The Connection Between Transpolar Arcs and the Recovery Phase of Substorms

C.R. Bryant, J.S. Murphree, and S.B. Mende


Contrasting the well observed and much discussed growth and expansion phases,
the recovery phase has received much less attention and little is known about
it. Conventional wisdom says that the recovery phase is the relaxation of the
magnetosphere back to a quiet auroral configuration. Optically, the recovery
phase appears to start when the auroral bulge stops moving poleward but
observations indicate that the recovery phase has considerable activity.
Measurements have established the basic relationships between auroral recovery
phase features and magnetotail regimes such as the double oval phenomenon.
Observations obtained using the FUV instruments on the IMAGE satellite show that
transpolar arcs (TPA's) are often associated  with the recovery phase of
substorms. These TPA's are controlled by the interplanetary magnetic field
(IMF), in particular the By component. Examples of recovery phases emphasizing
the timing of the TPA's compared to onset and the TPA's relationship to the IMF
will be the focus of this presentation.

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Presentation, Fall A.G.U. Meeting, San Francisco, CA, 13-17 December 2004