Re: Re: OT-CHAT: weather
- Subject: Re: [iris-talk] Re: OT-CHAT: weather
- From: G* S*
- Date: Sat, 17 Mar 2001 16:33:51 -0800
Linda Mann wrote:
>
> That was embarrassing enough that I went to the web:
> <http://www.msue.msu.edu/ipm/CAT98_fruit/F04-28-98.htm>
> "Use of dewpoint in determining frost potential"
>
> <From past experience, you may have noticed that the minimum temperature
> during one of these events [the most common spring frost scenario:
> clear, calm conditions with cold air drainage and vertical temperature
> stratification] commonly remains a few degrees above the dewpoint
> temperature. This is probably because the air temperature is taken at 5
> feet above the surface, and under these calm, clear conditions, it is
> warmer than the temperature at or near the surface, which is
> relatively cooler and has reached the dewpoint.>
>
> In other words, temps probably do equal dewpoint at the boundary layer
> between the plant surface and the air, but 'regular' air temps are
> slightly warmer and <may> be above freezing, while boundary layer temps
> <may> be below freezing.
And add to this the fact that solid objects cool off faster
than the air (they emit more infrared radiation than the air,
so they cool faster. They emit more IR at night because they
absorb more light in the daytime, and emissivity is proportional
to absorptivity--black body experiment and all that).
Gerry, with Tantrum and Perfume Shop blooming, and Amethyst Winter and
Harbinger almost there
--
g*@mediaone.net
Gerry Snyder, AIS Symposium Chair, Region 15 RVP
Member San Fernando Valley, Southern California Iris Societies
in warm, winterless Los Angeles--USDA 9b-ish, Sunset 18-19
my work: helping generate data for: http://galileo.jpl.nasa.gov/
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