Hi,
I am trying to calculate the sea ice extent from sea ice fraction data
for CAM3.1 in T85 grid.
I used the area_global_rectilinear_grid function to calculate the area
of each of the grid box. But I am trying to estimate the area over the
pole as the latitudes ends at 88.92773. For doing that I tried
calculating in the following way. But what confused me is that why the
sum of the grid areas calculated using the function is greater than the
surface area of the earth. Is there any better way to estimate the area
of the small circle over the pole?
;****************************************************
; Calculate area at each grid point
;****************************************************
; T85
nlat = 128
lat = latGau(nlat, "lat", "latitude", "degrees_north")
mlon = 256
lon = lonGlobeF(mlon, "lon", "longitude", "degrees_east")
print(lat)
area = area_global_rectilinear_grid (lat, lon, False)
areaa = dble2flt(area)
printVarSummary(areaa)
printMinMax(areaa, True)
R = 6371.220 ; in km
pi = 4d0*atan(1d0)
S_Area = 4d0*pi*R^2 ;Total surface area of the earth
print(S_Area)
Area_total = sum(areaa) ; Total area from the grid boxes
print(Area_total)
Pole_area = (S_Area - Area_total)/(10^6)*2 ; Area over the pole in 10^6
sq km
print(Pole_area)
Here are the printVarSummary results:
Variable: areaa
Type: float
Total Size: 131072 bytes
32768 values
Number of Dimensions: 2
Dimensions and sizes: [lat | 128] x [lon | 256]
Coordinates:
lat: [-88.92773..88.92773]
lon: [ 0..358.5938]
Number Of Attributes: 8
long_name : area of each grid cell
units : km^2
area_total : 5.101007e+08
area_lat : <ARRAY of 128 elements>
rearth : 6371.22
area_sphere : 5.100997e+08
area_ratio : 1.000002
typeConversion_op_ncl : double converted to float
(0)
(0) area of each grid cell: min=451.99 max=24355.4
Variable: S_Area
Type: double
Total Size: 8 bytes
1 values
Number of Dimensions: 1
Dimensions and sizes: [1]
Coordinates:
(0) 510099745.7121028
Variable: Area_total
Type: float
Total Size: 4 bytes
1 values
Number of Dimensions: 1
Dimensions and sizes: [1]
Coordinates:
(0) 5.101245e+08
Variable: Pole_area
Type: double
Total Size: 8 bytes
1 values
Number of Dimensions: 1
Dimensions and sizes: [1]
Coordinates:
(0) -0.04953257579445839
Thanks,
Soumik
-- "Numbing the pain for a while will make it worse when you finally feel it. ~J.K. Rowling" ***************************************** Soumik Basu Graduate Student, Research Assistant International Arctic Research Center University of Alaska Fairbanks Fairbanks,Alaska,USA ***************************************** _______________________________________________ ncl-talk mailing list List instructions, subscriber options, unsubscribe: http://mailman.ucar.edu/mailman/listinfo/ncl-talkReceived on Wed Oct 2 19:37:11 2013
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