#### Alex_Cantrel

##### New member

I have a question on PH (perturbation geopotential) and PHB (base-state geopotential) variables.

I am curious how these two variables vary in time. I have a 1-week analysis in which I store these two variables to calculate the height above the ground level (Height AGL).

I would like to ask if I could use the weekly mean value of PH and PHB in each height level to get a good approximation of these two variables (and the height AGL) for the rest of the year.

Does this makes sense or the estimation will be insufficient?

Thank you very much in advance.