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Re: (meteorobs) Fwd: Dust trails of the Ursids - limits of amodel...
Gary Kronk just wrote:
>With respect to the discrepancy
>between the radio observations of Lyytinen and Ondrejov I wonder what
>affects the aurora had that night? Lyytinen is in Finland and
I recently had some discussion with Esko Lyytinen via email. He responded
to my posting to IMO news that has now been forwarded to metorobs.
We happily figrured out that his and my graphs of our trail orbit
computations
look very similar.
We also speculated a bit on the reasons for the strange conflicting results.
He feels that the Ursids may have consisted largely of meteors of 5-6 mag,
which his system can detect, with a cutoff for fainter meteors.
The lmit of the radar at Ondrejov may be around 8 mag. Thus it may be
that the vast number of this sporadics effectively shielded the
increase in activity brought in by the Ursids. Many visual observers may
have had
problems to detect these faint meteors.
What I still find most confusing is that many European observers detected
an increase
in rates after 4:30 UT, with ZHRs around 20-30, until twilight interfered at
about 6:00 UT. In contrast several American observers had much lower rates.
One difference was certainly that the radiant was much higher under our
European
skies than in USA (California 27 deg, Germany 63 deg). Has anyone ever
checked
if the altitude of the radiant has a systematic effect on the observed
magnitude distribution?
Perhaps the vast number of Leonids during the 1999 storms seen at very
different
radiant altitudes (from < 20 to > 60 deg) may provide a good set of data to
look for this.
I once screened this dataset and found that there was a clear systematic
effect of
radiant altitude on the meteor rate seen (apart from the 1/sinh correction).
I however
did not check magnitude distributions that time.
Hartwig
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