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Re: (meteorobs) NASA News articles
Joe,
In assessing the cause of the "storm gap", it is important that the
frequencies be normalised by the probability of the Earth encountering the
narrower target area around the comet. The dust trails all converge on
the comet from in front and behind in the orbit, thus the smallest target
area is around the comet itself. The second factor is the mass dispersion
that favours the visual masses in the region trailing the comet where the
ratio of solar radiation pressure to gravitational attraction is about
0.001. The mass distribution in front of the comet does not favour big
displays, but the target area is extended. Close to the comet, the target
area is very small and comprises mostly resonant meteoroids, but some very
young dust trails will have high density. A year or two behind the comet,
the target area is wider and the mass distribution favourable for visual
storms. Further back, the target area is TOO wide (the Earth will miss
most trails) and in addition, the mass density is against a large number
of visual meteors.
Thus, I really do suspect there is a basis to what you describe, but I
believe it is a consequence of probabilities and that a major storm would
occur in this exclusion zone if the Earth/dust trail geometry is correct.
At an outstanding lecture John Mason gave on the Leonids in Edinburgh when
I was there three years ago, I pointed out the importance of normalising
the geometrical encounters for their actual probability of occurring (or
having occurred). I'll get around to it one day, hopefully soon!
Cheers, Rob
Robert H. McNaught
rmn@aaocbn.aaodot gov.au
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