Radiative cooling & partly cloudy nights
 

What is the mechanism by which the temperature *rises* when clouds come
over on otherwise clear nights*?

Common sense suggests that the most they could do would be to halt the
drop in temperature. After all, a rise in temperature *should* require a
heat source, and those are absent at night.

*I'm referring to nights with no frontal activity, of course.
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)

Radiative cooling & partly cloudy nights
 

On Sat, 28 Apr 2007 17:39:13 GMT, Paul Hyett
wrote:

What is the mechanism by which the temperature *rises* when clouds come
over on otherwise clear nights*?

Common sense suggests that the most they could do would be to halt the
drop in temperature. After all, a rise in temperature *should* require a
heat source, and those are absent at night.

*I'm referring to nights with no frontal activity, of course.

The fact that the weather changed "when clouds come over" tells you
that a front or weather cell of some sort moved in.

Warm fronts coming off of water are usually have a high moisture
content, so the dew point (DPT) should rise as well as the ambient
temp.


--

"Perhaps the meek shall inherit the Earth, but they'll do it
in very small plots - about 6' by 3'."
-- Robert A. Heinlein

Radiative cooling & partly cloudy nights
 

"Paul Hyett" wrote in message
...
What is the mechanism by which the temperature *rises* when clouds come
over on otherwise clear nights*?

Common sense suggests that the most they could do would be to halt the
drop in temperature. After all, a rise in temperature *should* require a
heat source, and those are absent at night.

A heat source is ceratinly not absent at night.What is the soil temerature
at, say, 10 cm?

Radiative cooling & partly cloudy nights
 

"Paul Hyett" wrote in message
...
What is the mechanism by which the temperature *rises* when clouds come
over on otherwise clear nights*?

Common sense suggests that the most they could do would be to halt the
drop in temperature. After all, a rise in temperature *should* require a
heat source, and those are absent at night.

*I'm referring to nights with no frontal activity, of course.
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)

Clouds absorb and re-radiate downwards the upwelling long-wave radiation
from the surface. When cloud cover replaces clear sky the surface radiation
continues, but can no longer escape to space. The air temperature near the
surface rises towards the ground temperature until a new balance is
achieved.

--
Bernard Burton
Wokingham, Berkshire, UK.

Satellite images at:
www.woksat.info/wwp.html
or
www.btinternet.com/~wokingham.weather/wwp.html

Radiative cooling & partly cloudy nights
 

In uk.sci.weather on Sat, 28 Apr 2007, Citizen Bob wrote
:
On Sat, 28 Apr 2007 17:39:13 GMT, Paul Hyett
wrote:

What is the mechanism by which the temperature *rises* when clouds come
over on otherwise clear nights*?

Common sense suggests that the most they could do would be to halt the
drop in temperature. After all, a rise in temperature *should* require a
heat source, and those are absent at night.

*I'm referring to nights with no frontal activity, of course.

The fact that the weather changed "when clouds come over" tells you
that a front or weather cell of some sort moved in.

Hi Bob.

Notice that I specifically referred to nights *without* frontal
activity, though...
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)

Radiative cooling & partly cloudy nights
 

In uk.sci.weather on Sat, 28 Apr 2007, Russel Sprout
wrote :

What is the mechanism by which the temperature *rises* when clouds come
over on otherwise clear nights*?

Common sense suggests that the most they could do would be to halt the
drop in temperature. After all, a rise in temperature *should* require a
heat source, and those are absent at night.

A heat source is ceratinly not absent at night.What is the soil temerature
at, say, 10 cm?

I don't measure that - but in any case, the 4" soil temperature doesn't
vary by 1C or more over a matter of half an hour, as the air temperature
does when cloud comes in, on an otherwise clear night.
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)

Radiative cooling & partly cloudy nights
 

In uk.sci.weather on Sat, 28 Apr 2007, Bernard Burton
wrote :

Clouds absorb and re-radiate downwards the upwelling long-wave radiation
from the surface. When cloud cover replaces clear sky the surface radiation
continues, but can no longer escape to space. The air temperature near the
surface rises towards the ground temperature

Do you mean the *cloud* temperature here, as the temperature at ground
level is invariably lower than at 4ft on clear nights?

until a new balance is
achieved.
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)

Radiative cooling & partly cloudy nights
 

"Paul Hyett" wrote in message
...
In uk.sci.weather on Sat, 28 Apr 2007, Bernard Burton
wrote :

Clouds absorb and re-radiate downwards the upwelling long-wave radiation
from the surface. When cloud cover replaces clear sky the surface
radiation
continues, but can no longer escape to space. The air temperature near
the
surface rises towards the ground temperature

Do you mean the *cloud* temperature here, as the temperature at ground
level is invariably lower than at 4ft on clear nights?

until a new balance is
achieved.
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)

No, I mean the ground temperature. The ground surface temperature reacts
quickest to the cloud cover, as there is usually a flux of heat from deeper
in the ground towards the surface. The ground surface temperature under
clear skies will fall rapidly until the heat loss by radiation is balanced
by the heat flux from lower in the ground (ignoring latent heat). The whole
ground temperature structure and air temperature structure will eventually
reach equilibrium in which the sum of all the heat losses is balanced by the
gains, provided that the external conditions (eg cloud cover, wind speed,
incoming radiation (from sun)), remain constant.

--
Bernard Burton
Wokingham, Berkshire, UK.

Satellite images at:
www.woksat.info/wwp.html
or
www.btinternet.com/~wokingham.weather/wwp.html

Radiative cooling & partly cloudy nights
 

On Sun, 29 Apr 2007 07:53:45 GMT, Paul Hyett
wrote:

What is the mechanism by which the temperature *rises* when clouds come
over on otherwise clear nights*?

Common sense suggests that the most they could do would be to halt the
drop in temperature. After all, a rise in temperature *should* require a
heat source, and those are absent at night.

*I'm referring to nights with no frontal activity, of course.

The fact that the weather changed "when clouds come over" tells you
that a front or weather cell of some sort moved in.

Notice that I specifically referred to nights *without* frontal
activity, though...

How can "clouds come over" if there is not some kind of frontal
activity.

Perhaps the term "front" is incorrect. What I was alluding to is
something like our Gulf Breeze along the Texas coast. It is not
referred to as a front per se, but it does act like one when it sweeps
the area, raising the DPT because of the increase in moisture.

The point is that something from the outside has come into the
picture.


--

"Perhaps the meek shall inherit the Earth, but they'll do it
in very small plots - about 6' by 3'."
-- Robert A. Heinlein

Radiative cooling & partly cloudy nights
 

On Sat, 28 Apr 2007 23:57:06 +0100, "Bernard Burton"
wrote:

Clouds absorb and re-radiate downwards the upwelling long-wave radiation
from the surface. When cloud cover replaces clear sky the surface radiation
continues, but can no longer escape to space. The air temperature near the
surface rises towards the ground temperature until a new balance is
achieved.

But how can that cause a temperature rise?


--

"Perhaps the meek shall inherit the Earth, but they'll do it
in very small plots - about 6' by 3'."
-- Robert A. Heinlein