The problem about Grid nudging

[yxli0323]

Hello, I have recently observed a deviation in the original differences after using the grid nudging option. What could be the reason for this?

The comparison in this figure shows the difference in wind speed with and without a wind farm. It can be seen that after adding nudging, there is a shift in the wind anomaly, with outliers appearing on the northeast side far from the wind farm.When if_zfac_xx=31, the deviation appears in the first hour; when if_zfac_xx=10, there is no deviation in the first hour, but overall average anomalies still show a shift.

My model consists of two layers, with nudging added to the outer layer.







However, QKE anomalies did not exhibit such a deviation.

 

[Ming Chen]

Grid nudging will employ large-scale forcing data to 'correct' the simulation of WRF. With different options of if_zfac_xx, the nudging will be conducted in different ways and the results are different.

We don't recommend using nudging when wind farm option is turned on. This is because the nudging can easily mess up the effect of wind farm.

 

[yxli0323]

Grid nudging will employ large-scale forcing data to 'correct' the simulation of WRF. With different options of if_zfac_xx, the nudging will be conducted in different ways and the results are different.

We don't recommend using nudging when wind farm option is turned on. This is because the nudging can easily mess up the effect of wind farm.

Thank you very much for your suggestion. However, I still have a question: how can I eliminate the instability of the model if I do not use nudging? Without nudging, the differences in wind speed will increase as the model runs. Additionally, I implemented nudging based on the following literature, and only applied it to the parent domain without wind farms. Will this also lead to such a situation?
Golbazi, Maryam, Cristina L. Archer, and Stefano Alessandrini. "Surface impacts of large offshore wind farms." Environmental Research Letters 17.6 (2022): 064021. DOI 10.1088/1748-9326/ac6e49

 

[Horks1986]

Thanks for sharing all these, did you find something??
Palm Beach County Property Appraiser

 

[Ming Chen]

Thank you very much for your suggestion. However, I still have a question: how can I eliminate the instability of the model if I do not use nudging?

You may turn on w_damping to suppress model instability. Your time step (30s) is already small for dx=10km.

Without nudging, the differences in wind speed will increase as the model runs. Additionally, I implemented nudging based on the following literature, and only applied it to the parent domain without wind farms. Will this also lead to such a situation?

We didn't run any tests with such options, and thus I am not sure about it ....

Golbazi, Maryam, Cristina L. Archer, and Stefano Alessandrini. "Surface impacts of large offshore wind farms." Environmental Research Letters 17.6 (2022): 064021. DOI 10.1088/1748-9326/ac6e49