North American Fruit Explorers mailing list at ibiblio

[jhecksel@voyager.net]

> 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.

-Joe