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(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 visual@imo.net 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
   profile! 

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
prompt cooperation!

Kind regards,

Rainer Arlt
Marc Gyssens


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
real.

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
above. 

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
Stork.

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
wgn@imo.net
---

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