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RE: (meteorobs) Leonid dust trail age vs. population index
Rob and others,
In our model, the "mean diameter" of meteoroid population, in a given dust
trail location is inversely proportional to da0. This is at least
qualitatively similar (for positive da0:s) as in Rob's model.
On Rob's enquiry on negative da0:s and "...ejection velocities above about
20 m/s which
may be inconsistent with the satellite model." and on the satellite model
itself, I tell the next. In this (meteorobs) I can not try to give a more
thorough answer.
With the Leonids, I have not seen a definite example of da0:s that are
negative, except by a very small amout. I recall that Rob got the 20m/s
velocity from the 1999 storm. With similar reasoning the 2000/2rev. trail
would give an even bigger velocity.
Because of the small width (in observed time) of this, I find as the
explanation of the radial departure from the trail center, the most
reasonable explanation the next. It is the "aside" reflection near aphelion
of solar radiation (I recall to have called: the direct spread by radiation
effects). Maybe contrary to intuition this effect changes the angular
momentum mostly near aphelion. This affects the perihelion distance q and
orbit plane (but not the orbital period, that is thought to be changed
(non-gravitationally) mainly by the seasonal Yarkovsky effect).
Because we observe the Leonids near perihelium, there is not much effect on
the ecliptic crossing longitude, even though the orbit plane is changed near
aphelion.
I can not state that Rob's conclusion is wrong. It is however that because
the radiation effects, if (maybe) not dominate over the ejection speed
effects, are at least of about the same magnitude, it is very difficult to
invert the observed distributions into ejection speeds. Observations of a
good one revolution encounter would be the best for this purpose.
In my opinion there do exist high ejection velocities, or other unmodelled
(in our model) properties. Our model doesn't explain (give an immediate
explanation) the very bright bolids, seen to hit the Earth and Moon. Also in
my opinion the particles in 1969 with quite large da0, do have quite large
ejection velocities. These can maybe be explained by splits of rotating
particles, near the comet.
In another stream, The Lyrids, the 1803 strong outburst of bright meteors,
seems clearly connected to the one revolution trail, with clearly negative
da0. Maybe the explanation is some small catastrofic event (as with Leonids
bolids), or non-gravitational effects due to sublimation in the big
meteoroids.
As a whole, I try to be open for what really happens and is eager to learn
more.
Another thing is that, if we would have started from more convertional
thoughts in the building of the modell, I am quite confident that the modell
we would then have, would not now be as good as we seem to have.
Best wishes, Esko
>>On Fri, 14 Dec 2001, ccmlt, Christophe wrote:
>> Rob :
>> The relevant parameter is not trail age, but the da0 for the trail
>>
>> It would be very nice if you can explain the da0 parameter or give a link
>> where we can get this informations ?
Rob's reply:
"
It is really necessary to read the original papers to fully understand the
details, but those who have some basic understanding of what is happening
might be able to understand the following.
The orbital period of the meteoroids in the portion of a dust trail that
meets the Earth, differ from that of the comet (by necessity or they would
return with the comet). Orbital period and semi-major axis are directly
related. The difference in semi-major axis at ejection between these
particles and the comet is "da0". In a standard ejection model the
number and size of particles with a particular da0 would be a function of
mass, mass index, ejection velocity and ejection direction. There are too
many parameters here to predict reliably what might be expected for a
specific trail (and it would be very model dependent). David and I did not
attempt to introduce any ejection model into the ZHR calculations because of
this model dependence, but we do know of a way to derive many quantities
like
those given above from different ejection models.
In ejection models, large particles would tend to be ejected at lower
velocities and thus have orbital periods closer to the comet (da0 tends
towards zero). Smaller particles ejected at higher velocities tend to
have da0 rather more distant from zero (both +ve and -ve). The effect of
solar radiation pressure is to skew all particles of a certain mass to
more +ve values of da0, with visual sized particles being skewed towards
da0~0.2. The overall effect is that for each portion of dust trail
encountered there will be a different function for the encountered masses.
This function can probably exhibit effective upper and lower mass limits
and have a variable mass index.
Esko could describe how the satellite model would differ (e.g. I don't
understand how that model can produce -ve da0's and David and I found that
some storms probably require ejection velocities above about 20 m/s which
may be inconsistent with the satellite model). However Esko's ZHR (dust
trail density model) looks excellent and may be quite independent of the
satellite model. I should know these details, but I'm sorry to say I don't.
Cheers, Rob
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If you are interested in complete links on the 2001 LEONIDS, see:
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