From: Soumik Basu <sbasu_at_nyahnyahspammersnyahnyah>

Date: Wed Oct 02 2013 - 19:37:00 MDT

Date: Wed Oct 02 2013 - 19:37:00 MDT

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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