[ncl-talk] Remove Global mean SST from the SST data

[Adam Phillips]

Hi Dickson,
If you want to remove the global mean value from each timestep at each grid
point, you could do something like this:
;arr is a 3D array dimensioned time x lat x lon, with coordinate variables
of the same name.
pi=4.*atan(1.0)
rad=(pi/180.)
coswgt=cos(rad*arr&lat)
coswgt!0 = "lat"
coswgt&lat= arr&lat
do ff = 0,dimsizes(arr&time)-1
     arr(ff,:,:) = (/ arr(ff,:,:) -
wgt_areaave(arr(ff,{-60:70},:),coswgt({-60.:60.}),1.0,0) /)
end do

Note that in the above I'm weighting the area by the cosine of the
latitude.
Hope that helps!
Adam

On Mon, Nov 4, 2019 at 9:31 PM Dennis Shea via ncl-talk <ncl-talk at ucar.edu>
wrote:

> One approach:
>
>
> ;--- Global: only 60S-60N
>
>   sstGlb    = f->SST(iStrt:iLast,{-60:60},:)          ; read Global data (limit 60S to 60N)
>   printVarSummary(sstGlb)
>
>   sstGlbClm = clmMonTLL(sstGlb)                       ; climatology for clm period
>   printVarSummary(sstGlbClm)
>
>   sstGlbAnom= calcMonAnomTLL ( sstGlb , sstGlbClm )   ; anomalies at each grid point
>   printVarSummary(sstGlbAnom)                         ; from base climatology
>
>
> On Mon, Nov 4, 2019 at 8:00 PM dickson mbigi via ncl-talk <
> ncl-talk at ucar.edu> wrote:
>
>> Dear concerned expert,
>> I am preparing a script to perfom  decadal MAM EOF over Indian oceans
>> using ERSSTV5 data set.
>> Steps prior to do EOF:
>> 1) Select the three months of March-May and do the seasonal mean;
>> 2) Do a 9-year running average (Lanczos filter)
>> 3) Do the linear regression on the global mean SST and keep the residual
>> for latter EOF analysis (i.e. remove the global mean component at each grid
>> point).
>>
>> I cannot figure out the third step on how to remove the global mean
>> component at each grid point.
>>
>> Kindly I am writing to ask for any assistance or directive regarding the
>> said concern.
>>
>> Regards,
>> Dickson.
>>
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-- 
Adam Phillips
Associate Scientist,  Climate and Global Dynamics Laboratory, NCAR
www.cgd.ucar.edu/staff/asphilli/   303-497-1726

<http://www.cgd.ucar.edu/staff/asphilli>
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