International Meteor Organization (IMO)

Bulletin 13 of the International Leonid Watch:
The 1998 Leonid Meteor Shower

published in WGN, the Journal of IMO 26:6 (December 1998), pp. 239-248

Introduction

Ghazalaha Al-Abed (ABEGH, 5.95h), Iyad Ahmad (AHMIY, 1.83h), Ahmad Al-Niamat (ALNAH, 5.00h), Rainer Arlt (ARLRA, 0.63h), Joseph D. Assmus (ASSJO, 3.11h), Zaid Ata (ATAZA, 5.00h), Juan Alberto Aveledo (AVEJU, 1.20h), Jlia Babina (BABJL, 3.28h), Halim Baituk (BAIHA, 2.30h), Ana Bankovic (BANAN, 4.12h), Rony Barry (BARRO, 0.54h), Luc Bastiaens (BASLU, 1.66h), Rizlane Bechar (BECRI, 1.67h), Sanae Bechar (BECSA, 1.67h), Luis R. Bellot Rubio (BELLU, 4.97h), Mahjoub Belfahim (BELMA, 6.83h), Pavel Belov (BELPA, 2.15h), Vladimir Belchenko (BELVL, 2.55h), Abdelaziz Bennouna (BENAB, 1.08h), Felix Bettonvil (BETFE, 4.39h), Neil Bone (BONNE, 1.97h), Mark Borg (BORMR, 6.25h), Michael Boschat (BOSMI, 4.00h), Joana M. Brunet (BRUJO, 5.30h), Marija Cajetinac (CAJMA, 5.75h), Arturo Carvajal R. (CARAR, 0.50h), Tal Carmon (CARTA, 0.04h), Andrew Casely (CASAN, 1.00h), Matthew Collier (COLMA, 0.24h), Tim Cooper (COOTI, 1.00h), Uros Cotar (COTUR, 1.03h), Stefano Crivello (CRIST, 5.78h), Hani Dalee (DALHA, 4.00h), Luigi d'Argliano (DARLU, 1.41h), Mark Davis (DAVMA, 7.50h), Goedele Deconinck (DECGO, 1.71h), Benoit Dejust (DEJBE, 2.00h), Marc de Lignie (DE MA, 15.23h), Vincent Desmarais (DESVI, 2.20h), Peter Detterline (DETPE, 5.06h), Asdai Diaz Rodriguez (DIAAS, 2.00h), Anton Dimitrov (DIMAN, 2.14h), Elena Dimovski (DIMEL, 6.08h), John Drummond (DRUJO, 2.50h), Tonis Eenmae (EENTO, 3.07h), Maurizio Eltri (ELTMA, 2.75h), Frank Enzlein (ENZFR, 2.69h), Tamás Fodor (FODTA, 1.93h), Keiiti Fukui (FUKKE, 11.73h), Nobuyuki Fukuda (FUKNO, 4.15h), Ofer Gabzo (GABOF, 0.25h), Christoph Gerber (GERCH, 15.18h), Jaroslav Gerbos (GERJA, 8.50h), Ivanka Getsova (GETIV, 3.52h), George W. Gliba (GLIGE, 3.25h), Orly Gnat (GNAOR, 0.17h), Shelagh Godwin (GODSH, 0.66h), Amit Gokhale (GOKAM, 2.05h), Sagar Gokhale (GOKSA, 1.03h), Yeshodhan Gokhle (GOKYE, 3.68h), Alexandra Golova (GOLAL, 3.28h), Prerana Gore (GORPA, 2.67h), Roberto Gorelli (GORRO, 8.20h), Valentin Grigore (GRIVA, 4.45h), Monica de la Guardia (GUAMO, 4.36h), Michal Haltuf (HALMI, 1.41h), Torsten Hansen (HANTO, 1.98h), Takema Hashimoto (HASTA, 10.50h), Roberto Haver (HAVRO, 5.12h), Kim Hay (HAYKI, 2.37h), Amera Hemsy (HEMAM, 5.33h), Kamil Hornoch (HORKM, 3.39h), Daiyu Ito (ITODA, 4.97h), Kiyoshi Izumi (IZUKI, 7.23h), Helle Jaaniste (JAAHE, 3.35h), Jan Janssens (JANJA, 12.50h), Vibor Jelic (JELVI, 4.52h), Ilhame Jemmah (JEMIL, 0.50h), Carl Johannink (JOHCA, 16.35h), Ivan Jokic (JOKIV, 2.20h), Kevin Jones (JONKE, 6.24h), Javor Kac (KACJA, 5.87h), Primoz Kajdic (KAJPR, 2.09h), D. Kalayda (KALDU, 3.33h), Dmitrij Karkach (KARDM, 3.28h), Niladri Kar (KARNI, 3.72h), Kenya Kawabata (KAWKE, 3.71h), Srdjan Keca (KECSR, 3.70h), Akos Kereszturi (KERAK, 3.53h), Katarina Kerekesova (KERKT, 8.78h), Noor Al-Khateeb (KHANO, 4.44h), Mark Kidger (KIDMA, 1.50h), Kevin Kilkenny (KILKE, 3.09h), André Knöfel (KNOAN, 7.68h), Daniel Köhn (KOHDA, 1.46h), Khalil Konsul (KONKH, 5.50h), Marija Kotur (KOTMA, 0.91h), Jakub Koukal (KOUJA, 11.36h), Zoran Kraljevic (KRAZO, 3.47h), Nikola Kresojevic (KRENI, 5.55h), Gary W. Kronk (KROGA, 6.50h), Tom Kucharski (KUCTO, 2.42h), Brigitte Kuneth (KUNBR, 2.00h), Werfried Kuneth (KUNWE, 1.00h), Zsolt Lantos (LANZS, 2.96h), Anne-Laure Lebacq (LEBAN, 1.71h), Adrian Lelyen (LELAD, 1.00h), Anna S. Levina (LEVAN, 3.33h), Mihir Limaye (LIMMH, 1.18h), Alister Ling (LINAL, 1.38h), Vladimir Lukic (LUKVL, 6.02h), Robert Lunsford (LUNRO, 5.00h), Hartwig Luthen (LUTHA, 9.20h), Mirjana Malaric (MALMR, 5.00h), Katuhiko Mameta (MAMKA, 1.50h), David Martinez Delgado (MARDA, 2.01h), José Alfonso dos Reis Martins (MARJO, 2.88h), Khalid Marwat (MARKH, 2.48h), Pierre Martin (MARPI, 4.65h), Takuya Maruyama (MARTA, 0.67h), Antonio Martinez (MARTI, 4.42h), Yukihisa Matumoto (MATYU, 1.50h), Alastair McBeath (MCBAL, 7.05h), Stephen McCann (MCCST, 0.23h), Bruce McCurdy (MCCBR, 1.38h), Kevin McKeown (MCKKE, 1.00h), Lukas Mecir (MECLU, 0.13h), Mark Mikutis (MIKMR, 12.20h), Ana Milovanovic (MILAA, 6.42h), Dragan Milisavljevic (MILDR, 1.02h), Iris Miljacki (MILIR, 2.65h), Hidekatu Mizoguchi (MIZHI, 2.41h), Amruta Modani (MODAM, 2.66h), Sirko Molau (MOLSI, 14.17h), William Morgan (MORWI, 1.84h), Erick Mota Perez (MOTER, 2.90h), Darshan Mundada (MUNDA, 3.86h), Sin Nakayama (NAKSI, 3.76h), Koji Naniwada (NANKO, 4.33h), Sven Näther (NATSV, 12.35h), Dalibor Nikolic (NIKDA, 2.46h), Prakash Nitsure (NITPR, 4.05h), Mohammad Odeh (ODEMO, 4.15h), Ibrahim Odwan (ODWIB, 4.75h), Eran Ofek (OFEER, 3.47h), Hiroyuki Okayasu (OKAHI, 4.98h), Masayuki Oka (OKAMA, 5.59h), Dragana Okolic (OKODR, 3.91h), Kazuhiro Osada (OSAKA, 8.50h), Ketan Pendse (PENKE, 1.33h), Miroslav Penev (PENMI, 2.15h), Alfredo Pereira (PERAF, 5.71h), Dusan Perovic (PERDU, 5.01h), Radame Perez (PERRA, 1.00h), Suyin Perret-Gentil (PERSU, 1.52h), Furio Pieri (PIEFU, 4.73h), Mila Popovic (POPMI, 1.20h), Dubravko Potkrajac (POTDU, 1.08h), Tushar Purohit (PURTU, 2.85h), Daniela Rapava (RAPDA, 7.09h), Pavol Rapavy (RAPPA, 8.34h), Simona Rapava (RAPSI, 2.96h), Ina Rendtel (RENIN, 1.08h), Jürgen Rendtel (RENJU, 21.68h), Mileny Roche Lamas (ROCMI, 1.00h), Francisco Rodriguez Ramirez (RODFR, 5.05h), Juan Rodríguez (RODJU, 3.72h), Victor Ruiz Ruiz (RUIVI, 3.91h), K.V. Sankaranarayanan (SANKV, 2.50h), René Scurbecq (SCURE, 4.22h), Abderazak Sersouri (SERAB, 1.67h), Shashank Shalgar (SHASH, 4.03h), Brian Shulist (SHUBR, 3.10h), Hendrik Sielaff (SIEHE, 5.67h), Hiroyuki Sioi (SIOHI, 5.24h), Vesna Slavkovic (SLAVE, 2.65h), James N. Smith (SMIJN, 6.65h), Andrey Solodovnik (SOLAD, 3.05h), Manuel Solano Ruiz (SOLMA, 1.25h), George Spalding (SPAGE, 4.92h), Ulrich Sperberg (SPEUL, 3.90h), Mark Stafford (STAMA, 1.82h), Enrico Stomeo (STOEN, 1.19h), Niko Stritof (STRNI, 3.04h), Paul Sutherland (SUTPA, 1.39h), David Swann (SWADA, 6.10h), Eva Szabados (SZAEV, 0.90h), Richard Taibi (TAIRI, 4.42h), Masaaki Takanasi (TAKMA, 0.75h), Mika Takanasi (TAKMI, 4.49h), Khaled Tell (TELKH, 10.47h), István Tepliczky (TEPIS, 1.51h), Kazumi Terakubo (TERKA, 1.00h), Neelima Thatte (THANE, 5.90h), Danilo Tomic (TOMDA, 2.40h), Yasuhiro Tonomura (TONYA, 1.83h), Michael Toomey (TOOMI, 2.60h), Tamas Tordai (TORTA, 4.10h), Hamid Touma (TOUHA, 3.25h), Gabrijela Triglav (TRIGA, 0.93h), Josep M. Trigo Rodriguez (TRIJO, 1.07h), Mihaela Triglav (TRIMI, 5.31h), Arnold Tukkers (TUKAR, 15.41h), Anne van Weerden (VANAE, 5.10h), Erwin van Ballegoy (VANER, 4.92h), Jan Verbert (VERJN, 1.60h), Ivaylo Videv (VIDIV, 2.30h), Miquel A. Villalonga Vidal (VILMQ, 1.36h), Catarina Vitorino (VITCA, 3.35h), Marija Vlajic (VLAMA, 2.40h), Björn Voß (VOSBJ, 8.60h), Maja Vuckovic (VUCMJ, 1.17h), Barbara Wilson (WILBA, 5.15h), Larry Wood (WOOLA, 1.38h), Kim S. Youmans (YOUKI, 3.88h), George Zay (ZAYGE, 12.08h), Jin Zhu (ZHUJI, 1.75h).

We would also like to encourage all those meteor observers to continue their efforts in meteor astronomy, whose reports did not go in the analysis because of insufficient data:

Andras Adrovicz, Farrahzadi Azzadeh, Joshi Bhargav, Bozorgi Behnaz, Worachate Boonplod, Ravi Brahmavar, Chun Byung-hun, Diadina Cotte, Szillard Csizmadia, Kunal Dhande, Marc de Lignie, David Dickinson, Zha Dong-yan, Alipour Elnaz, Kin Enriquez, David Farkas, Azeemlu Fatemeh, Alap Ghosh, Michael Gorshechnikov, Katalin Hidasi, Brujerdi Hoda, Peter Horvath, Hyabanyan Hossein, Aftab Husain, Mustafa Husain, Yu Ji-hong, He Jing-yang, Amaya Kaloti, Usha Kasinadhuni, Timo Kinnunen, D. Kothawala, Nanda Kumar, Csaba Lendvai, Doug Little, Keith Little, Y.L. Malathi Latha, Paul Maley, Maleki Mania, Fred Mason, Dan McIntosh, Karoly Mikics, Masjedi Morad, Pathak Mukesh, Chun Myung-in, Adam Nemeth, Shigemi Numazawa, Andras Petyus, Adam Pozsik, Raj Purohit, P. Radhika, L. Ramesh, Anand Rao, Rezaai Reza, Qi Rui, J. Rukmini, Khoeini Saloumeh, Moghimi Saman, Debasis Sarkar, Lamei Sepideh, Jang Seong-hwan, Kharrazi Sharmin, Amy Shelton, Ghassemi Sima, Szandor Szabo, Darren Tabbot, Hezareh Talayeh, Zoltan Tarnoki, Zoltan Toth, Kim Won-tag, Zoltan Zelko, Sajjadi Zeynab, Wang Zhen-shi, Wu Zhi-wei.

The list of residence countries of the observers is extensive; however, many of them were not observing from home:

Aruba, Austria, Bulgaria, Canada, China, Croatia, Cuba, Czech Republic, Ecuador, Estonia, Finland, Germany, Hungary, India, Iran, Israel, Italy, Japan, Jordan, Korea, Malta, Marocco, the Netherlands, New Zealand, Pakistan, Philippines, Portugal, Russia, Slovakia, Slovenia, South Africa, Spain, UK, Ukraine, USA, Venezuela, Yugoslavia.

with additional observing sites in Cyprus and Mongolia. We would like to acknowledge the great efforts of several amateur groups here, who popularized meteor observations and sent in their results quickly for the analysis, in particular the Jordanian Astronomical Society with reporter Mohammad Odeh, the Israeli Astronomical Association and Ilan Manulis, the Spanish Sociedad de Meteoros y Cometas de España and Luis Bellot Rubio, the North American Meteor Network and Mark Davis, and the Association of Meteor Observers in and around Tokyo Area from whose internet homepage a number of records were taken; a list which is certainly far from complete and without a ranking by its order. The list of contributors is so impressive, that we can say for sure the 1998 Leonids were the most successful observing campaign ever carried out. Thank you for all the observing reports!

Population index profile

The beginning of the whole activity period is covered by few data; the earliest r-value of 2.4 in the graph was derived from 4 magnitude distributions, and it indicates that the population index resembles values of other major showers off their maximum. The r-value starts to increase quickly after lambda=235.3° ending up at values of about 2.1 on November 19.

Figure 1: Population index profile of the 1998 Leonids.

The lowest r-value of 1.19±0.02 at lambda=234.43° (November 16, 23h 30m UT) coincides quite well with the highest ZHRs observed in 1998 (see below). Such a low population index is very rare even among major meteor showers. A value of r=1.0 means that no faint meteors are appearing at all. Because of the excitement of the observers and the abundance of meteors, we should bear in mind that the population index as well as the activity are lower limits for the true values. A considerable number of faint meteors may have been missed during the impressive show of fireballs. When operating with r-values, we should not forget that the population index as a power law may not be valid at all for a magnitude range as wide as in the bright-meteor component of the Leonids stream, and r may not be a suitable measure to define the mass distribution within the stream.

Figure 2: Small-scale variation of the population index of the 1998 Leonids around the faint-meteor component. The magnitude distributions were binned in 0.05 classes shifted by 0.025.

ZHR-profile

First impressions of the Leonid fireball night November 16-17 gave higher values for the hourly rate. The very low population index is probably the main reason for the ZHR being so much lower. First calculations with a major-shower r-value of 2.0 give rates which are 1.5 times higher at lm=5.5mag than with r=1.3. Again, the activity might be underestimated by some of the observers, since less attention may have been paid to faint meteors under the fireball display. A selection of those observations which report no meteors fainter than +2mag gives no preference to either high-rate or low-rate observers. Video records will tell us more objective numbers, though they will not cover the whole activity period.

Figure 3: ZHR profile of the 1998 Leonids. The radiant elevation is corrected for by the geometrical factor sin^-1h_R, which may underestimate low-elevation ZHRs. See the details in Figures 4 and 5 and the discussion in the text for final values of a maximum ZHR.

Figure 4: Small-scale ZHR profile of the 1998 Leonids around the time of highest activity. Only observations with radiant elevation h_R>50° were used to avoid any influence of non-geometrical zenith corrections. The obervations were binned in 0.05 classes shifted by 0.025.

The ZHR may be subject to deviations of the zenithal correction from the geometric value sin^-1h_R with h_R being the radiant elevation. The exponent may be altered to values higher or lower than unity. A general value of 1.4 was adopted in [3], and a re-calculation of the ZHR profile with a zenithal exponent of gamma=1.4 shifts the whole graph up with a maximum ZHR near 300, which is simply a consequence of gamma increasing the corrections at all elevations. The abundance of observations allowed a restriction to observations with h_R>50°, reducing the set of rates to those which are not strongly affected by the uncertainty in the zenith correction; the results for the broad component and the `storm' component are given in Figures 4 and 5. The ZHR appears to be significantly higher than the average of all elevations h_R>20°. The indications for gamma>1.0 contradict the finding in [4] that gamma is not larger than unity for the Leonids.

Another difficulty at very low population indices is the change in effective field of view. Usually, about 98% of all observed meteors appear within a field of 105° diameter. This will hardly be true for an abundance of fireballs. Future analyses should scrutinize the influence of a low r on the actual activity measure and on the spatial number density (flux density) in particular.

Despite the clear maximum near lambda=234.5°, we should pay attention to the additional activity enhancement which is close to the prediction for the storm component. This secondary peak was hardly detectable by the observers in the field, but the significant increase of the population index makes the enhancement more prominent. The ZHRs are far below even pessimistic predictions - no meteor storm was observed. Very fine temporal binning of ZHRs in windows of 0.02 length (about 30 min), shifted by 0.01, reveals a short peak at lambda=235.308°±0.010°, (November 17, 20h 30m UT) as shown in Figure 5. The set of observations was restricted to those with h_R>50° in order to find the actual peak ZHR being less affected by zenithal-correction uncertainties. Since systematical errors are involved additionally to the statistical uncertainty, we are well advised if we double the errors and fix the sharp peak at ZHR=180±20. The same rule gives a Leonid maximum of ZHR=340±20 for the bright-meteor component.

The extremely short period cut out in Figure 5 allows us to subtract a roughly linear decrease of the background component from the ZHR values, such as ZHR_back~ 40288-170.9 lambda. The full width at half maximum of the remaining component is 0.031° corresponding to about 45 minutes or B~20 in terms of [3] which is quite similar to B~30 for the Leonid outbursts in 1866, 1867, 1966, 1969. A first detection of the short-lived peak in this Leonid epoch (which has produced enhanced activity since 1994) was found in 1996 data in [5] with B~30.

Figure 5: Small-scale ZHR profile of the 1998 Leonids around the time of storm prediction. Again, only observations with h_R>50° were used. The obervations were binned in 0.02 classes shifted by 0.01.

The lowest population index of r=1.19 occurred about 0.09 earlier than the ZHR maximum in solar longitude (2.2 hours) which is not exceptionally much given the broad shape of the background component. The faint-meteor component peaks also at the end of the high population index period.

Spatial number densities