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(meteorobs) [IMO-News] SPA Meteor Section Preliminary Results: Leonids 2000




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Clear skies,
Lew Gramer <owner-meteorobs@jovian.com>

------- Forwarded Message

To: imo-news@egroups.com
From: Alastair McBeath <mcbal.gwyvre@virgindot net>
Date: Sat, 25 Nov 2000 12:17:01 +0000
Subject: [IMO-News] SPA Meteor Section Preliminary Results: Leonids 2000

SPA Meteor Section Preliminary Results: Leonids 2000

Thanks to an excellent and very rapid response by 39 observers (28 in
the UK) enough preliminary data have already been reported to the SPA
Meteor Section to make a first glimpse possible of how the shower was
perceived, just a week after the main maximum. Bright moonlight, poor
northern European weather, and the fact that no storm was seriously
expected from the Leonids this November proved no deterrents!

In Britain, observations on November 16-17 were possible from parts of
south Wales and much of central to eastern England, while much of
western England, Scotland and Northern Ireland seem to have been caught
beneath overcast skies. From the UK-only data, something of the November
17, ~06h UT minor peak identified in the early IMO results looks to have
been visible as dawn twilight was strengthening, when Leonid ZHRs (all
computed with r = 2.5 here) rose from a steady overnight ~50-70 +/-
15-20 between at least 02h-05h30m UT, to around 100 +/- 30 soon after
06h UT. A few minor fireballs (magnitude -3) were spotted, with a hint
of slightly more of these towards 06h UT, but not especially
convincingly. Initial checking of the meteor magnitudes does suggest
somewhat enhanced numbers of brighter Leonids near this time however. A
couple of observers commented on the rather strange observing
circumstances the Moon enforced, where Leonids were coming from "over
their shoulder", as they faced towards the northern skies to keep the
Moon as far from their line of sight as possible!

Unlike in 1999, southeastern England seems to have been the place to be
in Britain on November 17-18, as chiefly positive reports have arrived
from this area, including from four sites in Essex, two in Middlesex,
and others in Bedfordshire, Buckinghamshire, Cambridge, Kent,
Oxfordshire, Surrey and Sussex, plus one report of clearer skies late in
the night further north in West Yorkshire. Even so, observers often
struggled with clouds, though many reported seeing a superb 22-degree
radius halo around the Moon, thanks to a high-altitude cirriform
cloud-sheet ahead of an advancing frontal weather system. Healthy Leonid
rates of up to minor fireball-class meteors (magnitudes ~ -3 to -8) were
viewed by most in spite of this.

Computed ZHRs based on the British reports show a large scatter because
of the poor skies, but were generally around 200+ by 02h UT. There are
indications of possibly two or three submaxima on November 18, most
noticeably around 03h30m-04h15m UT when ZHRs were ~330 +/- 100, perhaps
with two stronger phases around 03h40m-03h45m and 04h10m-04h15m UT.
Drawing on overseas data as well as UK reports, another possible
submaximum may have happened around 02h50m +/- 10m (ZHRs ~300 +/- 130),
but this is not especially clear. Some of these "peaks" may simply have
been times when more brighter Leonids were apparent, given the unhelpful
conditions.

By contrast to southeast England, the frontal system produced generally
overcast skies, and sometimes rain, elsewhere. Clouds, rarely punctuated
by occasional sightings of a meteor or meteoric flash brightening the
overcast, were more typically observed from most places with active
watchers in northern England, Northern Ireland, Scotland and Wales on
November 17-18. Even so, most people greeted the lack of clear skies
philosophically, as November is traditionally one of the worst months
for clear weather in the UK, and those who had seen something the night
before were glad not to have wasted that opportunity at least. Under
good skies overseas, several Section correspondents commented that the
November 17-18 display seemed similar in strength and persistence to the
1998 Leonid fireball night, but this year's meteors were significantly
fainter, with very few notable fireballs.

By November 18-19, skies were overcast above much of southern and
western Britain, and very few positive reports have been received as
yet, the few that have indicating Leonid ZHRs had fallen back to around
30-40 +/- 15. Even that level is two or three times better than the
Leonids achieve in their more typical non-outburst years, of course.

Early radio results and comments from radio hams tend to support the two
stronger visual Leonid peak times on November 18 particularly (around
03h45m and 07h15m UT). Some also suggested system-saturation occurred
near these peaks. This may well have been due to increased atmospheric
ionization produced by the Leonids, which may be a type of Sporadic-E,
last detected this strongly from the shower in 1996 (as I discussed in
the IMO's journal WGN 25:1 (1997), pp. 45-53).

My grateful thanks go to all those who have provided results - whether
positive or negative - so far. All further reports would be very
welcome! An update to the information here is planned for mid to late
December on the Meteor Section pages of the SPA's Website:
http://www.popastro.com , as well as in printed form in the SPA News
Circulars, the IMO's journal WGN, and the SPAMS' 2000 Annual Review,
each to be published in due course. If you observed from Britain on
November 17-18, please also mention if you spotted a lunar halo that
night, and as there is one comment from an observer who saw all five
naked-eye planets with the unaided eye in a single night over the Leonid
epoch, it would be interesting to know who else managed this, wherever
they observed from.

Alastair McBeath,
SPA Meteor Section Director.

Contact address: 12A Prior's Walk, Morpeth, Northumberland, NE61 2RF,
England, UK.
E-mail: <vice_president@imodot net>

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