jbrande said:
I am trying to change the topography in ccsm and for this I need to know what topography is used for present day simulations. What puzzles me is that PHIS in the cami initial files (e.g. cami_0000-09-01_64x128_L26_c030918.nc) differs from PHIS in the restart files (e.g. b30.004.cam2.i.0601-01-01-00000.nc from the tar-file b30.004.ccsm.r.0601-01-01-00000.040223-110224.tar). The difference is quite large, up to 15000-20000 m^2/s^2 in some regions..
If someone can tell me why this is so it would really help!
Thanks,
Jenny
The PHIS field in cami_0000-09-01_64x128_L26_c030918.nc was mapped directly
from a high-resolution master topography dataset. As such it is not fully processed for
model use when running the Eulerian dynamics core (default dycore). The model
always performs at least one filtering operation every time it reads PHIS from any
IC file:
1) Spectral truncation. The model will always spectrally truncate PHIS on input. IF
the input PHIS is already spectrally truncated, this operation will only produce
roundoff differences between restart (or history) files and the IC file. In this
particular instance, PHIS in "cami_0000-09-01_64x128_L26_c030918.nc" is
*not* spectrally truncated, thus the model PHIS will differ significantly from
that of the IC file.
2) When "cami_0000-09-01_64x128_L26_c030918.nc" was created, a meta-flag
"from_hires" was set to "true" on the PHIS field. This indicates to the model
to perform a second filtering operation - del-4 diffusion.
Together these two operations account for the differences you see.
Both of these filtering operations are done in "dynamics/eul/spetru.F90"
