This function takes a sum over an X-Y region. The syntax is:
asum(expr, xdim1, xdim2, ydim1, ydim2)
where:
expr
- any valid GrADS expression xdim1
- starting X dimension expression xdim2
- ending X dimension expression ydim1
- starting Y dimension expression ydim2
- ending Y dimension expression For global summing, a shorthand may be used:
asum(expr, global)
or asum(expr, g)
asum(expr, lon=0, lon=360, lat=-90, lat=90)
asum
function always does its average to the
exact boundaries specified, in world coordinates. If the boundaries
specified via the dimension expressions do not fall on grid
boundaries, then the boundary values are weighted appropriately in the
sum.
asum(expr,x=1,x=72,y=1,y=46)
Here the boundary would be determined by using the grid values 0.5,
72.5, 0.5, and 46.5 which would be converted to world coordinates. If
we assume that x=1
is 0 degrees longitude and x=72
is 355 degrees longitude, then the averaging boundary would be -2.5 to
357.5 degrees, which would cover the earth. In the Y dimension, when the
boundary is beyond the pole, the asum
function recognizes
this and weights appropriately. To calculate a sum without any weighting,
use the asumg
function.