The four Cluster spacecraft showed that black aurorae are a kind of 'anti-aurora'
Measurements by the Cluster spacecraft confirmed that black aurorae, strange electrical phenomenon that generate dark, empty regions adjacent to the Northern and Southern Lights, are a kind of 'anti-aurora'.
The data showed that black aurorae represent holes in the ionosphere. Here, negatively charged electrons are being accelerated upwards into space inside regions known as positively charged electric potential structures.
This is the opposite process to that which creates visible aurorae, where electrons spiral down from space into the atmosphere within similar, negatively charged, structures.