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Questions about relative humidity

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New member
Dear MPAS community,

I'm a little confused about the relative humidity in MPAS. As described in the user manual, the "relhum" variable refers to the diagnosed relative humidity. I analysed the "relhum" variable in history* files, and found that the maximum value is 100 at initial time, while in subsequent times the maximum value goes beyond 100. The first question is, how to explain this phenomenon? While in WRF model, the RH variable in met_em* files can be a value of more than 100, I guess in MPAS init_atmosphere core, there may be a procedure that takes the maximum of relhum between its real value and 100, while the atmosphere core doesn't have such thing.

The second question is, how do MPAS calculate the value of relative humidity? I took a history file and processed with convert_mpas tool, and then checked a vertical slice of relhum variable, as the left column of the picture attached. Then I diagnosed RH manually, referring to the procedure of wrf_user_getvar in NCL software, the result is as the right column of the picture. As you can see, the results is not totally in consistent, what I feel strange is that the result of relhum variable showed the maximum RH at relative high model levels, while the manually calculated RH may seems more reasonable. So which of the results should I take, could you give me some advice? Thanks in advance.


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