The highly unexpected development of the 1998 Leonids, with high fireball activity way *before* the night of nodal crossing but no storm or even noticeable enhancement of activity around the crossing time is widely known by now - see e.g. the still evolving tabulation and ZHR plot at www.imo.net/news. The Mongolian observations (not included there at the time of this writing) were carried out by a high-profile joint Canadian-U.S. team led by Peter Brown (a grad student from Ontario Western University) and represented by Col. S.P. Worden of the U.S. Air Force, a 14-head German expedition (including the author) led by Juergen Rendtel, as well as several Slovakian and Croatian astronomers.
During the "maximum" night the Khurel Togoot observatory - normally a largely deserted place no longer maintained as an active astronomical research facility - was also host to a surprisingly large number of journalists called there by the Americans and Canadians. Most were international correspondents based in UB, but one had actually flown in from Canada. By pure coincidence a handful of bright meteors kept the spirits of the freezing crowd high just when Leo's head rose around midnight Mongolian time (16:00 UTC on Nov. 17). But there would be no replay of the stunning fireball show from 20 hours ago: Mainly faint meteors could be spotted, and in particular no increase of the rate when the 'magical' time of nodal crossing (ca. 3:30 local time) approached.
At 2:20 Mongolian time (18:20 UTC) Col. Worden broke the bad news to the press: "We're not seeing any increase that would indicate we'll have a major storm in the next few hours," he stated and suggested that one might as well go home. "Do you have any idea what happened?" someone inquired - Worden: "No!" But let there be no mistake: Last night's "very very strong bright shower of fireballs," according to Worden, "was probably one of the more impressive fireball shows on record." And he even referred to the German amateurs on the site: "Veteran meteor observers among both the German team and our team say that this is the most impressive fireball display they've ever seen." And for him personally - a solar astronomer by training - "that's the most impressive thing I've ever seen in the sky."
Amazingly the fireball storm - if one chooses to call that rare phenomenon that - had been a global phenomenon: It had "persisted obviously for at least 18 hours, because we have reports from across Europe and N. America, some of them visible in daylight - this is a very unusual situation," Worden summarized the first news that had reached him. (Even 3 days later the detailed activity profile is unclear as may teams haven't had an opportunity to report their data in; it seems however that Europe got at least as high a rate as Eastern Asia, with ZHR values approaching 500.)
A preponderance of fireballs long before nodal crossing is not exactly new, however, as Worden reminded the reporters: "1965 had a broad peak of very very bright meteors that lasted for 36 hours" - and was followed by a no-show at nodal crossing. 1966, however, had then brought a tremendous meteor storm at crossing time. For 1998 nearly all models had anticipated a profile similar to 1966, with a pronounced - although much smaller - peak at nodal crossing. Why the forecasts failed so completely is now a major mystery. It only seems clear that the big particles that the Earth had encountered well before - but not during - nodal crossing had been released by comet Tempel-Tuttle several hundred years ago. Since there were so many, Tempel-Tuttle must have experienced "a pretty major set of events" (Worden) back then. The small particles the Earth was encountering right now in contrast were young.
With these fresh insights into the vagaries of meteoritical science - and its strong resemblance to long-term weather forecasting - swallowed with the help of a few free beers (courtesy of the U.S. embassy) most of the press had left by 3:30 a.m., leaving behind the astronomers on the observatory who had largely missed Worden's 'official' cancellation of the show. There were the Germans from the AKM (Arbeitskreis Meteore) who had largely gathered on an isolated rock and were recording the meteor activity with an array of video cameras with image intensifiers, photographic cameras and visually. Last night individual observers had seen up to 100 meteors in one hour, most of them very bright or fireballs, often leaving spectacular trains behind (this number, corrected for geometrical and other effects, corresponds to a ZHR of about 250).
Now still some 35 to 40 meteors could be spotted in an hour, but the fireballs were largely gone, and the ZHR had clearly started to decline. And by the next night (18/19 Nov.) it would have dropped off dramatically, to some 10 Leonids per hour. The observing logs, photographs (hopefully) and especially the roughly 100 hours of videotape from all 4 nights will be a major source for further studies, perhaps helping in the end to explain "what went wrong" or rather why everything went so differently from the expectations this year.
Rather similar data material has been collected by the Canadian-U.S. expedition: Here, too, a battery of video cameras had been pointed at the sky, even from two sites (to get redundancy plus 3D vectors for selected meteors), and visual counts had been made. But the highly organized effort had had a second objective well beyond basic research: The visual counts as well as the data gleaned in real-time from one of the video cameras (by an experimental computer program, 'Meteorscan', as well as from someone watching a monitor) were telephoned every 15 minutes to Canada. From there the information - now transformed to ZHR's � was eventually passed on to the Air Force's Space (Weather) Forecast Center in Colorado, which would have warned satellite operators in case of a real storm brewing.
None had been, of course, and no obvious satellite anomalies were reported either: The Mongolian experiment had mainly been a demonstration of principle. But interestingly the prolonged exposure to comparatively large meteoroids for 24 hours could in principle be as harmful as a strong but short peak of activity. The further analysis of the Mongolian tapes and data in the coming months will help to quantify this possibility - and will hopefully lead to better predictions for the 1999 Leonids.
And the generally positive experience with the real-time analysis of meteor videos could one day lead to a world-wide network of automated monitoring stations - perhaps associated with an already existing network of U.S.A.F. telescopes keeping an eye on the Sun. The 1998 Leonids didn't live up to some peoples' expectations, no doubt, but they will eventually bring forward meteor science a great deal. And on an 'operational' level they have already made history.
The return of the Canadian-German meteor expedition from Ulaanbaatar has been delayed by at least 2 days as the only plane of MIAT airlines is standing disabled in Frankfurt... Now we hope to be back by Tuesday night in Berlin.
In other news we have had ample time to review the video tapes of the 'pre-maximum' night (Nov. 16/17) and are happy to report that many spectacular fireballs were captured. Part of the material has already premiered in the German embassy at a party on Nov. 20th. IMHO the material is far better than anything that has been on CNN so far, e.g. on yesterday's Science & Technology Week...
Message posted via telnet from the
International School of Ulaanbaatar
by Daniel Fischer, science writer, Koenigswinter, Germany
