Y. I. Feldstein

Magnetic storms and magnetotail currents

The magnetospheric magnetic field is highly time-dependent and may have explosive changes (magnetospheric substorms and geomagnetic storms) accompanied by significant energy input into the magnetosphere. However, the existing stationary magnetospheric models can not simulate the magnetosphere for disturbed conditions associated with the most interesting magnetospheric physics events (intensive auroras, particle injection in the inner magnetosphere, and precipitations at the high latitudes, etc.). We propose a method for constructing a nonstationary model of the magnetospheric magnetic field, which enables us to describe the magnetosphere during the disturbances. The dynamic changes of the magnetosphere will be represented as a sequence of quasistationary states. The relative contributions to the Dst index by various sources of magnetospheric magnetic field are considered using a dynamic model of the Earths magnetosphere. The calculated magnetic field is obtained by using the solar wind and geomagnetic activity empirical data of the magnetic storm of March 23–24, 1969 and the magnetic disturbance of July 24–26, 1986. The main emphasis is on the current system of the magnetospheric tail, the variations of which enable a description of the fast changes of Dst.

Dynamic model of the magnetosphere: Case study for January 9–12, 1997

The dynamics of the magnetospheric current systems are studied in the course of the specific magnetospheric disturbance on January 9–12, 1997, caused by the interaction of the Earths magnetosphere with a dense solar wind plasma cloud. To estimate the contribution of the different sources of the magnetospheric magnetic field to the disturbance ground measured, a dynamic paraboloid model of the magnetosphere is used. The model input parameters are defined by the solar wind density and velocity, by the strength and direction of the interplanetary magnetic field, and by the auroral AL index. The total energy of the ring current particles is calculated from the energy balance equation, where the injection function is determined by the value of the solar wind electric field. New analytical relations describing the dynamics of the different magnetospheric magnetic field sources dependent on the model input parameters are obtained. The analysis of the magnetic disturbances during the January 9–12, 1997, event shows that in the course of the main phase of the magnetic storm the contribution of the ring current, the currents on the magnetopause, and the currents in the magnetotail are approximately equal to each other by an order of magnitude. Nevertheless, in some periods one of the current systems becomes dominant. For example, an intense Dst positive enhancement (up to +50 nT) in the course of the magnetic storm recovery phase in the first hours on January 11, 1997, is associated with a significant increase of the currents on the magnetopause, while the ring current and the magnetotail current remain at a quiet level. A comparison of the calculated Dst variation with measurements indicates good agreement. The root mean square deviation is ∼ 8.7 nT in the course of the storm.

Modeling of geomagnetic field during magnetic storms and comparison with observations

This paper discusses: (a) development of the dynamic paraboloid magnetospheric (eld model, (b) application of this model for the evaluation of a variety of magnetospheric current systems and their contribution to the ground magnetic (eld variations during magnetic storms, (c) investigation of auroral electrojet dynamics and behavior of plasma precipitation boundaries, and (d) usage of the paraboloid magnetospheric (eld model for revealing relationships between geomagnetic phenomena at low altitudes and the large-scale magnetospheric plasma domains. The model’s input parameters are determined by the solar wind plasma velocity and density, the IMF strength and direction, the tail lobe magnetic 6ux F∞, and the total energy of ring current particles. The auroral particle precipitation boundaries are determined from, the DMSP particle observations; these boundaries are used to calculate the value of F∞. The in6uence of the (eld-aligned tail, and ring currents on the magnetospheric (eld structure is studied. It is found that the polar cap area is strongly controlled by the tail current. The paraboloid magnetospheric (eld model is utilized for the mapping of the auroral electrojet centerlines and boundaries into the magnetosphere. Analysis of the magnetic (eld variations during magnetic storms shows that the contributions of the ring current, tail current, and the magnetopause currents to the Dst variation are approximately equal. c

Auroral electrojets during geomagnetic storms

On the basis of digital magnetometers from the International monitor auroral geomagnetic effects (IMAGE) and European incoherent scatter (EISCAT) meridional chains in Scandinavia dynamics of the eastward and westward electrojets during the main phase of magnetic storms are considered. For the intense magnetic storm on May 10–11, 1992, with Dst = −300 nT, magnetograms of subauroral and midlatitudinal stations Leningrad, Borok, and Moscow were examined. It is found that the eastward electrojet center during the storm main phase shifts equatorward as |Dst| increases. The electrojet center is located at the corrected geomagnetic latitude Φ ∼ 59°–60° when Dst ∼ −100 nT and at Φ ∼ 54°–55° when Dst ∼ −300 nT. Data from meridional chains of magnetometers support earlier results pertaining to the relationship between the westward electrojet center position and the ring current intensity for intervals between substorms. During substorms expansive phases the westward electrojet expands poleward covering auroral latitudes Φ ∼ 65°. The electrojets location during the storm main phase and their dynamics in connection with substorms allow for interpretations of effects described in the literature: the AE indices saturation during the main phase of magnetic storms; approximately equal values of AU and AL indices during the storm initial phase and AL ≫ AU during the storm main phase.

Energetics of the magnetosphere during the magnetic storm

Abstract The most detailed studies of the energetic budget of the magnetosphere during the magnetic storms were done on the basis of the paraboloid model using the November 23–27, 1986 and May 6–8, 1988 magnetic storms. Calculations have shown that the energy injected in the course of the magnetic storms into the inner magnetosphere and ionosphere of both hemispheres amounts to ∼ 0.9 –2.2% of the solar wind kinetic energy on the magnetospheric cross section. The total energy injected into the magnetosphere from a distance of 60RE in the tail down to the ionosphere is ∼4.0–7.5% of the solar wind kinetic energy during the main phase of the two magnetic storms. The injected energy into the tail ETL is 1.03–1.18 of the total energy input into the inner magnetosphere and ionosphere of both hemispheres at the main phase of the two storms. The decay parameter for the energy stored in the magnetospheric tail is ∼5 h . The total energy dissipated in the ionosphere of both hemispheres, in the inner magnetosphere and in the tail during the two storms, is 1.85×1017 and 3.24×10 17 J , respectively. The total energy input into the magnetosphere is calculated to be 1.77×1017 and 3.16×10 17 J . The discrepancies of 0.08×1017 and 0.10×10 17 J amount to 4.3% and 3.1% of the total energy input and characterize the accuracy of the magnetospheric energy budget calculation. In the magnetotail the balance between the injected and dissipated energy of ∼1.09×10 17 J for one storm and ∼1.7×10 17 J for the other is preserved as well. We conclude that one-half of the energy which is injected into the magnetosphere from the solar wind during the storms enters the magnetotail and dissipates there. The coupling parameter ePA is widely considered to be a measure of the energy dissipation in the inner magnetosphere. The dissipation energy in the inner magnetosphere UT=UJ+UA+UDR is defined as the sum of the contributions of the Joule dissipation UJ, the energy of auroral particle precipitation UA, and the energy injection into the ring current UDR. In this paper, we find that ePA in the two storms investigated is substantially different from UT. The energy injected into the ring current region at the main phase of the storm amounts to ∼10 16 J . It is nearly 3 or 4 times smaller than the energy input into the magnetosphere via the field-aligned currents or the energy dissipated in the ionosphere by Joule dissipation. The energy injected into the magnetosphere is transferred mainly into processes different from the ring current generation. During the development of intensive auroral electrojets, the energy dissipation in the magnetotail and the increase in the energy of the tail current system occur simultaneously. The energy dissipation in the inner magnetosphere and ionosphere US occurs not only at the expense of energy previously stored in the magnetotail, but rather at the expense of energy that is injected into the near-Earth tail. This energy transfer from the solar wind into the magnetotail and the energy dissipation in the ionosphere increased simultaneously. Thus, during disturbances in the magnetosphere, simultaneously loading–unloading and directly driven processes occur. Loading- and unloading processes manifest themselves both in the storage of the solar wind energy in the magnetotail and the ring current, and subsequent dissipation. The directly driven processes become manifest in the direct dissipation of the energy which enters into the ionosphere through large-scale field-aligned current systems.

An alternative interpretation of auroral precipitation and luminosity observations from the DE, DMSP, AUREOL, and Viking satellites in terms of their mapping to the nightside magnetosphere

Abstract We present an interpretation, which differs from that commonly accepted, of several published case studies of the patterns of auroral electron precipitation into the high-latitude upper atmosphere in the near-midnight sector based on their mapping to the nightside magnetosphere. In our scheme bright discrete auroral structures of the oval and respective precipitation are considered to be on the field lines of the Central, or Main, Plasma Sheet at distances from 5–10 to 30–50 RE, depending on activity. This auroral electron precipitation pattern was discussed in detail by Feldstein and Galperin [(1985) Rev. Geophys.23, 217] and Galperin and Feldstein [(1991) Auroral Physics, p. 207. Cambridge University Press. It is applied and shown to be consistent with the results of case studies based on selected transpolar passes of the DE, DMSP, AUREOL-3 and Viking satellites. A diagram summarising the polar precipitation regions and their mapping from the magnetospheric plasma domains is presented. It can be considered as a modification of the Lyons and Nishida (1988) scheme which characterizes the relationship between the gross magnetospheric structure and regions of nightside auroral precipitation. The modification takes into account non-adiabatic ion motions in the tail neutral sheet, so that the ion beams characteristic of the Boundary Plasma Sheet (BPS) originate on closed field lines of the distant Central Plasma Sheet (say, at distances more than ~30 RE).

The ring current in the magnetosphere and the polar magnetic substorms

Measurements of charged particles made in the ATS-1, OGO-3, and Explorer-34 satellites and simultaneous measurements of the magnetic field at the ground are used to investigate the temporal-spatial characteristics of some magnetic storms. The following conclusions are reached: 1. (1) The low energy protons (5≤ E ≤ 50 keV) observed by Frank in space cannot be the initial cause of the development of magnetic disturbances at the Earths surface. 2. (2) To separate spatial and temporal variations of particle intensities it is necessary to use both ground-based and satellite data. It is then possible to define the parameters of the ring current responsible for the decrease of the geomagnetic field. 3. (3) The low-latitude bays that occur during polar disturbances may be explained by a partial ring current flowing outside the region of stable trapping. 4. (4) The diamagnetic effect of ring current particles is responsible for the decrease of the magnetic field at satellite orbits. The simultaneity of the magnetic disturbance development at the satellite and at the Earths surface is explained by the variation of the incoming particle density. 5. (5) The changes in the current system responsible for a highlatitude magnetic disturbance are traced. It is shown that an almost single-vortex current structure (the westward electrojet) occurs during the maximum of the substorm, and a twinvortex structure is observed during the onset of the disturbance development and during the recovery phase.

Features of the Planetary Distribution of Auroral Precipitation Characteristics during Substorms

A planetary pattern of substorm development in auroral precipitation has been constructed on the basis of the F6 and F7 satellite observations. The behavior of the auroral injection boundaries and characteristics of precipitating electrons in various precipitation regions during all phases of a statistically mean magnetospheric substorm with an intensity of AL ∼ −400 nT at a maximum is considered in detail. It is shown that during a substorm, the zone of structured auroral oval precipitation AOP and the diffuse auroral zone DAZ are the widest in the nighttime and daytime sectors, respectively. In the daytime sector, all precipitation regions synchronously shift equatorward not only at the origination phase but during the substorm development phase. The strongest shift to low latitudes of the daytime AOP region is observed at a maximum of the development phase. As a result of this shift, the area of the polar cap increases during the phases of substorm origination and development. It is shown that the average position of the precipitation boundaries and the energy fluxes of precipitating electrons at each phase are linearly related to the intensity of a magnetic disturbance. This makes it possible to develop a model of auroral precipitation development during each phase of substorms of any intensity.

Auroral oval planetary energetics

Abstract The energy associated with a polar substorm is deduced from photographs of the aurora.

Ring current asymmetry during a magnetic storm

The ring current dynamics during the magnetic storm has been studied in the work. The response of the magnetospheric current systems to the external influence of the solar wind, specifically, resulting in the development of the asymmetric ring current component, has been calculated using the magnetic field paraboloid model. The asymmetric ring current has been considered as a family of spatial current circuits in the Northern and Southern hemispheres, composed of the zones of the partial ring current in the geomagnetic equator plane, which close through the system of field-aligned currents into the ionosphere. The value of the total partial ring current has been estimated by comparing the calculated asymmetry of the magnetospheric magnetic field at the geomagnetic equator with the value of the Asym-H geomagnetic index. The variations in the symmetric and asymmetric components of the ring current magnetic field have been calculated for the magnetic storm of November 6–14, 2004. The contributions of the magnetospheric current systems to the Dst and AU geomagnetic indices have been calculated.