Re: Dew Formation

[Bernard Cleyet <anngeorg@PACBELL.NET>]

Tho black top is black it may not be for 10 + micron radiation, while
green grass may be black at 10  + microns.  There's also roughness --
grass may be rougher than black top  like the pyramids in an anechoic
chamber.

Of course Fred's pointing out transpiration may be the operative with
thermal inertia a close, or far, second.

Experiment: let one section of your lawn grow out.  Our front lawn is
easily six inches high, back lawn except one section (lawn mower spur
gear wore out) recently mown.  Must get up early to check.

bc, who suddenly doesn't need to mist his new concrete job.  (unusual
rapid weather change for Salinas Valley)

p.s.  must look at the photo's I took of the yard the morning of the
last dew freeze.  I do remember the top of the hot tub cover being
especially thick.  the water was a few deg. C and the cover well sealed,
so I suspect the dew didn't come from the tub.

Bob LaMontagne wrote:

> Yes, that cools the surface below the ambient air
> temperature - eventually approaching the dew point
> temperature of the air. But why does condensation occur
> preferentially on grass blades?
>
> Bob at PC
>
> *********** REPLY SEPARATOR  ***********
>
> On 3/13/2004 at 11:04 AM John Mallinckrodt wrote:
>
>
>
> > > When dew forms on clear nights, it will heavily wet lawns
> but will
>
>
> > > hardly ever leave visible moisture on concrete walkways
> or asphalt
>
>
> > > roads. There are many factors that regulate condensation:
> > > temperature, available condensation nucleii, curvature,
> hydrophilic
>
>
> > > surfaces, etc. - but I am having difficulty identifying
> the  primary
>
>
> > > one in this case. Any ideas out there?
> > The primary mechanism is radiation exchange with 2 pi
> steradians of a
>
>
> > 3 kelvin blackbody plus high resistance thermal conduction
> pathways
>
>
> > to the ground and the (still) air.
> >
> > --
> > John Mallinckrodt        mailto:ajm@csupomona.edu
> > Cal Poly Pomona          http://www.csupomona.edu/~ajm
> >
> > Visit my Interactive Physics[TM] page at
> > http://www.csupomona.edu/~ajm/ip.html
> >
> > ... and get FREE MUSIC (worth every penny) at
> > http://www.csupomona.edu/~ajm/personal.html#music