## Eta levels

### Eta levels

Hi,

I'm a recent user of WRF and I'm having some problem understandig eta levels... I chose e_vert=42 (42 eta levels) and did not specify eta_levels.

ZNW =
1, 0.993, 0.983, 0.97, 0.954, 0.934, 0.909, 0.88, 0.8503934, 0.8207868,
0.7911803, 0.7615737, 0.7071643, 0.6557633, 0.6072319, 0.561437,
0.5182505, 0.4775495, 0.4392157, 0.4031358, 0.3692009, 0.3373066,
0.3073525, 0.2792425, 0.2528844, 0.2281899, 0.2050741, 0.1834559,
0.1632576, 0.1444046, 0.1268257, 0.1104528, 0.09522035, 0.08106608,
0.06793022, 0.05575566, 0.0444878, 0.03407445, 0.0244657, 0.01561383,
0.007473174, 0 ;

What I want to know is:
1. each eta level correspond to which height?
I chose ARWPost 1000mb and did (ph+phb)/9.8 which gave me the lowest height: 72m. This corresponds to eta=1??
2. To calculate wind field at 60 m (hub height) what is the procedure?

Many thanks
MGM

Posts: 2
Joined: Mon Mar 05, 2012 1:00 pm

### Re: Eta levels

1-Thanks to the forum and particularly wikiroger, information about eta levels can be found here:
http://collaboration.cmc.ec.gc.ca/cmc/C%20...%20doc_e.html

2- To interpolate the wind in the PBL you can use the log profile.
u(eta=1)=(u*/k)ln(zeta/z0)
where u* (friction velocity) and z0 (roughness) are surface dependant, zeta is the altitude k is the Karman constant.

If you write both your velocity this way you can obtain:
u(z=60m)=u(eta=1)*ln((z=60m)/z0)/ln(zeta/z0)

Use ZNT in the WRF output as z0.

Hope it helps.
AlexFr

Posts: 9
Joined: Tue Jan 17, 2012 10:09 am

### Re: Eta levels

jan

Posts: 174
Joined: Wed Jun 15, 2011 3:48 am

### Re: Eta levels

>2- To interpolate the wind in the PBL you can use the log profile.
>u(eta=1)=(u*/k)ln(zeta/z0)
>where u* (friction velocity) and z0 (roughness) are surface dependant, zeta is the altitude k is the Karman >constant.

>If you write both your velocity this way you can obtain:
>u(z=60m)=u(eta=1)*ln((z=60m)/z0)/ln(zeta/z0)

>Use ZNT in the WRF output as z0.

Hi,
I have no ZNT variable in wrf history files. How do i can get this value?

Thanks
p.accerboni

Posts: 1
Joined: Fri Sep 28, 2012 11:01 am

### Re: Eta levels

Actually WRF uses sigma coordinate system, not eta system.
littleho_song

Posts: 8
Joined: Mon Dec 12, 2011 10:19 am

### Re: Eta levels

p.accerboni wrote:>2- To interpolate the wind in the PBL you can use the log profile.
>u(eta=1)=(u*/k)ln(zeta/z0)
>where u* (friction velocity) and z0 (roughness) are surface dependant, zeta is the altitude k is the Karman >constant.
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>If you write both your velocity this way you can obtain:
>u(z=60m)=u(eta=1)*ln((z=60m)/z0)/ln(zeta/z0)

>Use ZNT in the WRF output as z0.

Hi,
I have no ZNT variable in wrf history files. How do i can get this value?

Thanks

Posts: 8
Joined: Sat Dec 28, 2013 11:18 am

### Re: Eta levels

AlexFr wrote:1-Thanks to the forum and particularly wikiroger, information about eta levels can be found here:
http://collaboration.cmc.ec.gc.ca/cmc/C%20...%20doc_e.html

2- To interpolate the wind in the PBL you can use the log profile.
u(eta=1)=(u*/k)ln(zeta/z0)
where u* (friction velocity) and z0 (roughness) are surface dependant, zeta is the altitude k is the Karman constant.

If you write both your velocity this way you can obtain:
u(z=60m)=u(eta=1)*ln((z=60m)/z0)/ln(zeta/z0)

Use ZNT in the WRF output as z0.

Hope it helps.

Hi dear
How about To calculate CO2 concentration field at 60 m(or another height) (hub height) what is the procedure?
I am working on WRF_Chem, I would like to calculate the concentration of CO2 just in the Planetary boundary layer(I mean, I want to calculate CO2 from surface to top of PBL).in WRF How can I calculate the level of PBL. in WRF we have (PBLH: the height of PBL but it doesn't inform us what is the top level of PBL compare all level of the model?). my model has a 37vertical levels. If I Know the level of PBL, I will calculate the pressure weight of its level and calculate the contribution of PBL concentration. how can I find the concentration Of CO2 in PBL height considering the weight of PBL layer? thank you for all your guidance.
samira86

Posts: 2
Joined: Thu May 13, 2021 1:40 pm