[MITgcm-support] mnc missing values

[David Hebert]

Martin, Constantinos,

Thanks for your replies. I have used the gluemnc script on my little 
test cases and it does work nicely.

I can certainly see the implementing missing values can be complicated. 
My original thought was to use relevant hFac's to determine missing 
values. On the C grid I think this would mean using hFacW for U, hFacS 
for V, and  hFacC for W, T, S, Eta, Pressures. Are there other 
considerations regarding missing values I might be missing?

Also, perhaps the missing_value could be specified in data.mnc? This 
would allow users to customize values.

Thanks,

David


On 01/22/10 01:56, Martin Losch wrote:
> David,
>
> Constantinos is right, mnc can only write files per tile. However, there is a nifty script by Baylor utils/scripts/gluemnc und /utils/scripts/xplbode, which glue your "per-tile" nc-files into a single one (only for simple cartesian or lat-lon grids, though).
>
> About the missing value: I started to implement that, but there are so many things to look out for that for now it's only implemented for scalar fields such as THETA, SALT, ETAN, etc. All vector components have "0" over land (for u,v,w, that's even useful, because the first land point is actually the correct boundary condition of no-flow across the boundary).
>
> It only implemented for the diagnostics package, to turn it on
> #define DIAGNOSTICS_MISSING_VALUE
> in DIAG_OPTIONS.h and then you set missing_value, missing_value_int separately for float and integers (I think they default to 1e+15). You can (or have to) set different values for different lists, but I cannot remember, if that works, you'll have to try it out. I usually live the default value (although it's far from optimal). You can find the relevant code-bits in diagnostics_out.F
>
> Martin
>
> On Jan 21, 2010, at 7:11 PM, Constantinos Evangelinos wrote:
>
>    
>> On Thursday 21 January 2010 12:47:14 pm David Hebert wrote:
>>
>>      
>>> 1 Since mnc writes on per tile basis, is it best to use
>>> globalFiles=.TRUE. (and hence useSingleCpuIO=.FALSE.)?
>>>        
>> These AFAIK affect only the MDSIO package and not the MNC package.
>>
>>      
>>> 2) I see there is a logical flag "use_missing" in MNC_CW_READWRITE_I.F.
>>> Is this intended to be used to write missing values to netcdf output? If
>>> so, can someone point me to where this flag should be set (i.e., what
>>> namelist, don't seem to find it in any other .F files). Also, is a place
>>> to specify what the missing value is?
>>>        
>> Unfortunately the MNC output is not fully functioning - this appears to be a
>> half-way implemented feature. The resulting files also do not conform to the
>> CF conventions unfortunately.
>>
>> Constantinos
>> -- 
>> Dr. Constantinos Evangelinos
>> Department of Earth, Atmospheric and Planetary Sciences
>> Massachusetts Institute of Technology
>>
>>
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>
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