Asymmetric field aligned currents into the conjugate hemispheres

Abstract:

From simultaneous conjugate auroral imaging we have learned that when IMF has a By component, the auroral features in the two hemispheres will not be at the nominal conjugate foot points. The displacement of foot points are strongly correlated to the IMF By or clock angle, which implies that there is a By component on the closed field line as well. From modeling efforts we have learned that the By component in the closed magnetosphere is not a result of IMF By ´penetration´ but is induced by the asymmetric pressure in the lobes when the IMF has a By component.
This magnetic stress associated with the the induced By component will be released asymmetrically into the conjugate ionospheres and give rise to asymmetric Alfven aurora and currents consistent with the different convection patterns.
Some studies indicate that it will take an hour or more to induce this By component and consequently asymmetric foot points. Our own investigations based on auroral imaging and modeling indicate that this is established after 10-20 minutes.

Auroral imaging of the two hemispheres has also shown that there is a statistical significant brightness difference in the dusk side polar aurora correlated with an IMF Bx component. We have interpreted this difference in terms of a difference in solar wind dynamo in the two hemispheres. Although this effect is weak, the accumulated effect might be significant.