Is it possible to get the turbulence wind speed and thus the turbulence wind speed spectrum from the WRF simulation results? Does the wind speed at each output moment represent the instantaneous wind speed or the average wind speed for that time step, and how do I do that if I want to get the ten minute average wind speed? Thanks.
Turbulence wind field
- Thread starter yuankw
- Start date
To get turbulence, you need to run the model in the so-called LES mode. This means:
Finally, just because you have a very small time step (say 0.2 s), this does not mean that motions at such small scales are resolved. WRF smoothes fields internally, so only motions at scales of ~7 times the time (and space) step are resolved.
EDIT: Sorry, I did not read the last question. WRF field output is instantaneous, but if you are running WRF at a scale which is > 1 km, then this instantaneous output is representative of the 10-min mean output of "real" wind. So no need to average. You only average if you run the model at a much smaller scale.
- very small time and space step (less than 100 m, time step adjusted for CFL condition)
- disabling some physical parametrizations (bl_pbl_opt = 0)
- other stuff
Finally, just because you have a very small time step (say 0.2 s), this does not mean that motions at such small scales are resolved. WRF smoothes fields internally, so only motions at scales of ~7 times the time (and space) step are resolved.
EDIT: Sorry, I did not read the last question. WRF field output is instantaneous, but if you are running WRF at a scale which is > 1 km, then this instantaneous output is representative of the 10-min mean output of "real" wind. So no need to average. You only average if you run the model at a much smaller scale.
Thank you very much, I am currently using tslist, but it seems like there is only one elevation in the project output by tslist, I want to get the data for the height I want, can you reply me how to do that?
By the way,the first image is the VV output from the ts file, the elevation is shown as 2.2m, the second image is the PH elevation data, can I understand that VV corresponds to each column of PH?
Extremely grateful.
Well tslist as a default outputs several fields (as you probably know). One of them is a .TS file which has surface variables (T2, U10, V10 and so forth). All others represent variables such as U component of the wind velocity (UU). Each column corresponds to that variable at a height of a model level.
So, the first column is time, the second is UU at the first bottom_top level above the ground, third at the second etc. You can control how high this goes, I believe the default is 20 or 25 levels.
To get the output at a desired level, you can use the PH file which houses the perturbation geopotential at that same model level, which you can use to interpolate to a desired height. Now, I am not sure, but I believe PH is perturbation geopotential, so to get the height you would need to add the base geopotential to it, and then divide by 9.8 to get height above the mean sea level. Unsure if tslist also outputs the base geopotential (PHB).
So, the first column is time, the second is UU at the first bottom_top level above the ground, third at the second etc. You can control how high this goes, I believe the default is 20 or 25 levels.
To get the output at a desired level, you can use the PH file which houses the perturbation geopotential at that same model level, which you can use to interpolate to a desired height. Now, I am not sure, but I believe PH is perturbation geopotential, so to get the height you would need to add the base geopotential to it, and then divide by 9.8 to get height above the mean sea level. Unsure if tslist also outputs the base geopotential (PHB).
Dear Pechudin,
" PH is perturbation geopotential, so to get the height you would need to add the base geopotential". I am also interested in it. How can I get base geopotenital height (PHB)? I found PHB variable in wrfout file. But I could not do to get the PHB value with ncl function. Please, could you share me how to get PHB at each time step?
Thank you in advance for your time.
" PH is perturbation geopotential, so to get the height you would need to add the base geopotential". I am also interested in it. How can I get base geopotenital height (PHB)? I found PHB variable in wrfout file. But I could not do to get the PHB value with ncl function. Please, could you share me how to get PHB at each time step?
Thank you in advance for your time.
A cursory google found this:
wiki.openwfm.org
Here it is argued that the base geopotential is constant in time. So, you could just extract a profile of PHB from the same point as defined by tslist and add it to the PH fields for all the times. That way you get time-variable total geopotential field.
How to interpret WRF variables - openwfm
Here it is argued that the base geopotential is constant in time. So, you could just extract a profile of PHB from the same point as defined by tslist and add it to the PH fields for all the times. That way you get time-variable total geopotential field.
Dear Pechudin,
Thank you very much for your reply and information.
I also want to get PHB profile at the point defined in the tslist. At first, I thought I can get the PHB by using the wrf_user_getvar
function in the NCL command. But PHB and PH is not included in it. How can I extract the PHB profile at the point defined in ts list?
Thank you very much in advance for your time.
Thank you very much for your reply and information.
I also want to get PHB profile at the point defined in the tslist. At first, I thought I can get the PHB by using the wrf_user_getvar
function in the NCL command. But PHB and PH is not included in it. How can I extract the PHB profile at the point defined in ts list?
Thank you very much in advance for your time.
Don't know about NCL but you can use wrf-python to select a datapoint.
Dear Pechudin,
It's been a while since I've asked you for advice, and I've recently run into some problems. May I ask what is the elevation specified by in the first line of the tslist file? I don't remember giving the elevation value anywhere as it was verified that elevation is not equal to the value of the first eta_level, also does PH in the tslist.PH file have anything to do with eta_level, is it equal to (PH+PHB)/9.81,Looking forward to your reply, thank you very much!
PH is geopotential height of model levels above the specific place you give in tslist. It should be equal to geopotential height of eta_level at that place.