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(meteorobs) Preliminary ZHR California 17-11


Hello everybody,

I have done some very (VERY) preliminary calculations, using Bob 
Lunsfords data, to get some insight into the Zenit Hourly Rates (ZHR) 
experienced for the maximum period, which California presumably 
experienced or was very close at. You find them below.

Please note that this is very preliminary, and based on one observer 
only. So, it is only an indication (emphasis) of the ZHR levels. I choose 
Bob's data for several reasons: he reports a good Lm, made a good set of 
data available, and from earlier work with his data I now he has a 
perception which is quite the 'average' or 'standard' 
perception (i.e. Cp ~1.0). His sporadic rates combined with reported Lm's 
hint that his perception did not seriously alter due to the moonlight 
conditions. So for an indication, I think his data will suffice.

I calculated ZHR's in ~1 hour intervals, with gamma 1.4 in radiant 
altitude dilution (gamma 1.0 would result in only slightly lower rates).
I give two ZHR's: one under the assumption of a population index r=2.0, 
and one for r=2.5. The first assumes emphasis on bright meteors, the 
second assumes a faint component similar as what we saw in 1996 (but 
almost unnoticable due to the moonlight). For the moment, I think the 
r=2.0 column is most appropriate. In the last column, I give Bob's 
limiting magnitudes for reverence, because variations in Lm of course 
might influence rates slightly.


        r=2.0           r=2.5
UT     ZHR   +-        ZHR    +-      Lm

10:00   118   24       149    30      5.45
11:00   112   20       144    26      5.35
12:00   114   16       134    19      5.65
13:00   141   19       182    24      5.34


Please note the moonlight circumstances, so take it as an indication only.

Activity seems rather constant at just above ZHR 100. Perhaps, rates 
where higher in the last hour, but this is sensitive to the Lm estimate 
(the effect disappears largely if the true Lm was higher). But the report 
of increased fireball occurence during this last hour suggest that rates 
might really have been higher (perhaps peaking after twilight set in?). 
During our 1996 European narrow peak we also experienced a fireball 
flurry besides the faint meteors (both Koen and me personally saw at leat 
12 Leonids of -3 and brighter in one hour).

I did not look at our Dutch results yet (still have to listen to my 
tapes: due to some personal circumstances that was not possible untill 
now. Koen will report his data within 1-2 hours from now to me), but if 
our estimate of ZHR 30-40 during our European Nov 17 night interval is 
correct, this would pretty well line up with the rates at about 100 or 
slightly higer for California. It suggest a B~1 structure, like 
1994-1996, peaking over west USA/east Pacific.

-Marco Langbroek
 Dutch Meteor Society