Distortions of the magnetic field by storm-time current systems in Earth's magnetosphere

Abstract

Abstract. Magnetic field and current system changes in Earth's inner magnetosphere during storm times are studied using two principally different modeling approaches: on one hand, the event-oriented empirical magnetic field model, and, on the other, the Space Weather Modeling Framework (SWMF) built around a global MHD simulation. Two storm events, one moderate storm on 6-7 November 1997 with Dst minimum about −120 nT and one intense storm on 21-23 October 1999 with Dst minimum about −250 nT were modeled. Both modeling approaches predicted a large ring current (first partial, later symmetric) contribution to the magnetic field perturbation for the intense storm. For the moderate storm, the tail current plays a dominant role in the eventoriented model results, while the SWMF results showed no strong tail current in the main phase, which resulted in a poorly timed storm peak relative to the observations. These results imply that the the development of a ring current depends on a strong force to inject the particles deep into the inner magnetosphere, and that the tail current is an important external source for the distortions of the inner magnetospheric magnetic field for both storms. Neither modeling approach was able to reproduce all the variations in the B x and B y components observed at geostationary orbit by GOES satellites during these two storms: the magnetopause current intensifications are inadequate, and the field-aligned currents are not sufficiently represented. While the event-oriented model reproduces rather well the B z component at geostationary orbit, including the substorm-associated changes, the SWMF field is too dipolar at these locations. The empirical model is a useful tool for validation of the first-principle based models such as the SWMF.

Ion nose spectral structures observed by the Van Allen Probes

“…Because the realistic electric and magnetic fields are highly variable, we do not expect perfect agreement but we only intend to determine if the main observed features and trends can be reproduced. Additionally, most of the observations reported here occur during quiet times, when the magnetic field in the inner magnetosphere is very close to a dipole Journal of Geophysical Research: Space Physics 10.1002/2016JA022942 [Ganushkina et al, 2010]. Our particle tracing approach is the same as the one used by Ferradas et al [2015].…”

On the large-scale structure of the tail current as measured by THEMIS

“…Electric currents across the geomagnetic tail are controlled by the solar wind and cause geomagnetic variations, measured in the inner magnetosphere (radial distances < 8 R E ). In response to solar wind variations the tail current (like all other magnetospheric current systems) changes its shape, dimensions and intensity (Kaufmann, 1987;Lui and Hamilton, 1992;Sergeev et al, 1993;Pulkkinen et al, 1993;Runov et al, 2003;Ganushkina et al, 2010).…”

Space Weather Effects Produced by the Ring Current Particles

“…However, the Dst-index contains contributions from many other sources than the azimuthally symmetric ring current and their contributions can be significant or even largest during disturbed conditions. The suggested magnetospheric sources include (1) magnetopause currents, (2) cross-tail current, (3) partial ring current, and even (4) substorm current wedge (see the review by Maltsev 2004 and references therein) and also studies by Friedrich et al (1999), Munsami (2000), Ohtani et al (2001), Liemohn et al (2001a,b), Liemohn (2003), Ganushkina et al (2004Ganushkina et al ( , 2010, Kalegaev et al (2005). The magnetic field measured on the ground contains contributions from all current systems and there is no other way to separate them but to use magnetospheric models.…”

“…Inflation of the near-Earth magnetic field due to ring current changes (e.g. Parker and Stewart 1967;Ganushkina et al 2010) alters the drift paths of the relativistic electrons in the radiation belts, causing the adiabatic "Dst effect" (e.g. Kim and Chan 1997), which can become a real loss of particles at the magnetopause (e.g.…”