Statistics and variability of the altitude of elves. Issue 10 (23rd May 2016) - van der Velde, Oscar A.
Abstract: From June 2008 to January 2016 nearly 800 elves have been recorded by a low‐light camera in northeastern Spain. Elves occur in this region mainly over the lower topped cold air mass maritime thunderstorms, peaking from November to January. Cloud‐to‐ground strokes still produce elves when maritime winter storms are carried inland, suggesting that the cold season thunderstorm charge configuration favors strokes with large electromagnetic pulses. Altitudes of 389 elves were determined using optical data combined with a lightning location network. The overall median altitude was 87.1 km, near the typical OH airglow height, but average heights during individual nights ranged between 83 and 93 km. The lower elve nights (~84 km) occurred during slightly elevated geomagnetic conditions ( Kp >3‐, Ap ‐index >10). Elve altitude often shifts by several kilometers during the night, apparently in response to changing background conditions in the upper mesosphere. Key Points: Elves appear mainly November through February over the Bay of Biscay and western Mediterranean Sea Elve altitudes are determined combining optical methods and lightning location Nightly mean elve altitudes vary between 83 and 93 km and also vary over a time scale of hours