(meteorobs) IMO Press Release (1st update): Nov 16/17


       I M O   S h o w e r   C i r c u l a r


               LEONID Activity 2000
               ---   1st update ---

Observers saw no unusual activity during the nights of
November 15/16 and 16/17, though certain variations in the
activity level require further scrutiny. Additional
observations since the previous release confirm a peak
around 8h UT.

Zenithal hourly rates (ZHRs) seem to have risen from about
10 +/- 5 around Nov 16, 0h UT, to about 40 +/- 5 by Nov 17,
4h UT. After that, the picture becomes less clear. Observers
at the Canary Islands report high rates at the beginning of
their observations, resulting in a peak with ZHR around 110
+/- 20 at Nov 17, 6h00m +/- 5m UT. Activity drops again down
to about 60 +/- 15 afterwards, but American observers report
average activity around 105 +/- 10 between Nov 17, 6h45m and
Nov, 17, 8h30m UT, with a possible peak around Nov 17, 8h10m
+/- 10m of 150 +/- 20. Afterwards, activity drops again
significantly to 45 +/- 10 by Nov 17, 9h00m UT. 

The Nov 17, 6h00m UT peak is essentially based on 2
(non-independent) observations from Tenerife (Canary
Islands) and is still in need of independent confirmation.
The peak was reported at the beginning of the observations.
We may not forget that the bright Last Quarter Moon is a
disturbing factor which is not easy to account for
exactly. Several other observers, both in Europe and North
America, report to have seen their best activity during
the beginning of their observation. One may speculate the
continuous hindrance from the bright light of the Moon
makes observers less perceptive for fainter meteors after 
a while, resulting in a "decreasing peak branch" at the
beginning of their observations.

The Nov 17, 6h45m-8h30m UT activity enhancement with
possible peak around Nov 17, 8h10m +/- 10m UT is in good
agreement with a note from Pavel Koten (Ondrejov
Observatory) who detected two peaks with their backscatter
meteor radar, at Nov 17, 8h02m and 8h15m UT, respectively.
Tentatively, this period of increased activity, in
particular the peak(s),  may be associated with the
Earth passing the outer regions of the 1932 (2 revolutions
old) dust trail of the parent comet, 55P/Tempel-Tuttle, for
which a possible activity enhancement was predicted at Nov 17, 
7h53m UT by (among others) Asher and McNaught.

The following observers have contributed data immediately
after the event, from which the ZHR profile given below 
has been derived:

Birger Andresen, Joseph Assmus, Neil Bone, Andreas Buchmann,
Marc de Lignie, Petros Georgopoulos, Robin Gray, Rosely
Gregio, Valentin Grigore, Wayne Hally, Zoltan Hevesi, Robert
Leyland, Mike Linnolt, Robert Lunsford, Alastair McBeath,
Norman W. McLeod III, Michael Nezel, Arvid Parnajpye, Janne 
Pyykkoe, Gilberto Klar Renner, Josep Trigo, Arnold Tukkers, 
Vishnu Vardhan, George Varros, Cis Verbeeck, Jean-Marc Wislez, 
Ju Zhao, Jin Zhu, Xiaojin Zhu.

Date   Time (UT)  Sol. long. Intervals Leonids   ZHR   +-
Nov 15  22h05m     243.848       2         11     13    4
Nov 16  03h33m     234.067       1          7      8    3
Nov 16  21h16m     234.820       6         44     20    3
Nov 17   3h02m     235.062       9         50     33    4
Nov 17   4h53m     235.141      10         74     47    5
Nov 17   6h00m     235.187       3         30    108   20
Nov 17   6h16m     235.198       3         16     66   17
Nov 17   6h36m     235.212       4         22     57   12
Nov 17   7h59m     235.270      10        117    104   10
Nov 17   9h25m     235.330      10         64     44    5
Nov 17  13h15m     235.491       4         35     52    9

ZHRs are computed with a population index of 2.0, zenithal
exponent of 1.0.

Marc Gyssens, 2000 November 17, 23h UT.

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