Ultra-slow tails of sprite-associated lightning flashes
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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 ...