Modeling magnetic fields around magnetic clouds of different geometries

In-situ observations show that the maximum strength of the magnetic field draping around a magnetic cloud is of the order of the field inside the cloud. We investigate theoretically how this strength depends on geometrical parameters of magnetically closed bodies like cylinders, spheroids, or toroids. These bodies are inserted into an initially homogeneous ambient magnetic field and then a distortion of the external field is calculated under the assumption that the normal field component vanishes at the boundary of the body. If the external field is supposed to be potential, then the maximum increase in the magnetic field magnitude is around 2 times. Non-potential fields yield larger maxima and such increases may explain a trigger of a strong geomagnetic storm only by the B, component of the draped field, even if there is no strong B, component inside the cloud.