[AZ-Observing] Re: North country windstorm
- From: Brian Skiff <Brian.Skiff@xxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Tue, 24 Jun 2003 15:32:19 -0700 (MST)
>> some different technical definition of "wind" as I'm
>> pertaining to it, but I've noticed several times where a breeze of a
>> different temperature comes along and screws up the seeing.
That's a local effect, from cold-air drainage. Nearly all the
Arizona sites folks use have this problem (Vekol, Sunglow, probably all
the northern sites like Camp 613 etc etc). Lowell's Anderson Mesa site
has this problem, too, which limits seeing on otherwise calm nights.
This draft is very shallow on the Mesa, sometimes only a few tens of feet
deep: the anemometer/wind-vane on the weather mast 35 feet up will show
a light breeze from the southwest, but you step outside at ground level
at there's a chill draft from the northeast--from the higher ground on
the Mesa over the site toward Lake Mary below us.
>> I've found that a pinch of salt is needed with the Clear Sky Clocks.
The models are only as good as the input data, which is often
incomplete, and if you look at the details at the source URLs I sent
out this morning, the actual geographical sampling is very coarse.
The GIGO law still apples. Also as per the foregoing, local katabatic
effects are not accounted for at all, nor are thermal problems inside
your own telescope, which folks will often attribute to the atmosphere.
I was going to mention in re getting a bit above the local terrain
that the candidate site for the Lowell "Next Generation Telescope",
which is not far from Happy Jack, has median seeing of 0".8, now
measured on several dozen nights both winter and summer. There is nothing
special about this little cinder cone other than being one or two hundred
meters above the surroundings. There's gotta be lots of similar places
big enough to let in some vehicles that are all over Arizona both in the
desert and up on the plateau.
\Brian
--
See message header for info on list archives or unsubscribing, and please
send personal replies to the author, not the list.
Other related posts:
