Scheduled Downtime
On Friday 21 April 2023 @ 5pm MT, this website will be down for maintenance and expected to return online the morning of 24 April 2023 at the latest

DPSDT (surface pressure tendency) output

This post was from a previous version of the WRF&MPAS-A Support Forum. New replies have been disabled and if you have follow up questions related to this post, then please start a new thread from the forum home page.


New member

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.

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.
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.

Can you please tell me how DPSDT is calculated (which variables are used) in WRF?
I have looked into the file "module_diag_misc.F". I am unable to figure out what is "pk1m".

PK1M is lowest model level pressure in the previous time step. p8w(i,kms,j) is the pressure at the current time step.