Can someone explain to me what the divergence of radiative flux is, please? It seems to be measured in K per hour. Is it a change in flux, or the effect of a flux, or something different entirely?

Cheers, Alastair.

In message ,
Alastair writes
Can someone explain to me what the divergence of radiative flux is,
please? It seems to be measured in K per hour. Is it a change in flux,
or the effect of a flux, or something different entirely?

Cheers, Alastair.

I've just looked up the radiative flux article on Wikipedia, which I
confess has left me little the wiser, but perhaps you might get more out
of it:

https://en.wikipedia.org/wiki/Radiative_flux
--
John Hall
"Honest criticism is hard to take,
particularly from a relative, a friend,
an acquaintance, or a stranger." Franklin P Jones

Thanks John,

but what I am wanting is an explanation of radiation divergence that you would understand :-)

I had seen the Wikipedia item but it assumes that you know what it means.

BTW, Channel 4 is showing "Weird Weather" at the moment.

"John Hall" wrote in message
...
In message ,
Alastair writes
Can someone explain to me what the divergence of radiative flux is,
please? It seems to be measured in K per hour. Is it a change in flux, or
the effect of a flux, or something different entirely?

Cheers, Alastair.

I've just looked up the radiative flux article on Wikipedia, which I
confess has left me little the wiser, but perhaps you might get more out
of it:

https://en.wikipedia.org/wiki/Radiative_flux

Radiative flux is the flow of radiation from warm to cold body.
The velocity of the radiation at each point defines a vector field. While
air is heated in a region, it expands in all directions, and thus the
radiation field points outward from that region. The divergence of the
radiation field in that region would thus have a positive value. While the
air is cooled and thus contracting, the divergence of the radiation has a
negative value.

Will
--
" Some sects believe that the world was created 5000 years ago. Another sect
believes that it was created in 1910 "
http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------

On Saturday, April 2, 2016 at 7:21:56 PM UTC+1, Will wrote:

Radiative flux is the flow of radiation from warm to cold body.
The velocity of the radiation at each point defines a vector field. While
air is heated in a region, it expands in all directions, and thus the
radiation field points outward from that region. The divergence of the
radiation field in that region would thus have a positive value. While the
air is cooled and thus contracting, the divergence of the radiation has a
negative value.

Will
--
" Some sects believe that the world was created 5000 years ago. Another sect
believes that it was created in 1910 "
http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------

Thanks Will,

I see now where air flow comes into it, and that what I would call the effect of cold radiation is what meteorologists call negative radiative divergence, or radiative convergence, but let's not start the cold radiation debate all over again grim.

Cheers, Alastair.

On Saturday, 2 April 2016 21:50:35 UTC+1, Alastair wrote:
On Saturday, April 2, 2016 at 7:21:56 PM UTC+1, Will wrote:

Radiative flux is the flow of radiation from warm to cold body.
The velocity of the radiation at each point defines a vector field. While
air is heated in a region, it expands in all directions, and thus the
radiation field points outward from that region. The divergence of the
radiation field in that region would thus have a positive value. While the
air is cooled and thus contracting, the divergence of the radiation has a
negative value.

Will
--
" Some sects believe that the world was created 5000 years ago. Another sect
believes that it was created in 1910 "
http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------

Thanks Will,

I see now where air flow comes into it, and that what I would call the effect of cold radiation is what meteorologists call negative radiative divergence, or radiative convergence, but let's not start the cold radiation debate all over again grim.

Cheers, Alastair.

Radiation divergence, that's what makes the temperature on average decrease with height through the troposphere.
Radiation convergence starts as you reach the tropopause and enter the stratosphere. Change of composition with absorbing ozone present...

Len
Wembury

On Saturday, April 2, 2016 at 11:07:12 PM UTC+1, Len Wood wrote:
On Saturday, 2 April 2016 21:50:35 UTC+1, Alastair wrote:
On Saturday, April 2, 2016 at 7:21:56 PM UTC+1, Will wrote:

Radiative flux is the flow of radiation from warm to cold body.
The velocity of the radiation at each point defines a vector field. While
air is heated in a region, it expands in all directions, and thus the
radiation field points outward from that region. The divergence of the
radiation field in that region would thus have a positive value. While the
air is cooled and thus contracting, the divergence of the radiation has a
negative value.

Will
--
" Some sects believe that the world was created 5000 years ago. Another sect
believes that it was created in 1910 "
http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------

Thanks Will,

I see now where air flow comes into it, and that what I would call the effect of cold radiation is what meteorologists call negative radiative divergence, or radiative convergence, but let's not start the cold radiation debate all over again grim.

Cheers, Alastair.

Radiation divergence, that's what makes the temperature on average decrease with height through the troposphere.
Radiation convergence starts as you reach the tropopause and enter the stratosphere. Change of composition with absorbing ozone present...

Len
Wembury

Thanks Len,

I am trying to understand this abstract: Hoch, S. W., P. Calanca, R. Philipona, and A. Ohmura. ‘Year-Round Observation of Longwave Radiative Flux Divergence in Greenland’. Journal of Applied Meteorology and Climatology 46, no. 9 (2007): 1469–79. DOI: http://dx.doi.org/10.1175/JAM2542.1

Abstract

Longwave radiative flux divergence within the lowest 50 m of the atmospheric boundary layer was observed during the Eidgenössische Technische Hochschule (ETH) Greenland Summit experiment. The dataset collected at 72°35′N, 38°30′W, 3203 m MSL is based on longwave radiation measurements at 2 and 48 m that are corrected for the influence of the supporting tower structure. The observations cover all seasons and reveal the magnitude of longwave radiative flux divergence and its incoming and outgoing component under stable and unstable conditions. Longwave radiative flux divergence during winter corresponds to a radiative cooling of −10 K day−1, but values of −30 K day−1 can persist for several days. During summer, the mean cooling effect of longwave radiative flux divergence is small (−2 K day−1) but exhibits a strong diurnal cycle. With values ranging from −35 K day−1 around midnight to 15 K day−1 at noon, the heating rate due to longwave radiative flux divergence is of the same order of magnitude as the observed temperature tendency. However, temperature tendency and longwave radiative flux divergence are out of phase, with temperature tendency leading the longwave radiative flux divergence by 3 h. The vertical variation of the outgoing longwave flux usually dominates the net longwave flux divergence, showing a strong divergence at nighttime and a strong convergence during the day. The divergence of the incoming longwave flux plays a secondary role, showing a slight counteracting effect. Fog is frequently observed during summer nights. Under such conditions, a divergence of both incoming and outgoing fluxes leads to the strongest radiative cooling rates that are observed. Considering all data, a correlation between longwave radiative flux divergence and the temperature difference across the 2–48-m layer is found.
=================

I can't understand how they can have a cooling of -30 K per day without the temperature dropping to -100 C pretty quickly. However, I have a copy of the full paper so I will try to work it out from that using the clues from you and Will tomorrow.

Cheers, Alastair.

On 02/04/16 19:21, Eskimo Will wrote:

"John Hall" wrote in message
...
In message ,
Alastair writes
Can someone explain to me what the divergence of radiative flux is,
please? It seems to be measured in K per hour. Is it a change in
flux, or the effect of a flux, or something different entirely?

Cheers, Alastair.

I've just looked up the radiative flux article on Wikipedia, which I
confess has left me little the wiser, but perhaps you might get more
out of it:

https://en.wikipedia.org/wiki/Radiative_flux

Radiative flux is the flow of radiation from warm to cold body.
The velocity of the radiation at each point defines a vector field.

That doesn't sound right. The velocity of radiation is the speed of
light and is a constant.

Good definition here.
http://glossary.ametsoc.org/wiki/Radiative_flux_divergence

While air is heated in a region, it expands in all directions, and thus
the radiation field points outward from that region. The divergence of
the radiation field in that region would thus have a positive value.
While the air is cooled and thus contracting, the divergence of the
radiation has a negative value.

Will

In article , says...

That doesn't sound right. The velocity of radiation is the speed of
light and is a constant.


The speed of light is a constant. Its velocity is not.

Velocity is a vector quantity.

--
Alan LeHun

On 03/04/16 16:18, Alan LeHun wrote:
In article , says...

That doesn't sound right. The velocity of radiation is the speed of
light and is a constant.


The speed of light is a constant. Its velocity is not.

Velocity is a vector quantity.

Oops - What I was trying to say is that I don't see how the velocity
of radiation forms a vector field. EMR is radiated from a parcel of air
in all directions. For it to be a vector field you need a single vector
at each point. The temperature of each small packet forms a scalar
field. The velocity of each packet as the whole mass expands forms a
vector field - maybe that's what Will meant to say.