A CLASS OF 3-DIMENSIONAL ISOTHERMAL LAMINATED EQUILIBRIA AND THEIR STABILITY

Three-dimensional ideal magnetostatic equilibria with laminated magnet ic field in which one component of the magnetic field vanishes, are co nstructed for isothermal coronal plasmas in the presence of uniform gr avity. Three subsets of the general solution are found to be absolutel y stable, when subject to rigid anchoring of the magnetic field lines at the base of the atmosphere. The magnetic fields in these cases carr y currents. For equilibria with general magnetic strength variations, the criteria for stability are obtained by minimizing the energy integ ral. Numerical solutions for the Euler-Lagrange equations that result from the minimization procedure are given, and are used to determine c ritical equilibrium parameters that give a bound for the marginal stab ility. For low values of plasma beta(= 8pip/B2), the scale length of t he plasma density variation can be small and the magnetic shear can be large, suggestive of the observed fine plasma loops and the rapid flu ctuation of the inclination angle of the field lines in the sunspot pe numbra.