[Go-essp-tech] Incorrect use of missing value in some MRI ocean data -- correction

[martin.juckes at stfc.ac.uk]

I owe MRI an apology -- the use of zero instead of a missing value is in fact recommended in (http://cmip-pcmdi.llnl.gov/cmip5/docs/standard_output.xls),

regards,
Martin
________________________________________
From: Juckes, Martin (STFC,RAL,RALSP)
Sent: 04 December 2011 08:45
To: go-essp-tech at ucar.edu; Parton, Graham (STFC,RAL,SSTD); cmip5-users at jiscmail.ac.uk
Cc: Pascoe, Stephen (STFC,RAL,RALSP)
Subject: Incorrect use of missing value in some MRI ocean data.

Hello,

It has come to light that some MRI ocean data has land grid points set to zero rather than to the declared missing value. This is likely to confuse some applications reading and plotting the data -- I've notified Seiji Yukimoto at MRI,

sincerely,
Martin
________________________________________
From: Dennis Shea [shea at ucar.edu]
Sent: 03 December 2011 19:45
To: Zhang Tao
Cc: Juckes, Martin (STFC,RAL,RALSP); haley at ucar.edu; Gary Strand; Karl Taylor
Subject: Re: [ncl-talk] How to regrid CMIP5 ocean temp. data to regular 1X1 grid

CMIP5 users beware!   :-(

---

The first rule of data processing is to 'look at the data.'

The problem is *not* with the cdo. Rather the source data file
from CMIP5 has incorrect information. I read the  surface level

   a   =
addfile("thetao_Omon_MRI-CGCM3_piControl_r1i1p1_230101-230102.lite.nc","r")
   ta  = a->thetao(0,0,:,:)

   printVarSummary(ta)
   printMinMax(ta,0)


The variable has the following attributes

   missing_value :      1e+20
   _FillValue : 1e+20

I counted the number of number of _FillValue (nmsg1) and the
min/max temperatures.

(0)     Sea Water Potential Temperature: min=0   max=303.924
(0)     nmsg1=0

Obviously, a temperature of 0 is physically not correct. I printed
the array. No missing values (1e20) were encountered. What about land?
The actual _FillValue (missing_value) is 0.0. In an NCL
script I reset to 0.0

   ta at _FillValue = 0.0

I counted the _FillValue and the min/max

(0)     nmsg2=42671
(0)     Sea Water Potential Temperature: min=271.293   max=303.924

The temperature range is much more reasonable.

So the cdo treated the original 0.0 as valid values rather than
_FillValue. I used the NCO operator, ncatted, to create a copy of the
original source file but altered the _FillValue to 0.0

%> ncatted -O -h -a _FillValue,thetao,o,f,0
thetao_Omon_MRI-CGCM3_piControl_r1i1p1_230101-230102.lite.nc
thetao_Omon_MRI_FillValue.nc

Then ran the cdo to generate the weights

%> cdo genbil,r360x180 thetao_Omon_MRI_FillValue.nc
thetao_Omon_MRI_bilwgt.nc


Then did the remap

%> cdo remap,r360x180,thetao_Omon_MRI_bilwgt.nc
thetao_Omon_MRI_FillValue.nc thetao_Omon.r360x180.nc

I works!!

See: http://www.cgd.ucar.edu/~shea/TaoZhang.png

D


On 12/2/11 4:12 PM, Zhang Tao wrote:
> Dennis,
>
> I have attached 3 plots for you to take a look. MPI.pdf is the results
> from MPI model, I use "cdo remapbil,ll1deg_grid.nc <input file> <output
> file> " to get it.
>
> I plot out the contour and shaded plots of MRI-CGCM3 which is obtained
> from your command. clearly, the following command does not work
> well with this model. I use "cdo remapbil,ll1deg_grid.nc <input file>
> <output file> " for this model, similar results are obtained. There are
> lots of unrealistically points in the land.
>
> Tao
>
>
> %> cdo genbil,r360x180
> thetao_Omon_MRI-CGCM3_piControl_r1i1p1_230101-230102.lite.nc
> thetao_Omon_MRI_bilwgt.nc
>
> &> cdo remap,r360x180,thetao_Omon_MRI_bilwgt.nc
> thetao_Omon_MRI-CGCM3_piControl_r1i1p1_230101-230102.lite.nc
> thetao_Omon.r360x180.nc
>
>
>
>
> On 12/2/11 3:49 PM, Dennis Shea wrote:
>> %> cdo genbil,r360x180
>> thetao_Omon_MRI-CGCM3_piControl_r1i1p1_230101-230102.lite.nc
>> thetao_Omon_MRI_bilwgt.nc
>>
>> &> cdo remap,r360x180,thetao_Omon_MRI_bilwgt.nc
>> thetao_Omon_MRI-CGCM3_piControl_r1i1p1_230101-230102.lite.nc
>> thetao_Omon.r360x180.nc
>>
>> ftp ftp.cgd.ucar.edu
>> anonymous
>> email
>> cd pub/shea/ZhangTao
>> prompt
>> mget *
>> quit
>>
>>
>> =================
>> 10997404 Dec 2 15:46 thetao_Omon_MRI_bilwgt.nc
>> 1050660 Dec 2 15:47 thetao_Omon.r360x180.nc
>>
>> Hope it worked.
>>
>> I'm outta her!
>>
>> D
>>
>>
>> On 12/02/2011 03:00 PM, Zhang Tao wrote:
>>> Dennis,
>>>
>>> Could you write down the detailed CDO command to remap Japanese model?
>>> I can make a test.
>>>
>>> Thanks,
>>> Tao
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