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.     

Structure,luminosity, and dynamics of the Venus thermosphere

We review here observations and models related to the chemical and thermal structures, airglow and auroral emissions and dynamics of the Venus thermosphere, and compare empirical models of the neutral densities based in large part on in situ measurements obtained by the Pioneer Venus spacecraft. Observations of the intensities of emissions are important as a diagnostic tool for understanding the chemical and physical processes taking place in the Venus thermosphere. Measurements, ground-based and from rockets, satellites, and spacecraft, and model predictions of atomic, molecular and ionic emissions, are presented and the most important sources are elucidated. Coronas of hot hydrogen and hot oxygen have been observed to surround the terrestrial planets. We discuss the observations of and production mechanisms for the extended exospheres and models for the escape of lighter species from the atmosphere. Over the last decade and a half, models have attempted to explain the unexpectedly cold temperatures in the Venus thermosphere; recently considerable progress has been made, although some controversies remain. We review the history of these models and discuss the heating and cooling mechanisms that are presently considered to be the most important in determining the thermal structure. Finally, we discuss major aspects of the circulation and dynamics of the thermosphere: the sub-solar to anti-solar circulation, superrotation, and turbulent processes.     

Giant Planet Ionospheres and Thermospheres: The Importance of Ion-Neutral Coupling

Planetary upper atmospheres-coexisting thermospheres and ionospheres-form an important boundary between the planet itself and interplanetary space. The solar wind and radiation from the Sun may react with the upper atmosphere directly, as in the case of Venus. If the planet has a magnetic field, however, such interactions are mediated by the magnetosphere, as in the case of the Earth. All of the Solar System’s giant planets have magnetic fields of various strengths, and interactions with their space environments are thus mediated by their respective magnetospheres. This article concentrates on the consequences of magnetosphere-atmosphere interactions for the physical conditions of the thermosphere and ionosphere. In particular, we wish to highlight important new considerations concerning the energy balance in the upper atmosphere of Jupiter and Saturn, and the role that coupling between the ionosphere and thermosphere may play in establishing and regulating energy flows and temperatures there. This article also compares the auroral activity of Earth, Jupiter, Saturn and Uranus. The Earth’s behaviour is controlled, externally, by the solar wind. But Jupiter’s is determined by the co-rotation or otherwise of the equatorial plasmasheet, which is internal to the planet’s magnetosphere. Despite being rapid rotators, like Jupiter, Saturn and Uranus appear to have auroral emissions that are mainly under solar (wind) control. For Jupiter and Saturn, it is shown that Joule heating and “frictional” effects, due to ion-neutral coupling can produce large amounts of energy that may account for their high exospheric temperatures.     

基于FEM-PIM计及热效应的统计能量分析

结合有限元法（FEM）和模态坐标系下计及热效应的功率输入法（PIM）,给出一种热环境下适用于复杂结构的统计能量分析方法.以各边简支的L型折板为研究对象,开展雨流载荷作用下的数值模拟验证方法的准确性.开展3种工况条件下热效应对统计能量分析参数的影响研究:①仅考虑热效应引起的材料力学性能变化;②仅考虑热应力引起的附加刚度效应;③同时考虑考虑两者影响.结果表明:温升影响材料力学性能的同时会导致耦合损耗因子减小,但对内损耗因子的影响不大;热应力引起的附加刚度效应对内损耗因子和耦合损耗因子的影响较大,两者均随温度的升高而逐渐减小;同时考虑两者影响时,热应力对统计能量分析参数的影响占主导地位,内损耗因子和耦合损耗因子均随温度的升高而逐渐减小;模态密度与温度的变化趋势基本一致.      

A Review of the Effects of Non-migrating Atmospheric Tides on the Earth’s Low-Latitude Ionosphere

Solar thermal tides are planetary-scale waves in the neutral atmosphere with periods that are harmonics of 24?hours. In the thermosphere, they can achieve significant amplitude and can be the dominant source of variation in the atmosphere. Through their modification of the neutral atmosphere, they can also significantly modify the ionosphere, especially at low-latitudes where the dynamics of the Earth’s ionosphere is determined to a large extent by the neutral atmosphere. Much recent work has focused on characterizing and understanding the impact of one sub-group of tides, known as non-migrating tides, on the ionosphere. Whereas migrating tides are responsible for creating strong day-night variations in the ionosphere, non-migrating tides create longitudinal variations in the ionosphere, the signature of which can only be detected with distributed networks of ground-based observations or spacecraft. The present work reviews the recent observations and modeling efforts that have helped to characterize and explain this longitudinal variability. Emphasis is placed on the characteristics of tides throughout the thermosphere, their impacts on the chemical composition of the thermosphere, and impacts on the ionosphere.     

Wave motions in the atmosphere and related ionospheric phenomena

We review important studies in the field of stratosphere-ionosphere coupling, including recent studies of wave motions of planetary waves, atmospheric tides and internal gravity waves in the atmosphere. The interrelation between stratospheric sudden warmings and winter anomaly of radio absorption, a dynamical model of stratospheric sudden warmings and some production mechanisms of intensified electron density in the D region are discussed. Other topics presented are atmospheric tides in the lower thermosphere including dynamo action, and internal gravity waves, by which we intend to explain travelling ionospheric disturbances in the F ₂ region and sporadic E layer at midlatitude (wave-enhanced sporadic E). Thermospheric winds are also reviewed and wind effects on the F ₂ layer are discussed. For each atmospheric event systematic observations of suitable physical quantities with proper time and spatial intervals are desirable.     

Thermosphere-Ionosphere-Electrodynamics General Circulation Model for the Ionospheric Connection Explorer: TIEGCM-ICON

The NASA Ionospheric Connection explorer (ICON) will study the coupling between the thermosphere and ionosphere at low- and mid-latitudes by measuring the key parameters. The ICON mission will also employ numerical modeling to support the interpretation of the observations, and examine the importance of different vertical coupling mechanisms by conducting numerical experiments. One of these models is the Thermosphere-Ionosphere-Electrodynamics General Circulation Model-ICON (TIEGCM-ICON) which will be driven by tidal perturbations derived from ICON observations using the Hough Mode Extension method (HME) and at high latitude by ion convection and auroral particle precipitation patterns from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE). The TIEGCM-ICON will simulate the thermosphere-ionosphere (TI) system during the period of the ICON mission. In this report the TIEGCM-ICON is introduced, and the focus is on examining the effect of the lower boundary on the TI-system to provide some guidance for interpreting future ICON model results.     

气动力/热与结构多场耦合试验模型方案初步设计

以多渠道、多机制交叉耦合为热防护结构特点的新一代高超声速飞行器必须采用气动力/热与结构多场耦合计算方法进行研究。目前,国外已建立较完善的耦合分析系统并用于飞行器研制,国内的中国空气动力研究与发展中心(CARDC)也已自主研发了热环境/热响应耦合计算平台(FL-CAPTER)。为验证多场耦合计算平台所用方法的有效性和计算结果的准确性,设计并开展气动力/热与结构耦合的地面试验具有十分重要的意义。本文结合气动力/热与结构多场耦合试验设计需求,以现有材料和设备能力为依托,开展了试验风洞选取、模型尺寸估算、模型材料选择、模型气动设计与模型结构设计工作。初步研究表明,模型支撑结构附近迎风面局部高温热膨胀将有利于模型前体结构产生可观的整体变形量。本文以此设计了带压缩拐角的二级压缩面结构模型,通过短时间不锈钢模型验证试验和计算对比分析初步验证了模型设计的可行性,并以此为基础预测了高温合金模型的试验结果。为下一步开展高温合金长时间风洞试验奠定了技术基础。     

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.     

In-Situ CHAMP Observation of Ionosphere-Thermosphere Coupling

The coupling between the ionised plasma and the neutral thermospheric particles plays an important role for the dynamics of the upper atmosphere. Significant progress in understanding the related processes has been achieved thanks to the availability of continuous accurate measurements of thermospheric parameters like mass density and wind by high resolution accelerometers on board the satellites CHAMP and GRACE. Here we present some examples of ionosphere-thermosphere coupling where CHAMP observations contributed considerably to their interpretation. We start with the derived properties of the thermosphere at altitudes around 400 km. A new aspect is the significant control of the geomagnetic field geometry on thermospheric features. Phenomena discussed in some depths are the equatorial mass density anomaly, the cusp-related mass density enhancement and the thermospheric response to magnetospheric substorms. Here we consider both the effect on the density and on the wind. A?long predicted process is the wind-driven ionospheric F region dynamo. The high-resolution magnetic field measurements of CHAMP enabled for the first time a systematic study of that phenomenon considering longitudinal, local time, seasonal and solar flux dependences. Some open issues that require further investigations are mentioned at the end.     

Standing Slow-Mode Waves in Hot Coronal Loops: Observations, Modeling, and Coronal Seismology

Strongly damped Doppler shift oscillations are observed frequently associated with flarelike events in hot coronal loops. In this paper, a review of the observed properties and the theoretical modeling is presented. Statistical measurements of physical parameters (period, decay time, and amplitude) have been obtained based on a large number of events observed by SOHO/SUMER and Yohkoh/BCS. Several pieces of evidence are found to support their interpretation in terms of the fundamental standing longitudinal slow mode. The high excitation rate of these oscillations in small- or micro-flares suggest that the slow mode waves are a natural response of the coronal plasma to impulsive heating in closed magnetic structure. The strong damping and the rapid excitation of the observed waves are two major aspects of the waves that are poorly understood, and are the main subject of theoretical modelling. The slow waves are found mainly damped by thermal conduction and viscosity in hot coronal loops. The mode coupling seems to play an important role in rapid excitation of the standing slow mode. Several seismology applications such as determination of the magnetic field, temperature, and density in coronal loops are demonstrated. Further, some open issues are discussed.     

Solar and stellar seismology

This article reviews solar and stellar seismology, with emphasis on the enormous progress which has been made recently in the observation and understanding of solar p-modes. Precision measurements of p-mode frequencies and frequency splittings allow a greater understanding of the structure of the solar interior, while p-mode amplitudes and linewidths shed light on the mode excitation mechanism, which is probably stochastic excitation by turbulent convection. The prospects for making similar measurements on other stars are also discussed.     

UV Irradiation Effect on the Electrical Properties of ZnO Thermal Control Coating Pigment

Electron concentration and Hall mobility have been investigated in pure zinc oxide single crystals, while in the dark and under ultraviolet (UV) excitation. Mode of scattering in ZnO has been determined by studying the temperature dependence of various electrical parameters in the range from -170 to 120°C. It has been observed that the degradation to the crystals by UV irradiation is limited only to the surface layer and shows up only at relatively lower temperatures, which is in contrast to the degradation behavior in thin films and powders.     

Dynamic thermal coupling modeling and analysis of wet electro-hydrostatic actuator

The electro-hydrostatic actuator(EHA) used in more electric aircraft(MEA) has been extensively studied due to its advantages of high reliability and high integration. However, this high integration results in a small heat dissipation area, leading to high-temperature problems. Generally,to reduce the temperature, a wet cooling method of using the pump leakage oil to cool the motor is adopted, which can also increase the difficulty of accurately predicting the system temperature in the early desi...     

End-to-End Modeling of the Solar Terrestrial System

Traditionally modeling for space science has concentrated on developing simulations for individual components of the solar terrestrial system. In reality these regions are coupled together. This coupling can be as simple as the driving of the magnetosphere – ionosphere – thermosphere system by the solar wind or as a complicated as the feedback of the ionospheric conductivity and currents on the magnetosphere. As part of the CISM project we are beginning a concentrated effort to compressively model the entire system. This approach includes chains of models. In the first chain physics based numerical models are utilized while in the second chain empirical models are coupled together. The first half of this paper discusses the numerical modeling approach by highlighting the coupling of pairs of regions within the system. In the second section we present results from empirical models which are combined to make long term forecasts of conditions in the geospace environment. It is expected that a validated and reliable forecast model for space weather can be obtained by combining the strongest elements of each chain.     

高超声速飞行器热环境与结构传热的多场耦合数值研究

为了准确预测高超声速飞行器面临的严峻气动热/力环境以及结构的热力响应,发展了高超声速流动与结构传热耦合框架。采用分区求解方法,通过耦合界面的实时数据传递,实现了基于Navier-Stokes方程的高超声速化学非平衡计算流体力学（CFD）求解器与结构的热力全耦合有限元法（FEM）求解器的多场耦合计算,建立了高超声速飞行器的多场耦合数值分析方法。首先对经典高超声速圆柱绕流实验进行了耦合计算,结果与实验值吻合良好。然后针对典型的超高温陶瓷（UHTC）材料的耦合传热问题进行了数值研究,考虑热传导效应对气动热环境和结构热响应预测的影响,结果表明对于复杂外形且热导率相对较高的UHTC材料,结构内部热传导对热环境和表面温度分布的影响不可忽略。最后针对UHTC材料热物性（比热和热导率）非线性对高超声速流动传热过程的影响进行了研究,结果表明当比热和热导率处于合理的误差范围内时,材料表面温度响应对其变化并不敏感。     

烟火点火器多物理场耦合仿真分析

电火工品在复杂电磁环境下的物理状态变化一般都包含了电磁 -热耦合过程,采用单一物理场建模仿真的方法很难得到准确的结果。因此,采用 ANSYS Workbench仿真平台,建立了烟火点火器的多物理场耦合仿真分析模型。首先,建立了烟火点火器的 HFSS仿真模型,得到了桥丝上的功率损耗;然后,将桥丝的损耗功率输入稳态热分析模型作为激励条件,并通过稳态热仿真分析得到了桥丝上的温度分布。仿真结果表明,该方法物理过程清晰,仿真结果准确可靠。     

The infrared spectrum of the airglow

The techniques of studying the IR airglow are briefly discussed followed by a review of recent observations. The main emphasis is on the molecular emissions of OH and O₂ from the mesosphere and lower thermosphere with a shorter discussion of the F-region atomic emissions. The theoretical interpretations of these emissions are reviewed. It is concluded that dynamic effects must play a dominant and as yet incompletely understood part in the photochemistry of the molecular emission region. An atlas of recently available airglow spectra is included.NRCC No. 13554.     

Effect of non-uniform basic temperature gradient on the onset of Marangoni convection in a fluid with suspended particles

The effect of a non-uniform basic temperature gradient on the onset of convection driven by surface tension in a horizontal layer of a Boussinesq fluid with suspended particles confined between an upper free, constant heat flux boundary and a lower rigid isothermal boundary is considered. The microrotation is assumed to vanish at the boundaries. A linear stability analysis is performed. The Rayleigh–Ritz technique is used to obtain the eigenvalues. The influence of various parameters on the onset of convection has been analyzed. Six different non-uniform basic state temperature profiles are considered and their comparative influence on onset is discussed. It is observed that the fluid layer with suspended particles heated from below is more stable compared to the classical fluid layer without suspended particles. The problem has possible applications in microgravity situations.