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NCL Graphics: ISCCP Grid

Non-uniform grids and triangular mesh conversion

"ISCCP" stands for "International Satellite Cloud Climatology Project. The grid is generated on a cylindrical equidistant projection of the globe. First, horizontal lines are drawn, dividing the projection into 72 strips, each of which is 2.5 degrees of latitude in width. Then, each strip is divided, using vertical lines, into N pieces of equal size, where N is chosen so as to make each piece of the strip have an actual area, on the globe, as close as possible to the area of a 2.5-by-2.5-degree square on the equator. (The strips nearest the equator are divided into 144 pieces, while the strips nearest the poles are divided into only 3 pieces.) Each element of this grid is therefore the little patch on the globe defined by two lines of constant latitude and two lines of constant longitude.

You can use NCL's triangular mesh capability to contour this grid, rather than interpolating it to a uniform 2D grid first. Note that only contouring is available with triangular mesh conversion at this time.

If the input array to a gsn_csm graphical interface is one- dimensional, and also has one-dimensional lat/lon arrays of the same length, NCL automatically uses triangular mesh conversion. The lat/lon information must be provided by setting sfXArray and sfYArray.

For more information on non-uniform grids that NCL can handle, see the document "Non-uniform grids that NCL can contour."

isccp_1.ncl: The lat/lon information must be provided by setting the resources sfXArray and sfYArray.

This example shows how to create a raster contour plot, and then smooths the raster contours in the second frame. The third frame shows how to overlay the contours on a Lambert Equal Area map projection.