Dynamics of the ring current during severe magnetic storms 

Y. Ebihara and M.-C. Fok 


During severe magnetic storms, the strong ring current extensively modifies the
electromagnetic and particle environment. The strong ring current, which can be
driven by the convection electric field, alters the local magnetic field and
generates the Region 2 type field-aligned currents. To remove the space charge
deposited by the field-aligned current, Pedersen currents are established in the
ionosphere. As a consequence, the convection electric field is significantly
distorted during the severe magnetic storms. Post-midnight enhancements of
tens-of-keV ion flux as seen by IMAGE/HENA during large magnetic storms can be
explained by the distortion of the convection distribution on the morningside. On 20
November 2003, an intensive storm took place with Dst reaching -472 nT. Data from the
polar orbiting NOAA satellite shows that the ion flux with an energy range of 30-80
keV started decreasing immediately after the commencement of the recovery phase. This
rapid decay cannot be attributed to the usual charge exchange with neutral hydrogen.
Denser neutral hydrogen normal or stronger pitch angle diffusion taking place
globally is necessary to explain the rapid loss. Better models of neutral hydrogen
and pitch-angle diffusion will confirm the hypothesis. The inflation of the magnetic
field due to the enhanced ring current also has important effects on storm dynamics.
Simulated ENA images agree better with the IMAGE/HENA observation when we introduce
the inflated magnetic field model. However, the magnetic field model used in the
simulation is not self-consistently coupled with the ring current. In the future, a
realistic and self-consistent magnetic field, in which the force balance is
completely satisfied, is necessary for better understanding of the electromagnetic
coupling of the inner magnetosphere and the subauroral region.

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European Geosciences Union General Assembly, Vienna, Austria, 2-7 April 2006