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Re: (meteorobs) Leonid rate predictor URL

> [...] it is not sure whether the truth will match these predictions [...]

Very true! This morning Peter Jenniskens at the conference 'Meteoroids
2001' in Kiruna, Sweden (from where I'm posting right now), has presented
evidence that some of Tempel-Tuttle's dust trails are not exactly where
the Asher/McNaught/Lyytinen etc. models have them. The details are difficult
to explain (I'll try next week when I'm back in Germany) but what
Jenniskens concludes from the time profiles and heights of various recent
Leonid outbursts and storms (esp. 1998 to 2000 but also way back into the
19th century) is that all dust trails have moved a bit closer towards
the Sun than where they would be if only Kepler and solar radiation pressure
would be at work. This additional effect is apparently different for dust
released from TT at different perihelia (and may have something to do with
precession of the nucleus and highly aniostropic dust emission).

I've talked with Jenniskens for hours today, and he has at least convinced
me that there could be more at work than the (comparatively simple) classical
dust trail models take into account. They are (nearly) perfect in predicting
the times of the maxima but have had notorious problems with forecasting
ZHRs. The additional effect claimed by Jenniskens would not have been
obvious in 1999 (the year the dust trail approach triumphed) and 2000 -
but if it exists it COULD CHANGE THINGS THIS YEAR A LOT! Instead of having
maximum rates of 2000 meteors per hour in the U.S. and 6000 or more in
East Asia and Australia, we would get some 30,000 in the U.S. and a mere
2000 in Asia ...

Now what? Jenniskens has seen indications of shifting dust trails before
and presented ZHR predictions starkly different from Asher/Lyytinen before
(which saw the meteor storms all but over after 1999, with hardly a Leonid
in the sky in 2001 and 2002) - and after the Leonid activity profile of
2000 turned out completely different than he had predicted, he at first
withdrew his ideas (in a paper in WGN). But in the last few weeks, after
reanalyzing esp. the 2000 observations, he is more convinced than ever
that some of the trails ARE shifting and that the 2001 Leonids activity
profile will be very different than what everyone (including his own
website, at least until today...) predicts. There are several assumptions
about the 3D structure of dust trails going into this analysis which may
be right or wrong - but then again the traditional dust trail models also
are not free of assumptions ...

Three months and a few days from now we will know who was right - but I
doubt that there will be any universal agreement on the correct model
before that. While this is pure 'science in action' and kind of fun (esp.
when you're at a conference in a remote place, together with most of the
key scientists in the field), it doesn't make it any easier to decide
even which continent to travel to this fall ...

Daniel Fischer, at the Swedish Institute of Space Physics
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