# Questions about moisture budget analysis using WRF outputs

#### gnosis808

##### New member
Dear all,

I am doing moisture budget analysis with WRF outputs. I have a few questions:

The moisture budget equation I used is

(Seager and Henderson 2013)

Q1: When calculating the vertically integrated moisture flux, I modified the code of vertical integration from (NCL example)
Can I use the method to do vertical integration on (ua * Qvapor) / dx and (va * Qvapor) / dy, and then add them up?

Q2: In WRF output, how can I calculate the last term in the Eq (9)?
Should I use the wa (z-wind component") at the lowest level or should I use ua * gradient of terrain height?

Q3: Dose the variable P in the Eq (9) mean the RAINNC(t) - RAINNC(t-1) in WRF output? Cumulus parameterization is not used.
And how about E? What is the corresponding variable in WRF output?

Any information would be greatly appreciated.

Hi,
(1) Q1: When calculating the vertically integrated moisture flux, I modified the code of vertical integration from (NCL example)
Can I use the method to do vertical integration on (ua * Qvapor) / dx and (va * Qvapor) / dy, and then add them up?
Personally I think this is a reasonable approach. So the answer is yes.

(2) Q3: Dose the variable P in the Eq (9) mean the RAINNC(t) - RAINNC(t-1) in WRF output? Cumulus parameterization is not used.
And how about E? What is the corresponding variable in WRF output?
P is precipitation. It should be RAINNC(t2) - RAINNC(t1), t2 and t1 are the beginning and end time of the period you calculate the moisture budget.
Note that RAINNCV is accumulative precipitation from the initial time of model run.

Hi Ming,

Thank you so much for your information. I may have some follow up questions:

Related to previous Q2, I was wondering how to calculate omega (vertical velocity in pressure coordinate).
It seems like I need to use omega to compute the last term in Eq (9).

I do not see it in my WRF output.

Thank you!

I am really sorry for the typo. RAINNCV should be RAINNC, which is the accumulative resolved-scale precipitation.

For Q2, please see the formula below, which is what I used to calculate omega based on other wrfout variables:

omega=-grav*prs/(rgas*((tmk*(eps+qvp))/(eps*(1.+qvp))))*w

in which:
grav=9.81 ! m/s**2
prs is pressure in [mb]
rgas=287.04 !J/K/kg
tmk isTemperature in [K].
eps=0.622
qvp is water vapor mixing ratio in [kg/kg]
w is vertical velocity in [m/s]

Hope this is helpful for you.

I have a following question: what is the wrfout variable for surface evaporation?

SFCEVP(t) - SFCEVP(t-1) equals to the "E" in the equation, right?