Substorms, tail flows and plasmoids

Abstract

The GEOTAIL spacecraft has made comprehensive magnetic field and plasma observations in the Earth's magnetotail at radial distances of 10–210 Re. Data from the GEOTAIL spacecraft have led to the following conclusions regarding the relationship between substorms and field and plasma behaviors. Substorms produce systematic and repeatable signatures in magnetic field and plasmas in various radial distances in the magnetotail. A repeatable signature for substorms is tailward plasma flows with a southward magnetic field structure. These are often associated with plasmoids, as seen in the local magnetic field variations. Examples are presented of signatures seen at different distances from the Earth. From a statistical survey of the data, it is shown that magnetic reconnection takes place in the expansion phase at radial distances of 20–30 Re. Plasmoids are created there and travel tailward at high speeds. Earthward flows in the recovery phase appear only inside 100 Re. Plasmoids are dominant substorm signatures beyond 100 Re.