Re: hot air rising

["Daniel L. MacIsaac" <Dan.MacIsaac@NAU.EDU>]

> My car has an outdoor thermometer. I climb more than 1000 feet to
> get to Simon Fraser University, and I often see the temperature
> inversion mentioned earlier; it's not even rare. It is informative
> to take notice of that profile and then to note the sharpness of the
> smog top often visible over Vancouver*, the altitude of which is
> usually less than that of the university. Clearly, though I derive
> the adiabatic lapse rate for my students in our sophomore course, I
> do *not* tell them that the atmosphere, especially when measured in
> the boundary layer next to the surface of Burnaby Mountain,
> typically exhibits this temperature profile.
Leigh,

I'd be careful here.  Its been a while since I drove up the SFU campus
road, but it is probably blacktop over concrete slabs.  Two teachers and
I have been working on a special topics summer course on highway mirages,
and have been taking temperature measurements over blacktop.  Here in AZ,
air temp at 2m is pretty constant throughout the day, which agrees with our
references.  However, on exposure to sunlight blacktop around Flagstaff
rose from 20C to 42C between 10am and 2pm.  The gradient went over 3C per
cm in the first 5 cm of air above the blacktop.  This gradient is critical
to mirage formation and we have photos of some doozys.

Bottom line: I would trust no temperature measurement taken closer than
2m of the road surface to reflect any phenomena other than road or car heating
in the sunshine.  I imagine it has briefly stopped raining in Vancouver
these days, no?

Best regards,

Dan M

Dan MacIsaac, Assistant Professor of Physics and Astronomy, Northern AZ Univ
danmac@nau.edu          http://purcell.phy.nau.edu         PHYS-L list owner