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(meteorobs) [IMO-News] Leonids Electrophonics (fwd)
----- Forwarded message from Luigi Foschini -----
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From: Luigi Foschini <foschini@tesre.bo.cnrdot it>
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Date: Fri, 17 Nov 2000 09:28:24 +0100 (MET)
Reply-To: Luigi Foschini <foschini@tesre.bo.cnrdot it>
Subject: [IMO-News] Leonids Electrophonics
Dear Friends,
Every year, during the Leonids, many researchers and amateurs try to
record electrophonic sounds from meteors. The observational situation,
however, is not a simple one, and several difficult issues exist. Not the
least of these is the true identification of sources. In the past many
people have assumed that the apparent coincident sighting of a meteor and
the detection of a transient electromagnetic signal means that the two
must be causally related. This is not so. Before a coincidence can be
reasonably claimed several criteria must be satisfied. Firstly, one has to
demonstrate beyond reasonable doubt that the transient VLF signal is not
due to some other natural or terrestrial background source. The
association has to be established by eliminating the other possibilities,
and that means that there must be control data gathered and analyzed at
times when major meteor showers are not active. Meteors appear at random,
all of the time, so to do electromagnetic transients, simply recording the
two at the same instant, without control data, really means very little.
In essence, what should ideally be demonstrated is that the signal has
unique And identifiable qualities, that is, that it is distinguishable
from other background sources, and that it is reasonably associated with
the passage of a meteor. And perhaps one has to establish the coincidence
at several well-separated locations.
The issue of Leonid meteor electrophonics is also compounded by a lack of
consensus on generation mechanisms. An number of theories have been
proposed, but to date there is very little instrumental data that can be
reasonably presented as test material. All of the theories developed to
date make predictions with respect to bright meteors and consequently this
is the arena in which they should be tested. One cannot claim a theory is
correct, or indeed incorrect, when it is being compared to data about
which it makes no prediction. The electrophonic burster theory of Beech
and Foschini (1999, Astronomy and Astrophysics 345, 1999, L27), for
example, makes a clear enough prediction with respect to bright meteors,
but it doesn't say anything about faint, or sub-visual magnitude meteors.
These latter meteors may, or may not produce very low frequency radiation
(and we happen to think that is it highly unlikely that they do so), but
our point is that extraordinary claims require extraordinary scrutiny.
So, if you are thinking of listening for Leonid electrophonics please
don't stop after November 18. The outstanding issues will not be easily
solved, and what is paramount now is the acquisition of good quality data,
not just for the Leonids, but for sporadic and other annual meteor
showers.
Greetings and good luck!
Luigi Foschini
Institute TeSRE - CNR, Bologna (Italy)
Martin Beech
Department of Physics, University of Regina (Canada)
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----- End of forwarded message from Luigi Foschini -----
--
Rainer Arlt -- Astrophysikalisches Institut Potsdam -- www.aipdot de
Visual Commission - International Meteor Organization -- www.imodot net
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