[Prev][Next][Index][Thread]
(meteorobs) Re: A rethinking of upcoming Leonid rates
Hi Joe,
I agree that there is possible evidence of "gusts" (at the moment to over
50 knots outside, so I closed the dome!) in historical data, but it is
common for people to assume that a random distribution should be uniform,
and that non uniformity is non randomness. For this reason, unless the
data is tested and shown to be non random, I would tend to think this says
more of human psychology than the distribution of dust. Could there be
micro-structure in the dust trail caused by resonances? I doubt it.
Could jets from 55P/Tempel-Tuttle cause detectable localised "veins"
within the dust trail? Possibly. The velocity distribution at ejection
will extend the jet throughout the dust trail along it's length, the width
being determined by how collimated the jet is.
Regarding the ZHR of 1,500 for 1999 in the WGN article by David and I,
this should probably have been rounded to 1,000 (using ZHR0=1,200). I
rounded it to 1,500 because the center of the dust trail is expected to be
beyond the nominal center of the calculated dust trail and this would give
higher rates. The value of 1,200 was close to the boundary between
rounding up or down.
A more recent fit to the historical data, using slightly revised values
for da0 and re-rd (refer to WGN article) makes a slightly messier fit (20%
overall error to Peter Brown's historical ZHRs), but this is mostly now
due to a discrepancy between 1833 (predicted high) and 1966 (predicted
low). The new ZHR prediction for 1999 was somewhat lower than we got
before. Assuming the 1966 value by Peter Brown is reasonable, I would
increase the new 1999 prediction and again come out at around a ZHR of
1,000. For some future years, the situation has changed slightly,
but it makes no sense to pay much attention to those when we will
have another, and presumably the best so far, data point in just over two
weeks. So close! 33 years has gone by already!
Because of the uncertainty in historical rates, I think the dust trail
density model is restricted largely by the poor data. Also with improved
data over the next few years and a better theoretical profile in da0 and
re-rd than the assumed Gaussians, I would hope that the dust trail density
model could be confirmed.
What is needed is a good ZHR profile of the 1999 activity. That is in the
hands of all you visual observers!
Cheers, Rob
PS the origin of the 1866 activity is stated in our WGN article and by
Kondrat'eva et al much earlier.
To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html
References: