Abstract
The prominence of nulls in reconnection theory is due to the expected singular current density and the indeterminacy of field lines at a magnetic null. Electron inertia changes the implications of both features. Magnetic field lines are distinguishable only when their distance of closest approach exceeds a distance
$\varDelta _d$
. Electron inertia ensures
$\varDelta _d\gtrsim c/\omega _{pe}$
. The lines that lie within a magnetic flux tube of radius
$\varDelta _d$
at the place where the field strength
$B$
is strongest are fundamentally indistinguishable. If the tube, somewhere along its length, encloses a point where
$B=0$
vanishes, then distinguishable lines come no closer to the null than
$\approx (a^2c/\omega _{pe})^{1/3}$
, where
$a$
is a characteristic spatial scale of the magnetic field. The behaviour of the magnetic field lines in the presence of nulls is studied for a dipole embedded in a spatially constant magnetic field. In addition to the implications of distinguishability, a constraint on the current density at a null is obtained, and the time required for thin current sheets to arise is derived.
Publisher
Cambridge University Press (CUP)
Cited by
3 articles.
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