HYSPLIT Forum: hysplitbbs.arl.noaa.gov

Hello,

I'd like to improve the topography of the meteo data.

Performing WRF simulations and using the resulting meteo files is one option. I'm wondering if it is possible to use a gdas file and substitute the TERRAIN.ASC file with the topography that I'd like to use.

Many thanks
Regards

Federica

HYSPLIT uses the terrain from the meteorological file if it is available. The gdas 1 deg file has terrain data (named as SHGT).
For generating a TERRAIN.ASC file, you can follow the Readme_bdyfiles.txt in ~/bdyfiles subdirectory, or check the user guide: https://www.ready.noaa.gov/hysplitusersguide/S444.htm

There will be updated TERRAIN.ASC files for 1 deg, 0.5 deg, and 0.1 deg in the next HYSPLIT release.

Thanks for your reply. Is it possible to tell the code to use the user-defined TERRAIN.ASC even when the wind-field has its own ground elevation?

Many thanks
Regards
Federica

For using a user-defined TERRAIN.ASC, you will need to consider and do the following:
1) Check if the terrain data are in the met file. HYSPLIT uses it when it is available. In this case, you will need to remove the terrain data from the met file or modify HYSPLIT subroutine "metinp.f" to not reading in 'SHGT' from the met file.
2) HYSPLIT has three static files TERRAIN.ASC, LANDUSE.ASC, and ROUGLEN.ASC. They are packaged together with 1 deg and 0.5 deg resolution. You need to provide LANDUSE.ASC and ROUGLEN.ASC in the same resolution as the user-defined TERRAIN. ASC. Or you can remove those two files from the bdyfiles directory and let HYSPLIT use constant default values for them.

I think the better way is to run WRF simulations with your terrain data. This will prevent the issue of the inconsistency between the terrain data and surface fields associated with terrain.

Many thanks for your exhaustive reply! It helps me a lot.

Best Regards
Federica