The earth's palaeomagnetosphere as the third type of planetary magnetosphere

Abstract

From the viewpoint of dynamical topology, planetary magnetospheres are classified into three: Types 1, 2 and 3. When the rotation vector and dipole moment of a planet and the velocity vector of the solar wind are denoted as Ω, M, and V, respectively, the planetary magnetosphere with Ω∥ M⊥ V is called Type 1. The magnetospheres of the present Earth, Jupiter, and Uranus at its equinoctial points belong to this type. The magnetosphere with Ω∥ M∥ V is called Type 2, which includes the Uranian magnetosphere at its solstitial points. The magnetosphere with Ω⊥ M and Ω⊥ V is called Type 3. The Earth's palaeomagnetosphere is considered to have experienced Type 3 during excursions and transition stages of palaeomagnetic polarity reversals. In the Type 3 magnetosphere, drastic diurnal variations are expected in configurations of the dayside cusps, tail axis, neutral sheet, polar caps, and so on. A possible relation between the Type 3 palaeomagnetosphere and palaeoclimate of the Earth during polarity reversals and geomagnetic excursions is suggested. It is also suggested that the heliomagnetosphere during polarity reversals of the general field of the Sun exhibits a drastic configuration change similar to the Type 3 palaeomagnetosphere of the Earth. A relation between the perpendicular condition Ω⊥ M and magnetic variable stars and pulsars is briefly discussed.