Global aspects of solar wind–ionosphere interactions

Recent observations have quantified the auroral wind O⁺ outflow in response to magnetospheric inputs to the ionosphere, notably Poynting energy flux and precipitating electron density. For moderate to high activity periods, ionospheric O⁺ is observed to become a significant or dominant component of plasma pressure in the inner plasma sheet and ring current regions. Using a global circulation model of magnetospheric fields and its imposed ionospheric boundary conditions, we evaluate the global ionospheric plasma response to local magnetospheric conditions imposed by the simulation and evaluate magnetospheric circulation of solar wind H⁺, polar wind H⁺, and auroral wind O⁺. We launch and track the motions of millions of test particles in the global fields, launched at randomly distributed positions and times. Each particle is launched with a flux weighting and perpendicular and parallel energies randomly selected from defined thermal ranges appropriate to the launch point. One sequence is driven by a two-hour period of southward interplanetary magnetic field for average solar wind intensity. A second is driven by a 2-h period of enhanced solar wind dynamic pressure for average interplanetary field. We find that the simulated ionospheric O⁺ becomes a significant plasma pressure component in the inner plasma sheet and outer ring current region, particularly when the solar wind is intense or its magnetic field is southward directed. We infer that the reported empirical scalings of auroral wind O⁺ outflows are consistent with a substantial pressure contribution to the inner plasma sheet and plasma source surrounding the ring current. This result violates the common assumption that the ionospheric load is entirely confined to the F layer, and shows that the ionosphere is often an important dynamic element throughout the magnetosphere during moderate to large solar wind disturbances.     

Potential merits for substorm research from imaging of charge-exchange neutral atoms

The in situ observations of the Earth magnetosphere performed over the past decades of space research have provided a rather good understanding of many partial localized processes of the magnetospheric substorm. The continuing lack of global observations inhibits the construction of a coherent picture of the substorm as a whole, which is actually determined by the coupling of the partial processes. In this context the importance of global observations for the advancement of magnetospheric substorm studies is critical. This paper presents briefly a promising technique of global observations, namely the imaging of charge exchange neutral atoms, or neutral atom imaging (NAI) of the magnetosphere. Model and theoretical estimates of charge-exchange neutral atom fluxes, as well as appropriate spacecraft orbit and instrumentation requirements are presented and discussed for specific regions of interest and vantage points. The potential merits of NAI for substorm research are presented along with possible combinations with other types of observational methods. Substorm issues that would benefit from NAI should include among others the assessment of the ionospheric contribution to the hot magnetospheric plasma, the relative importance of various ionospheric ion source regions, the resolution of spatial and temporal characteristics of substorm ion injections. NAI observations can be precious complements to local observations and lead to the understanding of how local processes, many of which are resolved quite well today, combine to form the global process of the magnetospheric substorm.     

Ionospheric Signatures Of Bursty Bulk Flows

While the plasma convection in the Earth's magnetosphere was for a long timeconsidered to consist mostly of laminar flows with wide spatial extents, about adecade ago the phenomenon of bursty bulk flows (BBFs), which now could beunderstood as long, but narrow channels of fast earthward plasma flow in thecentral plasma sheet of the magnetospheric tail, was discovered. Soon after thisit became clear that such events are not exceptional, but a large portion of theearthward plasma flow in the inner part of the magnetospheric tail is organisedin this bursty, intermittent mode. Since the Earth's magnetosphere is connectedby highly conducting magnetic field lines with its ionosphere, the next logicalstep was the search for the ionospheric signatures of BBFs. We review the resultsobtained so far in this young field of Space Physics, in terms of theauroral and ground magnetic signatures caused by BBFs, the particle precipitationto the ionosphere, as well as of the ionospheric electrodynamics of the processesassociated with the BBFs in the magnetosphere. Finally, we briefly review somemodels of ionosphere-magnetosphere coupling with respect to their ability to explainthe ionospheric signatures observed.     

Weimer电场模式在地球磁层内的特征

地球磁层中的电场是研究磁层物理的重要参数,目前常用的对流电场有均匀晨昏电场和投影电场.电离层电场可以看做磁层电场沿磁力线在电离层的投影,本文选取的电离层电场模型为Weimer(2001模式)电场.利用T96磁场模式,沿磁力线将电离层电场投影到磁层空间,得到一个新的磁层电场模式,并讨论了磁暴、行星际磁场(IMF)、太阳风参数和亚暴等对磁层电场的影响.利用该模型计算的电场结果与卫星探测结果相符.     

The dynamic cusp at low altitudes: a case study utilizing Viking,DMSP-F7, and Sondrestrom incoherent scatter radar observations

Coincident multi-instrument magnetospheric and ionospheric observations have made it possible to determine the position of the ionospheric footprint of the magnetospheric cusp and to monitor its evolution over time. The data used include charged particle and magnetic field measurements from the Earth-orbiting Viking and DMSP-F7 satellites, electric field measurements from Viking, interplanetary magnetic field and plasma data from IMP-8, and Sondrestrom incoherent scatter radar observations of the ionospheric plasma density, temperature, and convection. Viking detected cusp precipitation poleward of 75.5○ invariant latitude. The ionospheric response to the observed electron precipitation was simulated using an auroral model. It predicts enhanced plasma density and elevated electron temperature in the upper E- and F-regions. Sondrestrom radar observations are in agreement with the predictions. The radar detected a cusp signature on each of five consecutive antenna elevation scans covering 1.2 h local time. The cusp appeared to be about 2○ invariant latitude wide, and its ionospheric footprint shifted equatorward by nearly 2○ during this time, possibly influenced by an overall decrease in the IMF B_z component. The radar plasma drift data and the Viking magnetic and electric field data suggest that the cusp was associated with a continuous, rather than a patchy, merging between the IMF and the geomagnetic field.     

Dependence of the Pc4 magnetic pulsation parameters on the radiated power of the EISCAT HF heating facility

The interaction between the Earth’s ionosphere and magnetosphere in a situation when artificial disturbances are generated in the F region of the auroral ionosphere with the EISCAT/Heating facility is studied. An experiment was performed in the daytime when the facility effective radiated power changed in a stepwise manner. Wavelike disturbances with periods of (130–140) s corresponding to Pc4 pulsations were simultaneously registered by the method of bi-static backscatter and with ground magnetometers. The variations in the Doppler frequency shift were correlated with the changes in the facility power. Incoherent scatter radar measurements at a frequency of 930 MHz (Tromsö) and numerical calculations were used in an analysis. It has been indicated that the ionospheric drift of small-scale artificial ionospheric irregularities was modulated by magnetospheric Alfvén waves. The possible effect of powerful HF radioemission on the Alfvén wave amplitude owing to the modification of the magnetospheric resonator ionospheric edge reflectivity and the generation of an outgoing Alfvén wave above the region where the ionospheric conductivity is locally intensified has been considered.     

On characteristic frequencies of a five-component model of magnetospheric plasma

Summary The author gives more general relations derived for characteristic frequencies of a more complex plasma model. One may assume that expressions derived herein, represent a more appropriate approximation of reality, especially in regions of ionospheric and magnetospheric plasma with a higher concentration of heavy ions.     

Geospheric effects of the solar flare of December 13, 2006

Disturbances in the magnetic field and magnetospheric and ionospheric plasma registered on December 14–16, 2006, during a strong magnetic storm caused by a solar flare of 4B/X3.4 class are studied. It is shown that in the north of Yakutia, interactions between the Earth’s magnetosphere and the region of high dynamic pressure of the solar wind led to the formation of sporadic layers in the ionospheric E and F regions, depletion of the critical frequency of the F2 layer, and total absorption. At the end of the magnetic storm’s main phase, anomalously high values of foF2 exceeding the quiet level by a factor of 1.5–1.7 were detected. It was found that the disturbances detected by ground-based observatories had developed on the background of changes in the temperature, density, and the pitch-angle distribution of particles at the geostationary orbit manifesting radial shifts of magnetospheric structures (magnetopause, cusp/cleft, and plasma sheet) relative to the observation points. A conclusion is drawn that in this case, changes in the near-Earth plasma and magnetic field manifest the dynamics of the physical conditions at the magnetospheric boundary and diurnal rotation of the Earth.     

Medium-scale splitting of outflowing field-aligned currents and kappa distribution of magnetospheric ions

The medium-scale (50–200 km in the projection onto ionospheric altitudes) splitting of the field-aligned currents flowing out of the ionosphere has been considered in the case when the approximation of the distribution function of hot magnetospheric ions by the kappa distribution is taken into account. It was assumed that the condition of magnetostatic equilibrium and isotropy of hot magnetospheric plasma pressure is satisfied in the magnetosphere. The theoretical parameter of magnetospheric plasma hot stratification has been obtained for the case of ion kappa distribution. The parameter characterizes the number of structures into which the band of the field-aligned current flowing out of the ionosphere is split. The theoretical predictions have been compared with the observations on the Intercosmos-Bulgaria-1300 and Aureol-3 satellites. It has been indicated that the number of measured structures is in better agreement with that of the theoretically predicted structures in 70% of cases if the non-Maxwellian tails of ion distribution functions are taken into account.     

Instability of the magnetosphere-ionosphere convection and formation of auroral arcs

In this paper we study an instability of the plasma moving towards the Earth near the inner plasma sheet boundary. We include both the interchange instability of the plasma sheet and the magnetosphere-ionosphere interaction instability caused by an effect of field-aligned currents (connected with electron precipitation) on ionospheric conductivity. The instability leads to the separation of steady-state magnetospheric convection into parallel layers. This instability may be responsible for the appearance of quiet auroral arcs inside region 2 of field-aligned currents flowing out of the ionosphere. This instability allows us to explain also the existence of crossing auroral arcs.     

On the remote sensing of plasma sheet from low-altitude spacecraft

The possibility to estimate plasma sheet parameters from low-altitude measurements looks quite attractive, but it critically depends on how isotropic the plasma pressure is in the flux tube. To evaluate the ion pressure anisotropy we compare the values of pressure in the ionospheric and equatorial parts of the field line. Ionospheric values were computed from proton measurements at NOAA low-altitude satellites, they were compared with pressure estimates computed from empirical magnetic field models as well as with average values known from direct plasma sheet measurements. Three different methods of mapping the plasma pressure from plasma sheet to low altitude have been tried; each uses the particle isotropic boundaries observed at low altitudes and/or computed from magnetospheric models. Excluding observations obtained during substorm expansion, from these comparisons we conclude that in the plasma sheet, at geocentric distances 9–20R_E, the pressure estimates in the ionospheric and equatorial parts of the plasma sheet flux tube agree very well, suggesting a good pressure isotropy and thus justifying a possibility to monitor the plasma sheet parameters based on low-altitude measurements. The results also illustrate the usefulness of isotropic boundaries as a label of tail current intensity and as reliable tool for establishing mapping between magnetosphere and ionosphere.     

On the possibility of using an electromagnetic ionosphere in global MHD simulations

Global magnetohydrodynamic (MHD) simulations of the Earths magnetosphere must be coupled with a dynamical ionospheric module in order to give realistic results. The usual approach is to compute the Reld-aligned current (FAC) from the magnetospheric MHD variables at the ionospheric boundary. The ionospheric potential is solved from an elliptic equation using the FAC as a source term. The plasma velocity at the boundary is the E × B velocity associated with the ionospheric potential. Contemporary global MHD simulations which include a serious ionospheric model use this method, which we call the electrostatic approach in this paper. We study the possibility of reversing the flow of information through the ionosphere: the magnetosphere gives the electric Reld to the ionosphere. The Reld is not necessarily electrostatic, thus we will call this scheme electromagnetic. The electric Reld determines the horizontal ionospheric current. The divergence of the horizontal current gives the FAC, which is used as a boundary condition for MHD equations. We derive the necessary formulas and discuss the validity of the approximations necessarily involved. It is concluded that the electromagnetic ionosphere-magnetosphere coupling scheme is a serious candidate for future global MHD simulators, although a few problem areas still remain. At minimum, it should be investigated further to discover whether there are any differences in the simulation using the electrostatic or the electromagnetic ionospheric coupling.     

Search for hidden periodicity in magnetometric measurements performed during auroras

A method for detecting discrete equidistant spectra in high-latitude magnetic observations is proposed. The method finds approximate solutions of the classical Schuster problem, which finds a hidden periodicity in observations with considerable noise. The usage of difference signals makes it possible to increase the latitudinal resolution of the magnetometric diagnostics. The equidistant spectra of two different types have been detected based on the proposed method. The spectra of the first type are interpreted as frequencies of coupled compressional-transverse magnetohydrodyncompressionalamic oscillations in the magnetospheric cavity. The origin of the second type of spectra can be related to a rotating source, i.e., a small-scale vortex of magnetospheric convection. Such an interpretation takes into consideration the Doppler frequency shift caused by entrainment of the ionospheric neutral gas by magnetospheric convection. The results confirm the conclusion that discrete auroral frequencies are stable under disturbed conditions.     

On effective conductivity of the ionosphere with random irregularities

The influence of stochastic irregularities of the ionosphere on its effective conductivity has been estimated. The study was carried out for large scale inhomogeneities and quasistationary electromagnetic fields. It is found, that Pedersen conductivity sharply increases in a strong geomagnetic field even for small stochastic ionospheric irregularities of the electron density. This peculiarity has to be taken into account during analysis of ionospheric and magnetospheric measurements.     

Implementation of Ionospheric Generators in the Numerical Model of the Global Electric Circuit

Geomagnetism and Aeronomy - The consistent inclusion of global electric circuit sources of ionospheric and magnetospheric origin in distributed numerical models of the circuit is discussed. It is...     

Estimation of the high-latitude topside electron heat flux using DMSP plasma density measurements

The high-latitude ionosphere interfaces with the hot, tenuous, magnetospheric plasma, and a heat flow into the ionosphere is expected, which has a large impact on the plasma densities and temperatures in the high-latitude ionosphere. The value of this magnetospheric heat flux is unknown. In an effort to estimate the value of the magnetospheric heat flux into the high-latitude ionosphere, and show its effect on the high-latitude ionospheric plasma densities, we ran an ensemble of model runs using the Ionosphere Forecast Model (IFM) with different values of the heat flux through the upper boundary. These model runs included heating from both auroral and solar sources. Then, for each heat flux value, the plasma densities obtained from the model runs, at 840 km, were compared to the corresponding values measured by the DMSP F13 satellite. The heat flux value that gave the best comparison between the measured and calculated plasma densities was considered to be the best estimate for the topside heat flux. The comparison was conducted for a 1-year data set of the DMSP F13 measured plasma densities (4300 consecutive orbits). Our systematic IFM/DMSP plasma density comparisons indicate that when a zero magnetospheric downward heat flux is assumed at the upper boundary of the IFM model, on the average, the IFM underestimates the measured plasma densities by a factor of 2. A good IFM/DMSP plasma density comparison was achieved for each month in 1998 when for each month a constant heat flux was assumed at the upper boundary of the model. For the 12-month period, the heat flux values that gave the best IFM/DMSP plasma density comparisons varied on the average from −0.5×10¹⁰ to −1.5×10¹⁰ eV cm⁻² s⁻¹.     

Nonlinear dynamics of 3D beams of fast magnetosonic waves propagating in the ionospheric and magnetospheric plasma

On the basis of the model of the three-dimensional (3D) generalized Kadomtsev-Petviashvili equation for magnetic field h = B _~/B the formation, stability, and dynamics of 3D soliton-like structures, such as the beams of fast magnetosonic (FMS) waves generated in ionospheric and magnetospheric plasma at a low-frequency branch of oscillations when β = 4πnT/B ² ? 1 and β > 1, are studied. The study takes into account the highest dispersion correction determined by values of the plasma parameters and the angle θ = (B, k), which plays a key role in the FMS beam propagation at those angles to the magnetic field that are close to π/2. The stability of multidimensional solutions is studied by an investigation of the Hamiltonian boundness under its deformations on the basis of solving of the corresponding variational problem. The evolution and dynamics of the 3D FMS wave beam are studied by the numerical integration of equations with the use of specially developed methods. The results can be interpreted in terms of the self-focusing phenomenon, as the formation of a stationary beam and the scattering and self-focusing of the solitary beam of FMS waves. These cases were studied with a detailed investigation of all evolutionary stages of the 3D FMS wave beams in the ionospheric and magnetospheric plasma.     

Interhemispheric comparison of TDIM E- and F-region ionospheres on 14 January 1988

The USU time-dependent ionospheric model (TDIM) simulated the northern (winter) and southern (summer) ionospheres as they responded to the changing solar wind and geomagnetic activity on 14 January 1988. This period began with moderately disturbed conditions, but as the IMF turned northward, the geomagnetic activity decreased. By 1400 UT, the IMF B_y component became strongly negative with B_z near zero; and eventually B_z turned southward. This began a period of intense activity as a magnetic storm developed. The magnetospheric electric field and auroral electron precipitation drivers for these simulations were obtained from the Naval Research Laboratories (NRL) Magnetohydrodynamic (MHD) magnetospheric simulation for this event.The F-region ionospheric simulations contrast the summer–winter hemispheres. Then, the difference in how the two hemispheres respond to the geomagnetic storm is related to the differences in magnetospheric energy deposition in the two hemispheres. This also emphasizes the role played by the E-region in the magnetosphere–ionosphere (M–I) coupling and subsequent lack of conjugacy in the two hemispheres. The F-region’s response to the changing geomagnetic conditions also demonstrates a striking lack of conjugacy. This manifests itself in a well-defined ionospheric morphology in the summer hemisphere and a highly irregular morphology in the winter hemisphere. These differences are found to be associated with the differences in the magnetospheric electric field input.     

Theoretical developments on the causes of ionospheric outflow

It is now well known that there is a substantial outflow of ionospheric plasma from the terrestrial ionosphere at high latitudes. The outflow consists of light thermal ions (H⁺, He⁺) as well as both light and heavy energized ions (H⁺, He⁺, O⁺, N⁺, NO⁺, O₂⁺, N₂⁺). The thermal ion outflows tend to be associated with the classical polar wind, while the energized ions are probably associated with either auroral energization processes or nonclassical polar wind processes. Part of the problem with identifying the exact cause of a given outflow relates to the fact that the ionosphere continuously convects into and out of the various high-latitude regions (sunlight, cusp, polar cap, nocturnal oval) and the time-constant for outflow is comparable to the convection time. Therefore, it is difficult to separate and quantify the possible outflow mechanisms. Some of these mechanisms are as follows. In sunlit regions, the photoelectrons can heat the thermal electrons and the elevated electron temperature acts to increase the polar wind outflow rate. At high altitudes, the escaping photoelectrons can also accelerate the polar wind as they drag the thermal ions with them. In the cusp and auroral oval, the precipitating magnetospheric electrons can heat the thermal electrons in a manner similar to the photoelectrons. Also, energized ions, in the form of beams and conics, can be created in association with field-aligned auroral currents and potential structures. The cusp ion beams and conics that have been convected into the polar cap can destabilize the polar wind when they pass through it at high altitudes, thereby transferring energy to the thermal ions. Additional energization mechanisms in the polar cap include Joule heating, hot magnetospheric electrons and ions, electromagnetic wave turbulence, and centrifugal acceleration.Some of these causes of ionospheric outflow will be briefly reviewed, with the emphasis on the recent simulations of polar wind dynamics in convecting flux tubes of plasma.     

Numerical Simulation of the High-Latitude Non-Stationary Ionospheric Alfvén Resonator During an IPDP Event

The ionospheric Alfvén resonator (IAR) was numerically simulated under non-stationary ionospheric and magnetospheric conditions of the IPDP event of December 4, 1986. The full numerical wave method was applied using height profiles of the ionospheric plasma parameters obtained from the Scandinavian EISCAT radar measurements close to the Ivalo latitude. An attempt to model the inverse problem of numerical simulation—prolongation of the electron density profiles at altitudes above the ionospheric F layer—was made on the basis of the IAR simulation in correlation with the IPDP frequency increase. The change of the IAR wave characteristics during the substorm was illustrated by height profiles of the total wave amplitude and various polarization characteristics, taking into consideration the ordinary L-mode and the extraordinary R-mode waves for parallel and non-parallel incidence with respect to the magnetic field line.