cdtarea documentation

The cdtarea function gives the approximate area of each cell in a lat,lon grid assuming and ellipsoidal Earth. This function was designed to enable easy area-averaged weighting of large gridded climate datasets. This function is similar to cdtdim.

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Contents

Syntax

A = cdtarea(lat,lon)
A = cdtarea(lat,lon,'km2')

Description

A = cdtarea(lat,lon) gives an approximate area of each grid cell given by lat,lon. Inputs lat and lon must have matching dimensions, as if they were created by meshgrid.

A = cdtarea(lat,lon,'km2') gives grid cell area in square kilometers.

Example

Given a 10 degree global grid made by cdtgrid.

[lat,lon] = cdtgrid(10);

Each grid cell has these dimensions:

A = cdtarea(lat,lon,'km^2');

Plot the grid cell area:

p = pcolor(lon,lat,A);
axis image
ylabel('latitude')
xlabel('longitude')
cb = colorbar;
ylabel(cb,'grid cell area (km^2)')

Just as we expect, grid cells are bigger close to the equator, and smaller near the poles. If you look closely at the map above, you may notice that the values at the top of the world do not appear to match the values at the bottom of the world. That's due to an unfortunate behavior of pcolor, which discards a row and a column of data. That behavior can be fixed by using interpolated shading or by using imagesc instead of pcolor, but I used pcolor above because it's an easy way to include grid lines.

Author Info

The cdtarea function was written by Chad A. Greene of the University of Texas Institute for Geophysics (UTIG).