Synthetic topography

[janac4]

Hello everyone,
I want to modify WRF input topography to create, for example, a smoother region or cut off high mountains. After researching the procedure, I found many people choose to modify HGT_M variable in geogrid output file. I tried this approach, and it worked well, resulting in consistently higher temperatures in the smoothed areas.
However, I found this post in the forum: Removing Terrain and Converting Land to Sea
It also talks about variables VAR, VAR_SSO, CON, OA[1-4], OL[1-4] in the geogrid file which are dependent on the surface terrain. Unfortunately, I couldn't find much information about these variables.For instance, OA[1-4] and OL[1-4] have the same description and lack units. Should I modify them accordingly if I already changed HGT_M field? Would it really make a difference?

 

[Ming Chen]

if you run WRF without gravity wave drag scheme, then you don't need to worry for these variables.
However, if the gravity wave drag option is turned on, then these variables may affect the results, although the impact is not big.
Usually we would recommend users to stay with the data provided by WPS, even if HGT_M is changed.

 

[janac4]

Thank you for your answer. I don't have gwd_opt specified in my namelist.input file, so I assume the default option is configured. Is the default option gwd_opt=1 (gravity wave drag and blocking activated)? Although I have this scheme activated, I'm relieved these variables don't have a big impact on the results.

 

[Ming Chen]

The default option is gwd_opt = 0, so you don't need to worry for those static fields related to GWD.

 

[janac4]

Thank you so much.