Remove Topography

Any WPS problems/questions that might not fall into the other topics in this category

Remove Topography

Postby marquijw » Fri Jan 31, 2014 5:45 pm

I'm doing a study on the Denver cyclone during a severe event. I'm trying to remove terrain to prove that a boundary was forced by terrain. Has anyone had any experience removing topography? Will I have issues with input data (being at about 850mb as opposed to 1000mb if I zero out terrain) or boundary conditions (discontinuity at the boundary)?

Any ideas are appreciated!
Thanks!
marquijw
 
Posts: 4
Joined: Fri Jan 31, 2014 5:39 pm

Re: Remove Topography

Postby Phillip » Sun Feb 02, 2014 2:59 pm

I have done something like that back in 2012. Run your geogrid.exe, then edit the terrain in your geo*.nc files, after than continue running ungrib.exe, metgrid.exe, real.exe and wrf.exe. You need something to edit the NetCDF-File though. MATLAB for example can do it.

While there are several terrain variables HGT_* WRF uses only HGT_M, at least as far as I know. So it's enough if you modify that one. The preprocessing will adjust the fields to the new topography. It's not perfect, but it works fine.
Phillip
 
Posts: 46
Joined: Thu Jul 19, 2012 3:29 am

Re: Remove Topography

Postby marquijw » Sun Feb 02, 2014 8:18 pm

I actually just talked to a few people in Atlanta, and it sounds like smoothing the terrain instead of zeroing it out may be better. It sounds like running a Fourier transform on the height then applying a low pass filter will probably be best.
marquijw
 
Posts: 4
Joined: Fri Jan 31, 2014 5:39 pm

Re: Remove Topography

Postby Phillip » Mon Feb 03, 2014 3:28 am

Yes, that should work. And don't forget that geogrid itself offers smoothing options, so you can do several passes of 1-2-1 filtering for example. There are other methods too... just in case the FT is not mandatory in your case, that might save you some work.
Phillip
 
Posts: 46
Joined: Thu Jul 19, 2012 3:29 am

Re: Remove Topography

Postby marquijw » Mon Feb 03, 2014 2:15 pm

How intuitive is it to input the geogrid files into Matlab? Is there a tool box I need to acquire?

Thanks in advance!
marquijw
 
Posts: 4
Joined: Fri Jan 31, 2014 5:39 pm

Re: Remove Topography

Postby Phillip » Fri Feb 07, 2014 10:43 am

You might check this website:
http://www.mathworks.fr/fr/help/matlab/ref/netcdf.html

I think that the support for NetCDF files doesn't require a toolbox, but I'm not 100% sure. I used it about two years ago in my university where it worked just fine.

And once you figured out how to use the commands for reading and writing the NetCDF files, which is pretty simple, the rest is very straightforward. You will get a 2D array containing the terrain heights for all grid points which you can use like any other 2D array in MATLAB. Once you are done with your modifications just write it back to the file and you are done. The array you are looking for is called HGT_M - m for mass points - AFAIK the other HGT_* are not used by WRF so you can ignore them.
Phillip
 
Posts: 46
Joined: Thu Jul 19, 2012 3:29 am

Re: Remove Topography

Postby manii » Sat Nov 01, 2014 8:44 am

I'm doing a study on the Denver cyclone during a severe event. I'm trying to remove terrain to prove that a boundary was forced by terrain. Has anyone had any experience removing topography? Will I have issues with input data (being at about 850mb as opposed to 1000mb if I zero out terrain) or boundary conditions (discontinuity at the boundary)?



____________________
Pass your 70-417 free exam questions - braindumps.com and testking exams in first try by using our University of California, San Diego and ISEB and best quality Isaca
manii
 
Posts: 1
Joined: Sat Nov 01, 2014 8:41 am


Return to Miscellaneous

Who is online

Users browsing this forum: No registered users and 2 guests