Simultaneous IMF reconnection aurorae in the northern and southern hemispheres

New article in Geophysical Research Letters:

During periods of sustained northward interplanetary magnetic field (IMF) movement and high solar wind pressure, the IMF can reconnect with the Earth’s magnetosphere, merging field lines and forming a bright, long-lived, ultraviolet auroral spot, called a cusp aurora. On 18 September 2000, such cusp aurorae were simultaneously viewed for 15 minutes by the Polar and IMAGE satellites in northern and southern hemispheres, respectively.

These rare images gave a unique opportunity to examine the IMF and dipole tilt control of the cusp aurora and theta aurora, the latter of which occurs when the interaction with a northward IMF splits the view of the auroral oval with a transpolar arc, forming an oval that looks like the Greek letter theta. Østgaard et al.used these images to verify their models of the reconnection geometry and predicted spot locations of such aurorae.

As suggested by past studies, they concluded that the longitudinal location of the cusp is controlled by the IMF By field direction, and that the latitudinal shifts was attributed to the effects of the dipole tilt angle. In addition, they found that the theta aurora is consistent with a strong positive IMF Bx, resulting in more efficient reconnection in the southern hemisphere.