Location
Yosemite National Park
Start Date
2-11-2014 7:10 PM
End Date
2-11-2014 7:25 PM
Description
In times when the Y-component of the IMF is dominant, the pull of the magnetic fields cause the polar caps to skew, with one cap shifted towards dusk and the other polar cap shifted towards dawn. A case with two hours of continuous dual-cap auroral imaging provides us with “ground truth” to test the amount of dawn-dusk shift predicted by commonly-used MHD models. With IMAGE/WIC observing in ultraviolet over the Earth’s sunlit northern pole and Polar/VIS over the dark southern pole, the skew is readily observed and mapped to the surface using Apex coordinates. The dawn/dusk offset for this case, measured as the difference of the colatitude of the polar cap boundary at dawn minus that at dusk, is up to ten degrees for this extreme case with By ~ 30nT. Four MHD models have been run through the CCMC at GFSC, using the real time solar wind propagated to the models. Only the LFM model yields a skew which is comparable in size to the that observed in the imaging data. The other models predict skews which are smaller or even of the wrong sense.
Testing MHD Models by Conjugate Aurora Imaging
Yosemite National Park
In times when the Y-component of the IMF is dominant, the pull of the magnetic fields cause the polar caps to skew, with one cap shifted towards dusk and the other polar cap shifted towards dawn. A case with two hours of continuous dual-cap auroral imaging provides us with “ground truth” to test the amount of dawn-dusk shift predicted by commonly-used MHD models. With IMAGE/WIC observing in ultraviolet over the Earth’s sunlit northern pole and Polar/VIS over the dark southern pole, the skew is readily observed and mapped to the surface using Apex coordinates. The dawn/dusk offset for this case, measured as the difference of the colatitude of the polar cap boundary at dawn minus that at dusk, is up to ten degrees for this extreme case with By ~ 30nT. Four MHD models have been run through the CCMC at GFSC, using the real time solar wind propagated to the models. Only the LFM model yields a skew which is comparable in size to the that observed in the imaging data. The other models predict skews which are smaller or even of the wrong sense.