On Tuesday, 16 February 2016 00:34:50 UTC, Alastair wrote:
On Monday, 15 February 2016 10:08:31 UTC, Len Wood wrote:
On Saturday, 13 February 2016 10:47:56 UTC, Alastair wrote:
On Saturday, 13 February 2016 10:08:33 UTC, Len Wood wrote:
Today I am taking my U3A Weather and Climate group on a visit to the high priesthood. That is, the Met Office HQ in Exeter.

They are an enthusiastic bunch of pensioners and will no doubt have many questions for the employees incarcerated there.

I will be interested to know how much leeway the operational meteorologists have to intervene when the model forecast for 12 hr or less ahead is going wrong.

Does anyone on this ng have a question for me to ask them?

Len
Wembury, SW Devon

I not sure that anyone you talk to will be able to answer this, but here it is anyway.

Is it true that the computer models assume that the boundary layer is warmed by convection and not by the absorption of radiation from the surface by greenhouse gases?
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1)You are right. No one there to answer that in any detail except, they are keen to publicise their 1.5 km model which takes more account of topography.

My answer: warming or cooling by surface fluxes according to surface type and synoptic situation (cloud) and worked out to give an energy balance at the surface. Pollution in terms of particles and greenhouse gas concentrations are fixed on the short time scale.

2)As regards probability forecasts, precipitation probability is all you get as you see on there website.
http://www.metoffice.gov.uk/public/w...u#?tab=fiveDay

They don't seem keen to go further. The TV weather presenters talk about confidence, as we do, having looked at ensembles.

Len, after a third trip to UKMO HQ on Saturday.

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Len,

Thanks for asking. I think if you had got an answer it would have been similar to Freddie's, but put a bit more politely :-?

It is not that the modelers are deliberately ignoring absorption. The problem is that the Schwarzschild equation of radiative transfer that they are using does not produce a net absorption. It is based on Kirchhoff's law of thermal radiation which can be roughly stated as absorption equals emission, i.e. no net absorption. https://en.wikipedia.org/wiki/Kirchhoff's_law_of_thermal_radiation#Theory

Your answer that "the air in the boundary layer is warmed and cooled by fluxes from the surface£ is also correct, but what are those fluxes? Are they conduction and convection or are they radiation? The cooling cannot be caused by conduction because cold air does not rise. Therefore the cooling must be caused by the net radiation between the surface and the air above. When the surface is warmer then the air warms, when the surface is cooler then the air cools.

This explains why recently warm air passing north over the South Devon coast was much colder when it reached Will, even allowing for the increase in altitude. It had been cooled by passing over cold land.

What do you think?

Cheers, Alastair.
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Of course with the substantial derivative there is the advection term and the term involving change at a point. That is what the numerical models are having to deal with. Unpleasantly non linear and therefore no exact solution.