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Re: (meteorobs) Leonid annual and outburst components



Actually, the Milon observations don't indicate a ZHR of 150,000 for 1966
but somewhat less due to the duration of the meteors being a significant
fraction of their 1 second glimpses, as I've detailed on this list before.

The best fit of the historical ZHRs to the dust trail parameters gives a
peak ZHR for 1999 at around 1,200.  The possibility that the center of the
trail is further out than the nominal value suggests possibly higher rates
(up to say 1,500), but I think the evidence for the trail center being so
displaced is weak.  The theoretical evidence is that a dust trail profile
is NOT Gaussian as one goes further from the Sun, but we have no data to
fit the shape, and just went with a Gaussian as the first approximation.

Actually I haven't seen many predictions of other groups, but there are
now three independent groups that have used a similar technique,
(Kondrat'eva, Muarav'eva and Reznikov, Asher and McNaught, and Lyytinen)
all working independently and having slightly different approaches.
However, all agree to within minutes in the calculations, although David
and I are the only group to also predict ZHR using this technique.  The
weight that can be given to various predictions will vary according to how
the technique

a) fits existing data
   1)time of maximum
   2)rate at maximum
   3)lack of false positives
   4)lack of false negatives
b) has theoretical rigour

David and I went to great lengths to validate the technique we used but it
is important to know what we are and are not predicting.  We are looking
ONLY at dust trails and short duration outbursts resulting from the
Earth's close approaches to these dust trails.  We say nothing about the
background activity (which we have not modeled) or old dust trails (for
which we haven't done the calculations).  It would appear that ZHRs 
of up to 500 can occur as a result of these sources, so even if you are
at the wrong longitudes for any predicted dust trail, an impressive
shower could still be witnessed. However we have validated out technique
with the following results

a 1)From the historical re-analysis of Peter Brown, for every Leonid storm
    or well defined short duration outburst that has a time of maximum
    determined reliably (within minutes), we calculate the time of maximum
    to within 5 minutes of the observed maximum (1866, 1867, 1869, 1966
    and 1969)
  2)Our dust trail density model fits Peter Brown's ZHR data from the
    storms of 1833, 1866, 1867 and 1966 (with a ZHR we derived for 1869)
    with a mean error of about 10-15%.  Even though the data is sparse,
    we were only fitting three parameters to a double Gaussian.  We do not
    claim the ZHR predictions are likely to be better than 50%.
  3)All the years of high rates we predict for the last 200 years were
    observed to have high rates or no data exists to refute a  prediction.
    The one 'problem' year is 1801 when we predict a minor storm over
    western Europe.  So far no data has come forward to dismiss or verify
    this prediction.
  4)There are no years of Leonid storms in the last 200 years that are not
    associated with close approaches to dust trails.
b) The technique used has full dynamical rigour, going from dust released
   from the comet till passage close to the Earth.

It should be noted that our starting data in this work was the comet's
orbit alone.  No data from the Leonid observations is used in the theory,
so the results (time of maximum and dust trail parameters) are totally
independent of observations.  The only way the observations become
involved is in fitting the dust trail parameters to the observed ZHRs.

The reason I became involved in Leonid prediction was the lack of rigour
in the predictions for last year, both in the theory and the inability to
explain past Leonid behaviour using those same techniques.  I have been
disappointed that our work (also the Russian work that been available
since 1985) is not being described by the science media as anything other
than "another shot in the dark".  When it is mentioned, it hasn't stated
our precise predictions or the method of validation.  We are not making
vague predictions with an poorly tested technique.  We believe Leonid
storm prediction is now an exact science.

Now, could I possibly dig a deeper hole for myself!

Cheers, Rob

Robert H. McNaught
rmn@aaocbn.aaodot gov.au

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