The size of the auroral belt during magnetic storms

Using the auroral boundary index derived from DMSP electron precipitation data and the <i>Dst</i> index, changes in the size of the auroral belt during magnetic storms are studied. It is found that the equatorward boundary of the belt at midnight expands equatorward, reaching its low...

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Bibliographic Details
Main Authors: N. Yokoyama, Y. Kamide, H. Miyaoka
Format: Article
Language:English
Published: Copernicus Publications 1998-05-01
Series:Annales Geophysicae
Online Access:https://www.ann-geophys.net/16/566/1998/angeo-16-566-1998.pdf
Description
Summary:Using the auroral boundary index derived from DMSP electron precipitation data and the <i>Dst</i> index, changes in the size of the auroral belt during magnetic storms are studied. It is found that the equatorward boundary of the belt at midnight expands equatorward, reaching its lowest latitude about one hour before <i>Dst</i> peaks. This time lag depends very little on storm intensity. It is also shown that during magnetic storms, the energy of the ring current quantified with <i>Dst</i> increases in proportion to <i>L<sub>e</sub></i><sup>–3</sup>, where <i>L<sub>e</sub></i> is the <i>L</i>-value corresponding to the equatorward boundary of the auroral belt designated by the auroral boundary index. This means that the ring current energy is proportional to the ion energy obtained from the earthward shift of the plasma sheet under the conservation of the first adiabatic invariant. The ring current energy is also proportional to <i>E<sub>mag</sub></i>, the total magnetic field energy contained in the spherical shell bounded by <i>L<sub>e</sub></i> and <i>L<sub>eq</sub></i>, where <i>L<sub>eq</sub></i> corresponds to the quiet-time location of the auroral precipitation boundary. The ratio of the ring current energy <i>E<sub>R</sub></i> to the dipole energy <i>E<sub>mag</sub></i> is typically 10%. The ring current leads to magnetosphere inflation as a result of an increase in the equivalent dipole moment.<br><br><b>Key words.</b> Ionosphere (Auroral ionosphere) · Magnetospheric physics (Auroral phenomena; storms and substorms)</p>
ISSN:0992-7689
1432-0576