Relationship Between Substorm Auroras and Processes in the Near-Earth Magnetotail |
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Authors: | A G Yahnin I V Despirak A A Lubchich B V Kozelov N P Dmitrieva M A Shukhtina H K Biernat |
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Institution: | (1) Polar Geophysical Institute, Apatity, Russia;(2) Institute of Physics, State University, Sankt-Petersburg, Russia;(3) Space Research Institute, Graz, Austria |
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Abstract: | Although the auroral substorm has been long regarded as a manifestation of the magnetospheric substorm, a direct relation
of active auroras to certain magnetospheric processes is still debatable. To investigate the relationship, we combine the
data of the UV imager onboard the Polar satellite with plasma and magnetic field measurements by the Geotail spacecraft. The
poleward edge of the auroral bulge, as determined from the images obtained at the LHBL passband, is found to be conjugated
with the region where the oppositely directed fast plasma flows observed in the near-Earth plasma sheet during substorms are
generated. We conclude that the auroras forming the bulge are due to the near-Earth reconnection process. This implies that
the magnetic flux through the auroral bulge is equal to the flux dissipated in the magnetotail during the substorm. Comparison
of the magnetic flux through the auroral bulge with the magnetic flux accumulated in the tail lobe during the growth phase
shows that these parameters have the comparable values. This is a clear evidence of the loading–unloading scheme of substorm
development. It is shown that the area of the auroral bulge developing during substorm is proportional to the total (magnetic
plus plasma) pressure decrease in the magnetotail. These findings stress the importance of auroral bulge observations for
monitoring of substorm intensity in terms of the magnetic flux and energy dissipation. |
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Keywords: | auroral substorm magnetotail plasma sheet magnetic reconnection |
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