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(meteorobs) IMO-NEWS: 1999 Beta Taurids Alert - Possible Swarm Appearance




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Date: Wed, 16 Jun 1999 15:55:49 +0100
From: Alastair McBeath <mcbal.gwyvre@virgin.net>
To: imo-news@imo.net
Subject: 1999 Beta Taurids Alert - Possible Swarm Appearance

1999 Beta Taurids Alert - Possible Swarm Appearance

>From Alastair McBeath, IMO Vice-President, e-mail:
vice_president@imo.net

In 1993 David Asher presented a paper to the International Meteor
Conference in Puimichel [1] describing a theoretical resonant swarm of
particles within the Taurid/Beta Taurid stream which could account for
various meteor shower enhancements, increased fireball fluxes and even
meteoritic impacts associated with the Taurid Complex of meteoroid
streams, asteroids and comets. He used this theory to suggest times when
future returns of the proposed "swarm" might lead to increased activity
from the nighttime Taurid showers active in October-November, and the
daytime Beta Taurids of June-July. He suggested that 1999 could see a
return of the swarm during the Beta Taurid activity period, which is the
purpose of this reminder warning now.
	Results from late October 1998 [2] suggested an enhanced Taurid period
had been detected by radio and visual observers in the closing days of
the month, along with an increased flux of minor Taurid fireballs
(magnitudes -3 to -8). Another of David's predictions for the swarm was
that a recurrence might be expected in October-November 1998, which may
well be what was recorded.
	The Beta Taurids are usually assumed to last from about June 5 to July
17, reaching an ill-defined single maximum around June 28 (solar
longitude 96.7 degrees (all solar longitudes given here are for eq.
J2000.0)) from a radiant at approximately alpha = 086 degrees, delta =
+19 degrees. There is some disagreement in the published data on the
shower concerning most of these parameters however (cf. [3]). Most
authors suggest a lengthy, flat maximum occurs in late June to early
July. Forward scatter radio results from 1994-1997 [4] indicated a
moderate-strength echo count enhancement occurred between roughly solar
longitudes 91-93 degrees, with signs of weaker activity bracketing this
"peak" between solar longitudes 89-99 degrees. It is not clear if this
activity belongs to the Beta Taurids, nor whether this represents a
shift in the maximum time by several days if so, but the 89-99 degrees
spell is at least comparable in length to the Taurid maximum time in
early November.
	From their orbital parameters, it is clear the Taurids and Beta Taurids
are linked, either as two encounters by the Earth with the same stream,
or as two separate streams which follow very similar orbits, so it is
not unreasonable we may extrapolate details for the Beta Taurids from
what we know of the Taurids. If we can do this, it is possible any swarm
enhancement of the Beta Taurids this June might occur up to 5-8 days
before the expected maximum, following the relative timings of events
seen last October.
	To identify what happens with the Beta Taurids this year, whether a
swarm event or not, I would suggest radio observers should be especially
alert between June 18-19 through to July 2-3 at least (still later in
July might be better, as some earlier results suggested a Beta Taurid
maximum around July 2 or 3; this has not been found in data from the
1990s so far, however), as continuously as possible. This should cover
whatever the shower produces and also provide non-peak data for
calibration. Ideally, 24-hour-a-day monitoring should be carried out,
but if this is not possible, try to make your observing runs at the same
time every day. The Beta Taurid radiant is above the horizon between
roughly 03-04h local time to about 18-19h, for northern hemisphere sites
between approximately 35-55 degrees north near June 28.
	There are likely to be problems because of Sporadic-E interference,
other atmospheric events (storms, etc.), and potentially Auroral-E as
activity builds in Solar Cycle 23. Times when any of these occurred
should also be included in your reports. Furthermore, there is the
possibility that the June Bootids, which produced their sudden, and
quite unexpected, outburst on 1998 June 27-28, may recur this year
(again on June 27-28 if their timing is the same as in 1998). So far, it
has not been possible to say why the Bootid outburst happened last June,
so telling when another one might transpire is presently impossible. The
overlap in radio-visibilities between the Beta Taurids and the June
Bootids is significant for sites north of about +45 degrees latitude,
which created problems in analysing the Bootid outburst by radio in
1998. This means any unexpected radio peak around June 28 this year need
not have resulted from the Beta Taurids. Only careful analysis of a
large enough body of data will reveal this.
	Non-radio observers are faced with a very difficult prospect, because
the centre of the Beta Taurid radiant is just 10 degrees or so west of
the Sun on June 28. Tropical or near-equator observers might possibly
see a few slow-moving shower fireballs in the strong predawn twilight an
hour or two before sunrise at some point during the dates given above,
if anything unusual happens from the shower this year. As even the outer
fringes of the radiant will be on or below the horizon however, the
meteors will probably have exceptionally long paths across the sky.
	For particularly northern hemisphere observers, there is the additional
possibility that a few daylight fireballs might occur if a swarm
appearance manifests. This is because the Beta Taurid radiant will be
high to very high above the horizon for a large part of the day near the
shower's expected best from such places. Those who routinely handle the
American DoD satellite reports which feature especially brilliant
meteors (Zdenek Ceplecha's "superbolides") should pay particular
attention to any events that occur during the late June to early July
period as well; an increased flux could represent something unusual from
the Beta Taurids. Although the nighttime Taurids do not have much of a
reputation for producing these especially brilliant fireballs, the Beta
Taurids may be capable of doing so, assuming for example that the major
clustering event of lunar impacts, detected by the Apollo programme's
seismometers, of about ten days' duration centred on 1975 June 22 was
due to this source.
	There are of course no guarantees that anything unusual will happen
from the Beta Taurids this year, but even establishing that no swarm
recurrence happened in 1999 June-July with some degree of certainty
would help refine David Asher's model of the Taurid Complex swarm. Even
a swarm appearance is not guaranteed to produce spectacularly high rates
or dozens of bright meteors. If the 1998 late October Taurid event was
due to a recurrence of the swarm, it should be noted that the visual
ZHRs from the shower were enhanced only to the level of normal maximum
rates (combined ZHRs ~9-10; usually no better than ~5-7 in late
October), while the Taurid fireball percentage was roughly double that
in normal years.
	Observations should be submitted to all the usual places you routinely
do, but copies can also be e-mailed to me as well. Please bear in mind
that I am still most unwell however (as noted in WGN 27:2), so do not
expect a rapid response. Good luck, and clear, Sporadic-E-free skies for
your data collection!

References:
[1] D. Asher, "Meteoroid Swarms and the Taurid Complex", in:
"Proceedings IMC, Puimichel 1993", ed. P. Roggemans, IMO, 1993,
pp.88-91.

[2] A. McBeath, "SPA Meteor Section Results: September-October 1998",
WGN (in press).

[3] G. W. Kronk, "Meteor Showers: A Descriptive Catalog", Enslow, 1988,
pp.115-118.

[4] A. McBeath, "The Forward Scatter Meteor Year", in: "Proceedings IMC,
Petnica 1997", eds. A. Knoefel & A. McBeath, IMO, 1998, pp.39-54.



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