calculation of zonal wind velocity at 10m

[anushree]

Hi all,
I want to calculate the zonal wind velocity component at 10m.How do i do it?
Why doesnt CAM have a zonal and merdional wind velocities at 10m?

Regards,
Anushree

 

[nusbaume]

Hi Anushree,

Sadly CAM only provides the horizontal wind speed at ten meters via the U10 variable, and not the wind vector components (e.g. U and V). After asking around it sounds like this is because of limits to the Monin-Obukhov (MO) Similarity theory used to determine the variation in atmospheric variables in the surface layer (which usually includes quantities at ten meters). Essentially, MO similarity theory uses the total horizontal wind speed, and not the wind vector components separately, and thus that is currently all we can provide. A detailed description of MO Similarity theory can be found in the CLM5 technical description here:

2.5. Momentum, Sensible Heat, and Latent Heat Fluxes — ctsm release-clm5.0 documentation

So if you need the vector components separately at the lowest vertical level possible, then your best bet is probably using the winds at the lowest CAM model level (e.g. UBOT and VBOT).

Anyways, I hope that helps, and have a great day!

Jesse

 

[anushree]

Hi Anushree,

Sadly CAM only provides the horizontal wind speed at ten meters via the U10 variable, and not the wind vector components (e.g. U and V). After asking around it sounds like this is because of limits to the Monin-Obukhov (MO) Similarity theory used to determine the variation in atmospheric variables in the surface layer (which usually includes quantities at ten meters). Essentially, MO similarity theory uses the total horizontal wind speed, and not the wind vector components separately, and thus that is currently all we can provide. A detailed description of MO Similarity theory can be found in the CLM5 technical description here:

2.5. Momentum, Sensible Heat, and Latent Heat Fluxes — ctsm release-clm5.0 documentation

So if you need the vector components separately at the lowest vertical level possible, then your best bet is probably using the winds at the lowest CAM model level (e.g. UBOT and VBOT).

Anyways, I hope that helps, and have a great day!

Jesse

Thank you Jesse for replying.
Can UBOT and VBOT be treated as surface winds?
In the vertical structure of the model,what is the pressure at the lowest level?Is it 1000mb?
Regards,
Anushree

 

[anushree]

Thank you Jesse for replying.
Can UBOT and VBOT be treated as surface winds?
In the vertical structure of the model,what is the pressure at the lowest level?Is it 1000mb?
Regards,
Anushree

I found a post Northward & Eastward Near Surface Wind Speed variables in which Gary mentions that the UBOT & VBOT are at bout ~60m elevation.Then it means that PM25_SRF,the lowermost PM25 level is also at about 60m?Am i correct?

 

[nusbaume]

Hi Anushree,

Yes, PM25_SRFis at the same height as UBOT and VBOT, so ~60m elevation.

Hope that helps!

Jesse

 

[Wu Yubing]

Hi Anushree,

Yes, PM25_SRFis at the same height as UBOT and VBOT, so ~60m elevation.

Hope that helps!

Jesse

Hi Jesse,
Can UBOT&VBOT be treated as surface wind in some high altitude areas (such as the Qinghai-Tibet Plateau)?
Or does it only represent wind speeds 60 meters above sea level?
Any advice would be appreciated!
Yubing

 

[nusbaume]

Hi Yubing,

Yes, the vertical coordinate in CAM is terrain-following, which means that UBOT and VBOT will always be ~60 meters above the actual land surface at that grid point, not just sea level. So they should be ok to use as surface winds, as long as you are ok with the fact that there is still tens of meters between the actual land surface and those wind values.

Hope that helps!

Jesse