SIMULATION OF MAGNETIC CLOUD PROPAGATION IN THE INNER HELIOSPHERE IN 2-DIMENSIONS .1. A LOOP PERPENDICULAR TO THE ECLIPTIC-PLANE

We present results of simulations of a magnetic cloud's evolution during its passage from the solar vicinity (18 solar radii) to approximately 1 AU using a two-dimensional MHD code. The cloud is a cylinder perpendicular to the ecliptic plane. The external flow is explicitly considered self-consistently. Our results show that the magnetic cloud retains its basic topology up to 1 AU, although it is distorted due to radially expanding solar wind and magnetic field lines bending. The magnetic cloud expands, faster near the Sun, and faster in the azimuthal direction than in the radial one; its extent is approximately 1.5-2x larger in the azimuthal direction. Magnetic clouds reach approximately the same asymptotic propagation velocity (higher than the background solar wind velocity) despite our assumptions of various initial conditions for their release. Recorded time profiles of the magnetic field magnitude, velocity, and temperature at one point, which would be measured by a hypothetical spacecraft, are qualitatively in agreement with observed profiles. The simulations qualitatively confirm the behavior of magnetic clouds derived from some observations, so they support the interpretations of some magnetic cloud phenomena as magnetically closed regions in the solar wind.