Earthward Flowing Plasmoid: Structure and Its Related Auroral Signature

Fritz, T., Zong, Q., Baker, D., Goldstein, M., Daly, P., Fu, S., Frey, H., 
Balogh, A., Reme, H.


An earthward-moving plasmoid on Oct. 28, 2002 has been observed by the Cluster
spacecraft with simultaneous auroral viewing by IMAGE satellite. This offers the
opportunity to ascertain the optical signature and its evolution in the
ionosphere of an earthward moving plasmoid for the first time. The intensity of
the current in the center of the plasmoid is found to be weaker than that in the
adjacent region. Also, the directions of the current in the central part of the
plasmoid are different from the background cross-tail current: they are more
field-aligned. The calculation of ${\bf J} × {\bf B}$ demonstrates that the
plasmoid is not a highly force-free structure. The unusually large bipolar
electric field found in the plasmoid (peak to peak values 6 and 8 mV/m) can be
explained as a dawn-dusk polarization electric field is generated to enhance the
flows as predicted in the bubble model. Broad-band electrostatic noise (BEN) and
bursty electrostatic electron cyclotron waves are found inside the plasmoid
which are closely associated with the acceleration of the plasma. Furthermore,
IMAGE data show the auroral forms moving to lower latitude, which is when an
earthward moving plasmoid observed by the Cluster spacecraft. Such an
equatorward auroral motion is consistent well with the observed earthward moving
plasmoid.

_______________
Fall Meeting, American Geophysical Union, San Francisco, U.S.A., 
5-9 December 2005