Auroral Conjugacy Studies

N. Ostgaard, S.B. Mende, H.U. Frey, and J.B. Sigwarth


Simultaneous imaging in the ultraviolet wavelengths by IMAGE and Polar, enable
us to examine auroral features in the conjugate hemispheres.  With an imaging
cadence of 2 min and 1 min for IMAGE/FUV and Polar VIS Earth camera,
respectively, we have examined both dynamic features as substorm onsets and cusp
precipitation as well as slowly varying phenomena as theta aurora. For substorm
onset locations, we have found that there exists a systematically displacement
in one hemisphere compared to the other. The relative displacement of onset
locations in the conjugate hemispheres is found to be controlled primarily by
the IMF clock-angle.  Compared with some of the existing magnetic field models,
the observed asymmetries are an order of magnitude larger than the model
predictions.  Two short periods where the cusp aurora associated with high
latitude lobe reconnection was imaged simultaneously in the conjugate
hemispheres.

These very rare images were taken during strongly northward IMF and high solar
wind pressure where both the proton and electron Aurora are fairly bright. The
longitudinal and latitudinal displacement of the cusp aurora in the conjugate
hemispheres are found to be controlled by IMF clock-angle and dipole tilt angle,
respectively. This study also confirms our earlier findings that transpolar arcs
during northward IMF can exist in one hemisphere but not in the other. We have
attributed this to the sign of the IMF Bx component, which controls in which
hemisphere lobe reconnection is most efficient.

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Global Aspects of Magnetosphere-Ionosphere Coupling, 2006 Yosemite Workshop, 
Yosemite National Park, CA, USA, 7-10 February 2006