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(meteorobs) Unrealistic ejection model?
Since David and I first published work on the Leonid dust trails, our
work has occasionally been criticised as having an "unrealistic ejection
model". This is pretty strange, as we have no ejection model and there
is no use of an ejection model in calculating dust trail parameters.
Recently, this was put to me again by a journalist and just for the
record I'll explain here what was in our original papers but has been
so often misunderstood. It is a little technical and only the brave
may wish to venture on. However anyone who wishes to comment on the
various Leonid storm prediction models must have this point clear or
they do not understand our work. So here goes (it is actually an
excerpt from an email I sent recently)
> Whilst I'm not stating, and don't believe, that the "dust trail theory"
> is all there is to storm prediction, there has been a consistent
> misunderstanding about the basis of the theory. In calculating the
> "center" of a dust trail, for some future date, the theory derives by
> an iterative process the precise orbital period, with consideration
> of solar radiation pressure, and full planetary perturbations, the
> subsequent nodal longitude and radius for precisely the time the Earth is
> at that nodal longitude. The bit that is misunderstood is that in doing
> this, we use a velocity difference from the comet (ejection velocity)
> *in the direction of the comet's motion vector* to derive the starting
> orbit. This has often been characterised as being "an unrealistic
> ejection model" presumably by people who have either not read or not
> understood the original papers by David or David and myself. We
> demonstrated in our original paper that the cross-section of a dust
> trail at nodal passage using the instantaneous orbits of dust ejected
> isotropically at perihelion, is basically invariant for some future
> nodal passage *for those specific particles that have the precise orbital
> period to be encountered at this later date.* (This last sentence is the
> stumbling block and I hope you can understand the way I've put it).
> Thus, the "center" we calculate will produce a dynamically invariant
> reference point on the dust trail on which all subsequent calculations
> are based.
David has pointed out to me that Kondrat'eva and Reznikov clearly
understood this in their 1985 paper. What on Earth is going on that
almost two decades later and well into the end of the Leonid storm
period, this point is not yet generally understood.
Rob McNaught
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