Magnetosphere inflation during the recovery phase of geomagnetic storms as an excellent magnetic confinement of killer electrons

Extreme flux enhancement of outer radiation belt electrons was observed at geosynchronous orbit during the recovery phase of a large magnetic storm on 27-30 July 2004. The storm main phase is driven by a very fast magnetic cloud of similar to 1000 km/s associated with a coronal mass ejection (CME). The high-speed stream of similar to 600 km/s originated from a coronal hole follows the magnetic cloud and the coronal hole stream (CHS) is rarefied due to the speed difference between the CME and CHS. During the storm recovery phase, the magnetosphere is surrounded by the very low-density CHS, causing an inflation of the magnetosphere. It is found that such a combination of the CME and CHS can be one of the most dangerous solar wind structures for the outer radiation belt, and the associated very low dynamic pressure can cause the magnetosphere inflation during the storm recovery phase as an excellent magnetic confinement of killer electrons.