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(meteorobs) IMO-NEWS: NUMERICAL MODEL PREDICTIONS FOR 1998 LEONIDS (fwd)




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From: Juergen Rendtel <jrendtel@aipdot de>
Subject: NUMERICAL MODEL PREDICTIONS FOR 1998 LEONIDS (fwd)
To: imo-news@imodot net
Date: Fri, 06 Nov 1998 9:05:35 MET

In a few days the Leonid maximum is expected. Appended is another
model prediction by Peter Brown of UWO, London, Canada, which
I thought is of general interest for all meteor observers.

Good luck with all observing projects!

Juergen Rendtel
IMO President

> 1998 Leonid Model Prediction
> 
> 
> 
>                              By Peter Brown, UWO Meteor Group. Issued
> November 5th, 1998.
> 
> 
> Using a total of 12 different models for the ejection of meteoroids from
> comet Tempel-Tuttle, a preliminary "best" guestimate for the location of
> the strongest peak in activity and its associated ZHR for the 1998
> Leonids has been found.
> 
> The 12 model approach involves using three major variations in meteoroid
> density (0.1, 0.8 and 4.0 g/cm^3 for bulk density of the
> meteoroid). For each of these three densities, four different variations
> in the initial ejection velocities are also employed - one follows
> the distributed production model of Crifo which produces broad
> distributions in initial ejection velocity which
> has a mean velocity lower than the classical Whipple/Jones ejection
> model. In addition to Crifos distributed production model, a
> Whipple/Jones ejection velocity model is used, as well as a second
> variant of the same with a heliocentric velocity dependance of
> r^-0.5 in place of the usual r^-1. The fourth model is again a variant
> on the Jones/Whipple model in which the ejection velocity at a
> given heliocentric distance is not single-valued in the monte carlo
> generating routine, but rather has a parabolic distribution of
> probable velocities about the average Jones/Whipple velocity for the
> chosen heliocentric distance. See Brown and Jones (1998), Icarus, v.
> 133, pp. 36 - 68 for more details.
> 
> 
> The results of the modelling for the Leonids, using ejections at all
> perhelion passages of the comet back to 1499 AD (ie 15
> revolutions of the comet prior to the current epoch). A simple summation
> of the meteoroids which are then visible at Earth at the
> present time from this ensemble and which would produce visually
> observable meteors (mass > 1 mg) was then computed from all
> ejecta. A meteoroid is defined as being Earth-intersecting if its nodal
> radius is within 0.005 AU of Earth at the longitude of its
> descending node. All models suggested a steep increase in activity
> beginning in December, 1997/early 1998 accompanying the
> passage of Tempel-Tuttle. The resolution of the modelling is of order 2
> months and thus all models suggest that this November will
> show significantly increased activity relative to 1997 (when the peak
> ZHR reached just short of 100), and likely activity approaching meteor
> storm levels (ZHRs of order 1000). Using 1997 as a baseline and taking
> the peak ZHR to have been 96 +/- 13 at 235.22 +/- 0.02 (J2000) in 1997
> we have extrapolated the relative model difference between the activity
> strength predicted by the model in 1997 to that observed and that
> predicted for 1998. Using a mean of all  models, produces a predicted
> location for the peak in 1998 of 235.26 +/- 0.04 (J2000) with a peak ZHR
> of 1200 +/- 280. This solar longitude corresponds to Nov 17 at 19:20 UT
> with a 1-sigma uncertainty of 60 minutes. We emphasize that due to the
> model results sensitive dependance on density of the meteoroids, the
> range of possible ZHRs extends from slightly lower than the bound given
> above to nearly 10 000 (the higher values associated with the models
> using the least dense meteoroids and lowest ejection velocities).
> 
> The use of relative modelling difference between 1997 and 1998 implies
> that the veracity of the prediction in 1998 relies entirely on the
> accuracy of the magniude of the ZHR reported in 1997 under full moon
> conditions. As well as the above, the models suggest that broad
> activity, persisting for of order a full day centred about this peak
> should be noticeably above normal Leonid background levels and should be
> rich in larger meteoroids in 1998 most notably after the time of the
> peak. The model suggests ZHRs of order 100 or greater in the 3-4 hour
> window prior to the peak and ZHRs of order 100-200 persisting for many
> hours after the peak.
> The mass index near the time of the peak over the visual magnitude range
> will be near 1.6 +/- 0.1. It is worth noting that a significant decrease
> in the mass index from 1.8 +- 0.1 several hours prior to the peak to
> this lower value and then upward again after the peak is visible in most
> models.
> 
> 
> --
> *********************************************************************
> Peter Brown
> Meteor Physics Lab
> Department of Physics and Astronomy
> University of Western Ontario
> London, Ontario
> N6A 3K7
> Canada
> 
> Voice:1-519-679-2111 x6458
> Fax:1-519-661-2033
> *********************************************************************

--
*******************************************************************
Juergen Rendtel                     Astrophysical Institute Potsdam
                                  International Meteor Organization
jrendtel@aipdot de                           Arbeitskreis Meteore e.V.
http://aipsoe.aipdot de/~rend/rnl-p.html

Phone: (+49) 331 - 960727   (priv.)
       (+49) 331 - 288 2327 (office)                 Gontardstr. 11
Fax:   (+49) 331 - 288 2310                         D-14471 Potsdam
*******************************************************************

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