On ionospheric aerodynamics

This paper presents theoretical methods to determine the gas dynamic and the electrostatic effects due to the interaction caused by a rapidly moving body in the ionosphere. The principles of the methods are derived from the kinetic theory of collision-free plasma. It is shown that the collective behavior of the collision-free plasma makes it possible to use the fluid approach to treat the problems of ionospheric aerodynamics. Various solutions to the system of fluid and field equations that have direct bearing on the ionospheric aerodynamics are presented and discussed. Physical significances of the mathematical results are stressed. Some outstanding unsolved problems in ionospheric aerodynamics are elaborated and discussed.     

Effects due to an artificial earth satellite in rapid motion through the ionosphere or the interplanetary medium

Conclusion In this paper we have been concerned with the results of theoretical calculations of the interaction between a fast moving body and a tenuous plasma. Particular attention was paid to the case where the velocity of the body is much smaller than the velocity of neutral particles and ions, while the dimensions of the body are sufficiently large in comparison with the Debye radius. Such conditions are realized during the motion of artificial satellites or space rockets through the ionosphere, or through the interplanetary medium in the immediate neighborhood of the earth. Although this case has, on the whole, been investigated quite extensively, there are still a number of problems which require further analysis. Firstly, it is necessary to take into account the effect of the electric field on the motion of ions in the near zone at the rear of the body. Another important problem is that of magnetic disturbances. In the case of scattering of radio waves by the trail of the body, it would be interesting indeed to know the increase in the effective cross-section in the resonance region in which 0. A number of other research problems which arise in the analysis of phenomena in the neighborhood of a moving body have been noted in the Introduction.In the lower layers of the ionosphere it is important to allow for the fact that the dimensions of the body are comparable with the mean free path. Under these conditions there is the further interesting problem of the heating and additional ionization of the plasma, the disintegration of the surface, and the emission of waves. At large distances from the surface of the earth, the dimensions of the body may become comparable with the Debye radius, and the velocity of the body in the given region may become smaller than the thermal velocity of the particles. The character of the various disturbances introduced by the body under these conditions will also require a special investigation.Thus, the interaction of a moving body with plasma leads to special and exceptionally varied effects. Disturbances due to the body are very considerable, so that the physical state of the region surrounding the body is very different from the state of the undisturbed medium.The above results indicate that the phenomena in the neighborhood of satellites and space rockets in the ionosphere, or the interplanetary medium, must be taken into account, in the processing of experimental data when it is required to deduce information about the state of the undisturbed medium. This is particularly important in the analysis of the results of measurements obtained with various types of probes. Considerable errors may be introduced if these effects are not allowed for.Further extensive experimental and theoretical studies of the structure of the disturbed region in the neighborhood of moving bodies in plasma are clearly necessary. Such investigations will, in particular, lead to the development of the most effective methods of studying the properties of the media through which satellites and space rockets travel.Translated from the Russian: Ob effektah vyzyvaemyh iskusstvennym sputnikom bystro dviimsja v ionosfere ili meplanetnoj srede (Uspehi fizieskih nauk 79, 23–80) by Express Translation Service.     

Plasma Flow and Related Phenomena in Planetary Aeronomy

Understanding the processes involved in the interaction of solar system bodies with plasma flows is fundamental to the entire field of space physics. The features of the interaction can be very different, depending upon the properties of the incident plasma as well as the nature of the obstacle. The properties of the atmosphere/ionosphere associated with the obstacle are of particular importance into understanding the plasma interaction process, especially for non-magnetized obstacle. This paper discusses in detail the roles of the atmosphere and ionosphere systems of plasma interaction around Venus, Mars, comets and some particular satellites. The coupling between magnetosphere and ionosphere is also discussed for Earth and Giant planets.     

Aerodynamic Interactions Between Contralateral Wings and Between Wings and Body of a Model Insect at Hovering and Small Speed Motions

In this paper, we study the aerodynamic interactions between the contralateral wings and between the body and wings of a model insect, when the insect is hovering and has various translational and rotational motions, using the method numerically solving the Navier-Stokes equations over moving overset grids. The aerodynamic interactional effects are identified by compar-ing the results of a complete model insect, the corresponding wing pair, single wing and body without the wings. Horizontal, vertical and lateral translations and roll, pitch and yaw rotations at small speeds are considered. The results indicate that for the motions considered, both the interaction between the contralateral wings and the interaction between the body and wings are weak. The changes in the forces and moments of a wing due to the contralateral wing interaction, of the wings due to the pres-ence of the body, and of the body due to the presence of the wings are generally less than 4.5%. Results show that aerodynamic forces of wings and body can be measured or computed separately in the analysis of flight stability and control of hovering in-sects.     

Primary sources of large-scale Birkeland currents

We review generation mechanisms of Birkeland currents (field-aligned currents) in the magnetosphere and the ionosphere. Comparing Birkeland currents predicted theoretically with those studied observationally by spacecraft experiments, we present a model for driving mechanism, which is unified by the solar wind-magnetosphere interaction that allows the coexistence of steady viscous interaction and unsteady magnetic reconnection. The model predicts the following: (1) the Region 1 Birkeland currents (which are located at poleward part of the auroral Birkeland-current belt, and constitute quasi-permanently and stably a primary part of the overall system of Birkeland currents) would be fed by vorticity-induced space charges at the core of two-cell magnetospheric convection arisen as a result of viscous interaction between the solar wind and the magnetospheric plasma, (2) the Region 2 Birkeland currents (which are located at equatorward part of the auroral Birkeland-current belt, and exhibit more variable and localized behavior) would orginate from regions of plasma pressure inhomogeneities in the magnetosphere caused by the coupling between two-cell magnetospheric convection and the hot ring current, where the gradient-B current and/or the curvature current (presumably the hot plasma sheet-ring current) are forced to divert to the ionosphere, (3) the Cusp Birkeland currents (which are located poleward of and adjacent to the Region 1 currents and are strongly controlled by the interplanetary magnetic field (IMF)) might be a diversion of the inertia current which is newly and locally produced in the velocity-decelerated region of earthward solar wind where the magnetosphere is eroded by dayside magnetic reconnection, (4) the nightside Birkeland currents which are connected to a part of the westward auroral electrojet in the Harang discontinuity sector might be a diversion of the dusk-to-dawn tail current resulting from localized magnetic reconnection in the magnetotail plasma sheet where plasma density and pressure are reduced.     

Venus: Review of present understanding of solar wind interaction

The results of Soviet and American spacecraft plasma and magnetic experiments show that a bow shock of Venus forms as a result of the direct interaction of the solar wind with the ionosphere. The shape and the position of the Venus bow shock, in general, correspond to a very weak dissipation of solar wind energy in the ionosphere.The measured magnetic field near the planet is strongly influenced by IMF; this fact is evidence of an induced magnetosphere. Some results of laboratory simulation and computer experiments are also in favor of such an induced magnetosphere.The interaction with the ionosphere manifests itself in the existence of a boundary region on the nightside where solar wind entry into the optical umbra of the planet is observed.Proceedings of the Symposium on Solar Terrestrial Physics held in Innsbruck, May–June 1978.     

Magnetospheric and Plasma Science with Cassini-Huygens

Magnetospheric and plasma science studies at Saturn offer a unique opportunity to explore in-depth two types of magnetospheres. These are an ‘induced’ magnetosphere generated by the interaction of Titan with the surrounding plasma flow and Saturn's ‘intrinsic’ magnetosphere, the magnetic cavity Saturn's planetary magnetic field creates inside the solar wind flow. These two objects will be explored using the most advanced and diverse package of instruments for the analysis of plasmas, energetic particles and fields ever flown to a planet. These instruments will make it possible to address and solve a series of key scientific questions concerning the interaction of these two magnetospheres with their environment. The flow of magnetospheric plasma around the obstacle, caused by Titan's atmosphere/ionosphere, produces an elongated cavity and wake, which we call an ‘induced magnetosphere’. The Mach number characteristics of this interaction make it unique in the solar system. We first describe Titan's ionosphere, which is the obstacle to the external plasma flow. We then study Titan's induced magnetosphere, its structure, dynamics and variability, and discuss the possible existence of a small intrinsic magnetic field of Titan. Saturn's magnetosphere, which is dynamically and chemically coupled to all other components of Saturn's environment in addition to Titan, is then described. We start with a summary of the morphology of magnetospheric plasma and fields. Then we discuss what we know of the magnetospheric interactions in each region. Beginning with the innermost regions and moving outwards, we first describe the region of the main rings and their connection to the low-latitude ionosphere. Next the icy satellites, which develop specific magnetospheric interactions, are imbedded in a relatively dense neutral gas cloud which also overlaps the spatial extent of the diffuse E ring. This region constitutes a very interesting case of direct and mutual coupling between dust, neutral gas and plasma populations. Beyond about twelve Saturn radii is the outer magnetosphere, where the dynamics is dominated by its coupling with the solar wind and a large hydrogen torus. It is a region of intense coupling between the magnetosphere and Saturn's upper atmosphere, and the source of Saturn's auroral emissions, including the kilometric radiation. For each of these regions we identify the key scientific questions and propose an investigation strategy to address them. Finally, we show how the unique characteristics of the CASSINI spacecraft, instruments and mission profile make it possible to address, and hopefully solve, many of these questions. While the CASSINI orbital tour gives access to most, if not all, of the regions that need to be explored, the unique capabilities of the MAPS instrument suite make it possible to define an efficient strategy in which in situ measurements and remote sensing observations complement each other. Saturn's magnetosphere will be extensively studied from the microphysical to the global scale over the four years of the mission. All phases present in this unique environment — extended solid surfaces, dust and gas clouds, plasma and energetic particles — are coupled in an intricate way, very much as they are in planetary formation environments. This is one of the most interesting aspects of Magnetospheric and Plasma Science studies at Saturn. It provides us with a unique opportunity to conduct an in situ investigation of a dynamical system that is in some ways analogous to the dusty plasma environments in which planetary systems form. This revised version was published online in August 2006 with corrections to the Cover Date.     

The ionospheres and plasma tails of comets

The present understanding of cometary ionospheres and plasma tails is critically evaluated. Following a brief introduction of the significance of the study of cometary ionospheres and tails (Section 1), the observational statistics and spectroscopic observations are summarized in Sections 2 and 3.The complicated and time varying morphology of the plasma tail and the ionosphere as revealed both by photographs as well as visual drawings is discussed in Section 4.The evidence for a strong comet-solar wind interaction, the possible nature of this interaction and also the use of comets as probes of the solar wind are considered in the next 3 sections (5, 6, 7). This is followed by a discussion of the various processes so far proposed for the ionization of cometary gases and their limitations (Section 8).Hydrodynamic models of the solar wind-comet interaction, which refers essentially to the region outside the tangential discontinuity, are presented and evaluated in Section 9. A discussion of the ion chemistry and structure of the region inside the tangential discontinuity (which is here referred to as the cometary ionosphere) follows in Section 10.The largely indirect evidence for the existence of substantial magnetic fields in cometary ionospheres and type 1 tails is evaluated and their likely origin is considered in Section 11. The associated electric currents; their size and closure as well as their importance as sources of ionization in the inner coma are also discussed.Finally in Section 12, some of the directions in which future research should progress, in order to provide a more complete and secure knowledge of cometary ionospheres and plasma tails, are stressed.     

Electric Fields and Plasma Processes in the Auroral Downward Current Region, Below, Within, and Above the Acceleration Region

The downward field-aligned current region plays an active role in magnetosphere-ionosphere coupling processes associated with aurora. A quasi-static electric field structure with a downward parallel electric field forms at altitudes between 800 km and 5000 km, accelerating ionospheric electrons upward, away from the auroral ionosphere. A wealth of related phenomena, including energetic ion conics, electron solitary waves, low-frequency wave activity, and plasma density cavities occur in this region, which also acts as a source region for VLF saucers. Results are presented from sounding rockets and satellites, such as Freja, FAST, Viking, and Cluster, to illustrate the characteristics of the electric fields and related parameters, at altitudes below, within, and above the acceleration region. Special emphasis will be on the high-altitude characteristics and dynamics of quasi-static electric field structures observed by Cluster. These structures, which extend up to altitudes of at least 4–5 Earth radii, appear commonly as monopolar or bipolar electric fields. The former are found to occur at sharp boundaries, such as the polar cap boundary whereas the bipolar fields occur at soft plasma boundaries within the plasma sheet. The temporal evolution of quasi-static electric field structures, as captured by the pearls-on-a-string configuration of the Cluster spacecraft indicates that the formation of the electric field structures and of ionospheric plasma density cavities are closely coupled processes. A related feature of the downward current often seen is a broadening of the current sheet with time, possibly related to the depletion process. Preliminary studies of the coupling of electric fields in the downward current region, show that small-scale structures appear to be decoupled from the ionosphere, similar to what has been found for the upward current region. However, exceptions are also found where small-scale electric fields couple perfectly between the ionosphere and Cluster altitudes. Recent FAST results indicate that the degree of coupling differs between sheet-like and curved structures, and that it is typically partial. The mapping depends on the current-voltage relationship in the downward current region, which is highly non-linear and still unclear, as to its specific form.     

Dayside Proton Aurora: Comparisons between Global MHD Simulations and IMAGE Observations

The IMAGE mission provides a unique opportunity to evaluate the accuracy of current global models of the solar wind interaction with the Earth's magnetosphere. In particular, images of proton auroras from the Far Ultraviolet Instrument (FUV) onboard the IMAGE spacecraft are well suited to support investigations of the response of the Earth's magnetosphere to interplanetary disturbances. Accordingly, we have modeled two events that occurred on June 8 and July 28, 2000, using plasma and magnetic field parameters measured upstream of the bow shock as input to three-dimensional magnetohydrodynamic (MHD) simulations. This paper begins with a discussion of images of proton auroras from the FUV SI-12 instrument in comparison with the simulation results. The comparison showed a very good agreement between intensifications in the auroral emissions measured by FUV SI-12 and the enhancement of plasma flows into the dayside ionosphere predicted by the global simulations. Subsequently, the IMAGE observations are analyzed in the context of the dayside magnetosphere's topological changes in magnetic field and plasma flows inferred from the simulation results. Finding include that the global dynamics of the auroral proton precipitation patterns observed by IMAGE are consistent with magnetic field reconnection occurring as a continuous process while the IMF changes in direction and the solar wind dynamic pressure varies. The global simulations also indicate that some of the transient patterns observed by IMAGE are consistent with sporadic reconnection processes. Global merging patterns found in the simulations agree with the antiparallel merging model, though locally component merging might broaden the merging region, especially in the region where shocked solar wind discontinuities first reach the magnetopause. Finally, the simulations predict the accretion of plasma near the bow shock in the regions threaded by newly open field lines on which plasma flows into the dayside ionosphere are enhanced. Overall the results of these initial comparisons between global MHD simulation results and IMAGE observations emphasize the interplay between reconnection and dynamic pressure processes at the dayside magnetopause, as well as the intricate connection between the bow shock and the auroral region.     

Heliosphere-Geosphere Interactions Using Low Energy Neutral Atom Imaging

Development of the low energy neutral atom (LENA) imager was originally motivated by a need to remotely sense plasma heating in the topside ionosphere, with the goal of greatly enhanced temporal resolution of an otherwise familiar phenomenon. During ground test and calibration, the LENA imager was found to respond to neutral atoms with energies well above its nominal energy range of 10–750 eV, up to at least 3–4 keV, owing to sputtering interactions with its conversion surface. On orbit, LENA has been found to respond to a ubiquitous neutral atom component of the solar wind, to the neutral atoms formed by magnetosheath interactions with the geocorona during periods of high solar wind pressure, and to the interstellar neutral atoms flowing through the heliosphere during the season of maximal relative wind velocity between spacecraft and interstellar medium. LENA imaging has thus emerged as a promising new tool for studying the interplanetary medium and its interaction with the magnetosphere, in addition to the ionospheric heating and outflow that result from this interaction. LENA emissions from the ionosphere consist of a fast component that can be observed at high altitudes, and slower components that evidently create a quasi-trapped extended superthermal exosphere. The more energetic emissions are responsive to solar wind energy inputs on time scales of a few minutes.     

Plasma instabilities and their simulations in the equatorial F region – Recent results

In this paper the developments made in the last five years on numerical simulation/modeling studies of a complex nighttime equatorial spread F phenomenon are reviewed. Emphasis is given to the Indian work and necessary comparisons are done with other international works on this field. Investigations involving the important aspects, namely the confinement of the plasma bubble in the bottomside of the ionosphere, linear and nonlinear effects of molecular ions in the development of plasma bubbles, interaction of two modes as a seed perturbation are discussed in detail. This revised version was published online in August 2006 with corrections to the Cover Date.     

Upstream of Saturn and Titan

The formation of Titan??s induced magnetosphere is a unique and important example in the solar system of a plasma-moon interaction where the moon has a substantial atmosphere. The field and particle conditions upstream of Titan are important in controlling the interaction and also play a strong role in modulating the chemistry of the ionosphere. In this paper we review Titan??s plasma interaction to identify important upstream parameters and review the physics of Saturn??s magnetosphere near Titan??s orbit to highlight how these upstream parameters may vary. We discuss the conditions upstream of Saturn in the solar wind and the conditions found in Saturn??s magnetosheath. Statistical work on Titan??s upstream magnetospheric fields and particles are discussed. Finally, various classification schemes are presented and combined into a single list of Cassini Titan encounter classes which is also used to highlight differences between these classification schemes.     

The Near-Earth Plasma Environment

An overview of the plasma environment near the earth is provided. We describe how the near-earth plasma is formed, including photo-ionization from solar photons and impact ionization at high latitudes from energetic particles. We review the fundamental characteristics of the earth’s plasma environment, with emphasis on the ionosphere and its interactions with the extended neutral atmosphere. Important processes that control ionospheric physics at low, middle, and high latitudes are discussed. The general dynamics and morphology of the ionized gas at mid- and low-latitudes are described including electrodynamic contributions from wind-driven dynamos, tides, and planetary-scale waves. The unique properties of the near-earth plasma and its associated currents at high latitudes are shown to depend on precipitating auroral charged particles and strong electric fields which map earthward from the magnetosphere. The upper atmosphere is shown to have profound effects on the transfer of energy and momentum between the high-latitude plasma and the neutral constituents. The article concludes with a discussion of how the near-earth plasma responds to magnetic storms associated with solar disturbances.     

On the outer ionosphere (and its transition into interplanetary space)

Some properties of the outer ionosphere and its boundary region are discussed on the basis of recent experimental results.The analysis of the new data has shown that the outer ionosphere, a plasma above the ionospheric main maximum, extends to a distance of 3 to 3.5 earth radii from the earth's surface, that is, up to the region of the so-called knee, detected and observed by means of whistlers. During periods of relatively weak magnetic storms, from time to time the electron concentration at this ionospheric boundary jumps downward by factors of 10 to 100, over a height range of only a few hundred kilometres. The inflow of charged particles into the ionosphere apparently takes place through the boundary region. Sometimes these particles are swept into it from the overlying regions.There is a great number of names for the outer ionosphere. Some of these terms, for instance the geocorona, are not at all applicable to the outer ionosphere.From the new experimental results it can be inferred that in a great part of the outer ionosphere there is no quasineutrality, that there are rather strong electric fields, and that the Maxwell ion distribution law of particle velocities breaks down. Therefore, to analyze the ionization balance one should know the particles' velocity distribution functions. Otherwise it would hardly be possible to solve the problem of the formation of the ionosphere.It is shown that within the limits of uncertainty all experimental results are in good agreement and produce a single, comprehensive picture of the structure of the outer ionosphere. Only some data, deduced from measurements of particle streams by means of ion traps, are an exception. They contradict the numerous experimental results. This discrepancy is in particular due to the difficulties of determining the plasma concentration from current density measurements.Some methods are discussed briefly. For instance, the analysis of low-frequency waves, in particular the so-called whistler and the low-frequency plasma radiation, represents a physically adequate and fruitful method for investigating the outer ionosphere.For a theoretical analysis of the above-mentioned data, it is in some cases required to take into account the effect of kinetic corrections to the refraction coefficient, of cyclotron and erenkov attenuation and radiation, etc. Over the next few years this method will come to play a great part in the exploration of the outer ionosphere, interplanetary space, and planets.Measurements of the energy spectra of incoherent back scattering of radio waves on the electron fluctuations will make another very interesting source for studying the outer ionosphere. This method is based on the interaction phenomena of radio waves with the plasma. Therefore, the scattering spectra are functions of the oscillating properties of the plasma. However, these data should be subjected to a thorough theoretical treatment on the basis of a complete theory of scattering.Up till now a sufficiently complete probe theory has not been evolved due to essential theoretical difficulties. Often this does not allow one to interpret adequately the results of measurements and considerably limits the possibilities of these methods.     

Plasma waves in the frequency range 0.001 – 10 cps in the earth's magnetosphere and ionosphere

The plasma model for the magnetosphere and ionosphere is first discussed. A review of some parts of the theory for a warm collisionless plasma of interest in the magnetosphere in connection with waves of periods between 0.1 and 1000 seconds is given. The theory for magnetohydro-dynamic waves in a slightly ionized gas is then summarized. The available observational data about magnetospheric and ionospheric phenomena, which may be interpreted in terms of waves with periods between 0.1 and 1000 seconds, are briefly surveyed and some theoretical applications to the ionosphere and magnetosphere are finally discussed. The theory of shock phenomena and transients in the magnetosphere is not included in the report.     

Plasma Morphology at Mars. Aspera-3 Observations

A total of about of 400 orbits during the first year of the ASPERA-3 operation onboard the Mars Express spacecraft were analyzed to obtain a statistical pattern of the main plasma domains in the Martian space environment. The environment is controlled by the direct interaction between the solar wind and the planetary exosphere/ionosphere which results in the formation of the magnetospheric cavity. Ionospheric plasma was traced by the characteristic “spectral lines” of photoelectrons that make it possible to detect an ionospheric component even far from the planet. Plasma of solar wind and planetary origin was distinguished by the ion mass spectrometry. Several different regions, namely, boundary layer/mantle, plasma sheet, region with ionospheric photoelectrons, ray-like structures near the wake boundary were identified. Upstream parameters like solar wind ram pressure and the direction of the interplanetary electric field were inferred as proxy from the Mars Global Surveyor magnetic field data at a reference point of the magnetic pile up region in the northern dayside hemisphere. It is shown that morphology and dynamics of the main plasma domains and their boundaries are governed by these factors as well as by local crustal magnetizations which add complexity and variability to the plasma and magnetic field environment.     

Blue Jets: Upward Lightning

Blue jets are beams of blue light propagating from the tops of active thunderclouds up to altitudes of ～50 km. They resemble tall trees with quasi-vertical trunk and filamentary branches. Their apparent speeds are in the range of 10 s to 100 s km/s. Other events, having essentially lower terminal altitudes (<26 km), are named blue starters. These phenomena represent the first documented class of upward electrical discharges in the stratosphere. Some of upward discharges, termed gigantic jets, propagate into the lower ionosphere at much higher speeds in the final phase. We describe salient features of the upward discharges in the atmosphere, give an assessment of the theories of their development, and discuss the consequences for the electrodynamics and chemistry of the stratosphere. We argue that this upward lightning phenomenon can be understood in terms of the bi-directional leader, emerging from the anvil.