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Ultra‐slow tails of sprite‐associated lightning flashes
Author(s) -
Füllekrug Martin,
FraserSmith Antony C.,
Reising Steven C.
Publication year - 1998
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/98gl02590
Subject(s) - sprite (computer graphics) , physics , amplitude , polarization (electrochemistry) , ionosphere , very low frequency , magnetic field , geophysics , computational physics , optics , astronomy , chemistry , quantum mechanics , computer science , computer vision
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.