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Re: (meteorobs) Re: Leonid 'gusts' -the 1997 Japanese video!!

At 08:27 PM 1999-11-02 +0100, you wrote:
>if we entertain for a moment the notion 
>that such occurrences (breakup of dustballs/meteoroids in pre-luminous 
>trajectory resulting in a flurry of simultanious meteors) could be typical 
>of fresh dust such as in an outburst structure. With this, I 
>want to say, that similar phenomenon might occur on a smaller scale, and 
>need not be that intensive as the unique 1997 video phenomenon.

With that notion having been introduced, I'd like to bring up another such
observation regarding radio meteors. Quite often during the late summer,
Shel Ennis and I will hear a meteor "ping" that was what we've termed a
"double"; that is, one ping quickly followed by another, spaced a few
hundredths or less milliseconds apart. It seems likely to me that those
radio observers listening with FM radios may not even notice this since the
reflections at lower frequencies last much longer than at the frequency
where Shel and I have head these double pings, 144 MHz (that is, the second
of the double ping may be obscurred by the long-lasting first of the double
ping). We aren't the first to notice them, either; radio amateurs have long
heard double pings since the beginnings of radio amateur meteor scatter
work in the early 1950's.

It doesn't seem logical to me, though, that these double pings can be due
to one object fragmenting since the echos are sequential rather than
simultaneous. And in fact, I'm not sure that we could tell when an object
actually fragmented, creating several objects with individual echoes,
unless we were able to observe the phase angle of the returning echoes,
because the echoes would likely occur simultaneously. There might be a
first, loud, ping then followed by a sudden change in amplitude as the
object fragments; but I've never knowingly recorded such an echo.

We don't hear double pings very often at all other than during the late
summer-early fall. They occur something like less than 1 out of 10 "normal"
reflections, too, although there are sometimes days when we may hear a
higher number than other days. One day in October, I recorded four double
pings within 20 minutes.

It's also possible that the double ping may be some kind of low-atmospheric
phenomena such as a reflection within an inversion; but the time delay
would seem to rule that out, not to mention that the amplitude of the
reflection within the duct would most likely be much lower due to
reflection loss within the duct.

I'm wondering whether you experienced visual observers may have noticed
more meteors during the late summer/early fall months that might flare,
extinguish, then flare again, all within less than a second. I have a
number of audio WAV recordings of these doubles, and even several that
sound like triples. When displayed on an elapsed time axis using
reduced-speed audio recording software, the "signature" of the double pings
is unique and obvious.

Carrying this "notion" a little further, one might think that perhaps we
hear echoes from two closely-spaced meteors. But the WAV recordings almost
always show the second ping to be somewhat weaker in amplitude to the
first; i.e., the first ping is almost always the loudest, whether doubles
or triples. One would expect either the first, or the second, ping to be
louder than the other; but never only the first. In addition, the time
frame within which the doubles occur is unique; we've heard what are
definitely two individual meteors occurring almost simultaneously, and
there is no mistaking when that happens.

Could there be some difference in the makeup of Perseids meteors that
causes them to flare and extinguish, then flare again, compared to
sporadics or meteors from other showers?

SteveH
Shrewsbury MA
Amateur Radio Meteor Station K0XP
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