Magnetic flux annihilation and the development of magnetic field depletions in the sectored heliosheath

Abstract:

The dynamics of magnetic reconnection in the sectored heliosheath is
explored with the goal of identifying signatures that can be compared
with Voyager observations. Simulations now include much more realistic
initial conditions, including unequal magnetic fluxes in adjacent
sectors and very high β. Large numbers of small magnetic islands
form early but rapidly coalesce to sector-size structures. The
late-time magnetic structure of the sector zone differs greatly from
that obtained in earlier simulations. Bands of unreconnected azimuthal
magnetic flux thread through the simulation domain separating regions
of depleted magnetic field strength. The depletion regions have radial
scale sizes somewhat greater than the initial sector width. The
boundaries of the magnetic depletions are sharp and reveal little
change in the direction of B. The characteristic minima of the
depletions are one third of the initial magnetic field strength. At
late time surviving magnetic islands are widely spaced and occur in
pairs. Cuts across the domain in the radial direction reveal mostly
unipolar flux except when a cut crosses one of the remnant magnetic
islands. This unusual late time magnetic structure is generic result
of reconnection in a high β system. The magnetic depletions
exhibit many of the properties of ``proton boundary layers'' seen in
the Voyager 1 magnetic field data. The simulations suggest that significant flux loss should take place in the heliosheath, which is consistent with Voyager measurements. The long periods of unipolar flux
seen by Voyager 1 prior to crossing the heliopause likely results from
the annihilation of the sectors rather than an exit from the sector
zone.