Thermal issues and seeing

The Winter Star Party in the Florida Keys is coming next month. From past trips to WSP I know that the seeing there is legendary--for deep sky observing and planetary observing as well. I have heard some veteran amateur astronomers attribute this legendary seeing to "the laminar air flow off the Caribbean" and other characteristics of the atmosphere. The other day I saw a graphic display of the month by month temperatures in the Florida Keys. The difference between the high and low temps for the day in all months is 10 or 11 degrees. It makes me wonder how much of the legendary seeing is due to stable atmosphere, and how much can be attributed to a thermal environment in which it is possible to get the delta in temp between one's primary mirror or refractor objective reduced to a very small difference. It may be that such environments create thermal stability within the atmosphere and small deltas between glass and air and that both are major factors in the legendary seeing. I continue to find that the pre-dawn hours in the American Midwest give me the best looks at deep sky and planetary targets. Those hours are the ones when ambient temperature drop is slowing down compared to the hours just after sunset and seem to be the hours when there is less twinkling of bright stars.
I suppose that astronomers who are monitoring the delta between their primaries and ambient temperature and doing active/passive cooling can dissect out the portion of seeing that is due to thermal/boundary layer issues compared to that portion that is atmospheric.

Kim--
I can't speak to the thermal vs. "laminar air flow" explanation of WSP seeing, though I'm surprised others here haven't jumped in--but the attached image by Mr. Christen came to mind, and pretty clearly there's more going on there than just thermal equilibration or lack thereof. OTOH I'm sure everyone agrees temperature difference is a big part of seeing problems with reflectors--usually not a huge problem for me here in the SF bay area, but lately we've had steep 20 degree drops at night, and even my 10" can't catch up--last night I finally put a small house fan directly in front of the mirror, set on low, and finally got some decent views of Saturn at 400X.

--George

Attached Image:

Part of it is that the jet stream is usually far to the north of the Florida Keys.

Here is a chart I look at. http://squall.sfsu.edu/gif/jetstream_init_00.gif

Today's chart doesn't look good for Florida, but does look good for me in S. California!

Mike

I have also noticed that I get excellent seeing here in
Baltimore area when the day-night temperature change is
small (less than 10-15 degrees F which hardly even happens
when its clear). I think you are right that the small
temperature variations account for the excellent seeing at WSP.

I think it is both effects -- the atmosphere is more stable,
and the glass / air temperature difference (or more
exactly -- the rate of change) is smaller.
Though the above certainly applies to refractors as well,
which emphasizes the atmospheric component.

The same probably applies to your early pre-dawn seeing.
By then the air, ground, etc., has cooled off somewhat
and stabilized -- there is less convection from warm ground
to cold air.

Ironically the same atmospheric effects at WSP that make
good seeing also turn viewing into a battle with dew.
Ultimately it seems like you are limited by whatever measures
you have taken to keep the optics dry (heaters, heat guns,
fans, etc.).

Just for fun I will attach an old image I took at WSP last
year with an 11 inch Dob. I can't get anywhere near this
image quality from home.

Attached Image: