A new look at driven magnetic reconnection at the terrestrial subsolar magnetopause

Abstract

[1] The physics of steady driven magnetic reconnection at Earth's subsolar magnetopause is addressed. Three-dimensional, global magnetohydrodynamics (MHD) simulations of the magnetopause are compared with analytical solutions of the resistive MHD equations [Sonnerup and Priest, 1975] corresponding to magnetic field annihilation driven by an incompressible stagnation point flow. The simulations demonstrate that under steady southward interplanetary magnetic field conditions and when the plasma resistivity is spatially uniform, subsolar magnetopause reconnection occurs in long, thin Sweet-Parker current sheets via a flux pileup mechanism [Sonnerup and Priest, 1975;Priest and Forbes, 1986] (rather than in Petschek slow shock configurations). Magnetic energy piles up upstream of the magnetopause current sheet to accommodate the sub-Alfvénic solar wind inflow. The scaling of the pileup with Lundquist number, S, is consistent (approximately / S 1/4 ) with that predicted by the analytical, incompressible stagnation point flow solutions (though there are small corrections due to plasma compressibility in the simulations). Since there is a finite energy in the magnetosheath available to drive the magnetic pileup (and associated rapid magnetic reconnection), we expect the pileup to saturate and the reconnection rate to drop as the upstream plasma pressure drops to accommodate the pileup. Thus we expect the reconnection to stall, the rate vanishing in the limit S ! 1. We discuss the role of Hall electric fields in allowing the magnetic pileup to saturate before the reconnection begins to stall, permitting Alfvénic reconnection to occur in thin current sheets in the limit S ! 1.

Magnetopause reconnection across wide local time

“…Crooker, 1979;Crooker et al, 1998) and those which occur for a range of shear angles across the magnetopause (component reconnection, e.g. Sonnerup, 1970;Cowley, 1973Cowley, , 1974aCowley, , b, 1976Gonzalez and Mozer, 1974;Dorelli et al, 2004;Hesse and Schindler, 1988;Craig and Henton, 1995), since the role of a guide field in MR is important in controlling the onset and rate of the reconnection process. Antiparallel sites depend on IMF orientation.…”

Magnetopause mapping to the ionosphere for northward IMF

“…Using global MHD simulations, Dorelli et al (2004) supported the Alexeev (1986) result (B n ∼R −1/4 m ), which was obtained analytically, both for a simpler kinetic approach and for the parabolic magnetopause shape. Dorelli et al (2004) demonstrated that if the plasma resistivity is spatially uniform, magnetic reconnection occurs in the thin current sheet at a rate which is consistent with that predicted by the analytical, incompressible flow solutions (though there are small corrections in simulations due to the plasma compressibility). Let us demonstrate the IMF draping of the solar wind flow past the magnetosphere for high conductivity of the solar wind plasma.…”

“…The solution inside the magnetosphere, found by Alexeev (1986), is a spatially uniform magnetic field penetrated into the magnetosphere, given by B n ∼R −1/4 m . Dorelli et al (2004) also demonstrated that the annihilation rate scales, for instance, like R −1/4 m for magnetic reconnection at the terrestrial subsolar magnetopause. Using global MHD simulations, Dorelli et al (2004) supported the Alexeev (1986) result (B n ∼R −1/4 m ), which was obtained analytically, both for a simpler kinetic approach and for the parabolic magnetopause shape.…”

“…Dorelli et al (2004) also demonstrated that the annihilation rate scales, for instance, like R −1/4 m for magnetic reconnection at the terrestrial subsolar magnetopause. Using global MHD simulations, Dorelli et al (2004) supported the Alexeev (1986) result (B n ∼R −1/4 m ), which was obtained analytically, both for a simpler kinetic approach and for the parabolic magnetopause shape. Dorelli et al (2004) demonstrated that if the plasma resistivity is spatially uniform, magnetic reconnection occurs in the thin current sheet at a rate which is consistent with that predicted by the analytical, incompressible flow solutions (though there are small corrections in simulations due to the plasma compressibility).…”

Flux pile-up and plasma depletion at the high latitude dayside magnetopause during southward interplanetary magnetic field: a cluster event study

“…They also present evidence for PDL formation tailward of the cusp during conditions with a very strong southward IMF (B z <−20 nT ) and large dipole tilt. From a theoretical point of view, the physics governing reconnection at the Earth's subsolar magnetopause is still far from well understood, including the role of magnetic flux pileup in sustaining fast, driven magnetic reconnection (Dorelli et al, 2004).…”