albedo for irrigated artificial soil

Discussions about the Version 4 concerning the core model simulations
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Arnaud
Posts: 68
Joined: Wed Dec 19, 2018 8:13 am

albedo for irrigated artificial soil

Post by Arnaud »

Hi,

I use a profile with an artificial soil at the top layer and a natural soil at the bottom layer. This profile is set as "irrigated". I understood by reading other topics on the forum that the water will not reach the lower layers as the top one is not porous.

I could not find details on the "irrigated option" process in the different topics. Does it mean that the surface is always irrigated (day and night) ?
Is there a particular thickness of water film ? Or it may not impact the results ?
I set the albedo of the profile as 0,4 but I can see during the simulation an evolution of this albedo (see attached picture). It is probably due the water on the surface. Is the albedo calculation based on 4.3.1 in Bruse1999 document ?

Thanks
albedo_evolution.PNG

helge
Posts: 307
Joined: Mon May 15, 2017 12:27 pm

Re: albedo for irrigated artificial soil

Post by helge »

Hi,

the curve you see in the irrigated surface is caused by the suns height angle which is used to calculate the irrigated artificial soil's albedo. Is is a approximation from Pielke (Pielke, R. A. (1984). Mesoscale Meteorological Modelling. Academic Press, New York.)

albedo = -0.0139 + 0.0467 * tan(90 - sun.height)

Best
Helge

Arnaud
Posts: 68
Joined: Wed Dec 19, 2018 8:13 am

Re: albedo for irrigated artificial soil

Post by Arnaud »

Dear Helge, thanks for the information.

Regards.

Arnaud.

Arnaud
Posts: 68
Joined: Wed Dec 19, 2018 8:13 am

Re: albedo for irrigated artificial soil

Post by Arnaud »

Dear Helge, do you have information concerning the film of water when it is irrigated ? (thickness, is the temperature calculated at each time with diffusion, etc.) ?

Thanks a lot.

helge
Posts: 307
Joined: Mon May 15, 2017 12:27 pm

Re: albedo for irrigated artificial soil

Post by helge »

Dear Arnaud,

No, this effect is parameterized in the model - so there is no actual water film

Best
Helge

Arnaud
Posts: 68
Joined: Wed Dec 19, 2018 8:13 am

Re: albedo for irrigated artificial soil

Post by Arnaud »

Dear Helge,

Thanks. But what is parameterized ? Only the latent heat of vaporization ? one part of the energy is used to vaporize and the other to increase the surface temperature ?

helge
Posts: 307
Joined: Mon May 15, 2017 12:27 pm

Re: albedo for irrigated artificial soil

Post by helge »

Dear Arnaud,

ENVI-met supports irriagted artifical soils as typical evaporative cooling devices. We cannot calculate an halstead-Parameter for a non-natural soil. So to calculate the surface humidity, we take an assumption that it is at 80% of the water content at saturation (calculated based on the current temperature). This surface humidity is then used to calculate the latent heat flux

Best
Helge

Arnaud
Posts: 68
Joined: Wed Dec 19, 2018 8:13 am

Re: albedo for irrigated artificial soil

Post by Arnaud »

Dear Helge,

Thanks, i'll ask about these terms to better understand the way it works.

Regards.

Arnaud.

Arnaud
Posts: 68
Joined: Wed Dec 19, 2018 8:13 am

Re: albedo for irrigated artificial soil

Post by Arnaud »

Dear Helge, i would need some additional information please :

- how can we consider water content at saturation at 80% for an artificial material which is supposed to be impermeable ?

We thought that the artificial material could not account for any water content or hydraulic flux.

Thanks.

helge
Posts: 307
Joined: Mon May 15, 2017 12:27 pm

Re: albedo for irrigated artificial soil

Post by helge »

Hi,

sorry what i meant to say is it is calculated by 0.8 of the watercontent at saturation of the temperature at the boundary layer. Basically the air temperature right at the boundary between air and surface

Best
Helge

Arnaud
Posts: 68
Joined: Wed Dec 19, 2018 8:13 am

Re: albedo for irrigated artificial soil

Post by Arnaud »

Dear Helge, thanks. It is clear for us.

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