On Fri, 03 Aug 2007 10:25:56 +0200, Mxsmanic
wrote:
>Hatunen writes:
>
>> Radiative heat loss is common-place here in Arizona but it has to
>> be night, else radiative heat gain will balance the loss. The
>> loss is to the the black body and very cold night sky, and can be
>> distinctly felt once the sun sets. A bare arm held out feels
>> distinctly cool on its upper surface. You rally have to be in the
>> desert to feel this, since it requires a dry atmoshphere else the
>> water vapor in the air will be opaque to infrared and becomes the
>> black body instead of deep space.
>
>I've felt it--it is very distinctive and memorable. You can feel the
>temperature drop as the sun disappears below the horizon. You may be hot at 5
>PM, and chilled twenty minutes later.
>
>But few places on our planet have such clear, dry air. And while desert
>terrain readily radiates its heat into space, large cities do not. For this
>reason, the experiment generally works only outside built-up areas.
Rubbish. Large cities and small towns radiate into space like
crazy. But the effect on your own skin may not be noticable in
heavily built up areas because tall nearby buildings cut down on
the amount of open sky available, and also radiate some of their
own daytime-acquired heat down onto you.
--
************* DAVE HATUNEN (hatunen@cox.net) *************
* Tucson Arizona, out where the cacti grow *
* My typos & mispellings are intentional copyright traps * |
