[AZ-Observing] Re: North country windstorm

  • From: Brian Skiff <Brian.Skiff@xxxxxxxxxx>
  • To: az-observing@xxxxxxxxxxxxx
  • Date: Tue, 24 Jun 2003 02:58:21 -0700 (MST)

     Just in case folks get the wrong impression, Steve "almost"
perpetuates two myths about seeing (i.e. atmospheric turbulence):

>>  Even though the breeze did make the seeing mediocre...

and

>>  All the brightest stars, regardless of their altitude,
>>   were blinking on and off....not just twinkling.

     First, the wind, per se, does _not_ make the seeing bad.  The reason
the seeing was relatively poor (it wasn't in fact that bad), was because
we're at the bottom of a fairly sharp trough.
     Secondly, naked-eye scintillation is not directly correlated with
seeing in the telescope (say, as measured by the image-blur size and
its motion in small apertures).  
     The seeing is actually pretty predictable, and is shown in simple
graphic form extending 36 hours downstream by the well-known 'Clear Sky
Clock' pages.  You can also see more geographic details (though the models
have rotten spatial resolution) at:

http://www-frd.fsl.noaa.gov/mab/tke/tke_new.cgi

or...

http://www.rap.ucar.edu/projects/itfa/turbfc1.html

...which are different flavors of the same turbulence model.  These are
intended for aviation use, so have short look-ahead times, but the 'Clear
Sky Clock' set-up extends them out farther.  When taken together with
considerations of local effects (in Arizona, cool air drainage especially),
it makes fairly accurate predictions of seeing.

\Brian
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