Energetic particles in the paleomagnetosphere: Reduced dipole configurations and quadrupolar contributions

Abstract

[1] The Earth's magnetosphere acts as a shield against highly energetic particles of cosmic and solar origin. On geological timescales, variations of the internal geomagnetic field can drastically alter the magnetospheric structure and dynamics. This paper deals with energetic particles in the paleomagnetosphere. Scaling relations for cutoff energies and differential particle fluxes during periods of reduced dipole moment are derived. Particular attention is paid to high rigidity galactic cosmic ray particles in the GV range and to lower rigidity solar energetic particles. We find that in the paleomagnetosphere of a strongly reduced dipole moment, solar protons of several tens of MeV may access the Earth's atmosphere even at midlatitudes. Higher-order core-field components can widen the polar caps and open new particle-entry regions around the equator. Potential field modeling of the paleomagnetosphere and magnetohydrodynamic (MHD) simulations are utilized to study the impact of solar particles on the Earth's atmosphere for more complex field configurations that are likely to occur during geomagnetic polarity transitions. Copyright 2007 by the American Geophysical Union.