[AZ-Observing] Re: Flagstaff nighttime cloudiness/sky brightness
- From: Brian Skiff <bas@xxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Wed, 13 Jun 2007 11:56:05 -0700 (MST)
I'll admit to having not analyzed the data in any proper way.
The main reason is that it was clear from "inspection" that the
year-to-year variations are large, and completely swamp any trends
one might imagine. If there were 300 years rather than 30 years of data,
you might be able to see something interesting. The general average
is that we get about 100 completely clear nights per year +/- about 30
(thus some great years, some lousy years), another 50 or so "partial"
nights (3 hours clear at a minimum, but often all but one hour of an
an entire night), and about 1000 to 1200 clear hours reckoned in those
three-hour minimum chunks.
In that respect 2006 was pretty average, with May having the
peak number of clear nights, April (surprisingly) not far behind.
Notice however that January, plus the Oct-Nov-Dec regime had a lot
of clear _hours_. The best clear run was 9 nights consecutive photometric
from Nov 29 through Dec 7 --- _not_ during the May-June-early-July period.
Southern Arizona probably gets a slightly greater number of
clear nights, maybe 120 or so as a guess, but I don't know of any
data taken in consistent manner to determine this, and certainly not in
as conservative way as I have done. In the last couple of years I have
been comparing rather casually the state of the sky in the Kitt Peak
webcams. It is remarkable the degree to which the Flagstaff scene
and the KPNO one resemble each other on any given day, but there are
some days/nights when it is certifiably clear down there while it's
cloudy or cirrusy up here, but not so often the reverse.
\Brian
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