Kisabeth and Rostoker showed how three-dimensional current systems associated with magnetospheric substorms can be used to quantitatively evaluate the magnetic field perturbation at any location on the ground. The ionospheric solution for electric field is mapped back to the inner boundary of the MHD model and is used to define the boundary condition for the plasma velocity via velocity. The contours of constant electrostatic potential are streamlines of flow in the ionosphere. By using semiempirical models for the conductances the electrostatic potential is computed. The height-integrated current continuity equation yields the perpendicular current density (both Hall and Pedersen) in the ionosphere. This parallel current is mapped into the ionosphere along unperturbed dipole magnetic field lines. In the LFM Global MHD model, at the inner boundary located at 2–3 R E from the Earth, the parallel current density J ∥ is computed at each instant of time.
We first briefly outline some relevant parts of the code that facilitate the understanding of our model. In the present work we have used the time history of the ionospheric currents computed by the ionosphere module of the LFM code to develop a model for calculating the time history of the perturbed magnetic field at various ground-based locations to compare with magnetometer data. It was concluded that both the solar wind magnetic field and ram pressure are important in determining the structure of the magnetosphere and the activity in the ionosphere during the 10–11 January 1997 magnetic storm. They showed that during the period of southward interplanetary magnetic field (IMF) the ionospheric activity was strongly correlated with the solar wind density variation. The simulation results agreed well with ground-based and geosynchronous satellite observations. The results of the three-dimensional (3-D) MHD simulation of this event and its consequence on the magnetosphere and ionosphere have been presented by Goodrich et al. Forty-eight hours of real-time development of the geomagnetic activity in the magnetosphere and ionosphere were simulated. The simulation was initialized using upstream Wind satellite data. Lyon from Dartmouth College, simulated the 10–11 January 1997 storm event. Using the Lyon-Fedder-Mobarry (LFM) Global magnetohydrodynamic (MHD) simulations, the group at Maryland (Goodrich, Wiltberger, Lopez, and Papadopoulos) in collaboration with J.
Global MHD simulations that include ionospheric response and are dynamically driven by upstream satellite data allow for direct comparison with the field and flow quantities measured by detectors on magnetospheric satellites, ground-based instruments and images from the Polar satellite. Early on January 10, WIND first observed the (CME associated) magnetic cloud, which produced a complex magnetic storm lasting 22 hours. The SOHO Large-Angle Spectrometric Coronograph (LASCO) experiment observed the CME expanding from the solar surface apparently toward the Earth on January 6. This storm was the first solar terrestrial disturbance whose temporal development was followed from its solar source and its subsequent effects on the magnetosphere and ionosphere using the entire suite of resources of the International Solar Terrestrial Physics (ISTP) program. On 10 January 1997 a magnetic cloud produced a major geomagnetic storm.
The limitations of the global MHD model in calculating perturbed ground magnetic field are also discussed. The model including the dependence of the current sheet height on the precipitating electron energy reduces 10% error compared to the model with fixed current sheet height. The comparison shows reasonable agreement between observations and simulations. By applying the model to the 10 January 1997 magnetic storm event we have calculated the perturbed magnetic field for four magnetometers and compared with observations. The model uses the computed ionospheric currents and the height dependence of the electrojet current above the ground, by evaluating the penetration depth of the precipitating energetic electrons, to calculate the perturbed magnetic field on the ground using Biot-Savart's law. A model has been developed to calculate the perturbed magnetic field at various ground-based magnetometer sites using the output of the ionospheric currents from the Lyon-Fedder-Mobarry Global MHD code.