The three-dimensional structure of 'loop-like' coronal mass ejections

Measurements of the brightness and latitudinal extent of the depleted (cavity) region behind the leading edge of three coronal mass ejection (CME) events from the Skylab epoch are reported. The preevent coronal brightness was matched by a model corona, assuming both a background contribution and a contribution from a range of hypothetical streamer models, distinguished by differing longitudinal extent. Under the assumption that the cavities are voided regions in which the local electron density is negligible, their minimum line-of-sight extent is estimated and found to be comparable to, or greater than, their measured latitudinal extent. This is suggested to unambiguously demonstrate the 3D nature of these events.