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Re: (meteorobs) A rethinking of the upcoming Leonid meteor rates



>    Those who have read my Leonid paper in WGN 27:3/4 will have noted how 
>through orbital simulations I had integrated material from the great Leonid 
>storm in 1833 forward to 1866.  What I discovered was that the orbital 
>separation between the Earth's orbit and this 1833 material had widened to 
>almost 0.007 a.u. by 1866.  Also, I integrated material from the 1966 forward 
>to 1999 and found a separation between Earth's orbit and this material of 
>nearly 0.003 a.u.  
>
>    My initial supposition was that such a difference between 1866 and 1999 
>would result in 1999 seeing much higher hourly rates compared to the 6000 to 
>10,000 rates of 1866 (as noted in Icarus 138, 287-308 by Peter Brown).  
>
>    Last week however, I had a chance to e-mail David Asher and inquire why 
>he left out the meteor trail map for 1866 from the Armagh Observatory 
>internet site.  He kindly -- and very quickly -- responded by adding the map 
>to the site, which indicated that a meteor trail shed by 55P/Tempel-Tuttle in 
>1733 was primarily responsible for the 1866 display.  Over this past weekend, 
>I performed an integration for 1733 myself and found that this material 
>passed ~0.001 to 0.002 a.u. from Earth's orbit in 1866, pretty much 
>confirming what David had indicated. 
>      
>    As a result of this, I am toning-down my original "guesstimate" of Leonid 
>activity to 2,000 to 6,000 per hour.  In WGN 27:2, David and Rob McNaught 
>suggest a peak of 1,500 per hour -- a rate that is quite close to the 
>lower-end of my revised range.  
>
>    I should, however, point out something that is not-often cited in 
>predicting Leonid rates and that is the propensity of meteor activity during 
>a storm apparently coming in "waves" or "surges."  The oft-quoted "40 meteors 
>per second" from Dennis Milon's team at Kitt Peak Observatory in 1966 was 
>arrived at after a consensus, but was probably the ABSOLUTE UPPERMOST LIMIT 
>of observed activity.  Indeed, there were others who claimed to have seen 
>similar, if not even higher rates (James Young at Table Mountain Observatory 
>suggested 50 per second!) but again, this may have only been an extreme upper 
>limit.  As I comment in a footnote in my WGN paper, many other witnesses of 
>the 1966 storm noted lower rates of "only" 10 to 30 per second.  A very 
>telling description came from Dana K. Bailey of Boulder, Colorado, who 
>commented in the January 1967 Sky & Telescope that " . . . no fewer than 10 
>new meteors were appearing each second, for many minutes, yet  sometimes the 
>rate was double or triple that . . . "
>
>    Another suggestion of meteor activity apparently coming in surges, comes 
>from a description of the 1866 Leonids as reported in The London Times:  
>
>"The spectator had soon counted half a dozen; then he felt sure he had seen 
>thirty; then six or seven in a minute . . . Then there came two or three 
>together; then not less than a dozen of all kinds."  
>
>    In essence . . . if indeed, a maximum of 1,500 per hour occurs this year, 
>that's 25 per minute or one meteor every two or three seconds.  It would not 
>be surprising however, if -- based on the above description -- there come 
>brief intervals when the rates may actually reach several times this rate.  
>You've heard of major storms that, for example, produced " . . . sustained 
>winds of 50 miles per hour, but with occasional gusts to 80."  Well . . . in 
>1999, it could very well be that we'll hear of overall sustained 
>single-observer rates of say, 2,000 per hour with occasional bursts ("gusts") 
>to 7,000!
>
>-- joe rao         
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>
Norman W. McLeod III
Staff Advisor
American Meteor Society

Fort Myers, Florida
nmcleod@peganet.com

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