# area weighted average with irregular ocean grid

From: Mira Berdahl <mberdahl_at_nyahnyahspammersnyahnyah>
Date: Wed Jul 10 2013 - 14:36:49 MDT

Hi there,

I'm trying to calculate the area weighted average of sea surface
temperature in a certain region of the North Atlantic, but my input file
is on an irregular ocean grid. When I try to use lat2d and lon2d I am
unable to convert from i,j to lat,lon so I get an error saying that my
coordinate subscripts are out of range. Code and output are below.

Do I have to go through and regrid the dataset in order to obtain lat lon
as degrees? Or is using lat2d and lon2d sufficient, but I'm doing
something incorrectly?

Many thanks,
Mira

The code is:

;************************************************
; NA_tos.ncl
;************************************************
;************************************************
begin

tos_mpi = in->tos
tos_mpi!1 = "lat"
tos_mpi!2 = "lon"
tos_mpi&lat = in->j
tos_mpi&lon = in->i
tos_mpi@lat2d = in->lat
tos_mpi@lon2d = in->lon

printVarSummary(tos_mpi)

;%%%%% read in the weights (area of grid cells %%%%%%%%%%%%%%%%
cellarea_mpi = in->areacello
printVarSummary(cellarea_mpi)

cellarea_mpi!1 = "lat"
cellarea_mpi!2 = "lon"
cellarea_mpi@lat2d = in->lat
cellarea_mpi@lon2d = in->lon

;%%% calculate the area weighted NA temperature based on area of grid cells.

NA_tos_mpi =
wgt_areaave2(tos_mpi(:,{50:65},{310:340}),cellarea_mpi({50:65},{310:340}),0)

delete(cellarea_mpi)
delete(tos_mpi)
delete(wgtx)
delete(wgty)
delete(NA_tos_mpi)

end

;***************************************************************

Here is the output after running the script:

[mlosic@ncoeus Ocean]\$ ncl testing_mpi.ncl
University Corporation for Atmospheric Research
NCAR Command Language Version 5.1.0
The use of this software is governed by a License Agreement.
See http://www.ncl.ucar.edu/ for more details.

Variable: tos_mpi
Type: float
Total Size: -1591607296 bytes
675840000 values
Number of Dimensions: 3
Dimensions and sizes: [time | 12000] x [lat | 220] x [lon | 256]
Coordinates:
time: [15.5..365226.5]
lat: [1..220]
lon: [1..256]
Number Of Attributes: 12
lon2d : <ARRAY of 56320 elements>
lat2d : <ARRAY of 56320 elements>
standard_name : sea_surface_temperature
long_name : Sea Surface Temperature
comment : "this may differ from ""surface temperature"" in regions
of sea ice."
units : K
cell_methods : time: mean
cell_measures : area: areacello
missing_value : 1e+20
_FillValue : 1e+20
associated_files : baseURL:
http://cmip-pcmdi.llnl.gov/CMIP5/dataLocation gridspecFile:
gridspec_ocean_fx_MPI-ESM-P_past1000_r0i0p0.nc areacello:
areacello_fx_MPI-ESM-P_past1000_r0i0p0.nc
coordinates : lat lon

Variable: cellarea_mpi
Type: float
Total Size: 225280 bytes
56320 values
Number of Dimensions: 2
Dimensions and sizes: [j | 220] x [i | 256]
Coordinates:
j: [1..220]
i: [1..256]
Number Of Attributes: 7
standard_name : cell_area
long_name : Ocean Grid-Cell Area
units : m2
missing_value : 1e+20
_FillValue : 1e+20
associated_files : baseURL:
http://cmip-pcmdi.llnl.gov/CMIP5/dataLocation gridspecFile:
gridspec_ocean_fx_MPI-ESM-P_past1000_r0i0p0.nc
coordinates : lat lon
fatal:NclOneDValGetRangeIndex: start coordinate index out of range, can't
continue
fatal:Could not obtain coordinate indexes, unable to perform subscript
fatal:Execute: Error occurred at or near line 39 in file testing_mpi.ncl

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Received on Wed Jul 10 14:36:57 2013

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