DPSDT (surface pressure tendency) output

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meteorology1
Posts: 1
Joined: Sat May 01, 2021 3:44 am

DPSDT (surface pressure tendency) output

Post by meteorology1 » Sat May 01, 2021 3:55 am

Hello,

I am running my WRF model version 4 with time step of 6 seconds and I have set the model to output every 6 seconds.
However, I am trying to output DPSDT at initial time but the model outputs non-zero DPSDT values only from 12 second output, i.e., in the wrf output file of 0 and 6 seconds DPSDT is 0.
Can you please let me know why is this happening.

Thanks

Ming Chen
Posts: 1456
Joined: Mon Apr 23, 2018 9:42 pm

Re: DPSDT (surface pressure tendency) output

Post by Ming Chen » Tue May 11, 2021 6:10 pm

Hi,
I have read through the codes and find no problems with the dpsdt calculation.
However, I run a test case with time step =60s and model output even time step. My results indicate that dpsdt is zero everywhere in the first 10 minutes of integration. I am not sure yet what the reason could be. I will continue to look at this issue and get back to you after I know for sure. Thanks for your patience.
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Ming Chen
Posts: 1456
Joined: Mon Apr 23, 2018 9:42 pm

Re: DPSDT (surface pressure tendency) output

Post by Ming Chen » Mon May 17, 2021 5:57 pm

Hi,
I examined the code and found nothing wrong. In my previous test, I didn't set diag_print, which is the reason why all dpsdt = 0 in wrfout.
After this error is corrected, I can get reasonable dpsdt after the first tilmestep of WRF integration.
It is understandable that in the first wrfout, dpsdt should be zero everywhere (the first wrfout includes data at the initial time). Once the model starts to integrate, dpsdt will have values.
I am not sure of your case. It is rare but still possible that dpsdt is zero everywhere during the model integration over just a single time step, which means that little changes occur during that time step.
If the dpsddt values in other wrfout files look reasonable, then I guess the codes just work as expected.
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