MHD Modelling of Space Weather Drivers

Abstract

The heliolatitudinal dependence of the solar wind quantities is discussed by comparing observations with analytical and numerical modelling. First, an analytical MHD model is outlined which is obtained via a non-linear separation of the variables in the governing full set of the steady MHD equations describing the axisymmetric helicoidal magnetized outflow of the solar wind. This analysis yields three parameters, which measure the anisotropy in the latitudinal distribution of various flow quantities. The parameters are estimated by comparing observations by SoHO/CDS and Ulysses to the analytical solution. The solution is also checked by means of a numerical solution of the full, time dependent MHD equations which yields a steady state and in which the out-flow slightly deviates from radiality at large distances from the Sun. The calculated proton flux is compared with SOHO Lyman α observations and it is analytically explained why the proton flux of the solar wind decreases with in-creasing latitude, despite magnetic focusing which would favour the opposite trend.