Dipole model of the Earth's magnetic field

About: Dipole model of the Earth's magnetic field is a research topic. Over the lifetime, 2756 publications have been published within this topic receiving 83021 citations.

The free energies of partially open coronal magnetic fields

Abstract: A simple model of the low corona is examined in terms of a static polytropic atmosphere in equilibrium with a global magnetic field. The question posed is whether magnetostatic states with partially open magnetic fields may contain magnetic energies in excess of those in fully open magnetic fields. Based on the analysis presented here, it is concluded that the cross-field electric currents in the pre-eruption corona are a viable source of the bulk of the energies in a mass ejection and its associated flare.

Cosmic ray threshold rigidities and the earth's magnetic field

Abstract: Approximate corrections to the vertical threshold rigidities for cosmic rays in the earth's magnetic field are given, which take into account both the effects of the non-dipole part of the internal field and the penumbra. The thresholds obtained are tabulated every 2½° geographic latitude and every 5° geographic longitude. The accuracy of these thresholds is discussed and it is shown that they fit experimental data better than do previous approximations.

Development of the 3‐D MHD model of the solar corona‐solar wind combining system

Abstract: [1] In the framework of integrated numerical space weather prediction, we have developed a 3-D MHD simulation model of the solar surface-solar wind system. We report the construction method of the model and its first results. By implementing a grid system with angularly unstructured and increasing radial spacing, we realized a spherical grid that has no pole singularity and realized a fine grid size around the inner boundary and a wide-range grid up to a size of 1 AU simultaneously. The magnetic field at the inner boundary is specified by the observational data. In order to obtain the supersonic solar wind speed, parameterized source functions are introduced into the momentum and energy equations. These source functions decay exponentially in altitude as widely used in previous studies. The absolute values of the source functions are controlled so as to reflect the topology of the coronal magnetic field. They are increased inside the magnetic flux tube with subradial expansion and reduced inside the magnetic flux tube with overradial expansion. This adjustment aims to reproduce the variation of the solar wind speed according to the coronal magnetic structure. The simulation simultaneously reproduces the plasma-exit structure, the high- and low-temperature regions, the open and closed magnetic field regions in the corona, the fast and slow solar wind, and the sector structure in interplanetary space. It is confirmed from the comparison with observations that the MHD model successfully reproduces many features of both the fine solar coronal structure and the global solar wind structure.

Complex image method for calculating electric and magnetic fields produced by an auroral electrojet of finite length

Abstract: . The electromagnetic field due to ionospheric currents has to be known when evaluating space weather effects at the earth's surface. Forecasting methods of these effects, which include geomagnetically induced currents in technological systems, are being developed. Such applications are time-critical, so the calculation techniques of the electromagnetic field have to be fast but still accurate. The contribution of secondary sources induced within the earth leads to complicated integral formulas for the field at the earth's surface with a time-consuming computation. An approximate method of calculation based on replacing the earth contribution by an image source having mathematically a complex location results in closed-form expressions and in a much faster computation. In this paper we extend the complex image method (CIM) to the case of a more realistic electrojet system consisting of a horizontal line current filament with vertical currents at its ends above a layered earth. To be able to utilize previous CIM results, we prove that the current system can be replaced by a purely horizontal current distribution which is equivalent regarding the total (=primary + induced) magnetic field and the total horizontal electric field at the earth's surface. The latter result is new. Numerical calculations demonstrate that CIM is very accurate and several magnitudes faster than the exact conventional approach. Key words. Electromagnetic theory · Geomagnetic induction · Auroral ionosphere