Periodic black auroral patches at the dawnside dipolarization front during a substorm

Periodic black auroral patches were observed in the Canadian postmidnight sector by ground‐based all‐sky cameras during an auroral substorm. The aurora consisted of several black patches of ∼50 km (∼1° in longitude) scales that appeared along the equatorward edges of the proton auroras over a 3 h local time segment from Gillam to Sanikiluaq ground stations 15 min after the auroral intensification occurred in Alaska. To the best of our …