Vertical profile of Wind

[Khin Myat]

Hi
I would like to know about vertical profile of u and v component wind from TS file. In the ts files, there are vertical profile of wind components and vertical profile of geopotential height at each time step.
Does the vertical profile of u and v ,w correspond to wind component at the geopotential height of TS file?

Thank you in advance for your time.

 

[kwerner]

Hi,
Yes, it does. The first column in both the *.UU and *.PH files (for e.g.,) indicates the model time (in hours). Each additional column is the value of, say U-wind and geopotential height at each model level. So the value in the first row (not counting the header) and column 2 in the *.UU file is at the same model height as the value in the first row and column 2 of the *.PH file.

The only difference is that the U/V/W values are output on a staggered grid, while all other variables are unstaggered. There is an option to unstagger U/V/W, if you want. You can find information about all of this in the WRF/run/README.tslist file.

 

[Khin Myat]

Hi @kwerner,
Thank you very much for your reply as always. May I ask more questions about geopotential height? As far as i understand, the ratio of pressure/mass is equal to geopotential height. In wrf dynamics, i think geopotential height is the prognostic variable and mass is conserved at all time. My confusion is whether the mass of one grid cell changes with time or not.
When i read the previous posts, the model height can be obtained by dividing the geopotential height with 9.81. If I divide the PH value with 9.81 and plot with u , v, and w , can we say vertical profile of wind component at each model level? But, that height is not altitude or height above from ground. is it right? or can we say that it is height above sea level?
Thank you in advance for your time.

Best ,
Khin

 

[kwerner]

My confusion is whether the mass of one grid cell changes with time or not.

Mass is conserved within in each grid cell, as well. It's conserved locally and globally.

When i read the previous posts, the model height can be obtained by dividing the geopotential height with 9.81. If I divide the PH value with 9.81

Note that to get total geopotential height, you need to use [(PH + PHB)/9.81]

But, that height is not altitude or height above from ground. is it right? or can we say that it is height above sea level?

It should be the height above sea level.

 

[Khin Myat]

Hi @kwerner,
Thank you very much for your reply.
I am still confusing. if the ts list PH file gives geopotential height at each time step, is that value equal to (PH+PHB) or (PH+PHB)/9.81? Mapping vertical levels to physical altitude, in this post, Ming Chen told that (PH+PHB)/9.81 gives the real altitude of the model. So, I thought that if the PH files gives the geopotential height at each time step and if i divide the geopotential height by 9.81, real altitude of the model will be got.
When I read PH and PHB , PH and PHB refer to perturbation geopotential and base-state geopotential. Why do we need to combine these two values to get total geopotential heights? is it because the wrf calculates the changes of variables or (atmospheric condition) from base state or previous time step?

I am sorry for that if my questions are so stupid and bother you.
Thank you in advance for your time.

Best,
Khin

 

[Ghatee]

You need to combine PH and PHB to get the total geopotential height (Z):

• Z = PH + PHB

Here's the reasoning:

• The model simulates deviations (perturbations) from the base state. PH captures these deviations in geopotential height.
• The base state itself has a specific geopotential height distribution represented by PHB. nulls brawl

By adding PH (the perturbation) to PHB (the base state), you recover the total geopotential height (Z) at each model level and time step.

 

[Khin Myat]

@Ghatee
Thank you very much for your explanation.

 

[Joshua42]

I am still confusing. if the ts list PH file gives geopotential height at each time step, is that value equal to (PH+PHB) or (PH+PHB)/9.81? Mapping vertical levels to physical altitude, in this post, Ming Chen told that (PH+PHB)/9.81 gives the real altitude of the model. So, I thought that if the PH files gives the geopotential height at each time step and if i divide the geopotential height by 9.81, real altitude of the model will be got.
When I read PH and PHB , PH and PHB refer to perturbation geopotential and base-state geopotential. Why do we need to combine these two values to get total geopotential heights? is it because the wrf calculates the changes of variables or (atmospheric condition) from base state or previous time step?

You are correct that the combination of PH (geopotential of perturbation) and PHB (geopotential base state) gives the height of the total geopotential. Because the WRF model calculates the deviation from the base state, divide it by (PH + PHB) 9.81 to get the actual height given the gravitational acceleration.