From: Marc Gyssens, IMO Date: Thu, 18 Nov 1999 08:59:57 +0100 I N T E R N A T I O N A L M E T E O R O R G A N I Z A T I O N Press release Leonid meteor storm materializes around expected peak time (UPDATE) =================================================================== Experienced visual observers watching near Malaga and at the Sierra Nevada Observatory in Spain and near the Gorges du Verdon in the French Provence report that Leonid meteor activity peaked at up to 30 meteors per minute shortly after 2 am Greenwich Mean Time. This activity was characterized by a lot of faint meteors and almost no fireballs. Meteor astronomers reduce the actual numbers of meteors seen to a standard value, called the Zenithal Hourly Rate (ZHR), which takes into account the quality of the sky as well as the direction from which meteoroids enter the atmosphere. The peak activity reported by the abovementioned groups of observers corresponds with a ZHR around 5000, which is considerably more than what most meteor observers had hoped for (around 1000). Preliminary reports of other observing groups at Tenerife, Canary Islands, near Valencia in Spain, and in Jordan confirm the picture sketched above. Radio observations from Japan and the Czech Republic also indicate a peak time between 2:00 and 2:10 am Greenwich Mean Time. The observed peak time coincides almost perfectly with the peak time of 2:08 am Greenwich Mean Time predicted by Asher and McNaught, indicating that the activity was due to the dust trail created the Leonids' parent comet, Tempel-Tuttle, about 100 years ago (i.e., 3 revolutions ago of the Comet around the Sun). Marc Gyssens International Meteor Organization Below is a more technical description of the observed Leonid peak activity. ---- From: Marc Gyssens, IMO Date: 1999 November 18, 7h UT. ------------------------------------- I M O S h o w e r C i r c u l a r ------------------------------------- LEONID Activity 1999 Visual observations of the 1999 Leonids revealed a distinctive peak with a ZHR of about 5000 on November 18, 2h05m +/-10m UT (solar longitude 235.287 +/- 0.007, eq. 2000.0). ZHR levels were above 1000 from roughly 1h30m UT to 3h00m UT corresponding to 235.26 to 235.32 degrees in solar longitude. 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. 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) and Casper ter Kuile (Dutch Meteor Society, observing near Valencia, Spain) 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. 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. The following observers have contributed data immediately after the event, from which the ZHR profile given below has been derived: Per Aldrich, C.L. Chan, Asdai Diaz, Yuwei Fan, Fei Gao, Lew Gramer, Andre Knoefel, Wen Kou, Alastair McBeath, Tom Roelandts, Sirko Molau, Renke Song, Wanfang Song, Honglin Tao, Dan Xia, Dongyan Zha, Jinghui Zhang, Yan Zhang, Jin Zhu. (For groups of observers, only the name of the contributing observer has been mentioned.) Date Period (UT) ZHR +- --------------------------- Nov 17 0600-1000 16 2 Nov 17 1600-2010 30 5 Nov 17 1900-2200 53 14 Nov 18 0030-0100 130 90 Nov 18 0100-0115 490 230 Nov 18 0115-0130 770 160 Nov 18 0130-0145 1040 660 Nov 18 0145-0202 4100 840 Nov 18 0200-0215 5000 1100 Nov 18 0212-0230 2400 280 Nov 18 0243-0247 1100 160 Nov 18 0320-0330 470 70 Nov 18 0420-0430 180 40 --------------------------- ZHRs are computed with a population index of 2.0, zenithal exponent of 1.0. ---- From: Marc.Gyssens Date: Fri, 19 Nov 1999 03:11:48 +0100 (MET) LEONID Activity 1999 ==================== UPDATE ==================== New ZHR calculations have been made. On the one hand, newly received observations have been included, and, on the other hand, data based on estimated counts have been replaced by data based on actual counts. Visual observations of the 1999 Leonids revealed a distinctive peak with a ZHR of about 5000 on November 18, 2h04m +/-5m UT (solar longitude 235.286 +/- 0.004, eq. 2000.0). Ten minutes earlier, 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. Apart from this secondary peak, the ZHR profile looks remarkabAll observers who were able to view the peak under good sky conditions reported an abundance of faint meteors and a relative absence of fireballs. 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), and Ilan Manulis (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. 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. 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), 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), 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), Renke Song (China), Wanfang Song (China), Jan Verbert (France), Catarina Vitorino (Portugal), Jean-Marc Wislez (France), Mariusz Wisniewski (Poland), Dan Xia (China), Dongyan Zha (China), Jinghui Zhang (China), Yan Zhang (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 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 0512-0712 0557 235.449 61 12 Nov 18 0700-1100 0905 235.581 44 5 ZHRs are computed with a population index of 2.0, zenithal exponent of 1.0. ---- From: Marc Gyssens, IMO Date: 1999 November 20, 18h UT ------------------------------------- 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 smooth, even at the level of 5-minute intervals. ZHR levels were above 1000 from roughly 1h20m UT to 2h45m UT corresponding to 235.26 to 235.31 degrees in solar longitude.