Ciao, Ivaldo!
presumo che dalle parti di Lugano non abbia temporaleggiato come qui al "sud"...
ricordo anche a te un mio vecchio pallino relativo alla possibilita' di triggeraggio di fulmini (e TLE) da parte di meteore e micrometeore...
rinfresco la memoria anche agli altri con un paio di riferimenti.
Credo che un approfondimento susciterebbe qualche interesse.
> Su relazione Lampi-Meteore (i lampi triggerati da meteore)
> Muller, R.A., Red sprites triggered by meteors?, in EOS Trans., AGU, 76, 1995, p.105. Che
Anche,
CHAPTER IX
INFRASONIC SIGNATURES ASSOCIATED WITH
TRANSIENT ELECTROMAGNETIC EVENTS
(With contributions from Dr. Al Bedard, NOAA/ETL)
http://www.fma-research.com/Sprites99/CHAPTER-IX.pdf
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www.ingentaconnect.com/search/expand?pub=infobike://ap/is/2000/00000148/00000001/art06517&unc=
Meteor Trails and Columniform Sprites
Authors: Symbalisty E.M.D.1; Roussel-Dupré R.A.1; ReVelle D.O.1; Suszcynsky D.M.2; Yukhimuk V.A.3; Taylor M.J.4
Source: Icarus, Volume 148, Number 1, November 2000 , pp. 65-79(15)
Publisher: Academic Press
Abstract:
A theoretical model of columniform sprites (or c-sprites), a distinctive class of high altitude, temporally brief optical emissions, is presented and compared to observations which extends earlier work (1998, E. M. D. Symbalisty, R. Roussel-Dupré, and V. Yukhimuk, EOS Transactions of the AGU 79, No. 45, p. F129) by making a strong connection with meteors. The key features of the model are: (1) an ambient conductivity profile that falls between a measured nighttime and a measured daytime conductivity; (2) an aerosol reduced conductivity in a trail from a meteor that passed through some time during the evening, and (3) a cloud-to-ground (hereafter CG) lightning stroke, with sufficient charge transfer, subsequent to and occurring within an hour of the development of the reduced conductivity trail. The model predicts a temporally brief column of light resulting from the conventional breakdown of air in a strong electric field in the observed altitude range. For the case of a positive CG stroke the emissions are extinguished by the passage of a runaway electron beam. The electron beam is initiated by the same positive CG lightning stroke that allows the high altitude conventional breakdown to occur and propagates from the cloud tops to the ionosphere. Based on our modeling results, a negative CG lightning stroke, for the same amount of charge transfer, produces a column of light about twice as bright. The emissions are extinguished, in this case, by the ambient conductivity taking into account the increase due to the conventional breakdown of air. In both cases, for the CG lightning stroke parameters examined here, the simulated c-sprite emissions are brief and last less than 17 ms, or one CCD video field. Copyright 2000 Academic Press.
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Wescott, E.M., Stenbaek-Nielsen, H.C., Sentman, D.D., Moudry,
M.J.D.R., Sao-Sabbas, F.T., 2001. Triangulation of
sprites, associated halos and their possible relation to
causative lightning and micrometeors. Journal of Geophysical
Research 106 (A6), 10467–10477.
http://www.agu.org/pubs/crossref/2001/2000JA000182.shtml
Abstract
Sprite halos were recently identified as an impulsive but spatially diffuse phenomenon that sometimes occurs just prior to, but distinct from, sprites. The lack of discernible spatial structure and the temporal development sequence in halos differs markedly from the highly structured bodies and tendrils and the complex development sequences of sprites. However, both phenomena are thought to result from an electric field due to charge moment changes usually associated with large positive cloud-to-ground (CG) lightning but also following negative CG flashes. Three-dimensional triangulations of sprites and sprite halos were made between stations in South Dakota and Wyoming in August 1999 during the NASA Sprites99 balloon campaign. Halos were found to have a Gaussian 1/e diameter of ∼66 km and 1/e thickness of ∼4 km. Comparison with the location of the underlying lightning strokes, as recorded by the National Lightning Detection Network (NLDN), confirms that the horizontal position of sprites may be laterally offset by as much as 50 km from the underlying parent lightning discharge, as has been previously reported. The point of maximum apparent brightness for sprite halos occurs at an altitude of ∼78 km, similar to that of sprites. However, unlike sprites, this point tends to be centered directly above the underlying parent lightning discharge, 4.6±2.7 km mean distance from the center of the halo to the NLDN location. This difference in spatial location relative to the underlying lightning suggests that the electrical breakdown associated with discrete sprites may require a random ionizing event such as a micrometeor. In contrast, sprite halos do not appear to require such a random component.
2001 American Geophysical Union
Index Terms: 0649 Electromagnetics: Optics; 2439 Ionosphere: Ionospheric irregularities; 3324 Meteorology and Atmospheric Dynamics: Lightning; 9810 General or Miscellaneous: New fields (not classifiable under other headings).
Titolo: 20090502-03 
Dom Mag 03, 2009 7:10 am
