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RE: (meteorobs) (Leonid) Questions :>




Hi Jure and all,

I try to give some answers to your questions.

Question 1.
In our modell, the trail-width is expected to increase according to the
orbit number, 
so a simple approximation will give the maximum ZHR to decline according
to 1/N^3.
(This is in a central encounter. Having an encounter well outside the
peak, at a given 
miss-distance, the effects of weakening and widening (in the 'base'
modell (ignoring A2-effect)) almost compensate the effects of each
other.)
Then comes especially with old trails the "A2-effect" or "continuous
acceleration" 
because of non-gravitaional forces (non-gravitaioal forces are also
expected toa 
affect in the 1/N^3 dependence). Thet A2-effect causes the spread not
directly but 
by means of altered planatery perturbations and so is very much case
dependent.
In the 2001 10 and 11 rev. trails the spreading effect was expected to
be very strong,
in the 7- and 9. rev. trails moderate (also helping to bring particles
more close to the
Earth orbit). However ir 2002 in the same 7-rev. trail, the (A2-caused)
spreading effect was
even astonsihingly small, according to the modeling.
McNaught and Asher have included (after the early model) a furher
exponential decline (according to the orbit number)of the rates.
Jenniskens assumes the trails not to get more wide with increasing orbit
number. He had in 2002 the best prediction for the width. It is however
worth to note that if there is no widening (in any form) expected, 
then his model contains the implicit assumption of the total meteoroid
number changing, declinig in old trails. 
Actually if I construct some (non real) exapmle case predictions with
our 'base' model and these 
are represented in graph similar to Peters graph (with dependence on
Log(da0/N), 
I get curves closely resembling those in Peter's modell, this in spite
of the very different assumptions. 
As to Jeremie Vaubaillon's modell, (as I understand) this has some
widening with orbit number, in part caused by slightly different (within
the particle population) planetary perturbations, in part the included
Poynting-Robertson-effect (especially in the smallest range of
particles) to some degree has a similar type effect than the A2-effect.
I hav't seen, what his modell would give for favorable young trails
encouters like in 1966, so how much declinign this modell would really
give.
(I made some remarks on the modells of others. I hope that I didn't tell
enything wrong. If I did, I hope that you correct yourself (and/or
possibly explain more, as needed, even if there were not anything
wrong).)

As to THE QUESTION; I would say that in any case outbursts are possible
well after 4 years past the comet, 
but these are less likely stroms. I think that no definite (storm)limit
can however be given. For example the mean anomaly factor behaves quite
irregularly and there could in principle be cases, when this has high
values far behind the comet. We have the prediction of the 2003 (Nov.
13!) encounter when the trail is more than one revolution behind the
comet. The comet has made a little more than 15 revolutions and the
train only 14. The calculated fM is well above 1. (This folds into two
sections near the encounter and the more far section has fM around 2 to
3, the more near has this close to 1 ; recall. (One revoltuion trail has
the fM value of 1.)) This is caused because the particles are in the 1/3
resonace with Jupiter. Unfortunately the miss-distance is not quite
small. This is NOT predicted as storm, but an outburst and mostly
contains small meteor(oid)s. (To get into that resonance requires
relatively big da0, meaning small particles.) Resonant trails will
typically keep more condensed (for many revolutions) than non resonant,
and the fM can actually increase. With the Ursids, there is a 'simpler'
(that can be given by means of small integers) resonance than with the
parent comet close by (in the orbital period (or semimajor axis)) in the
longer period side. In the modell, it is (some of) the particles that
were captured in the simpler resonance that have the rD lowered (near
the Re value) more quickly (in time or orbit number) than with the
parent comet.

Question 2.
I recall that the outbursts were not storms in all those years that you
give. Most of these are 
explained (I recall), but I can't keep these in mind. Some may be caused
by more than one trail as in 1832 (recall). I will try to get the orbit
numbers for those that I have, during the weekend (unless someone else
gets these sooner).

Question 3.
This is more or less the same than Q.1, and already partly answered. In
short I expect that outbursts 
can happen, maybe not (or at least less likely) storms. The trails
(especially non resonant) typically depart from the original rD or the
required rE quite a lot when getting older and more far away from the
parent comet. Encounters are less like than near the comet, but in
principle could happen. We have the predictions of young (2-rev.) trail
encounters for the years 2006 and 2007. Because of the big da0, the
visual rates are predicted not big (maybe at the hundred range).
Although there is no 'reference', I think that these may be quite strong
telecopiocal outbursts and also in video (capable of capturing to about
mag 6). There is the known 1969 outbrst, but observed only visually, as
far as I know. I have made some inspections of possible older trail
encounters and if I reacll correctly, the year 2007 is predicted quite
favorable also with these. Tnere may be some level 
encounters with oldish trails (maybe with more than one). Im have no
well derived ZHR-predictions, but what I, 
recall from the inspections, these may also be around the (ZHR)
hundred(s) range. So I expect that we may still 
have some interesting outbursts with the Leonids in this decade, but
nothing storm-like is predicted (at least visually).

Fine Geminids! Esko

>>>

HiGH all!

   There are some questions poking me in the head and I have to get them
out, 
so here it goes:

1. Maximum ZHR in a n-rev trail: in a paper by Asher (I think from
IMC99), it 
is stated that at least to a first approximation and for trails not too
old, 
the peak ZHR of the trail declines with 1/N, where N is the number of 
revolutions. If the peak ZHR of a 1-rev trail at optimal da0 is about
300 000, 
then a trail would be capable of producing ZHR > 1000 for 300
revolutions. 
Okay, that may be a bit optimistic, so let's say it decreases with
1/N^2. Then 
a trail would be capable of producing ZHR > 1000 for about 17
revolutions. Ok, 
still with me? Good. Now, the center of the trail lags behind the comet
and the 
lag increases with time (number of revolutions). 
THE QUESTION: The 7-rev trail was more than capable of producing storm
level 
activity this year. Could older trails produce storms even further away
from 
the comet than 4 years? Has anyone calculated this?

2. Also, I've seen dust trail predictions for past storms in 1833, 1866
and 
1966. What trails caused the 1832, 1867, 1868, 1900 and 1901 storms? 

3. Ok, one more (I've spent far too much time thinking about this...).
Esko 
hinted at the possibility of an Ursid outburst for this year - when the
Ursid 
parent comet is around aphelion. Ok, perhaps nothing will materialise,
but 
there was an outburst in 1985 when the comet was also around aphelion.
Old 
Ursid dust trails are capable of producing outbursts even halfway around
the 
orbit. Could something like this happen with the Leonids? (see the 1.
question 
again). Perhaps it happened but nobody saw it?

I hope this was not too much!

Clear skies!

Jure A.

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