Abstract Using a 2.5-dimensional ideal MHD model in Cartesian coordinates, we investigate the equilibrium properties of coronal magnetic flux ropes in background magnetic fields that are completely closed. The background fields are produced by a dipole, a quadrupole, and an octapole, respectively, located below the photosphere at the same depth. A magnetic flux rope is then launched from below the photosphere, and its magnetic properties, i.e., the annular magnetic flux &Phi_p; and the axial magnetic flux &Phi_z;, are controlled by a single emergence parameter. The whole system eventually evolves into equilibrium, and the resultant flux rope is characterized by three geometrical parameters: the height of the rope axis, the half-width of the rope, and the length of the vertical current sheet below the rope. It is found that the geometrical parameters increase monotonically and continuously with increasing &Phi_p; and &Phi_z;: no catastrophe occurs. Moreover, there exists a steep segment in the profiles of the geometrical parameters versus either &Phi_p; or &Phi_z;, and the faster the background field decays with height, the larger both the gradient and the growth amplitude within the steep segment will be.
Keywords Sun: magnetic fields --- Sun: corona
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