L. I. Gromova

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.

Dynamics of the auroral electrojets and their mapping to the magnetosphere

Abstract Data of the EISCAT and IMAGE magnetic observatories chains in combination with data of three Russian observatories (St. Petersburg, Borok and Moscow) were used to determine the eastward and westward electrojet dynamics in the course of magnetic storms. During the storm main phase and maximum substorm intensity the eastward electrojet is located at latitudes lower than usual. During intervals between substorms the westward electrojet centre shifts equatorwards as Dst increases. At a substorm maximum the westward electrojet widens polewards. The spectrograms of precipitating electrons and ions of auroral energies obtained onboard the DMSP F8, F10 and F11 satellites allow to connect the regions of the electrojet location with characteristic plasma structures at ionospheric altitudes. The eastward electrojet in the evening sector is located in the region of diffuse electron precipitations. The electrojet centre coincides with the latitude of an energy flux maximum of auroral protons. In the course of substorms the westward electrojet at the nightside is located at latitudes of both diffuse and discrete electron precipitations. The electrojets and plasma region boundaries are mapped to the magnetosphere. The paraboloid model of the magnetosphere is used here. The influence of paraboloid model input parameters on the dayside cusp latitude, on the ionospheric boundaries between open and closed as well as dipole-like and tail-like field lines is considered. It is shown that tail currents influence magnetic field line configuration in the nightside magnetosphere stronger than the ring current.

The Fields of Magnetospheric Current Systems on the Earth's Surface in an Interval of the Magnetic Storm Studied under the International Program on Solar–Terrestrial Physics

Using the magnetic storm in January 1997 as an example, we examined the possibilities to employ the magnetospheric field T96 [1, 2] and the dynamic paraboloid model PM of the magnetosphere [3] for modeling the Dst variation. We have revealed the necessity to refine the results of normalizing the free parameters of the model T96 according to the solar wind parameters. The contributions to the Dst variation of magnetic fields of basic large-scale magnetospheric current systems (the field DCF on the magnetopause, the field DR of the ring current, and the field DT in the magnetotail) are estimated for different phases of the storm from model calculations. Possible causes of a discrepancy between the results of modeling Dst using the T96 and PM models are discussed. Special emphasis is made on the ratios of contributions into the Dst variation of the fields of the magnetotail and the ring current in the main phase of magnetic storms and on the contributions to Dst of the fields of various current systems at the recovery phase.