Purpose of flndtopo in CLM4 when running as CESM component with CISM

[wadewei]

Hi all,

I noticed an additional input file (flndtopo) was included when running CESM1.2 with active CISM. It looks like this file has the topo info in it. Since I changed the topography used with CAM, I assume this has to be modified as well.

However, just to make sure, shall I simply change the value to that used in CAM, or are there any additional treatment needed? Also, out of curiosity, can someone please explain why this file is needed, rather than simply use the topo in CAM's bndtopo file or CLM's topo field in surfdata?

Thank you!

Wade


cat CaseDocs/lnd_in
...
flndtopo = '/home/sharing/inputdata/lnd/clm2/griddata/topodata_1.9x2.5_USGS_061130.nc'
...

 

[sacks]

Sorry for the slow reply. Your understanding is correct: flndtopo is meant to agree with CAM's topography. It is used for lapse rate-based adjustments of the atmospheric forcings to the height of each column in glacier regions. If I remember correctly, this file should agree exactly with the topography used in CAM: no other treatments are needed.

In more recent versions of CESM, we get the atmosphere model's topography directly from the atmosphere model (as you suggest) rather than having this separate file. (CLM's topo field in surfdata is generated from a different dataset, so doesn't agree with the atmosphere's topography. For the purposes for which this file is used – downscaling the atmosphere forcings – we want to know the actual topographic heights used in the atmosphere model.)