Ultra-slow tails of sprite-associated lightning flashes
Article first published online: 7 DEC 2012
Copyright 1998 by the American Geophysical Union.
Geophysical Research Letters
Volume 25, Issue 18, pages 3497–3500, 15 September 1998
How to Cite
- Issue published online: 7 DEC 2012
- Article first published online: 7 DEC 2012
- Manuscript Accepted: 21 JUL 1998
- Manuscript Received: 6 MAY 1998
We describe the terrestrial excitation of horizontal magnetic field variations in the Pc1 frequency range (0.2–5.0 Hz) by tropospheric, sprite-associated lightning flashes, measured ∼1900 km west from the source. These variations, which we call ultra-slow tails, exhibit amplitudes on the order of tens of pT, they have a duration of ∼3 seconds, and they occur immediately following the initial pulse of the sprite-associated lightning flash. The ultra-slow tails exhibit two peaks in the frequency domain at 0.67 Hz and 1.67 Hz. The mean polarization ellipses at these two frequencies are oriented ∼45° clockwise from geographic north and exhibit right-hand and left-hand polarization respectively with a weak ellipticity of ∼0.1. The horizontal magnetic intensity of the initial pulse is related to the horizontal magnetic intensity of the ultra-slow tail, in agreement with the interpretation of ultra-slow tails as ionospheric Alfven resonances.