No. 117: May-June 1998
Flash auroras are ephemeral auroral displays lasting only a few seconds. They occur when auroral and geomagnetic activity is subdued worldwide. Under such quiet conditions, scientists do not expect to see auroras of any kind. Yet, experienced aurora observers keep on reporting these transient events.
June 13/14, 1987. Winnipeg, Saskatche wan. T. Lohvinenko saw a fragmentary active rayed arc in a clear sky at 0644 UT. It lasted for only a few seconds.
February 13/14, 1991. Near Glasgow, Scotland. While facing south, A. Simmons observed rays and a luminous patch at an altitude of 45°. The phenomenon lasted 2 minutes.
In both of the above instances, the geomagnetic field was quiet and auroral activity virtually zero worldwide.
"It is unprofitable at this stage to speculate on the cause or causes of the mid-latitude flash aurora as it is known in the Aurora Section. More authenticated observations need to be built up before they can become statistically meaningful. The geomagnetosphere is a very dynamic and restless organism in which some instability may develop to cause what, in engineering parlance, might be referred to as a short circuit in the magnetospheric dynamo."
(Livesey, R.J.; "The Flash Aurora," British Astronomical Association, Journal, 107:36, 1997.)