Solar Wind Control of the Morphology of Earth's Ring Current 

Craig James Pollock (Southwest Research Insitute, San Antonio, TX, 78238)


ENA images from the IMAGE mission have clearly demonstrated that Earth's
storm-time ring current undergoes a transition from an asymmetric configuration
localized to the night side (typical of storm main phase), to a highly symmetric
configuration displaying local time uniformity (typical of the storm recovery
phase). Sometimes multi-dip storms display cyclic behavior, with several
transitions between symmetric and asymmetric ring current states. The asymmetric
state of the ring current during storm main phase is believed to be caused by
strong electric fields that are imposed on to the magnetosphere by the solar
wind, and that cause ring current drift paths to intersect the magnetopause,
accounting for massive ring current loss. The absence of these strong electric
fields allows the ring current to close on itself, forming a symmetric torus
around Earth. We will present global ENA observations of Earth's ring current,
focusing on transitions between the symmetric and non-symmetric states. We will
also present concurrent solar wind observations, and attempt to demonstrate a
causal relationship between transitions in observed in solar wind properties,
and those observed in the state of Earth's ring current.

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Presented at the August 2003 AGU Chapman Conference, Helsinki, Finland