Potential Flow Formulation of Parker's Unsteady Solar Wind Model and Nonlinear Stability Aspects Near the Parker Sonic Critical Point

The purpose of this paper is to present the first ever systematic theoretical formulation to address the long-standing issue of regularization of the singularity associated with the Parker sonic critical point in the linear perturbation problem for Parker's unsteady solar wind model. This is predicated on the necessity to go outside the framework of the linear perturbation problem and incorporate the dominant nonlinearities in this dynamical system. For this purpose, a whole new theoretical formulation of Parker's unsteady solar wind model based on the potential flow theory in ideal gas dynamics is given, which provides an appropriate optimal theoretical framework to accomplish this task. The stability of Parker's steady solar wind solution is shown to extend also to the neighborhood of the Parker sonic critical point by going to the concomitant nonlinear problem.