[VLF_Group] VLF and Meteor study link

Da: Thomas Ashcraft <ashcraft@heliotown.com>
Risposta: <VLF_Group@yahoogroups.com>
Data: Tue, 19 May 2009 10:21:41 -0600
A: <VLF_Group@yahoogroups.com>
Oggetto: [VLF_Group] VLF and Meteor study link

Here is a research paper link of possible interest to some on the list:

"Possible Detection of GEMINID 2007 Meteor Shower During Day-Time from
VLF Radiation Spectra?" (Guha, Anirban; de, Barin Kumar; Roy, Rakesh)
Published April 2009.

http://www.jodrellbank.manchester.ac.uk/meteor/docs/Guha2009.pdf

------Messaggio inoltrato
Da: Paul <paul@abelian.netcom.co.uk>
Risposta: <VLF_Group@yahoogroups.com>
Data: Tue, 19 May 2009 20:52:46 +0100
A: <VLF_Group@yahoogroups.com>
Oggetto: Re: [VLF_Group] VLF and Meteor study link


Thanks Thomas, that is a very interesting report.

It seems that every paper we see that claims VLF detection
of meteors reports a different frequency range and signal
characteristic. Soon, we will have the entire band covered!
Having said that, this report does seems to be more thorough
in its analysis compared with others.
They refer to two kinds of emission previously reported,

a) sustained for a few seconds - from the turbulent trail;

b) 'busters', lasting a fraction of a second - from shockwaves
along the plasma column;

The majority of reports are of (a), with (b) about 10%.
To be on the safe side we must keep an open mind about the
signature, but we can keep a look out for these burst of
noise, weaker than sferics, lasting 'a few seconds', in the
range 8kHz to 12kHz.
There should be sporadic events every day. Can we find anything
like this in our spectrograms? It also will be worth having
another look at the recording of the Jan 17th fireball, because
at the time we were looking for pulse-type signals, rather than
noise bursts above 8kHz.
Oh, the pdf works fine here with 'xpdf'.
--
Paul Nicholson
--


------Messaggio inoltrato
Da: drobnock2 <drobnock@penn.com>
Risposta: <VLF_Group@yahoogroups.com>
Data: Wed, 20 May 2009 12:02:46 -0000
A: <VLF_Group@yahoogroups.com>
Oggetto: [VLF_Group] Re: VLF and Meteor study link

Hi
Question for Paul Nicholson, concerning the recent paper from India. Paul you made
the following statement:

"There should be sporadic events every day. Can we find anything
like this in our spectrograms? It also will be worth having
another look at the recording of the Jan 17th fireball, because
at the time we were looking for pulse-type signals, rather than
noise bursts above 8kHz."

Please differiante between the "pulse-type signals" and "noise bursts."

Another comment, the paper discusses the detection of VLF signatures at a local
geographical site from a known meteor shower.

The paper brings the research of meteors and and the generation of vlf signatures closer
to an answer about meteors generating electromagnetic signatures. The reader needs to
keep in mind that the Guha work is presenting additional information that a meteor
shower -- meteors in numbers -- generate signatures that are detectable.

Individual meteors can generate individual VLF signatures, but when a meteor cell
enters the upper atmosphere there is a greater chance to detect the activity. Consider
the meteor shower as having a series of meteors together -- a cell -- creating a more
concerated signature and the length of the signature having a longer time period.

Again the work of Guha's group backing up the observations conducted during the
1990-2000 Leonid meteor research. The Guha research is bringing additional
information forward that at a local level , meteors cells can be detected from their own
electromagnetic signature.

The detection of signatures at different frequencies as commented by Paul ,may be an
indication that the signature from a meteor may be the result of the various duration of
the meteors flight. The length of the ionized trail determining the frequency of
resonance.

George John Drobnock