Comparison of force-free flux rope models with observations of magnetic clouds

Recently, we have found a force-free solution inside an elliptic cylinder for magnetic cloud models. For a diminishing oblateness, the solution tends to the widely used Lundquist constant-alpha force-free solution inside a circular cylinder. The solution may include effects of a flux rope expansion. A comparison of this new solution and the Lundquist solution with magnetic cloud observations is done for magnetic clouds with flat magnetic field magnitude profiles. In such cases, oblateness improves fits of magnetic field magnitude profiles in clouds significantly.