Several theoretical models and in situ observations consistently suggest that the process of nightside reconnection associated with Earth's magnetospheric substorms is also taking place in the midnight tail region of Jupiter. We report the observation of a new auroral feature which takes the form of isolated spots appearing near the northern dusk-midnight limb, poleward of the main auroral oval. This feature was clearly detected in three HST-STIS data sets obtained on 14, 16, and 18 December 2000. Its position poleward of the main auroral oval, and lagging corotation, shows that it is magnetically connected to a distant region of the nightside magnetosphere. It is therefore suggested that these transient spots are the auroral signatures of reconnection processes occurring in the nightside tail of the distant Jovian magnetosphere. The cause of this reconnection is somewhat analogous to the case of a solar coronal mass ejection, so one may refer to it as a Jovian mass ejection.