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 duri ng its passage from the solar vicinity (18 solar radii) to approximate ly 1 AU using a two-dimensional MHD code. The cloud is a cylinder perp endicular to the ecliptic plane. The external flow is explicitly consi dered self-consistently. Our results show that the magnetic cloud reta ins its basic topology up to 1 AU, although it is distorted due to rad ially expanding solar wind and magnetic field lines bending. The magne tic cloud expands, faster near the Sun, and faster in the azimuthal di rection than in the radial one; its extent is approximately 1.5-2x lar ger in the azimuthal direction. Magnetic clouds reach approximately th e same asymptotic propagation velocity (higher than the background sol ar wind velocity) despite our assumptions of various initial condition s for their release. Recorded time profiles of the magnetic field magn itude, velocity, and temperature at one point, which would be measured by a hypothetical spacecraft, are qualitatively in agreement with obs erved profiles. The simulations qualitatively confirm the behavior of magnetic clouds derived from some observations, so they support the in terpretations of some magnetic cloud phenomena as magnetically closed regions in the solar wind.