The draping of heliospheric magnetic fields upstream of coronal mass ejecta

The propagation of a fast coronal mass ejection through the interplanetary medium results in compression and draping of existing heliospheric magnetic fields, forming an upstream sheath. Such sheaths are a common context for planar magnetic structures, where the magnetic field is ordered into laminar sheets. A technique is presented to estimate the location of spacecraft with respect to the large‐scale structure of ejecta which they encounter. The technique employs the characteristics of sheath planar magnetic structures, assuming that they are formed by field‐line draping. The technique's results for four magnetic clouds encountered by the Ulysses spacecraft are compared to those of a flux rope model. Very good agreement is found, suggesting that this is a promising technique for estimating an ejection's location from single‐spacecraft data.