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 event-oriented 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 Bx and By 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 Bz 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.
Highlights
During geomagnetic storms the near-Earth magnetic field exhibits changes over a wide range of spatial and temporal scales and becomes highly distorted from its typical, quiettime, dipolar configuration (e.g., Parker and Stewart, 1967; Tsyganenko et al, 2003)
We present results for two storms, one moderate on 6–7 November 1997 with Dst minimum of −120 nT, and one intense on 21–23 October 1999 when Dst reached to −250 nT
Model results for 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 compared
Summary
During geomagnetic storms the near-Earth magnetic field exhibits changes over a wide range of spatial and temporal scales and becomes highly distorted from its typical, quiettime, dipolar configuration (e.g., Parker and Stewart, 1967; Tsyganenko et al, 2003). Current systems responsible for these distortions include: (a) the cross-tail current in the near-Earth plasma sheet that stretches field lines on the nightside, (b) the partial ring current that bulges out the field in some localized regions across the evening and nightside, (c) the Chapman-Ferraro magnetopause currents that compress the dayside magnetic field, (d) the various field-aligned currents that twist the field lines in their local neighborhood, and (e) the symmetric ring current that inflates the entire inner magnetospheric field All of these processes lead to numerous space weather effects, such as, for example, the radial expansion of relativistic electron drift paths in the outer radiation belt. Analyzing the accuracy of the TS04 model is not the goal of this paper
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