MHD Models of the Ambient Solar Wind Constrained by the Wang-Sheeley-Arge and Fisk Models

The ambient solar wind controls the propagation properties of Coronal Mass Ejections (CMEs) in the interplanetary space. It is therefore crucial to resemble realistic ambient conditions in the solar corona and inner heliosphere when modeling a space weather event from the Sun to the Earth. Traditionally, the solar wind acceleration is treated in global MHD models through (1) empirical source terms, (2) the WKB approximation of Alfven turbulence, or (3) by using a non-uniform polytropic index distribution. Here, we adopt the latter approach to drive the solar corona and the inner heliosphere modules of the Space Weather Modeling Framework (SWMF). Assuming the Bernoulli integral conservation along a magnetic field line, the value of the polytropic index at the base of the corona can be related to the asymptotic value of the solar wind speed at large distances form the Sun. This allows us to prescribe the distribution of the polytropic index as a function of the ultimate solar wind speed and the radial distance from the Sun. In our model, we calculate the self- consistent MHD steady-state solution using the polytropic index distribution in the energy equation. The input for the final solar wind speed is obtained by employing either the empirical Wang-Sheeley-Arge (WSA) model, or the physics-based Fisk model (i.e., by calculating the Pointing flux at the base of the corona). We present results of the obtained steady-state solutions, and we compare the two solar wind inputs.