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Removing Terrain and Converting Land to Sea

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Hi all,

I am doing sensitivity experiments on the effects of terrain and land surface (of an island) to tropical cyclone. I would like to do the following three things:

1. Remove the whole island and replace it with ocean
2. Keep the island but remove its terrain completely (zero height)
3. Alter the height of the island terrain

For 2, I read from somewhere else that I could simply set HGT_M to 0 in my geo*.nc prior to running ungrib.exe, metgrid.exe, real.exe and wrf.exe. I have yet to discover information on how to do 1 and 3.

In particular, besides modifying HGT_M in my geo*.nc, is there anything that I should modify for my wrfinput?

Any help is greatly appreciated. Many thanks!

- KH
I think you're on the right track.

1. I recommend taking a look at an NCL option that allows you to change a field for specific grid cells. Take a look at this presentation on NCL given at our WRF Tutorials, and start with slide 40. You could swap out the values of the terrain for water points.

2. Yes, setting HGT_M to zero for each grid cell would be the way to go.

3. This would be similar to what you're doing for option 2, but you would just modify each cell to the value you wish to use.

I assume you could use an NCL program for options 2 and 3, as well. If you have questions regarding NCL, we have a specific section of the forum dedicated to the program, and someone who is an expert with NCL views and responds to those inquiries.

As for making sure the modifications stick throughout the simulation, you can choose to make the modifications to the geogrid, metgrid, or wrfinput output files, and you should make sure to set "surface_input_source = 3" in the physics section of your namelist.input. This ensures that the values from WPS are used and are not recalculated by other physics options.
Hello and thanks for the reply! Converting HGT_M in geo*.nc to 0 seems to work.

A further question: I think that the variables VAR, VAR_SSO, CON, OA[1-4], OL[1-4] are dependent on the surface terrain and used in the gravity wave drag option. Now that I have removed the terrain of a certain region, should I set the above variables to zero within the region of removal?

Many thanks.
I'm glad to hear you were able to get things working! Yes, I believe you would want those values to be zero, as well. They should match the value of the surrounding water, which I assume is all zeros.