near-Earth Plasma Research Articles

A statistical study on the correlations between plasma sheet and solar wind based on DSP explorations

Abstract. By using the data of two spacecraft, TC-1 and ACE (Advanced Composition Explorer), a statistical study on the correlations between plasma sheet and solar wind has been carried out. The results obtained show that the plasma sheet at geocentric distances of about 9~13.4 Re has an apparent driving relationship with the solar wind. It is found that (1) there is a positive correlation between the duskward component of the interplanetary magnetic field (IMF) and the duskward component of the geomagnetic field in the plasma sheet, with a proportionality constant of about 1.09. It indicates that the duskward component of the IMF can effectively penetrate into the near-Earth plasma sheet, and can be amplified by sunward convection in the corresponding region at geocentric distances of about 9~13.4 Re; (2) the increase in the density or the dynamic pressure of the solar wind will generally lead to the increase in the density of the plasma sheet; (3) the ion thermal pressure in the near-Earth plasma sheet is significantly controlled by the dynamic pressure of solar wind; (4) under the northward IMF condition, the ion temperature and ion thermal pressure in the plasma sheet decrease as the solar wind speed increases. This feature indicates that plasmas in the near-Earth plasma sheet can come from the magnetosheath through the LLBL. Northward IMF is one important condition for the transport of the cold plasmas of the magnetosheath into the plasma sheet through the LLBL, and fast solar wind will enhance such a transport process.

Phase Fluctuations of Radio Waves Behind a Turbulent Phase Screen

We consider the problem of phase fluctuations of radio waves behind a turbulent optically thin irregular layer (phase screen). Expressions are derived for the main statistical characteristics of phase fluctuations in the case where modern direct methods based on measurements of the complex field of the received radiation are used to obtain these characteristics. Regimes of weak and saturated scintillations of signals are analyzed. It is shown that in the case of weak scintillations, such statistical characteristics of phase fluctuations of the received radiation as the structure function and the fluctuation spectra for single-point and interference reception almost coincide with those at the screen output. In the regime of saturated scintillations, we obtain an information on the structure function of phase fluctuations of the received radiation in the cases of relatively large and small spatial separations of the reception points. The results obtained allow one to correctly analyze the data of modern experiments on remote sensing of the near-Earth and space plasmas with the help of direct phase methods for environmental diagnostics.

Observation of mixed ion populations deep inside earth magnetosphere as evidence for reconnection during northward IMF with substantial By component

We present and discuss observations of a region in the high-latitude near-Earth outer magnetosphere when over a distance of 9 R E – from GSM [0.83 R E, 1.6 R E, 8.5 R E] to [−0.957 R E, 10.175 R E, 12.738 R E] – Interball-1 observed multiple alternative changes in plasma characteristics: hot plasma sheet population is replaced by a region of mixed magnetosheath – plasma sheet population with the presence of ionospheric ions and vice versa. In the ‘mixed’ region, both ion populations were nearly stagnant, their velocity rarely exceeded 50 km/s and plasma-sheet electrons were absent. Most of the time interplanetary magnetic field (IMF) clock angle was less than 90°, rotating to more than 270° at the end of the interval, IMF B x being positive and dominating. A flux transfer event was registered near the magnetopause. Plasma characteristics suggest that observations took place at the high-latitude boundary of the near-Earth plasma sheet on closed field lines. We suggest that the mixed regions are formed on filed lines first reconnected to the magnetosheath magnetic field, then draped and convected duskward and tailward and secondary reconnected and closed.

Space technologies for short-term earthquake warning

Recent theoretical and experimental studies explicitly demonstrated the ability of space technologies to identify and monitor the specific variations at near-earth space plasma, atmosphere and ground surface associated with approaching severe earthquakes (named as earthquake precursors) which appear several days (from 1 to 5) before the seismic shock over the seismically active areas. Several countries and private companies are in the stage of preparation (or already launched) the dedicated spacecrafts for monitoring of the earthquake precursors from space and for short-term earthquake prediction. The present paper intends to outline the optimal algorithm for creation of the space-borne system for the earthquake precursors monitoring and for short-term earthquake prediction. It takes into account the following: 1. Selection of the precursors in the terms of priority, considering their statistical and physical parameters. 2. Configuration of the spacecraft payload. 3. Configuration of the satellite constellation (orbit selection, satellite distribution, operation schedule). 4. Different options of the satellite systems (cheap microsatellite or comprehensive multisatellite constellation). Taking into account that the most promising are the ionospheric precursors of earthquakes, the special attention is devoted to the radiophysical techniques of the ionosphere monitoring. The advantages and disadvantages of such technologies as vertical sounding, in-situ probes, ionosphere tomography, GPS TEC and GPS MET technologies are considered.

Stationary Charge Distribution of Grains in Near-Earth Plasma: Analytical Solution of Discrete Population Balance Equations

At zero photo/secondary emission rates we present the analytical solution of the discrete population balance equations giving the stationary charge distribution on grains in near-Earth plasma. It is shown that the envelope of the stationary charge distribution can be described by the Gaussian function up to very small (~10 nm) dust grains. The peak position of the enveloping curve is deviated from the charge obtained on the basis of equating primary electron and ion fluxes entering the grain. We propose an analytical dependence which is in close agreement with the exact solution in the region under study. We also demonstrate that the ratio of the mean grain surface energy to the electron temperature in energy units is not a constant as predicted earlier. The ratio has a form of a “shifted” hyperbolic law and for dust grains ~ 10 nm it is almost twice greater than the value obtained for micrometer-sized dust grains.

Thinning and expansion of the substorm plasma sheet: Cluster PEACE timing analysis

Abstract. The storage and subsequent removal of magnetic flux in the magnetotail during a geomagnetic substorm has a dramatic effect on the thickness of the cross-tail plasma sheet. The near-Earth plasma sheet is thought to thin during the growth phase and then rapidly expand after onset of the substorm. The direction of propagation, whether earthward or tailward along the GSM-X direction in the near-Earth tail, may suggest the time ordering of current-disruption and near-Earth reconnection, both of which are key to the substorm process. Cluster's Plasma Electron And Current Experiment (PEACE) allows 4-point observations of electrons at the plasma sheet - lobe boundary as this interface passes over the Cluster tetrahedron. The relative timings of the boundary passage at each spacecraft allow a determination of this boundary's speed and direction of motion, assuming this is planar on the scale of the Cluster separation scale. For those boundaries corresponding to the expansion of the plasma sheet, this direction is fundamental to determining the direction of expansion. We present an example of isolated thinning and expansion of the plasma sheet, as well as a multiple thinning-expansion event that occurs during a more active substorm. Data from the 2001 and 2002 tail passes have been analysed and the average plasma sheet – lobe boundary normal vectors and normal component velocities have been calculated. A total of 77 crossings, typically between 10 and 20 RE downtail, correspond to substorm associated expansion of the plasma sheet over the spacecraft. These had normal vectors predominantly in the GSM-YZ plane and provided no clear evidence for the formation of the near-Earth neutral line occurring before current disruption or vice versa. The expansions of the plasma sheet generally exhibit the appropriate GSM-Z direction expected for the given lobe, and tend to have GSM-Y components that support onset occurring near the origin of the GSM-YZ plane. This result is noteworthy in that it indicates a homogeneous plasma sheet expansion. These expansions have an average velocity along their normal of 60±37kms–1. Conversely we find an average thinning velocity of 43±32kms–1 from 66 substorm-associated thinnings. The normal vectors of the thinning plasma sheet vary considerably in the GSM-YZ plane across the entire magnetotail, suggesting that more complex dynamics govern this process.Key words. Magnetospheric physics (Magnetotail; Plasma sheet; Storms and substorms)bk\\rasphone.

An Alfvén wave maser in the laboratory

A frequency selective Alfvén wave resonator results from the application of a locally nonuniform magnetic field to a plasma source region between the cathode and anode in a large laboratory device. When a threshold in the plasma discharge current is exceeded, selective amplification produces a highly coherent (δω∕ω<5×10−3), large amplitude shear Alfvén wave that propagates out of the resonator, through a semitransparent mesh anode, into the adjacent plasma column where the magnetic field is uniform. This phenomenon is similar to that encountered in the operation of masers∕lasers at microwave and optical frequencies. The current threshold for maser action is found to depend upon the confinement magnetic field strength B0. Its scaling is consistent with the condition for matching the drift speed of the bulk plasma electrons with the phase velocity of the mode in the resonator. The largest spontaneously amplified signals are obtained at low B0 and large plasma currents. The magnetic fluctuations δB associated with the Alfvén maser can be as large as δB∕B0≈1.5% and are observed to affect the plasma current. Steady-state behavior leading to coherent signals lasting until the discharge is terminated can be achieved when the growth conditions are well-above threshold. The maser is observed to evolve in time from an initial m=0 mode to an m=1 mode structure in the transition to the late steady state. The laboratory phenomenon reported is analogous to the Alfvén wave maser proposed to exist in naturally occurring, near-earth plasmas.

Double Star Program in China

The Geospace Double Star Project (DSP) contains two satellites operating in the near-earth equatorial and polar regions respectively. The tasks of DSP are: (i) to provide high-resolution field, particle and wave measurements in several important near-earth magnetosphere active regions which have not been covered by existing ISTP missions in the geospace, 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; (ii) to investigate the trigger mechanisms of magnetic storms, magnetospheric substorms, and magnetospheric particle storms, as well as the responses of geospace storms to solar activities and interplanetary disturbances; (iii) 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 with a perigee at 565.5km and an apogee at 78959.9km, and the inclination is 28.17 ; while the orbit of the polar satellite is proposed with a perigee at 700km and an apogee at 40000km, as well as an inclination about 90. The equatorial satellite has been launched successfully in December 2003. Now the equatorial satellite (TC-1) and instruments operate normally. Payloads have provided good quality of data of fields and particles. Already very good conjunction in the dayside magnetopause and magnetotail with Cluster, CME effects could be investigated. The first results of data analysis have already shown great interesting. The polar (TC-2) satellite has been launched successfully in July 2004. Now the satellite operates normally. The commissioning of the payload has started since the end of July 2004 and will be finished in the middle of Sep.2004. The instrument has been normally operation and downlink the data.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Nonlinear drift-kinetic equation in the presence of a circularly polarized wave

This paper presents a theoretical description of plasma motion in the presence of a circularly polarized wave of arbitrary frequency with its wave vector directed along the ambient magnetic field. Both the equations of motion for a single particle and the nonlinear kinetic equation in the drift approximation are given. The nonstationarity and inhomogeneity of the plasma-wave system are taken into account. The distribution function is expressed with the help of initial, non-averaged variables, which is a transformation that greatly simplifies the calculation of the moments. The time-dependent part of the ponderomotive force is discussed, and it is shown that this component can be on the order of the other terms in the particle motion equation. The examples of ion acceleration in the auroral zone and the effects of lightning discharge are discussed to show that this theoretical study has applications to near-Earth space plasmas.

Multi-instrument observations of the ionospheric counterpart of a bursty bulk flow in the near-Earth plasma sheet

Abstract. On 07 September 2001 the Cluster spacecraft observed a "bursty bulk flow" event in the near-Earth central plasma sheet. This paper presents a detailed study of the coincident ground-based observations and attempts to place them within a simple physical framework. The event in question occurs at ~22:30 UT, some 10min after a southward turning of the IMF. IMAGE and SAMNET magnetometer measurements of the ground magnetic field reveal perturbations of a few tens of nT and small amplitude Pi2 pulsations. CUTLASS radar observations of ionospheric plasma convection show enhanced flows out of the polar cap near midnight, accompanied by an elevated transpolar voltage. Optical data from the IMAGE satellite also show that there is a transient, localised ~1 kR brightening in the UV aurora. These observations are consistent with the earthward transport of plasma in the tail, but also indicate the absence of a typical "large-scale" substorm current wedge. An analysis of the field-aligned current system implied by the radar measurements does suggest the existence of a small-scale current "wedgelet", but one which lacks the global scale and high conductivities observed during substorm expansions. Key words. Ionosphere (auroral ionosphere; ionospheremagnetosphere interactions; plasma convection)

Validity of the fluid description of critical β and Alfvén time scale of ballooning instability onset in the near-Earth collisionless high-β plasma

For a realistic, highly stretched, two‐dimensional tail configuration, in which the pressure gradient force is balanced with the curved field line tension force at the equator, the growth rates and the real frequencies of the ideal magnetohydrodynamic (MHD) and two component fluid (nonideal MHD) ballooning modes, in which the phrase “two component fluid” means that the Hall and the electron pressure gradient terms are included in the generalized Ohm's law, the ion bounce frequency ωbi, the ion magnetic drift frequency ωdi, the ion diamagnetic drift frequency ω*i, and the ion cyclotron frequency ωci are calculated numerically at the equator as a function of X from the near‐Earth tail (X = −15 RE) to the midtail (X = −30 RE). Contrary to the well‐known dipole field case, in which the bounce frequency decreases with increasing ∣X∣, the ion bounce frequency increases with ∣X∣ for the tail configuration. The ion magnetic drift frequency dominated by the curvature drift frequency also increases with increasing ∣X∣. The exact growth rates of the ideal and nonideal ballooning modes, γe and γne, which are nearly equal, are given by 1.22VA/Rc, where VA is the Alfvén velocity and Rc is the field line curvature radius at the equator, and satisfy ωbi, ωdi, ω*i < γe < ωci on average in the near‐Earth tail at X ∼ −15 RE. Also, the ion motion remains adiabatic in the near‐Earth tail at X ∼ −15 RE. Therefore it is a posteriori verified that the fluid or MHD description of the linear stability of the ballooning instability is valid, and the critical β and the Alfvén time scale τA ∼ Rc/VA of the ballooning instability onset obtained by the fluid theory are validated in the near‐Earth tail as close as 15 RE from the Earth. Despite the plasma being collisionless and high‐β in the near‐Earth tail, the subtle collisionless kinetic effects due to the field line curvature in high‐β collisionless plasma are not significant enough to invalidate the fluid description in the near‐Earth tail. The Alfvén time scale of an e‐folding growth of the Alfvén wave trapped within Rc in the equatorial region is of the order of a few tens of seconds or less in the near‐Earth tail. It is faster than the bounce time of the bulk of ions and can explain the observed rapid time scale of a substorm onset. There is excellent agreement between the critical β and the Alfvén time scale obtained analytically for the two component fluid plasma and those obtained by a three‐dimensional particle simulation.

The Potential and Equipotentiality of Spacecraft

The problem of maintenance of the equipotentiality of spacecraft surfaces is considered. The method under examination is the use of the “conductive thermal-vacuum multilayer blanket” (CMLB), whose outer surface represents a fabric woven of threads of glass fiber type with interwoven metal threads. The process of spacecraft potential formation and methods of the potential calculation are described, and the results of such a calculation for the illuminated and shadowed parts of spacecraft surfaces in some characteristic near-Earth plasma environments are presented. The CMLB model is described, and the potential distribution near the CMLB surface is calculated. The conclusion was drawn that the conductive thermal-vacuum multilayer blanket used in some cases on Russian spacecraft does not ensure the equipotentiality of spacecraft surfaces, and in the case of using CMLB, the differential spacecraft charging in outer regions of the Earth's magnetosphere may reach a dangerous level for onboard electronic systems. In spite of the fact that CMLB guards against large-scale powerful discharges, one cannot exclude discharges completely, what may result in broadband noise enhancement and cause onboard systems failures.

Remote identification of radioactive contamination by satellite measurements

The simultaneous measurements of the magnetic and electric component of ELF/VLF emission field, low-energy electrons and ambient satellite plasma temperature by “Intercosmos 19” satellite data are analyzed. It is established, that in the Barents–Kara Sea region the areas of the observation of simultaneous fluctuations of these parameters have coincided with zones of high contents of cesium ( 137Cs) at bottom sediments. The observation results in conjunction with ionospheric anomalies observed by the Japan ISS-b satellite instruments, that was active above Barents–Kara shelf region also, were analyzed (analysed). We prepare the maps of the hydrogen, helium and oxygen ions distribution above South Barents hollow by using the data of Japan satellite. It is established, that the area of registration of light ions by Japan satellite ISS-b has coincided with the area of the observation of simultaneous small-scale fluctuations of plasma parameters by Intercosmos 19 satellite data. On the basis of the all the method of detection of radiological contamination in the near-ground atmosphere layer, in the bottom sediment and in the water layer is offered. The method includes simultaneous measurement of parameters of near-earth plasma: magnetic and electrical component of ELF/VLF emission field, of low-energy electrons, of ambient satellite plasma temperature and intensity of light ions. Received results of our investigation can be utilised for forecasting in an ecology, seismology, in geology of oil and hydrogeology.

Physics of Substorm Growth Phase, Onset, and Dipolarization

A new scenario of substorm growth phase, onset and dipolarization during expansion phase and the corresponding physical processes are presented. During the growth phase, as a result of enhanced plasma convection, the plasma pressure and its gradient continue to be enhanced over the quiet-time values in the plasma sheet. Toward the late growth phase, a strong cross-tail current sheet is formed in the near-Earth plasma sheet region, where a local magnetic well is formed. The equatorial plasma beta (β eq ) can reach a local maximum with value larger than 50 and the cross-tail current density can be enhanced to over 10nA/m2 as obtained from 3D quasi-static magnetospheric equilibrium solutions for the growth phase. The most unstable kinetic ballooning instabilities (KBI) are expected to be located in the tailward side of the strong cross-tail current sheet region. The field lines in the most unstable KBI region map to the transition region between the region-l and region-2 currents in the ionosphere, which is consistent with the observed initial brightening location of the breakup arc in the intense proton precipitation region. The KBI explains the AMPTE/CCE observations that a low frequency instability with a wave period of 50–75 seconds is excited about 2–3 min prior to substorm onset and grows exponentially to a large amplitude at the onset of current disruption (or current reduction). At the onset of current disruption higher frequency instabilities are excited so that the plasma and electromagnetic field fluctuations form a strong turbulent state. Plasma transport takes place due to the strong turbulence to relax the ambient plasma pressure profile so that the plasma pressure and current density are reduced and the ambient magnetic field intensity increases by more than a factor of 2–3 in the high-β eq region and the field line geometry recovers from tail-like to dipole-like – dipolarization.

Flow Bursts in the Plasma Sheet and Auroral Substorm Onset: Observational Constraints on Connection Between Midtail and Near-earth Substorm Processes

Causality between near-Earth and midtail substorm processes is one of the most controversial issues about the substorm trigger mechanism. The currently most popular model, the outside-in model, assumes that near-Earth reconnection is initiated in the midtail region before substorm onset and that the associated flow burst causes tail current disruption in the near-Earth region. However, there remain some outstanding issues that may serve as critical tests of this model. The present article reviews recent satellite and ground observations addressing three such critical issues with a focus on substorm-related auroral features. First, near-Earth reconnection, even if it reaches the lobe magnetic field, does not necessarily trigger a global substorm, but it is often related to a pseudobreakup. This fact suggests that there is an additional or alternative condition for substorm development. Secondly, although there appears to be one-to-one correspondence between flow bursts in the plasma sheet and equatorward-moving auroral structures (auroral streamers), no such auroral feature that can be associated with the fast plasma flow can be identified prior to auroral breakups. On the other hand, the flow burst is widely regarded as a manifestation of reconnection and therefore, according to the outside-in model, should be created in the near-Earth plasma sheet before substorm onset. Finally, auroral arcs poleward of a breakup arc are not affected until the front of auroral intensification reaches those arcs. The last two points suggest that if substorm is triggered as the outside-in model describes, the ionosphere is electromagnetically detached from the magnetosphere, which, however, has not been addressed theoretically. Thus, it should be crucial for a better understanding of the substorm trigger process to implement the magnetosphere-ionosphere coupling in future modeling efforts and to address those basic issues as a guide for critically evaluating each model.

Bi-directional electrons in the near-Earth plasma sheet

Abstract. We have studied the occurrence characteristics of bi-directional electron pitch angle anisotropy (enhanced flux in field-aligned directions, F^ /F|| > 1.5) at energies of 0.1–30 keV using plasma and magnetic field data from the AMPTE/IRM satellite in the near-Earth plasma sheet. The occurrence rate increases in the tailward direction from XGSM = - 9 RE to - 19 RE . The occurrence rate is also enhanced in the midnight sector, and furthermore, whenever the elevation angle of the magnetic field is large while the magnetic field intensity is small, B ~ 15 nT. From these facts, we conclude that the bi-directional electrons in the central plasma sheet are produced mainly in the vicinity of the neutral sheet and that the contribution from ionospheric electrons is minor. A high occurrence is also found after earthward high-speed ion flows, suggesting Fermi-type field-aligned electron acceleration in the neutral sheet. Occurrence characteristics of bi-directional electrons in the plasma sheet boundary layer are also discussed.Key words. Magnetospheric physics (magnetospheric configuration and dynamics; magnetotail; plasma sheet)

Timing and localization of reconnection signatures - Is there a substorm model problem?

[1] Observations place ionospheric substorm onset signatures on field lines that map to the near-Earth plasma sheet, and field-aligned currents (FACs) are observed before dipolarization, equatorward of open field lines. The near-Earth neutral line (NENL) model, however, appears to suggest perturbations to originate from the x-line on newly reconnected field lines, which map to much higher latitudes. Its order of dipolarization, FACs, and subsequent ionospheric signatures contradicts the observations. Using large-scale kinetic simulations, we demonstrate that these “flaws” of the NENL model are misconceptions and that the timing and location of signatures in the model are indeed consistent with observations. In a thinned current sheet, energetic ions are virtually unmagnetized, get further energized when passing through the neutral sheet, and travel earthward quickly and close to the neutral sheet, thus providing a pathway for early substorm signatures at relatively low latitudes.

Imaging of near-Earth space plasma.

This paper describes the technique of imaging the ionosphere using tomographic principles. It reports on current developments and speculates on the future of this research area. Recent developments in computing and ionospheric measurement, together with the sharing of data via the internet, now allow us to envisage a time when high-resolution, real-time images and 'movies' of the ionosphere will be possible for radio communications planning. There is great potential to use such images for improving our understanding of the physical processes controlling the behaviour of the ionosphere. While real-time images and movies of the electron concentration are now almost possible, forecasting of ionospheric morphology is still in its early stages. It has become clear that the ionosphere cannot be considered as a system in isolation, and consequently new research projects to link together models of the solar-terrestrial system, including the Sun, solar wind, magnetosphere, ionosphere and thermosphere, are now being proposed. The prospect is now on the horizon of assimilating data from the entire solar-terrestrial system to produce a real-time computer model and 'space weather' forecast. The role of tomography in imaging beyond the ionosphere to include the whole near-Earth space-plasma realm is yet to be realized, and provides a challenging prospect for the future. Finally, exciting possibilities exist in applying such methods to image the atmospheres and ionospheres of other planets.

Kinetic simulations of reconnection and magnetospheric disruptions

Large-scale 3-D particle-in-cell simulations are used to investigate the nature of collisionless reconnection and to examine the process of braking of high speed flows in the near-Earth plasma sheet. The GEM magnetic reconnection study is generalized to the case of externally driven reconnection. The results are similar to the undriven case, and the reconnection process remains basically two-dimensional. Pressure gradient terms dominate the perpendicular current during flow braking, and the cross-tail current is enhanced in the kinetic treatment rather than being reduced as in MHD treatments.

A new framework for studying the relationship of aurora and plasma sheet dynamics

Auroras have been extensively studied using images obtained by space-borne experiments. We use global UVI images obtained from Polar and simultaneous plasma data obtained by the 3D instrument on Wind from the near-earth plasma sheet to study the dynamics of auroras with different size and intensity. Unstable phase space ion distributions are detected in the plasma sheet under diverse geomagnetic and solar wind IMF conditions (positive and negative B z ) and at all phases of a substorm. These results indicate that plasma instability processes with different disturbance levels operate in the plasma sheet and produce a continuum of auroral size and intensity. The criteria for triggering an instability are dependent on the local properties of the plasma distributions. These observations suggest a new framework to integrate previous and current results and a new way to examine the causal relationships of auroral and plasma sheet dynamics.