Fraser-Smith, Antony C., authorFüllekrug, Martin, authorReising, Steven C., authorAmerican Geophysical Union, publisher2007-01-032007-01-031998Füllekrug, Martin, et al., Ultra-Slow Tails of Sprite-Associated Lightning Flashes, Geophysical Research Letters 25, no. 18 (September 15, 1998): 3497-3500.http://hdl.handle.net/10217/68068We 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.born digitalarticleseng©1998 American Geophysical Union.Copyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.Text