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Re: (meteorobs) Ursid shower outburst confirmed
Title: Re: (meteorobs) Ursid shower outburst
confirmed
Dear Gary et al,
It strikes me that the visual
observations may not be the key data here. Instead, it's the the
radio activity profiles that tell the tale of the 2000 Ursids.
See http://leonid.arc.nasadot gov/leonidnews29.html. It would indeed be interesting to compare those data to
similar observations from other years, but perhaps the more important
comparison is how the data match Jennisken & Lytennin's
predictions, which are based on a physical model of the debris
stream. They seem to agree agree pretty well.
I would also like to see some data well
away (geographically) from Finland to confirm the peak -- there's
always a chance that local propagation anomalies can mimic a radio
meteor outburst. Regards, Tony
The radio activity profiles would be interesting to compare. I
am a bit surprised that only normal activity was recorded by the
Ondrejov backscatter radar from 6-9 hours UT on December 22,
while Ilkka Yrjola (Kuusankoski,
Finland) reports that rates of radio meteors began increaseing
after 4 hours UT and shot up just after 8 hours UT.
My interest in this year's Ursid rates are not necessarily to
support my prediction of just normal activity because of the effects
of Jupiter's perturbations on the entire Tuttle/Ursid stream every
11.86 years, but also because this has been one of the best monitored
Ursid displays ever.
We know the two significant Ursid outbursts in 1945 and 1986
were very prominent for visual observers, yet this year's visual
display was not as spectacular. So, how do the radar/radio-echo
reports of the past compare to this year's display?
I have saved all of Christian Steyaert's "Radio Meteor
Bulletins" for the last few years. I called up the report for
December 1999. The Ursid maximum was expected to occur around
December 23 at 0 hours UT. Pierre
Terrier (Canet, France), was monitoring a frequency of 102.5
MHz. He reported hourly rates of 0 to 22 meteors for every 24-hour
period from December 16 (0 hours UT) to December 22 (14 hours UT).
Beginning on December 22 at 15 hours UT, the hourly rates climbed to
34 and remained above 25 per hour until December 23 at 6 hours.
During that interval, the highest rates were 132 and 145, which were
recorded at December 22, at 21 hours UT, and December 23, at 2 hours
UT. These rates were the highest he recorded for the entire month of
December 1999, even higher than the Geminids which did not exceed 97
per hour. The entire activity curve is very comparable to that of
this year's curve reported by Ilkka Yrjola, but
centered around last year's expected maximum.
Now let's look at Yrjola's rates for last year. Instead of me
trying to summarize, here is the table of data copy and pasted out of
Steyaert's bulletin.
Ursids
1999
Meteor counts in one hour intervals starting at:
UT | 20 Dec 21 Dec
22 Dec 23 Dec
----+----------------------------------
0h |
168 172
199 213
1 |
183 162
259 216
2 |
192 200
199 179
3 |
211 156
165 183
4 |
207 232
216 203
5 |
263 252
271 236
6 |
321 274
293 301
7 |
240 333
276 267
8 |
307 483
278 261
9 |
229 379
336 190
10 |
351 220
290 247
11 |
415
400 304
12 |
287
472 266
13 |
241
619 208
14 |
215
193 159
15 |
151
179 175
16 |
159
150 141
17 |
155
149 155
18 |
141 245
219 155
19 |
190 170
186 160
20 |
197 198
279 174
21 |
168 239
285 235
22 |
189 242
270 225
23 |
183 235
306 177
----+----------------------------------
UT | 20 Dec 21 Dec
22 Dec 23 Dec
. tropo on Dec 22, 11h - 18h UT
Ilkka
Yrjola
(my addition here is that the frequency was 88.8 MHz)
For the 2000 Ursids (see the link at
http://leonid.arc.nasadot gov/leonidnews29.html), Yrjola's data indicates a strong increase in activity
at 4 hours UT, which persists in varying degrees until 14 hours UT.
Look at the table above. For December 20, 1999, the rates from 5
hours UT through 13 hours UT are higher than any other time on the
20th, with a peak at 415 per hour. For December 21, the peak from 5
hours UT through 13 hours UT are higher (with one exception) than any
of the earlier or later times on the 21st, with a peak of 619 per
hour. High rates are also present for the same period on the 22nd,
before the system was down, and you can once again see the highest
rates during the same time period on the 23rd. So Yrjola's own data
either indicates similar Ursid peaks in 1999 as in 2000, with a
periodic persistance that lasts at least 4 days in 1999, or rates
that increase and decrease because of some environmental
condition.
This is something we need to straighten out if we are to fully
understand what happened with the Ursids in 2000.
Gary W. Kronk
References: