The following question has just been asked in the RealClimate blog:
“Frost question.

Night starts out cloudless; ground cools; it gets cold enough; frost forms; early in the morning, still well before sunup, a bank of clouds appears.

Can the frost melt before solar hits it?�

I wonder what the answer should be; perhaps not just yes or no.

"Alastair B. McDonald" wrote in message
...
The following question has just been asked in the RealClimate blog:
"Frost question.

Night starts out cloudless; ground cools; it gets cold enough; frost forms;
early in the morning, still well before sunup, a bank of clouds appears.

Can the frost melt before solar hits it?"

I wonder what the answer should be; perhaps not just yes or no.

Yes. It of course depends on the height of the cloud, but if it is a bank of
low cloud, and not too thin, then yes. Cloud blocks heat from the earth's
surface from radiating to space, and absorbs the long-wave radiation from
the surface and re-radiates some of it back to the surface.
There is a good example this evening with patchy cloud.
Look at this net radiation graph from Reading Uni:

http://www.met.reading.ac.uk/weather..._graphs.html#7


--
Bernard Burton
Weather data and satellite images at:
www.woksat.info/wwp.html

On 16/03/2021 22:20, Alastair B. McDonald wrote:
The following question has just been asked in the RealClimate blog:
“Frost question.

Night starts out cloudless; ground cools; it gets cold enough; frost
forms; early in the morning, still well before sunup, a bank of
clouds appears.

Can the frost melt before solar hits it?�

Potentially yes provided that the bank of clouds is low enough to be
just above freezing. The frost is against the ground which is actually a
fairly good conductor of heat and without the heat escaping by radiation
to the very cold clear night sky it will slowly warm up again.

Car roofs being quite well thermally isolated from the ground are about
the first thing to develop a frost and the last thing to lose it.

I wonder what the answer should be; perhaps not just yes or no.

It is a definite maybe. One reason for a bank clouds appearing can be
that a warm front is approaching in which case the ground air
temperature also rises abruptly.

--
Regards,
Martin Brown

On Wednesday, 17 March 2021 at 09:13:39 UTC, Martin Brown wrote:
On 16/03/2021 22:20, Alastair B. McDonald wrote:
The following question has just been asked in the RealClimate blog:
“Frost question.

Night starts out cloudless; ground cools; it gets cold enough; frost
forms; early in the morning, still well before sunup, a bank of
clouds appears.

Can the frost melt before solar hits it?�
Potentially yes provided that the bank of clouds is low enough to be
just above freezing. The frost is against the ground which is actually a
fairly good conductor of heat and without the heat escaping by radiation
to the very cold clear night sky it will slowly warm up again.

Car roofs being quite well thermally isolated from the ground are about
the first thing to develop a frost and the last thing to lose it.
I wonder what the answer should be; perhaps not just yes or no.
It is a definite maybe. One reason for a bank clouds appearing can be
that a warm front is approaching in which case the ground air
temperature also rises abruptly.

Don't forget heat flux from the ground itself.

--
Freddie
Alcaston
Shropshire
148m AMSL
http://www.hosiene.co.uk/weather/
Stats for the month so far: https://www.hosiene.co.uk/weather/st...cs/latest.xlsx

On 17/03/2021 12:30, Freddie wrote:
On Wednesday, 17 March 2021 at 09:13:39 UTC, Martin Brown wrote:
On 16/03/2021 22:20, Alastair B. McDonald wrote:
The following question has just been asked in the RealClimate blog:
“Frost question.

Night starts out cloudless; ground cools; it gets cold enough; frost
forms; early in the morning, still well before sunup, a bank of
clouds appears.

Can the frost melt before solar hits it?�
Potentially yes provided that the bank of clouds is low enough to be
just above freezing. The frost is against the ground which is actually a
fairly good conductor of heat and without the heat escaping by radiation
to the very cold clear night sky it will slowly warm up again.

Car roofs being quite well thermally isolated from the ground are about
the first thing to develop a frost and the last thing to lose it.
I wonder what the answer should be; perhaps not just yes or no.
It is a definite maybe. One reason for a bank clouds appearing can be
that a warm front is approaching in which case the ground air
temperature also rises abruptly.

Don't forget heat flux from the ground itself.

Doesn't the wind strength also play a part?

On Wednesday, 17 March 2021 at 19:01:59 UTC, Metman2012 wrote:
On 17/03/2021 12:30, Freddie wrote:
On Wednesday, 17 March 2021 at 09:13:39 UTC, Martin Brown wrote:
On 16/03/2021 22:20, Alastair B. McDonald wrote:
The following question has just been asked in the RealClimate blog:
“Frost question.

Night starts out cloudless; ground cools; it gets cold enough; frost
forms; early in the morning, still well before sunup, a bank of
clouds appears.

Can the frost melt before solar hits it?�
Potentially yes provided that the bank of clouds is low enough to be
just above freezing. The frost is against the ground which is actually a
fairly good conductor of heat and without the heat escaping by radiation
to the very cold clear night sky it will slowly warm up again.

Car roofs being quite well thermally isolated from the ground are about
the first thing to develop a frost and the last thing to lose it.
I wonder what the answer should be; perhaps not just yes or no.
It is a definite maybe. One reason for a bank clouds appearing can be
that a warm front is approaching in which case the ground air
temperature also rises abruptly.

Don't forget heat flux from the ground itself.

Doesn't the wind strength also play a part?

Thanks for all those answers which seem to imply that the frost could melt but not always. Am I correct in thinking that if it does melt the lapse rate between the ground and the cloud base will be zero? In which case the wind strength will not matter..