# Re: question on how to calculate the area sum with two-dimensional coordinates data

From: Dennis Shea <shea_at_nyahnyahspammersnyahnyah>
Date: Wed Mar 27 2013 - 14:00:12 MDT

Try the following.

There are a few points on the grid that have repetitve values but
at other location, I thin the following works ok.

re = 6.37122e06 ; [m] average radius of earth
re2 = re^2

diri = "./"
fili = "sic_OImon_MRI-CGCM3_historical_r1i1p1_185001-200512.nc"
sic = f->sic ; sic(time, rlat, rlon)
latv = f->lat_vertices ; latv(rlat, rlon, vertices)
lonv = f->lon_vertices ; lonv(rlat, rlon, vertices)

area = re2*gc_qarea(latv, lonv)
area!0 = latv!0
area!1 = latv!1
area@long_name = "area of grid cells"
area@units = "m^2"

printVarSummary(area)
print("area: min="+min(area)+" max="+max(area))

;if (any(isnan_ieee(area))) then
; value = 1.e20
; replace_ieeenan (area, value, 0)
; area@_FillValue = value
; printVarSummary(area)
; print("area: min="+min(area)+" max="+max(area))
;end if

On 03/27/2013 01:12 PM, Dennis Shea wrote:
> Hi Tingting
>
> Can you please point me toward a dataset so I may look at it?
> Ideally, the file would contain an area variable. For example,
> the POP models have
>
> float TAREA(nlat, nlon) ;
> TAREA:long_name = "area of T cells" ;
> TAREA:units = "centimeter^2" ;
> TAREA:coordinates = "TLONG TLAT" ;
> TAREA:_FillValue = 9.96921e+36f ;
> TAREA:missing_value = 9.96921e+36f ;
>
> Consider:
>
> x(time,nlat,nlon) [ dimension #s (0,1,2) ]
>
> A global weighted mean would be
>
> xAVG = dim_sum_n(x*conform(x,TAREA,(/1,2/)),0)/ sum(TAREA)
>
> Then xAVG(ntim)
>
> On 3/27/13 11:40 AM, tingting@ucar.edu wrote:
>> Hello,
>> I am doing the MRI-CGCM3 model output validation and need to calculate
>> SIE(sea ice extent), the coordinates of MRI output are two-dimensional,
>> while the NCL function(wgt_areasum2) seems to deal with data with regular
>> coordinates, right?
>> So,my question is that how to calculate the area sum? Or, do I need to
>> regrid the MRI to regular-grid data?
>> Thank you for any coming help in advance.
>> Tingting
>>
>>
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Received on Wed Mar 27 14:00:22 2013

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