[MITgcm-support] Input data for MITgcm

[Martin Losch]

Hi Ankur,

basically you are responsible for the forcing data sets yourself, that  
involves the decision, which data sets to use. There is a large  
variety of possiblities to choose based on your research objective.  
The global_ocean.90x40x15 uses a very specific (and maybe very old)  
set. These data servejust as an example and are probably no longer the  
best choice for forcing an ocean model:
- initial hydrography and surface restoring values are based on the  
1994 "Levitus atlas". They should be replaced by a later version of  
this (e.g. WOA 2005, or PHC, or whatever is appropriate).
- wind forcing is precomputed wind stresses from a compilation,  
commonly called "trenberth winds" (Trenberth et al 1990). They are  
also very old
- buoyancy forcing is based on an old NCEP reanalysis (CDAS-1 also  
available somewhere on ldea.columbia.edu, I remember it was tricky to  
find it, here is what I found in my browser bookmarks: <http://iridl.ldeo.columbia.edu/SOURCES/.NOAA/.NCEP-NCAR/.CDAS-1/.MONTHLY/.Diagnostic/.surface/ 
 >). The DaSilva data set is also old. The buoyancy forcing in  
global_ocean.90x40x15 is "tuned" to have no net freshwater flux and no  
net heat flux. The original data are certainly biased and do not  
conserve heat and freshwater.

You can also force your model with atmospheric winds, air temperature,  
humidity, precipitation and incoming radiation etc., see lab_sea as an  
example (in fact as soon as you want to turn on a sea ice model you'll  
have to do it like that). Many standard forcing data sets are just  
that, e.g. CORE, ERA40, etc.

Surface restoring to surface temperature and salinity (SST, SSS) is  
possible (and probably required in many cases), and you need to  
specify the files you want to read from. If you don't, then the model  
doesn't look for any such files (in the above example these files are  
also compiled from the levitus hydrography).

Martin

On Dec 5, 2009, at 7:48 PM, ankur gupta wrote:

> Hello,
>
> I am a grad student at SIO, UCSD. I have run standard Global Ocean
> Simulation (3.12) at 4x4 resolution and trying to run a similar
> simulation at 1x1 resolution.
> I am trying to get the input data for 1x1 resoulution. The manual says
> initialization data and surface fluxes are from Levitus and DaSilva, I
> have found the data on ldeo.columbia.edu. However it seems 4x4
> simulation has input files for net fluxes and EPR (evaporation,
> precipitation, runoff) named like 'ncep_  '. Can I get the link to the
> data, if NCEP or otherwise, 4x4 simulation is using. I can use DaSilva
> for Q(net) and EPR, but it doesn't have the runoff data. If someone
> has used DaSilva for Q(net) what data sets are you using from
> DaSilva.. I am trying Q(net)=Q(net longwave) - Shortwave, but I found
> the DaSilva data set has more +ve Constrained net longwave than
> longwave itself.
>
> Further, for the temperature forcing, F= (T-T*)/tau - Q/(constant), I
> found out that for T* the code looks for data from the SST files.
> Please confirm.
>
> Thanks,
> Ankur
> Graduate Student
> Scripps Institution of Oceanography, UCSD
>
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