Auroral conjugacy studies based on global imaging

Simultaneous global 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 and 1 min for IMAGE-FUV and Polar VIS Earth camera, respectively, we have examined dynamic features such as substorm onsets and cusp precipitation as well as slowly varying phenomena such as theta aurora. In this paper, we review the main findings from these studies and present new evidence of the IMF clock angle control of the asymmetric substorm onset locations. Simultaneous images from the opposite hemispheres show asymmetric cusp auroras and their locations are controlled by IMF ByBy and dipole tilt angle. Our imaging results demonstrate that theta aurora can be a non-conjugate phenomenon. We suggest that IMF BxBx controls in which hemisphere the theta aurora occurs. For substorm onset locations, we have found that there exists a systematic 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. Statistical distribution of substorm onset locations in the southern and northern hemispheres for different clock angles enables us to validate the IMF clock angle control. Based on ∼3000∼3000 substorm onsets in the northern hemisphere and ∼1000∼1000 in the southern hemisphere observed by IMAGE we find a remarkable support for our previous findings.