General family of nonuniform reconnection models with separatrix jets

Details General family of nonuniform reconnection models with separatrix jets General family of nonuniform reconnection models with separatrix jets

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994gapfd..74..245s&link_type=abstract

Geophysical and Astrophysical Fluid Dynamics (ISSN 0309-1929), vol. 74, no. 1-4, p. 245-273

Astronomy and Astrophysics

Astrophysics

12

Magnetic Effects, Magnetic Field Reconnection, Magnetohydrodynamic Flow, Magnetohydrodynamic Waves, Mathematical Models, Pressure Effects, Astrophysics, Fluid Flow, Magnetohydrodynamics, Plasma Jets, Reynolds Number

Scientific paper

The Nonuniform Magnetic Reconnection model presented by Priest and Lee (1990) was the first to incorporate several features observed in previous numerical models, in particular the highly curved field in the inflow region, which relaxes one of the key assumptions of the classical Almost-Uniform reconnection model of Petschek (1964). Also present is a strong jet of plasma emerging from the reconnection region along the separatrix and a negative current spike at the outflow from the central diffusion region. In this paper we present a generalization of the Priest-Lee model to include pressure gradients in the inflow region, so relaxing the other main assumption of the Petschek and Priest-Lee models, namely that the inflow is current-free or potential. This produces several reconnection regimes similar to those described by Priest and Forbes (1986) in their Unified Almost-Uniform solutions, where significant pressure gradients are included, but their inflow, like Petschek's, is almost-uniform with slightly curved field lines. We investigate the behaviour of the inflow magnetic field without linearizing about a uniform field. We study both a shockless, incompressible outflow and one containing weak shocks, where the type of reconnection is dictated by both the inflow and outflow boundary conditions. In order to introduce a pressure gradient into the Priest-Lee model an extra non-potential field in the x-direction is added. This field has a uniform current and does not alter the Y-point nature of the neutral points at the ends of the diffusion region but does alter the position of the separatrix, where the flow becomes singular, and hence the position of the Alfvenic discontinuity and the strength of the plasma jet. The maximum reconnection rate given by the model scales as (1 + c)(exp 3/2)R(sub me)(exp -1/2), where the parameter c is a measure of the current and is such that c greater than 0 gives fast- or slow-mode expansions and c less than 0 gives slow-mode compressions. These regimes are also found in the Unified Almost-Uniform model. Fast reconnection with a reconnection rate in excess of the pure Sweet-Parker scaling is therefore possible in the flux pile-up regimes with c greater than 0. For a given large magnetic Reynolds number, a fast reconnection rate of, say, 0.1 times the Alfven speed is possible provided c is large enough (e.g. c greater than 10 for R(sub me) = 10(exp 5)).

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