High conductivity magnetic tearing instability

The field-reconnection instability of a magnetic neutral sheet is studied using magnetohydrodynamic theory, including the electron-inertia term in Ohm's law. The behavior is described for the full range of the Coulomb-resistivity vs collisionless skin-depth parameter zeta=1020/sup ./3B T1/sup ./5/lnΛ) a2/sup ./5 n2/sup ./3 (cgs), describing the field reversal. Such long-wavelength tearing can occur over a wide span of physical conditions from those of solar active regions (zetavery-much-less-than1) to those in the geomagnetic tail (zetavery-much-greater-than1). In particular, the growth rate of the infinite-conductivity instability may be expressed as ωapprox. =1020/sup ./9B/a2/sup ./5n1/sup ./3, for a hydrogen plasma. In this limit, the time scale of auroral development is found to be 103/sup ./2 sec, a value close to that observed. The regime of applicability of this formulation is also discussed, and the results are compared with those obtained by other methods, including the Vlasov equation