atmospheric discharges like collision frequency, mean free path and critical electric field strength. Any discharge current in the atmosphere is clearly carried only by electrons. Above the lower boundary of the mesosphere the electrons must be considered magnetized with the conductivity becoming a tensor. Moreover, the collisional mean free path in the upper atmosphere becomes relatively large which lowers the critical electric field there and more easily enables discharges than at lower altitudes. Finally we briefly mention the importance of such discharges as sources for wave emission.     

Thermospheric gravity waves: Observations and interpretation using the transfer function model (TFM)

Gravity waves are prominent in the polar region of the terrestiral thermosphere, and can be excited by perturbations in Joule heating and Lorents force due to magnetospheric processes. We show observations from the Dynamics Explorer-2 satellite to illustrate the complexity of the phenomenon and review the transfer function model (TFM) which has guided our interpretation. On a statistical basis, the observed atmospheric perturbations decrease from the poles toward the equator and tend to correlate with the magnetic activity index, Ap, although individual measurements indicate that the magnetic index is often a poor measure of gravity wave excitation. The theoretical models devised to describe gravity waves are multifaceted. On one end are fully analytical, linear models which are based on the work of Hines. On the other end are fully numerical, thermospheric general circulation models (TGCMs) which incorporate non-linear processes and wave mean flow interactions. The transfer function model (TFM) discussed in this paper is between these two approaches. It is less restrictive than the analytical approach and relates the global propagation of gravity waves to their excitation. Compared with TGCMs, the TFM is simplified by its linear approximation; but it is not limited in spatial and temporal resolution, and the TFM describes the wave propagation through the lower atmosphere. Moreover, the TFM is semianalytical which helps in delineating the wave components. Using expansions in terms of spherical harmonics and Fourier components, the transfer function is obtained from numerical height integration. This is time consuming computationally but needs to be done only once. Once such a transfer function is computed, the wave response to arbitrary source distributions on the globe can then be constructed in very short order. In this review, we discuss some numerical experiments performed with the TFM, to study the various wave components excited in the auroral regions which propagate through the thermosphere and lower atmosphere, and to elucidate the properties of realistic source geometries. The model is applied to the interpretation of satellite measurements. Gravity waves observed in the thermosphere of Venus are also discussed.     

流动稳定性中小扰动波传播速度的数值研究

在保守系统中，小扰动波如线性水波及线性重力内波等均以其群速度传播，且群速度等于能流速度，在非保守系统中，波的传播速度还是个不十分清楚的问题。本文用数值计算的方法研究流动稳定性问题中小扰动波的传播速度，结果表明，波的传播速度并不等于能流速度，而与复群速度的实部近似相等。本文还用一简单的模型对此给予了解释。     

考虑效率最大化的新型感应电机转子磁链给定

为提高感应电机(IM)运行效率,在考虑铁损数学模型的基础上,给出了高低转速工况下的电压电流约束条件,将保证损耗最小的最优转子磁链给定转化为在约束条件下的目标函数求最小值问题。通过定义广义Lagrange函数,结合Kuhn-Tucker定理分别求解出恒转矩区和恒功率区约束条件下的最优转子磁链给定,保证IM在整个工作范围内的效率最大化。试验结果验证了该方法的有效性。     

Flux-Transport Solar Dynamos

Large-scale solar dynamo models were first built by Parker (1955). Over the past half a century these models have evolved significantly. We discuss here the development of a class of large-scale dynamo models which include, along with the α-effect and Ω-effect, an important third process, flux transport by meridional circulation. We present the properties of this ‘flux-transport’ dynamo, including the crucial role meridional circulation plays in giving this dynamo predictive power.     

Signature of the 11-Year Cycle in the Upper Atmosphere

In the last 45 years I have studied the thermal structure of the atmosphere from the thermosphere down to the stratosphere, and found evidence of its variability in relationship with the change of solar irradiation during the 11-year solar cycle. I would review, in the light of recent model results, the measurements which I had made since the 1960s and which, for some of them, did not find any explanation at the time of their publication. The data were obtained by two different techniques, rockets and lidars and correspond to different regions of the atmosphere from the upper thermosphere to the stratosphere. The expectation was until recently that the atmosphere should be warmed by an increase of solar flux in the course of the solar cycle due to the increase of UV flux. It has been shown to be the case in the tropical stratosphere and at all latitudes in the upper thermosphere. But, at high and mid latitudes and at other altitudes, the reverse situation was found to exist and, until recently, this cooling observed in parts of the atmosphere with increasing solar flux had never been simulated by models. In addition to reviewing our own data, the paper will present recent results using other dataset which support our observations. It is only recently that we succeeded with a model able to tune the forcing by planetary waves at the tropopause level and thus reproduce such behaviour.     

一个新非线性方程组解的存在性定理

作为微积分中连续函数介值定理在n维欧氏空间Rn中的推广,G.Aumann建立了一个定义于n维矩形上非线性方程组解的存在性定理,J.Rohn利用Brouwer不动点定理,把定理推广到定义域为紧凸集的情形。利用Brouwer拓扑度理论,证明定理中凸性条件进一步减弱为星形区域时,其结论仍然成立。     

Discharges in the Stratosphere and Mesosphere

In the present paper salient features of discharges in the stratosphere and mesosphere (namely sprites, halos, blue starters, blue jets, gigantic jets and elves), are discussed. The electrostatic field due to charge imbalance during lightning processes may lead to stratospheric/mesospheric discharges either through the conventional breakdown based on streamers and leaders or relativistic runaway mechanism. Most (not all) of the observed features of sprites, halos and jets are explained by this processes. Development and evolution of streamers are based on the local transient electrostatic field and available ambient electron density which dictate better probability in favor of positive cloud-to-ground discharges, and thus explains the polarity asymmetry in triggering sprites and streamers. Elves are generated by electromagnetic pulse radiated by return stroke currents of cloud-to-ground/inter-cloud discharges. Generation of the both donut and pancake shape elves are explained. Electrodynamic features of thunderstorms associated with stratospheric/mesospheric discharges are summarized including current and charge moment associated with relevant cloud-to-ground discharges. The hypothesis relating tropospheric generated gravity waves and mesospheric discharges are also discussed. Finally some interesting problems are listed.     

渤海冬夏季环流的数值研究

用三维陆架海模式对渤海的冬夏季环流进行了研究。指出：就垂向平均而言、渤海的冬夏季环流结构基本一致,且与垂向平均的潮余流相似。渤海环流有显著的三维结构,冬季,上层主要为风漂流,下层主要为风漂流,下层为补偿流;夏季;潮,风和密度对环流的贡献较大,表现为复杂的三维结构。