Multipoint spacecraft observations of a magnetic cloud on 22 May 2007 have given us the opportunity to apply a multispacecraft technique to infer the structure of this large‐scale magnetic flux rope in the solar wind. Combining WIND and STEREO‐B magnetic field and plasma measurements, we construct a combined magnetic field map by integrating the Grad‐Shafranov equation, this being one of the very first applications of this technique in the interplanetary context. From this we obtain robust results on the shape of the cross section, the orientation and magnetic fluxes of the cloud. The only slightly “flattened” shape is discussed with respect to its heliospheric environment and theoretical expectations. We also relate these results to observations of the solar source region and its associated two‐ribbon flare on 19 May 2007, using Hα images from the Kanzelhöhe observatory, SOHO/MDI magnetograms and SECCHI/EUVI 171 Å images. We find a close correspondence between the magnetic flux reconnected in the flare and the poloidal flux of the magnetic cloud. The axial flux of the cloud agrees with the prediction of a recent 3‐D finite sheared arcade model to within a factor of 2, which is evidence for formation of at least half of the magnetic flux of the ejected flux rope during the eruption. We outline the relevance of this result to models of coronal mass ejection initiation, and find that to explain the solar and interplanetary observations elements from sheared arcade as well as erupting‐flux‐rope models are needed.
