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| Titel |
Mesospheric electron detachment and LORE recovery times |
| VerfasserIn |
Francisco J. Gordillo-Vázquez, Christos Haldoupis, Alejandro Luque |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250110467
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| Publikation (Nr.) |
 EGU/EGU2015-10465.pdf |
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| Zusammenfassung |
| We present new results concerning the recovery times (> 10 minutes) of LOng Recovery
Early VLF events (LORE) in the upper mesosphere connected to electromagnetic pulses
(EMP) of large (> 250 kA km) charge moment change (CMC) ± CG (cloud to ground)
lightning capable of producing elves or elve-sprite pairs (in the case of +CG parent
lightning) [1], [2]. We have modeled two possible scenarios considering first the
relaxation of slightly perturbed ambient electron densities (ne0 + δne) without
an impulsive ionization source and another scenario where the ambient electron
density is considerably enhanced due to an impulsive ionization source (the lightning
EMP).
The full non-equilibrium kinetic and 2D EMP modelling of the perturbed mesosphere in
the 76 km - 92 km range during LORE occurring conditions indicates that the electron
density relaxation time (defined as the time the perturbed electron density, δne, takes to
decay a factor 1/e of the way to the ambient electron density (ne0)) is critically controlled
at each altitude by the relative importance of associative detachment (of O- by,
respectively, O and CO and of O2- by O) with respect to electron loss mechanisms
(mainly 3-body, 2-body attachment and electron-ion recombination at the highest
altitudes).
We found that the maximum electron density relaxation time (> 15000 s) occur
between 80 km and 82 km while it decreases with increasing altitudes to 12000 s
(at 85 km) and about 2000 s (at 92 km). However, LORES are presumably due to
VLF scattering from electron density enhancements caused by lightning-induced
EMPs in the uppermost D region ionosphere (85 - 92 km). Thus the observed VLF
signal recoveries (LORE recovery times) should associate with the relaxation of the
maximum enhanced electron densities produced by elves between 85 km and 92 km
[3].
Finally, our results for the lowest altitudes considered (76 km and 77 km) are in good
agreement with the recovery times (between 20 s and 120 s) of the typical early VLF events
associated to sprites [4], [5].
[1] Haldoupis, C., M. Cohen, E. Arnone, B. Cotts, and S. Dietrich (2013), Step-like and
long-recovery early VLF perturbations caused by EM pulses radiated by powerful ± CG
lightning discharges, J. Geophys. Res., 118, doi: 10.1002/jgra-50489.
[2] Salut, M.M., M. B. Cohen, M. A. M. Ali, K. L. Graf, B. R. T. Cotts and S. Kumar
(2013), On the relationship between lightning peak current and early VLF perturbations, J.
Geophys. Res. Space Physics, 118, doi: 10.1002/2013JA019087
[3] Inan, U. S., and W. A. Sampson (1996), Space-time structure of optical
flashes and ionization changes produced by lighting-EMP, Geophys. Res. Lett., 23, 2,
133-136.
[4] Mika, A., and C. Haldoupis (2008), VLF studies during TLE observations in Europe:
A summary of new findings, Space Sci. Rev., 137, 489-510, doi: 10.1007/s11214008-9382-8.
[5] Inan, U. S., S. A. Cummer, and R. A. Marshall (2010), A survey of ELF/VLF research
of lightning-ionosphere interactions and causative discharges, J. Geophys. Res., 115,
A00E36, doi: 10.1029/2009JA014775. |
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