[cam-users] Time step ?

[Ragoth Sundararajan]

hello,

I am trying a CAM run which starts at June 1 1981, and should go for a 9 
month period. I am using the boundary data in the file, 
/fs/cgd/csm/inputdata/atm/cam2/sst/sst_HadOIBl_bc_64x128_1949_2001_c020411.nc 
for forcing. Everything else is the same as one would do in a standard 
one-day run (including the time step of 1200 secs) as suggested by the user 
guide. After about 100 time steps the horizontal courant number exceeds one 
and the run gets into problems. Does this mean a 1200 sec time step is too 
large ? I noticed that even for the customary oneday run forced with 
climatologocal SST values, the horizontal courant number starts at 0.89 or 
something like that and pretty much gets closer to unity. Has anyone faced 
this problem ? Is 1200 sec the default time step used in standard CAM runs 
? For example, were the AMIP runs with CAM2 done using 1200 sec. ? I would 
appreciate, if some one can give useful tips on this. Thanks in advance.

This is the namelist i am using:
--------------------------------------------------------------------------------------------------------------------------------------------------------------
&camexp
  absems_data            = 
'/fs/cgd/csm/inputdata/atm/cam2/rad/abs_ems_factors_fastvx.052001.nc'
  bndtvo         = '/fs/cgd/csm/inputdata/atm/cam2/ozone/noaao3.1990.21999.nc'
  bndtvs         = 
'/fs/cgd/csm/inputdata/atm/cam2/sst/sst_HadOIBl_bc_64x128_1949_2001_c020411.nc'
  caseid         = 'jun19810126L'
  dtime          = 1200
  iyear_ad               = 1980
  ncdata         = 
'/fs/cgd/csm/inputdata/atm/cam2/inic/gaus/cami_0000-09-01_64x128_T42_L26_c020514.nc' 

  nelapse                = -273
  nhtfrq         = 0
  nsrest         = 0
  sstcyc         = .false.
  start_tod              = 0
  start_ymd              = 19810601
/
&clmexp
  finidat                = 
'/fs/cgd/csm/inputdata/lnd/clm2/inidata/cam/clmi_0000-09-01_64x128_T42_c020514.nc'
  fpftcon                = 
'/fs/cgd/csm/inputdata/lnd/clm2/pftdata/pft-physiology'
  fsurdat                = 
'/fs/cgd/csm/inputdata/lnd/clm2/srfdata/cam/clms_64x128_c020514.nc'
/
--------------------------------------------------------------------------------------------------- 
---------------------------------------------

Ragoth Sundararajan.
MIT.