On the location of trapped particle populations in quadrupole magnetospheres

Abstract

Abstract. Populations of trapped particles in Earth's magnetic field are intimately linked to prominent magnetospheric phenomena, for example, to the radiation belts and the ring current. Particles are forced to bounce between both hemispheres because field lines converge from the magnetic equatorial region toward the poles owing to the dominating dip olaf component. The scenario may change essentially if the so-called paleomagnetosphere is considered, that is, the terrestrial magnetosphere during a polarity reversal period. This report deals with particle trapping in general field configurations and concentrates on the quadrupole case as a potential scenario for paleomagnetospheric studies. By using the tensor representation of the quadrupole field, we show that its topology is controlled by a single "shape" parameter which is a measure for the relative strength of quadrupole tensor components, or equivalently, coefficients in the spherical harmonics expansion of the potential. In order to locate centers of particle bounce motion the concept of a magnetic equatorial surface is extended to a more general type of "trapping center surface" by means of geometrical criteria such as B. VB = 0. The quadrupole case yields two such surfaces. As does the field line topology, those surfaces and the resulting drift orbits vary strongly with the quadrupole shape parameter.

Concerning long-term geomagnetic variations and space climatology

“…Also, the effect of energetic particles in the magnetosphere is not discussed here. A first discussion on this can be found in the work by Vogt and Glassmeier (2000).…”

Magnetic Null Points in Kinetic Simulations of Space Plasmas

“…It is hypothesized that the total dipole magnetic field energy is transferred to quadrupole or octupole moments (Vogt & Glassmeier 2000;Zieger et al 2004). Therefore, the quadrupole component can be strong enough to generate a fully pledged magnetosphere, as well as to prevent the solar wind from directly impacting the atmosphere (at least in some parts of the globe).…”

Cosmic ray and solar energetic particle flux in paleomagnetospheres

“…To get a simple approximation for the magnetic field line topology in the magnetosphere, the inner dipole field and the ring current field are combined to a magnetic field of a modified dipole moment. Vogt and Glassmeier (2000) showed that in quadrupole magnetospheres the configuration and location of the ring current may be totally different from the present situation. In some cases one cannot even speak of a ring current any more.…”

“…Galactic cosmic rays may have an influence on cloud coverage, which in turn influences the global radiation budget and thus the climate (Svensmark and Friis-Christensen, 1997;Marsh and Svensmark, 2000). Trapped particle populations and ring current geometries in quadrupolar magnetospheres were studied by Vogt and Glassmeier (2000). The scaling behavior of different classes of energetic particles in dipolar and quadrupolar paleomagnetospheres was investigated by Vogt et al (2007).…”