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

How does the WPS/WRF maintain the geostrophic balance when the meteorological input data is modified

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
Hi all,

I'm interested in running a pseudo global warming simulation by WRF. Namely, I will modify the meteorological input data (which is ERA5) with the temperature deltas between the historical period and the future period projected by the CMIP6 models. Because the temperature deltas are different at each gridpoint, it's clear that the geostrophic balance will not be held in the modified meteorological input data; however, the WPS/WRF can still run successfully with modified meteorological input data. Could anyone please tell me how does the WPS/WRF maintain the geostrophic balance in the meteorological input data?

Thank you so much for your help!

Hi Zeyu,
I apologize that it looks like this inquiry was overlooked. I'm not sure of the answer to your question, but I'll try to track down someone who may know and will get back to you. Again, I apologize, and thank you for your question.
Hi Zeyu,
I reached out to our physics expert who said he was already discussing this issue with you and thought it was resolved. He forwarded me those emails, and a summary of the information given in that email is:

In the PGW approach, the wind, surface pressure, and humidity are also perturbed in the metgrid file. No adjustments are done in WPS. The real.exe program only does a vertical hydrostatic adjustment where height is integrated from the virtual temperature. Since height is perturbed and wind is not, there may be some adjustment the model must do when it runs, so we recommend perturbing winds, along with temperature to give the model less to adjust. This remains important at the boundaries. Temperature information will go into the new height field. If the wind is perturbed, it should already be close to balanced with the new height field.

You may not see obvious noise because the perturbations are large scale, but it is possible that adding the wind perturbation will end up with a slightly different mean state.

Regarding literature, we are not aware of anyone who studies the difference in PGW adjustments by not varying both winds and thermodynamic fields.
People have used FDDA nudging to study nudging one or the other.

Do you still have additional questions?

Thank you so much for reaching out. Yes, Dr. Dudhia explained it to me last month and I'm still looking for some references for those adjustments so that I can cite them in the paper and better understand how does the WRF make it. Could you please give me some suggestions?

I'm also not aware of any references I could point you to. I would have asked Dr. Dudhia, so since they don't know, I unfortunately don't either. I apologize for the inconvenience.