Date: Sat, 18 May 2002 13:55:16 +0000 (US/Eastern)
> This morning one thermometer showed 17F, another 22F, does anyone
have a good brand and model to recommend? Del
Del:
Both thermometers might be correct. You can get those kinds on
differences on calm, clear nights due to differences in radiant heat-
loss effects. Consider the vehicle with frost on the roof but no
frost on the side panels. The roof is facing outer-space and the
other is getting some radiant loading from surrounding objects.
It is my understanding that the US Weather Service has incredibly
detailed specifications for the enclosures for min/max temp
thermometers. They want to measure the temperature of the ambient air
and not have the measurements polluted by radiant heat loss or gain.
Also, I think Bob Purvis once noted in a Pomona article that black
trickle irrigation lines often show frost/freezing when no other
objects are hit.