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Re: (meteorobs) Two question regarding meteor rates?
In message <6.0.0.22.2.20040425182501.03d10308@in.pandoradot be>, Geert
Barentsen <geert.barentsen@pandoradot be> writes
>
>Hello David!!
>
>I'm sure some people on this list know a lot more about this topic than I
>do. I hope they will correct my errors :-)
Hi Geert,
thanks for the reply.
>
>If Earth's tilt were the only mechanism involved, I guess we would expect
>the seasonal variation in the southern hemisphere to "mirror" the activity
>in the northern hemisphere... However, this is not the case! My memory
>tells me that a graph in IMO's "Handbook for visual meteor observers" shows
>this. Unfortunately I don't have a copy.
I'll have to get hold of a copy too.
>
>In fact, the sporadic "sources" (Helion, Antihelion, Northern Apex,
>Southern Apex and the mysterious Toroïdal sources) seem to vary quite a lot
>over the year! Apex and Antihelion are quite calm in the first half, but
>very active in the second half of the year! Why? I don't know :-) ...but
>there is an obvious link with comets! Antihelion particles all have low
>incilination, prograde eccentric orbits, wich are essentially identical to
>short-period comets. Apex particles have orbits similar to long-period comets.
>
>Jones&Brown have written excellent articles on this topic, some of wich are
>available through NASA's ADS (I can look up references if you want). These
>studies are all based on radar observations, wich is obviously the best
>possible data to do this. I recently tried to show sporadic source
>variation as well using IMO's VMDB, but the results I obtained were rather
>poor.
>
Thanks for the pointer to the ADS, which I hadn't used before. That'll
keep me busy for a while. For anyone not familiar, its
http://adswww.harvarddot edu/
>By the way: some time ago I discovered an interesting graph through Google:
>http://www.asdot itb.ac.id/~ferry/Articles/MeteorFenomena/image5.gif
>I do not understand the language of the originating webpage (
>http://www.asdot itb.ac.id/~ferry/Articles/MeteorFenomena/MeteorFenomena.html
>), but the graph seems to illustrate the effect of the seasonal variation
>on the daily variation! This is very interesting material for people who
>are trying to understand sporadic variation!
Yes, interesting. In 'Meteor Science and Engineering' McKinley suggests
that the repeatability of the diurnal curves, for a given month,
indicates that, despite the best efforts to remove the effects of the
known showers, the data still includes meteors from minor showers. If
only we could resolve them.
The annual variation, shown on that site, is very much the same
information that the ITU provide in recommendation P.843-1. Again
looking through 'Meteor Science and Engineering', I think the source may
be forward scatter radio observations made by Vogan and Campbell in
Canada in 1957. I think the distinction between data sourced from visual
rates and that sourced from radio and radar scatter rates is a
significant one - the former being limited to the hours of darkness and
the other not.
>
>PS: It's very fun and informative to play with the data in the VMDB!! I
>recommend it to everyone!
>
Thanks again. I haven't tried that either.
http://www.imodot net/visual/vmdb.html
--
David Entwistle
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