(meteorobs) call for observing report + newly updated Leonid circular
CALL FOR LEONID OBSERVATIONS !
We found it necessary to produce one more update of the IMO Leonid
Shower Circular. Reading it gives you a taste of what a proper global
data analysis may yield in terms of confirming features of existing
models and revealing new features which will allow meteor astronomers
to refine these models for the upcoming storm years!
Making such a global analysis will be the next endeavor of the IMO, as
the rough techniques used for rapid information dissemination have now
been stretched to their limits. A preliminary such analysis is planned
to go in the December issue of WGN and should therefore be completed
in less than 2 (!) weeks!
Therefore it is important the IMO Visual Commission receives the full
reports of observers as soon as possible! Send your observations to
Rainer Arlt at email@example.com or in any other way you are accustomed
to. When preparing your reports, mind the following two issues:
1) Report in narrow time intervals! It is in particular recommended -
to the extent possible - to report 1-minute intervals (or shorter!)
for the full hour between 1h30m and 2h30m UT. There are reasons to
suspect minor peaks in this interval besides the two reported on in
the Circular. These minor peaks will be smoothed out if you report
in wider intervals - with 5-minute intervals, they disappear! Only
if you report in narrower intervals will we be able to see which of
these minor peaks are real and which are merely statistical
fluctuations. Also for the remainder of the activity, report in
narrow intervals, the length of which must be chosen depending on
the number of meteors seen! Ideally, none of these interval should
contain more than 10 meteors!
2) It goes without saying that magnitude distributions - which were
not required in the "express reports" - must be included! Without
these magnitude distributions, it is not possible to compute the
population index - a measure for the ratio between fainter and
brighter meteors - and its variation throughout the Leonid
activity. This information is vital to compute a correct ZHR
3) Mention the center of your field of view! Also notice that the
cloud/obstruction correction factor refers to the field of view
ONLY! Clouds outside the field of view must NOT be accounted for!
Many of the above recommendations can also be found in Rainer Arlt's
article "Hints for Visual 1999 Leonid Observations" which was sent
out via the IMO News and MeteorObs mailing lists and which is printed
in the October issue of WGN.
We already thank those observers who have not awaited this message to
send in their complete data; the others we thank in advance for their
UPDATED SHOWER CIRCULAR
We added some data at the beginning and the end of last circular's
activity profile. It is interesting to see that the 1h53m UT secondary
peak may correspond to the 1-revolution old dust trail (although Asher
and McNaught did not expect activity from this trail, they quote
exactly this time as nodal crossing time for the 1-revolution old
trail). Also, there is evidence for enhanced activity on November 18
between 15h and 20h UT (in the order of magnitude of 100+), which in
turn corresponds to a prediction by Emel'yanenko based on an older
dust trail. These two features only give a taste of what is still to
come once a global analysis is underway!
I M O S h o w e r C i r c u l a r
LEONID Activity 1999
*** 2nd UPDATE ***
ZHRs pertaining to the pre- and post-peak activity of the Leonids have
been added. Additional comparisons with other observational reports
have been made. Some cautious interpretations are suggested.
Visual observations of the 1999 Leonids revealed a distinctive peak
with a ZHR above 5000 on November 18, 2h04m +/-5m UT (solar longitude
235.286 +/- 0.004, eq. 2000.0).
It seems that the peak time of 2h08m UT predicted by Asher/McNaught is
confirmed within a margin of at most a few minutes, although the
observed activity is significantly higher. It is reasonable to
conclude that the peak activity has been caused by the 3-revolutions
old dust trail of 55P/Tempel-Tuttle.
All observers who were able to view the peak under good sky conditions
reported an abundance of faint meteors and a relative absence of
fireballs. If this impression is real, taking it into account may
result in ZHR values somewhat higher than those quoted below.
Ten minutes before the abovementioned peak time, at 1h53m +/- 5m UT
(solar longitude 235.278 +/- 0.004, eq. 2000.0), the ZHR profile shows
a secondary peak with of ZHR of about 3500. This secondary peak does
not only occur in the combined ZHR profile below, but also in the ZHR
profile of several individual observers, and is therefore probably
Asher and McNaught mentioned 1h53m UT as the nodal crossing time for
the 1-revolution old trail, but did not expect activity from it.
ZHR levels were above 1000 from roughly 1h20m UT to 2h45m UT (solar
longitude 235.26-235.31, eq. 2000).
Apart from the secondary peak mentioned above, the ZHR profile around
the peak time looks remarkably smooth, even at the level of 5-minute
intervals. However, observers in the French Provence report that, at
the level of 1-minute intervals, additional minor peaks are visible
between 1h30m UT and 2h30m UT. Whether these are significant will be
one of the issues in a forthcoming detailed first global analysis.
Some observers noticed a drop in the population index (i.e., a larger
fraction of brighter meteors) after the peak.
Reports from Mohammad Odeh (Jordanian Astronomical Society),
Casper ter Kuile (Dutch Meteor Society, observing near
Valencia, Spain), Mark Kidger (Canary Islands), and Ilan Manulis and
Alex Mikishev (Israel) are very consistent with the picture sketched
In addition, radio data from K. Maegawa (Toyokawa Meteor Observatory,
Aichi, Japan) reported by Kazuhiro Suzuki and the backscatter
radar data from Ondrejov Observatory (Czech Republic) reported by
Petr Pridal and Rosta Stork yield a peak time between 2h00m UT
and 2h10m UT.
When the Americans took over from the Europeans on November 18 UT,
activity stayed stable with a ZHR of 56 +/- 2 between 0500 UT and
1400 UT (solar longitude 235.409-235.787, eq. 2000.0). The ZHR during
the interval between 1400 UT and 1500 UT, however, doubles in the
observations of Hawaiian-based Jim Bedient. Kun Zhou reports ZHRs
above 100 for the interval between 1625 UT and 1936 UT (solar
longitude 235.889-236.023, eq. 2000.0).
Masaaki Takanashi of the Nippon Meteor Society reports ZHRs above 100
between 1500 UT and 2000 UT (solar longitude 235.829-236.040); in the
first half of this period even up to around 300. Rates drop sharply
towards the end of the Japanese observing window.
ZHRs during the West-European observing window of November 18/19 were
consistently around 25. This is consistent with very low activity
registered by the Ondrejov radar that night, as reported by Pridal and
Although the available data are not yet conclusive, it seems that
there are consistent indications for enhanced activity with ZHRs
around or above 100 between November 18, 1500 UT and 2000 UT (solar
longitude 235.829-236.040, eq. 2000.0).
It is interesting to note that Emel'yanenko predicted a small secondary
peak on November 18.7 UT due to an older duster trail.
Emel'yanenko also expects significant Leonid activity on November
19.7-19.8 UT (solar longitude 236.960, eq. 2000.0). Whether or not
this activity materializes, and whether any other peaks in the
observed activity profile exist, can only be revealed by a detailed
global analysis of data, which is forthcoming.
The following observers (with their observing sites, not their
nationality or country of residence) have contributed data immediately
after the event, from which the ZHR profile given below
has been derived:
Rainer Arlt (Spain), Jim Bedient (Hawaii), Felix Betonvil (Canary
Islands), C.L. Chan (China), Mark Davis (USA), Asdai Diaz (Cuba),
Yuwei Fan (China), Fei Gao (China), Lew Gramer (USA), Rafael Haag
(Brazil), Wayne T. Hally (USA), Dave Hostetter (USA), Andre Knoefel
(Spain), Detlef Koschny (Spain), Wen Kou (China), Alastair McBeath
(UK), Alfredo Pereira (Portugal), Josep Ma. Trigo-Rodriguez (Spain),
Helena Valero-Rodriguez (Spain), James Smith (Canada), Renke Song
(China), Wanfang Song (China), Jan Verbert (France), Catarina Vitorino
(Portugal), Jean-Marc Wislez (France), Mariusz Wisniewski (Poland),
Dan Xia (China), Kim S. Youmans (USA), Dongyan Zha (China), Jinghui
Zhang (China), Yan Zhang (China), Kun Zhou (China), Jin Zhu (China).
(For groups of observers, only the name of the contributing
observers have been mentioned.)
Date Period (UT) Time (UT) Sol. Long. ZHR +/-
Nov 17 0057-0545 0339 234.344 14 2
Nov 17 0600-1000 0800 234.527 16 2
Nov 17 1600-2010 1805 234.951 30 5
Nov 17 1900-2200 2030 235.052 53 14
Nov 17 2300-2400 2330 235.178 82 6
Nov 18 0000-0050 0026 235.217 210 60
Nov 18 0030-0100 0048 235.233 370 80
Nov 18 0050-0130 0110 235.248 560 90
Nov 18 0115-0145 0132 235.263 1160 180
Nov 18 0139-0155 0148 235.275 2360 600
Nov 18 0145-0200 0153 235.278 3430 750
Nov 18 0154-0205 0158 235.282 2820 550
Nov 18 0159-0209 0204 235.286 5400 880
Nov 18 0200-0215 0209 235.289 3540 580
Nov 18 0212-0233 0222 235.298 2110 580
Nov 18 0223-0247 0238 235.310 1140 280
Nov 18 0244-0320 0257 235.323 690 150
Nov 18 0315-0400 0340 235.353 240 60
Nov 18 0347-0505 0423 235.383 153 59
Nov 18 0500-0630 0537 235.435 57 11
Nov 18 0609-0800 0656 235.490 62 11
Nov 18 0711-0900 0756 235.532 51 9
Nov 18 0812-0925 0847 235.568 57 4
Nov 18 0901-1100 0958 235.618 59 9
Nov 18 1100-1400 1254 235.741 56 4
Nov 18 1400-1500 1430 235.808 90 12
Nov 18 1625-1936 1825 235.973 106 13
Nov 19 0018-0445 0306 236.338 23 2
Marc Gyssens, 1999 November 20, 18h UT
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