Plasmaphere and plasmapause region characteristics as measured by DE-1

Thermal ion composition measurements by the Retarding Ion Mass Spectrometer (RIMS) on Dynamics Explorer-1 have revealed new and intriguing features of the thermal ion distributions in the plasmasphere and plasmapause regions. Some of the interesting new findings include: the presence of intense fluxes of heated and equatorially-trapped light ions within the plasmapause region; the existence of a heavy ion (0+, 0++, N+) ‘torus’ or ‘shell’ in the outer plasmasphere; and the relatively stable nature of the He+/H+ concentration ratio (∼0.2–0.3) within the plasmasphere. The relatively short (∼7.5 hours) orbital period of DE-1 has also allowed improved observations on the formation of the new outer plasmasphere during the recovery of geomagnetic storms. Statistical studies of plasmaspheric density structure and boundaries are beginning to reveal a picture of their relation to other magnetospheric boundaries, such as the inner edge of the electron plasma sheet, and trends in the internal density structure of the plasmasphere.     

Conical ion distributions at one earth radius — observations from the acceleration region?

Thermal ion measurements from the Retarding Ion Mass Spectrometer (RIMS) on Dynamics Explorer 1 (DE 1) in the night side auroral region were surveyed for evidence of ion acceleration. The RIMS measurements showed evidence for ion acceleration in the 2–10,000 km altitude range, with ion distributions peaked near 90°, and with temperatures of 1 to 10 eV. Two illustrations of the RIMS data for such observations are given here. The conical distributions are found at the low latitude edge of the auroral region, just outside the plasmapause. In the first example, the three major ion species (H+, He+, and O+) show evidence of acceleration. The angular distributions are peaked at different pitch angles, indicating that the different species have been accelerated at different altitudes. The H+ flux is higher than the O+ flux in this first example, in the RIMS energy range (0–50 eV). This is apparently typical of the RIMS observations on the night side. In the second example, only O+ is transversely accelerated.     

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.     

连续磁活动对等离子体层演化的影响

利用嫦娥三号极紫外相机观测的2014年2月21日等离子体层极紫外对数图像，分析了一系列磁活动状态下等离子体层晨侧视角的演化.由等离子体层质子的相空间分布，模拟了2014年2月18—22日发生一系列磁暴事件时等离子体层在磁赤道面的演化.通过观测与模拟发现，等离子体层实际的填充速度大于模拟时等离子体层的填充速度.推测昏侧与日侧之间的羽结构对侧面视角下向阳侧等离子体层顶的位置会造成影响.模拟中等离子体层整体对磁暴的响应在3h内，大磁暴对等离子体层的影响时间较长，可以达到1～2天.连续的磁暴事件对等离子体层的影响有叠加的效果.等离子体层的回填比侵蚀需要更长的时间.      

Low-energy ion flows into the magnetosphere

Ion flows from the ionosphere into the magnetosphere fall into two main categories: cold (<1eV), “classical” polar wind and heated (>1eV), suprathermal ion outflows. A wealth of new understanding of these outflows has resulted from the Dynamics Explorer Mission. This review describes both the confirmation of the predicted classical polar wind as well as the revelation of a great variety of low-energy suprathermal outflows: the cleft ion fountain, the nightside auroral fountaion (X-events, toroids and field-aligned flows) and polar cap outflows. The main emphasis is placed on flows at energies below about 50eV, observed by the Retarding Ion Mass Spectrometer (RIMS) on board the Dynamics Explorer 1 satellite; limited comparisons are made with results from other instruments which sample different energy ranges.     

Nightside plasmapause positions observed by DE-1 as a function of geomagnetic indices: Comparison with whistler observations and model calculations

We have analysed 28 plasmapause crossings made by the DE1 satellite in the night local time sector (from January to March 1982). Different signatures obtained by the Retarding Ion Mass Spectrometer instrument (RIMS) have been used for this analysis. The observed plasmapause positions (Lpp) have been organized as a function of geomagnetic indices. They are compared with the empirical relationship deduced by Carpenter and Parks (1973) from whistler observations. Moreover, the dependence of Lpp versus K_p has been inferred from model calculation using K_p dependent electric and magnetic fields derived from McIlwain's (1974) E3H electric field model and M2 magnetic field model respectively. Stationary models, as well as time dependent ones, have been used to determine the positions of the plasmapause. The results of the model calculations are compared to the observations.     

Do ring current ions set the outer plasmasphere in motion?

GEOS-2 experiments have observed on a regular basis the transition from teh plasmasphere to the trough revealing a more tenuous and energetic population. This transition occured typically between 18 and 21 h local time under quiet geomagnetic conditions. On the plasmasphere side of the transition, large electric fields of several mV/m, mainly in the duskward direction, were observed. The present statistical results, over one year of data, assess clearly the mean magnitude and direction of these electric fields in relation to the boundary between these two plasma regimes under quiet geomagnetic conditions. The possibility of ring current energetic ions loosing part of their energy to the plasmasphere and accelerating this plasma sunward will be discussed.     

Towards multi-dimensional space weather modeling for energetic oxygen ions in the earth''s inner magnetosphere: Equilibrium configuration

We report the first 3+1 dimensional model development for energetic atomic oxygen ions in the Earth's radiation belts. Energetic Oxygen ions cans be supplied to the Earth's Inner magnetosphere from the sun (as a component of solar wind and solar energetic particles), from anomalous cosmic rays, and from acceleration processes acting on ionospheric atomic oxygen ions. We have built a multi-dimensional oxygen ion model in the following free parameters: geomagnetic L-shell, the magnetic moment, the second adiabatic invariant, and the discrete charge state number. Quiet time, steady state oxygen ion distributions have been obtained numerically from an assumed outer radiation zone boundary condition at L=7, average values of the radial diffusion coefficients, and standard values for the exospheric neutral densities due to the MSIS-86 upper atmosphere and exosphere neutral thermal particle density model. Average distributions of free electrons in the plasmasphere were also assumed with a mean plasmapause location just beyond L=4. We included the six lowest ionic charge states of atomic oxygen (¹⁶O) based on an existing charge exchange cross section compilation by Spjeldvik and Fritz (1978). Computed oxygen ion distributions include the resulting equilibrium structure of energy oxygen ions between 10 KeV and 100 MeV.     

Energetic ion emission for active spacecraft control

Future space missions aiming at the accurate measurement of cold plasmas and DC to very low frequency electric fields will require that the potential of their conductive surfaces be actively controlled to be near the ambient plasma potential. In the near-Earth space these spacecraft are usually solar-cell powered; consequently, parts of their surface are most of the time exposed to solar photons. Outside the plasmasphere, a positive surface potential due the dominance of surface-emitted photoelectrons over ambient plasma electrons is to be expected. Photo- and ambient electrons largely determine the potential and positive values between a few Volts up to 100 V have been observed. Active ion emission is the obvious solution of this problem. A liquid metal ion emitter and a saddle field ion emitter are nearing the stage of flight unit fabrication. We will attempt to clamp the spacecraft potential to values close to the plasma potential. We present first results from vacuum chamber tests and describe the emission behaviour and characteristics of emitters producing, respectively, In⁺ and N₂⁺ beams with an energy of ≥ 5 keV.     

Satellite observations of new particle and field signatures associated with SAR arc field lines at magnetospheric heights

Enhancements in thermal ion densities, an oxygen dominated ring current at energies below 17 kev, and invariant latitude-limited bands of intense ELF hiss have been discovered on Stable Auroral Red (SAR) arc field lines at magnetospheric heights. These new signatures were revealed by an examination of 31 coordinated data sets taken simultaneously at magnetospheric and ionospheric heights by the DE-1 and -2 satellites during SAR arc traversals within the period September 1981 through April 1982. Data sets from DE-2, for the first time, provide information on the location of a SAR arc (determined by the F region electron temperature enhancement) during the nearly simultaneous passage of these field lines by DE-1 in the magnetosphere. These new high altitude signatures are examined in the context of possible magnetospheric SAR arc energy source mechanisms.     

A study of the plasmasphere density distribution using computed tomography methods from the EUV radiation data

In this paper, we introduce a new topic for imaging plasmasphere density with CT techniques. Both parallel-beam and fan-beam reconstruction formulas are derived with a special weighting function. Different from the traditional X-ray CT, the extreme ultraviolet (EUV) radiation may be totally absorbed by the Earth. Only the portion between the Earth and the detector enters the EUV sensor and be measured. The key step in our derivation is to remove the complete absorption effect with a specific weighting function. Computer-simulation studies are present to verify our formulas for the plasmasphere density.     

Ion cyclotron waves observed near the plasmapause

Pc2 electromagnetic ion cyclotron waves at 0.1 Hz, near the oxygen cyclotron frequency, have been observed by ISEE-1 and -2 between L = 7.6 − 5.8 on an inbound near equatorial pass in the dusk sector. The waves occurred in a thick plasmapause of width ⋍ 1 R_e and penetrated ⋍ 1 R_e into the plasmasphere. Wave onset was accompanied by significant increases in the thermal (0–100 eV) He⁺ and the warm (0.1–16 keV/e) O⁺ and He⁺ heavy ion populations. Wave polarization is predominantly left-handed with propagation almost parallel to the ambient magnetic field, and the spectral slot and polarization reversal predicted by multicomponent cold plasma propagation theory are identified in the wave data. The results are considered an example of wave-particle interactions occurring during the outer plasmasphere refilling process at the time of the substorm recovery phase.     

Plasma transport in the plasmasphere

The plasmasphere is filled with very low energy plasma upwelling from the topside ionosphere. The field-aligned distribution of this thermal ionospheric plasma is controlled by the gravitational and centrifugal potential distribution. There are two extreme types of hydrostatic plasma distribution in this field-aligned potential : the Diffusive Equilibrium distribution and the Exospheric Equilibrium distribution corresponding respectively to a saturated and to an almost empty magnetic flux tube. As a result of pitch angle scattering by Coulomb collisions an increasing number of ions escaping from the ionosphere are stored on trapped orbits with mirror points at high altitudes in the low density region. As a result of collisions the field-aligned density distribution gradually changes from exospheric equilibrium with a highly anisotropic pitch angle (cigar like) distribution to a diffusive equilibrium with a nearly isotropic pitch angle distribution. It is shown that the suprathermal ions become anisotropic much more slowly than ions of energies smaller than 1 eV. The Coulomb collision times have been estimated for flux tubes at different L values. A numerical simulation of the flux tube refilling process has been presented. The diurnal variation of the equatorial plasma density has been illustrated for plasma elements convected along drift paths which have a large dawn- dusk asymetry. The formation of a Light Ion Trough is discussed. Finally, evidence has also been given for the existence of a ‘plasmaspheric wind’ corresponding to a slow subsonic and continuous radial expansion of the plasma stored in the plasmasphere.     

Neutral temperatures from Thomson scatter measurements: Comparisons with the CIRA(1972)

Neutral exospheric and lower thermospheric (100–130 km) temperatures from Thomson scatter measurements at Millstone Hill (42°N) are compared with CIRA temperatures with a view towards identifying deficiencies in the CIRA and recommending revisions. CIRA models the observed diurnal mean temperatures (T₀) to within 10% over a wide range of solar conditions (75? F_10.7 ? 250), but consistently underestimates the diurnal temperatures with maximum deviations approaching 50% of observed amplitudes (180–240 K) at solar maximum (1200 K ? T₀ ? 1400 K). The observed semidiurnal amplitudes, which lie in the range of 20K–80K, are always underestimated and frequently by more than 50%. In the lower thermosphere, tidal oscillations of temperature of order 20K–40K occur which are not modelled by CIRA. In addition, an analysis of exospheric temperatures at Millstone Hill during a magnetic disturbance indicates a response within 1–2 hours from storm onset, whereas CIRA assumes a 6.7 hour delay. Although some of these deficiences are addressed by the more recent MSIS model, there exists a sufficient data base to recommend several additional revisions to the CIRA temperatures at this time.     

Ionospheric electron temperature at solar maximum

Langmuir probe measurements made at solar maximum from the Dynamics Explorer-2 satellite in 1981 and 1982 are employed to examine the latitudinal variation of electron temperature, T_e, at altitudes between 300 and 400 km and its response to 27 day variations of solar EUV. Comparison of these data with T_e models based on the solar minimum measurements from Atmosphere Explorer-C suggest that the daytime T_e does not change very much during the solar cycle, except at low latitudes where an especially large 27 day variation occurs. The 27 day component decreases from about 7°/F10.7 unit at the equator to 3°/F10.7 unit at 851V 3 middle and higher latitudes. From these DE-2 measurements, and those from AE-C, we conclude that the daytime T_e near the F₂ peak is more responsive to short-term (daily) variations in F10.7 than to any longer term changes that may occur between solar minimum and solar maximum. To investigate this sensitivity of the dayside ionosphere to solar activity we employ the inverse relationship of T_e and N_e, that was found at solar minimum, to see if it can be used to order the T_e behaviour at solar maximum. We introduce a simple quadratic correction for the F10.7 influence on T_e based on the entire daytime AE-C and DE-2 data base between 300 and 400 km. Although this equation may be found useful, the systematic deviations of the DE-2 data suggest that the solar minimum model does not accurately describe the T_e-N_e relationships at solar maximum, at least above 300 km where the DE-2 measurements were made. Future work with this data base should attempt to see if such a relationship exists.     

Impulsive plasma waves observed by DE-1 in the magnetosphere

Impulsive plasma waves (1–9 kHz) with durations less than 100 msec have been found in DE-1 wide-band electric field data (650 Hz – 40 kHz) received at Kashima, Japan. The waves are associated with a strong narrow-band ELF hiss, and were observed at geocentric distances from 3.1 to 4.9 Re (earth's radius) in the low-latitude nightside magnetosphere. Local electron densities and plasmapause locations estimated suggest that the waves were observed outside the nightside plasmapause. The waves are discussed in terms of Landau resonant trapping of magnetospheric electrons by the associated whistler-mode ELF hiss.     

Polar/TIMAS statistical results on the outflow of molecular ions from earth at solar minimum

Ion composition data from the first 22 months of operation of the Polar/TIMAS instrument, covering the 15-eV/e to 33-keV/e energy range, have been surveyed to determine the typical abundance, at solar minimum, of N₂⁺, NO⁺ and O₂⁺ ions in the auroral ion outflow, as compared to that of the better known O⁺ ions. The results indicate that molecular ions have roughly the same energy distribution as the O⁺ ions, with maximum differential flux occurring below 400 eV, but are far less abundant, by two orders of magnitude. The molecular ions also differ from the O⁺ ions in that they seem more specifically associated with enhanced geomagnetic activity.     

Specification of the Earth’s plasmasphere with data assimilation

In this paper we report on initial work toward data assimilative modeling of the Earth’s plasmasphere. As the medium of propagation for waves which are responsible for acceleration and decay of the radiation belts, an accurate assimilative model of the plasmasphere is crucial for optimizing the accurate prediction of the radiation environments encountered by satellites. On longer time-scales the plasmasphere exhibits significant dynamics. Although these dynamics are modeled well by existing models, they require detailed global knowledge of magnetospheric configuration which is not always readily available. For that reason data assimilation can be expected to be an effective tool in improving the modeling accuracy of the plasmasphere. In this paper we demonstrate that a relatively modest number of measurements, combined with a simple data assimilation scheme, inspired by the ensemble Kalman filtering data assimilation technique does a good job of reproducing the overall structure of the plasmasphere including plume development. This raises hopes that data assimilation will be an effective method for accurately representing the configuration of the plasmasphere for space weather applications.     

First results of operational ionospheric dynamics prediction for the Brazilian Space Weather program

It is shown the development and preliminary results of operational ionosphere dynamics prediction system for the Brazilian Space Weather program. The system is based on the Sheffield University Plasmasphere–Ionosphere Model (SUPIM), a physics-based model computer code describing the distribution of ionization within the Earth mid to equatorial latitude ionosphere and plasmasphere, during geomagnetically quiet periods. The model outputs are given in a 2-dimensional plane aligned with Earth magnetic field lines, with fixed magnetic longitude coordinate. The code was adapted to provide the output in geographical coordinates. It was made referring to the Earth’s magnetic field as an eccentric dipole, using the approximation based on International Geomagnetic Reference Field (IGRF-11). During the system operation, several simulation runs are performed at different longitudes. The original code would not be able to run all simulations serially in reasonable time. So, a parallel version for the code was developed for enhancing the performance. After preliminary tests, it was frequently observed code instability, when negative ion temperatures or concentrations prevented the code from continuing its processing. After a detailed analysis, it was verified that most of these problems occurred due to concentration estimation of simulation points located at high altitudes, typically over 4000 km of altitude. In order to force convergence, an artificial exponential decay for ion–neutral collisional frequency was used above mentioned altitudes. This approach shown no significant difference from original code output, but improved substantially the code stability. In order to make operational system even more stable, the initial altitude and initial ion concentration values used on exponential decay equation are changed when convergence is not achieved, within pre-defined values. When all code runs end, the longitude of every point is then compared with its original reference station longitude, and differences are compensated by changing the simulation point time slot, in a temporal adjustment optimization. Then, an approximate neighbor searching technique was developed to obtain the ion concentration values in a regularly spaced grid, using inverse distance weighting (IDW) interpolation. A 3D grid containing ion and electron concentrations is generated for every hour of simulated day. Its spatial resolution is 1° of latitude per 1° of longitude per 10 km of altitude. The vertical total electron content (VTEC) is calculated from the grid, and plotted in a geographic map. An important feature that was implemented in the system is the capacity of combining observational data and simulation outputs to obtain more appropriate initial conditions to the ionosphere prediction. Newtonian relaxation method was used for this data assimilation process, where ionosonde data from four different locations in South America was used to improve the system accuracy. The whole process runs every day and predicts the VTEC values for South America region with almost 24 h ahead.     

Whistler studies of the plasmasphere shape and dynamics

Whistler studies of the plasmapause/plasmasphere are traced from their beginnings during the IGY through the early 1960's, when extensive data from Antarctica became available. Highlights of this period include discovery of the ‘knee’ in the equatorial electron density profile, initial comparisons with results from the Lunik probes, identification of magnetic storm effects, and discovery of the duskside bulge, or region of larger plasmasphere radius, as well as smaller-scale (Δφ ≈ 20°) variations in radius with longitude. In the mid-1960's, whistlers provided the first evidence of cross-L plasma drift patterns in the outer plasmasphere. From a present day perspective, the plasmasphere is seen as a region penetrated, perhaps most efficiently in the dusk sector, by the unsteady component of high latitude electric fields. In the pre-dawn sector, post substorm outward drifts may be an aftereffect of the shielding of the plasmasphere against the steadier components of the substorm electric fields. The available indirect whistler evidence of plasmasphere erosion during large disturbances suggests that erosion occurs primarily in the dusk-premidnight sector.