Hemispheric asymmetry of the afternoon electron aurora

Using ultraviolet images from two global auroral imagers, IMAGE FUV in the northern hemisphere and Polar UVI in the south, we present the first synoptic scale conjugate observations of the dayside aurora. We find that the morphology of the afternoon aurora is significantly different in the two hemispheres. Multiple spots in a “string of pearls” configuration are seen in the southern hemisphere while the northern aurora is unstructured. We relate the observed asymmetry in the aurora to the Y GSM component of the IMF: a strong IMF BY modifies the ionospheric convection and field aligned current patterns, leading to the auroral asymmetry. Additionally, we suggest that the instability giving rise to the multiple spot morphology occurs at low altitude.