Ion precipitation into the ionosphere during geomagnetic storms

This review presents numerous recent examples of interesting variations in the composition and intensity of the hot ion flux (10 eV - 15 keV/e) provided by the AUREOL-3 satellite as a function of latitude and local time during periods of magnetic activity. In particular, these results reveal that although H⁺ is the most abundant ion during magnetically quiet periods, the ion composition of hot plasma at ionospheric altitudes is quite variable, and depends strongly on magnetic activity; results obtained during main and recovery phases of several magnetic storms demonstrate clearly (below 15 keV/Q) the great importance of the low altitude ionospheric source (H⁺, O⁺, and to a lesser degree He⁺) particularly at low latitudes (L ～ 3 - 4) where the flux of O⁺ ions becomes very large and even dominates. The results of the AUREOL-3 ion spectrometers establish the fact that upflowing suprathermal ionospheric ions (E_i < 100 eV/e) appear over large regions of the auroral ionosphere, the polar caps, and the polar cusp, as well as in or at the boundary of the plasmasphere during magnetospheric substorms or magnetic storms, and may consequently contribute significantly to the plasma sheet and to the inner storm time ring current. Most of the properties of the storm time ring current found by the GEOS, SCATHA, and ISEE satellites apply to lower altitudes, although the role of the ionospheric and/or plasmaspheric source appears accentuated.     

An updated theory of the polar wind

The ‘classical’ polar wind is an ambipolar outflow of thermal plasma from the terrestrial ionosphere at high latitudes. As the plasma escapes along diverging geomagnetic flux tubes, it undergoes four major transitions, including a transition from chemical to diffusion dominance, a transition from subsonic to supersonic flow, a transition from collision-dominated to collisionless regimes, and a transition from a heavy to a light ion. A further complication arises because of horizontal convection of the flux tubes owing to magnetospheric electric fields. Recent modelling predictions indicate that the polar wind has the following characteristics: (1) The ion and electron distributions are anisotropic and asymmetric in the collisionless regime; (2) Elevated electron temperatures ( ∼ 10,000 K) act to produce significant escape fluxes of suprathermal O⁺ ions; (3) The interaction of the hot magnetospheric and cold ionospheric electron populations leads to a localized (double layer) electric field which accelerates the polar wind ions; (4) A time-dependent expansion produces suprathermal ions; and (5) Large perturbations lead to the formation of forward and reverse shocks. These and other results are reviewed.     

Structure of the distant terrestrial magnetotail

The ISEE-3 Geotail Mission has extended our knowledge of the terrestrial magnetotail out to distances of 235 R_e. This paper presents a review of the observations from this mission pertaining to the size, shape, and structure of the magnetotail. The data sets available include magnetic fields, electron plasma, electromagnetic waves, plasma composition, energetic ions (H, He, C, N, O) and electrons (2D), and energetic ion spectra in 3D. The observations show that the distant terrestrial magnetotail is similar to the the near-earth region, except that the predominant direction of flows is away from the earth. The shape becomes elliptical, with the major axis in the east-west direction. A semi-permanent X-line is deduced to be near 80 to 100 R_e. A solar wind component is found in the ion compositions. Vortex-like events and magnetic flux ropes, both known from other missions, have also been found.     

Positive ion distributions in the morning auroral zone: Local acceleration and drift effects

We report on the typical structure of the large scale ion precipitation in the morning sector of the auroral zone and associated low frequency electromagnetic waves. Data obtained during near radial passes of the AUREOL-3 satellite point to a distinction between two main precipitation regions: 1) In the poleward part of the auroral zone the latitudinal variation of the average energy (or temperature) of the precipitated ions (mainly H⁺) indicate that they are adiabatically accelerated in the outer magnetosphere. This “high energy” (? 3 to > 20 keV) precipitation is usually associated with a low energy (E < 110 eV) upward flowing 0⁺ and H⁺ component, and 2) near the boundary between discrete and diffuse electron aurorae a drastic change in the ion characteristics is observed. The flux of energetic precipitated H⁺ ions is sharply reduced, which suggests the formation of an Alfvén layer. However, intense fluxes of precipitated H⁺, O⁺, and He⁺ ions with energies < 3 keV are observed equatorward of the Alfvén layer, in coincidence with the diffuse aurora and in association with quasi-monochromatic electromagnetic waves with frequencies around the proton gyrofrequency. As the characteristic convection and bounce times of the low energy upward flowing ion component are comparable (τ > 3 hours) we suggest that the precipitation of ionospheric ions inside the diffuse aurora results from convection and corotation of the ions accelerated to suprathermal energies at higher latitudes.     

磁尾瓣区的场向电流

本文利用ISEE-2卫星的磁场和粒子资料(电子:75keVδ<1300keV,质子:170keVp<400keV),发现在磁尾远离等离子片的尾瓣区,常常同时探测到粒子脉冲和横向磁场扰动,表明有场向电流片存在。电流片的积分强度在3.3—21mA/m之间,与Frank等在磁尾等离子片边界上测量到的场向片电流积分强度可相比较。电流片总是成双成对,电流片的强度与AE指数或亚暴的关系密切。和磁层其他区域不同,在磁尾瓣区,经常探测到△B_x和△B_y同时存在,且△B_x和△B_y可相比拟的情形,它们可以用运动的线电流或不均匀密度的电流片来解释。      

Transport of ions in presence of induced electric field and electrostatic turbulence: Source of ions injected into ring current

The transport of ions from the polar ionosphere to the inner magnetosphere during stormtime conditions has been computed using a Monte Carlo diffusion code. The effect of the electrostatic turbulence assumed to be present during the substorm expansion phase was simulated by a process that accelerated the ions stochastically perpendicular to the magnetic field with a diffusion coefficient proportional to the energization rate of the ions by the induced electric field. This diffusion process was continued as the ions were convected from the plasma sheet boundary layer to the double-spiral injection boundary. Inward of the injection boundary, the ions were convected adiabatically. By using as input an O⁺ flux of 2.8 × 10⁸ cm^?2 s^?1 (w > 10 eV) and an H⁺ flux of 5.5 × 10⁸ cm^?2 s^?1 (w > .63 eV), the computed distribution functions of the ions in the ring current were found to be in good agreement, over a wide range in L (4 to 8), with measurements made with the ISEE-1 satellite during a storm. This O⁺ flux and a large part of the H⁺ flux are consistent with the DE satellite measurements of the polar ionospheric outflow during disturbed times.     

Variation of energetic particle precipitation with local magnetic time

The detailed study of the precipitation of magnetospheric particles into the atmosphere is complicated by the rather complex spatial configuration of the precipitation region and its variability with geomagnetic activity. In this paper we will introduce polar oval coordinates and apply them to POES observations of 30 keV to 2.5 MeV electrons and comparable protons to illustrate the dependence of particle precipitation on local time and geomagnetic activity. These coordinates also allow an easy separation of the spatial precipitation patterns of solar and magnetospheric particles. The results indicate that (a) the spatial precipitation pattern of energetic magnetospheric electrons basically follows the pattern of the field parallel Birkeland currents up to MeV energies and (b) at least in the mesosphere the influence of magnetospheric electrons is comparable to the one of solar electrons. Implications for modeling of atmospheric chemistry will be sketched.     

Comparative study of plasma wave activity in the plasma sheet boundary and near Earth plasma sheet

The general structure of low frequency wave activity in the Earth's plasma sheet and its boundary layer is studied on the basis of the measurements made by ‘Prognoz-8’ satellite in the northern night and morning parts of the magnetotail. Pronounced wave activity is permanently observed in the high latitude parts of the plasma sheet boundary layer. The level of perturbations diminishes when a spacecraft moves towards tail lobes and drops rather sharply when it moves to the central plasma sheet. The peaks near the low hybrid resonance frequency (correlating with the local strength of the magnetic field) are evident in the electric field fluctuations spectra. A plasma instability of low hybrid type driven by transverse current is though to be the possible candidate for the excitation of these waves. Wave activity in tail lobes is related mainly to the isolated hot and cold plasma streams.     

Relative contributions of terrestrial and solar wind ions in the plasma sheet

A major uncertainty concerning the origins of plasma sheet ions is due to the fact that terrestrial H⁺ can have similar fluxes and energies as H⁺ from the solar wind. The situation is especially ambiguous during magnetically quiet conditions (AE < 60γ) when H⁺ typically contributes more than 90% of the plasma sheet ion population. In this study we examine that problem using a large data set obtained by the ISEE-1 Plasma Composition Experiment. The data suggest that one component of the H⁺ increases in energy with increasing activity, roughly in proportion to $\text{1}\text{4}$ the energy of the He⁺⁺, whereas the other H⁺ component has about the same energy at all activity levels, as do the O⁺ and the He⁺. If we can assume that the H⁺ of solar wind origin on the average has about the same energy-per-nucleon as the He⁺⁺, which is presumably almost entirely from the solar wind, then the data imply that as much as 20–30% of the H⁺ can be of terrestrial origin even during quiet conditions.     

Sources and losses of ring current ions: An update

The cleft ion fountain has been identified as a prodigious source of upflowing suprathermal ionospheric plasma. Modeling efforts have traced the path of these ions from the polar ionosphere along trajectories where the ions are energized to keV energies and deposited in the near earth plasma sheet. Mass and energy dispersion of these ions accounts in a natural way for the observed variation in heavy ion content of the plasma sheet. Observations of ion composition in the plasma sheet by the AMPTE and ISEE spacecraft establish that ionospheric ions dominate in the near earth plasma sheet but solar wind ions become significant tailward. The heavy ion content of the plasma sheet increases with both solar cycle and magnetic activity. Direct injection of ionospheric ions into the ring current has been observed in the outer plasmasphere. Several mechanisms for the direct injection of ions from the plasmasphere and ionosphere into the ring current have appeared. Estimation of ionospheric source strengths and residence times have led to an estimate of the magnetospheric densities that would result solely from an ionospheric outflow populating the magnetosphere. Estimated densities were quite reasonable even without inclusion of a solar wind source of ions. Ring current ions decay primarily via charge exchange with the hydrogen geocorona, however, the roles of pitch angle diffusion and Coulomb collisions in this decay process are being clarified.

Modeling and observations of ENA by the 1SEE1 spacecraft has led to a re-affirmation of the dominant role of charge exchange in ring current decay. Ion cyclotron waves contribute to ring current decay in the dusk bulge region. The role of low frequency. (< 1 Hz) ion cyclotron waves in the plasmasphere is still unclear. Other wave modes may be responsible for the pitch angle diffusion and subsequent loss of ring current ions. Coulomb collisional energy losses from ring current O⁺ to thermal electrons are sufficient to power SAR arcs and represent an energy sink for ring current O⁺ within the plasmasphere. Coulomb collisions may be important for decay of low energy (< 10 KeV) ring current ions in the plasmasphere.     

Plasma flow in the near and distant geomagnetic tail

Measurements of the bulk flow of plasma in the outer magnetosphere were first made a little over a decade ago with Los Alamos instruments on the Vela satellites. During the intervening years, as flow measurements have been made with improved instruments and by other satellites they have come to play a crucial role in the development of our understanding of the structure and dynamics of the magnetosphere. For example, they were the means of discovery of the magnetosphere's boundary layer and of plasma vortices within the plasma sheet. They were the essential ingredient in the identification of signatures of magnetic reconnection at the magnetopause. And they were indispensible in clarifying the complex phenomena in the magnetotail accompanying substorms and in showing that these phenomena are consistent with a substorm model involving magnetic reconnection at a near-earth neutral line. Most recently, magnetotail plasma flow measurements by the ISEE-3 satellite at distances as great as 230 R_E have been instrumental in fixing the average location of the “distant” neutral line at ～ 60 to 120 R_E and in identifying plasmoids (i.e., severed sections of the plasma sheet), released during substorms and escaping down-tail. This paper reviews the features of magnetotail plasma flow, describes the most recent observations, and discusses their implications for magnetospheric physics.     

The Jovian magnetotail

This paper will review the present state of knowledge of plasma, magnetic field and plasma wave characteristics of the Jovian magnetotail, near Jupiter and to distances as great as 9,000 Jupiter radii, and from both the large and small scale perspectives. Our knowledge of Jupiter's tail, especially the distant tail, comes primarily from data from five experiments onboard Voyager 2, some of which will be presented. The Jovian tail has many unusual properties, such as the large scale sausage-string shape of its outer boundary, but shares some important properties with earth's magnetotail, such as a central current sheet and a surrounding region resembling a plasma sheet consisting of hot ions (E > 28 keV). This new interpretation of the existence of a “plasma sheet” clears up the dilemma of the so-called core regions, which we will discuss. There is a significant flow of plasma of solar wind origin in the distant tail lobes having (tailward) speeds and densities suggestive of boundary layer plasma. We will discuss tail size, estimated magnetic flux content, degree of field helicity, magnetic turbulence (in near vs. far tail regions), and evidence for the tearing away of the tail (probably by field reconnection) at the time of an interplanetary magnetic sector boundary passage.     

DEMETER and DMSP satellite observations of the disturbed H/O ratio caused by Earth’s seismic activity in the Sumatra area during December 2004

In the present paper, plasma probe data taken from DEMETER and DMSP-F15 satellites were used to study the ion density and temperature disturbances in the morning topside ionosphere, caused by seismic activity at low latitudes. French DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) micro-satellite mission had been especially designed to provide global scale observations in the topside ionosphere over seismically active regions. Onboard the DEMETER satellite, the thermal plasma instrument called “Instrument Analyser de Plasma” (IAP) provides ion mass and densities, ion temperature, three component ion drift and ion density irregularities measurements. As a part of “Defense Meteorological Satellite Program”, DMSP-F15 satellite is on orbit operation since 1999. It provides ionospheric plasma diagnostics by means of the “Special Sensor-Ion, Electron and Scintillations” (SSIES-2) instrument. We examined few examples of possible seismic effects in the equatorial ionosphere, probably associated with seismic activity during December month in the area of Sumatra Island, including main shock of giant Sumatra event. It is found that the localized topside ionospheric disturbances appear close to the epicenters of certain earthquakes in the Sumatra region. In two cases, ion H⁺/O⁺ ratio rises more than one hour before the main shock, due to the O⁺ density decrease at the winter side of the geomagnetic equator, with longitudinally closest location to the epicenter of the earthquakes. These anomalous depletions in O⁺ density do exist in all cases of SSIES-2 data. Particularly for Sumatra main event, more than one hour after the main shock, we observe large-scale depletion in O⁺ density northward of the geomagnetic equator at winter side hemisphere. Associated with O⁺ depletion, ion temperature latitudinal profile around the geomagnetic equator shows enhanced asymmetry with minimum at the summer side and maximum in positive Ti deviation from mean value at the winter side. This disturbance lasted for more than three hours, later in time observed at the same place by IAP/DEMETER.     

等离子体片边界层处离子的随机加速

本文讨论宽频带静电噪声对等离子体片边界层处粒子的随机加速问题.计算表明:宽频带静电噪声会使离子轨道在相空间Poincare截面上一定范围内无规行走, 该范围与扰动电场的振幅、频率和波矢有关;引起的离子随机加速使一部离子能获得较高的能量, 在等离子体片参数下预计最大能量可达1000keV量级;对电子, 随机效应不明显.该结果为等离子体片中高能离子的存在这一长时观测特性提供一种新的可能产生机制.      

Acceleration of low-energy magnetospheric plasma

Low-energy plasma originates in the ionosphere and is accelerated and transported to the plasma sheet and ultimately to the ring current. Using observations and basic MHD concepts, it is argued that the acceleration results basically from entrainment in flows that are rapid compared with initial ion thermal speeds. Spatial or temporal variations of such flows launch impulsive waves of the appropriate variety (acoustic, shear Alfven, or magnetosonic) to effect readjustment to the imposed boundary conditions. The most violent transient events are the earthward inductive surges of plasma in the inner plasma sheet, which launch magnetosonic waves. A number of observations strongly suggest that the induction surge waves break as they reach the inner plasma sheet or outer plasmasphere, forming transient shock waves and dissipating their energy in turbulent flows, plasma heating, and acceleration of energetic particles, forming the substorm injection boundary. Preliminary work indicates that the magnetosphere is typically configured so as to produce wave breaking near synchronous orbit, and has other interesting optical properties for MHD wave propagation as well. Exploration of magnetospheric plasma wave optics will require a better empirical knowledge of the plasma distribution.     

A BRIEF INTRODUCTION TO GEOSPACE DOUBLE STAR PROGRAM

The Geospace Double Star Exploration Project (DSP) contains two small satel lites operating in the near-earth equatorial and polar regions respectively. The tasks of DSP are: (1) to provide high-resolution field, particle and wave mea surements in several important near-earth active regions which have not been covered by existing ISTP missions, such as the near-earth plasma sheet and its boundary layer, the ring current, the radiation belts, the dayside magnetopause boundary layer, and the polar region; (2) to investigate he trigger mechanisms of magnetic storms, magnetospheric substorms, and magnetospheric particle storms, as well as the responses of geospace storms to solar activities and in terplanetary disturbances; (3) to set up the models describing the spatial and temporal variations of the near-earth space environment.To complete the mission, there are eight instruments on board the equatorial satellite and the polar satellite, respectively. The orbit of the equatorial satellite is proposed with a perigee at 550km and an apogee at 60 000km, and the inclination is about 28.5°; while the orbit of the polar satellite with a perigee at 700 km and an apogee at 40 000 km, as well as an inclination about 90°. The equatorial and polar satellites are planed to be launched into orbits in June 2003 and December 2003 respectively to take coordinating measurements with Cluster Ⅱ and other missions.     

Ion dynamics of magnetic reconnection in the magnetotail

We discuss the kinetic processes of plasma thermalization, acceleration, and mixing in magnetic reconnection. Non-Maxwellian, gyrotropic ion distribution functions such as anisotropic ion beams in the plasma sheet boundary layer (PSBL) and counter-streaming ions (CSIs) in the plasma sheet are often observed during a plasmoid passage of a satellite in the Earth's magnetotail. Non-gyrotropic ion distribution functions are also sometimes observed just after the passage of the plasmoid. We study the behavior of non-Maxwellian ion distribution functions observed by GEOTAIL. We further study theoretically the ion dynamics by using a particle-in-cell simulation, and discuss the role of non-Maxwellian distribution functions in magnetic reconnection.     

F-Region ion composition modeling

Measurements of the principal ion species of the F₁- and F₂- regions have been used to develop an empirical model of the ion composition for altitudes between 150 and 500 km. The species measured by the S3-1 satellite include N⁺, O⁺, N₂⁺, NO⁺ and O₂⁺. The data were obtained near the minimum of the solar cycle, thus limited information on the ionospheric variation with solar flux is available. However, the range of latitude, altitude, local time and geomagnetic activity does provide a useful basis for modeling the F-region. The ion composition measurements have been used to provide a model for relative ion composition which is compatible with the total ion density from the International Reference Ionosphere model.     

Development of Operational Space Weather Prediction Models

In this report, we summarize the needs of space weather models, and recommend that developing operational prediction models, rather than transitioning from research to operation, is a more feasible and critical way for space weather services in the near future. Operational models for solar wind speed, geomagnetic indices, magnetopause, plasma sheet energetic electrons, inner boundary of ion plasma sheet, energetic electrons in outer radiation belt, and thermospheric density at low Earth orbit, have been developed and will be introduced briefly here. Their applications made a big progress in space weather services during the past two years in China.      

A Brief Introduction and Recent Progress of the Geospace Double Star Program

The Geospace Double Star Project (DSP) consists of two small satellites operating in the near-earth equatorial and polar regions, respectively. The goals of DSP are: (1) to provide high-resolution field, particle, and wave measurements in some important near-earth active regions which have not been covered by current ISTP missions, such as the near-earth plasma sheet and its boundary layer, the ring current, the radiation belts, the dayside magnetopause boundary layer, and the polar region; (2) to investigate the trigger mechanisms of magnetic storms, magnetospheric substorms, and magnetospheric particle events,as well as the responses of geospace storms to solar activities and interplanetary disturbances; (3) to set up the models describing the spatial and temporal variations of the near-earth space environment.To realize the above goals, the equatorial satellite TC-1 and the polar satellite TC-2 will accommodate, respectively, eight instruments on board. TC-1was launched successfully in December 2003 while the polar satellite (TC-2)will be launched in July 2004. The orbit of the equatorial satellite TC-1 consists of a perigee at 550 km, an apogee at 60 000 km, and an inclination of about 28.5; while the orbit of the polar satellite will have a perigee of 700 km, an apogee of 40 000 km, and an inclination of about 90. The two satellites will take coordinated measurements with Cluster Ⅱ and will first form a "six-point exploration" in geospace.The operational status of TC-1 are introduced in this paper.