On Friday, June 22, 2018 at 3:46:09 AM UTC-6, Martin Brown wrote:
On 20/06/2018 20:21, Gary Harnagel wrote:
On Wednesday, June 20, 2018 at 5:39:43 AM UTC-6, Paul Schlyter wrote:
But clouds reduce the heat flux coming up from the surface.
No, they don't. But the clouds do radiate IR radiation back to the
ground. And since the clouds are cooler than the ground, the clouds also
reduce IR radiation out into space. Maybe that's what you meant.
I'm talking about the NET effect. Clouds reduce the amount of heat
escaping into space, but they also reduce the amount of solar energy
coming in.
The net effect depends both on the height and *type* of the cloud.
See the options in MODTRAN.
High cirrus is optically thin, cold and lets in plenty of solar energy
but is dense to outgoing thermal radiation and have a net warming effect.
It's not that simple:
https://experts.illinois.edu/en/publ...-pool-microphy
Low optically dense clouds reflect a high proportion of incoming solar
radiation are warm and have a slight net cooling effect - although their
main effect is to significantly reduce diurnal temperature variation.
Deep convective clouds tend to be just about neutral for energy balance.
See:
http://nenes.eas.gatech.edu/Cloud/NASAClouds.pdf
For a reasonably accessible review.
--
Regards,
Martin Brown
"The balance between the cooling and warming actions of clouds is very
close although, overall, averaging the effects of all the clouds around
the globe, cooling predominates."
The gatech link is pretty old but did mention a NASA program (CERES) which was
launched just last year:
https://ceres.larc.nasa.gov/
"A new study suggests that most global climate models may underestimate the
amount of rain that will fall in Earth's tropical regions as our planet
continues to warm. That's because these models underestimate decreases in
high clouds over the tropics seen in recent NASA observations, according to
research led by scientist Hui Su of NASA's Jet Propulsion Laboratory in
Pasadena, California."
So more outgoing radiation?