Difference between ZA and (PH+PHB)/9.8 as the first atmospheric height

[y333cubed]

Hi,

I'm using WRF-Chem to simulate air quality near urban centers and getting confused with a physical definition.

I'm wondering the difference between ZA (defined as first atmospheric level as a lowest boundary condition in module_sf_urban.F under ./WRF/phys) and (PH+PHB)/9.8. I learnt from another thread that (PH+PHB)/9.8 represents the height of each model level. In my case, I modified module_sf_urban.F to print out the variable ZA and it's around 19. But (PH+PHB)/9.8 at the first model level is around 38, almost double.

I'm wondering which represents the height of the first atmospheric layer and what are the differences bewteen them?

Thank you!
April

 

[Ming Chen]

April,
(PH+PHB)/9.8 is full model level height, ZA is the height of the first half-model level.

 

[y333cubed]

April,
(PH+PHB)/9.8 is full model level height, ZA is the height of the first half-model level.

Hi Ming,

Thanks for your answer!

A following-up question: Can I interpret that 2*ZA = (PH+PHB)/9.8 at the first layer?

 

[Ming Chen]

yes that is correct.