Hemispheric Asymmetries in the Dayside Aurora

M.O. Fillingim, M. Spasojevic, G.K. Parks, T.J. Immel, and S.B. Mende University
of California, Berkeley, Space Sciences Laboratory, Berkeley, CA


Using global auroral images from Polar UVI in the southern hemisphere and IMAGE
FUV in the north, we have analyzed the asymmetries in the dayside aurora for a
five-month period. The observed asymmetries were related to the interplanetary
magnetic field (IMF). Initial results suggest that the direction of the IMF
plays a major role in influencing the asymmetrical behavior of the dayside
aurora. When the IMF is southward and a significant dawnward component exists,
there is  an enhancement in the afternoon aurora in the northern hemisphere. If
there is a significant duskward component to the IMF,  then an enhancement in
the afternoon aurora in the southern hemisphere is observed. Additionally, when
the ratio of the magnitudes of the Y and Z components of the IMF are greater
than about 2, distinct structure (i.e., a string of pearls configuration) is
seen in the hemisphere with enhanced emission. These results are in general
agreement with models and observations of the IMF influence on ionospheric
convection. A strong Y component of the IMF can lead to a strong shear flow  at
the dayside convection reversal boundary. Strong flow shear can lead to strong
field aligned currents (i.e., elelctron precipitation for upward current) in
this same region. If the flow shear exceeds some threshold, an instability
(e.g., a Kelvin-Helmholtz instability) can develop leading to discrete
structures.

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