GrADS Function: atot

## atot()

Thie `atot` function (in GrADS version 2.0.2+) duplicates the summing capability of `asum` but adds the latitude-weighting feature of `aave`. The syntax is:

`atot(expr, xdim1, xdim2, ydim1, ydim2)`

### Usage Notes

Please see the reference page for `asum` for details on the command syntax and usage notes.

### Examples

1. An instructive sanity check is to calculate the total area over globe on any grid of data that has a constant value of 1 and no missing values:
   `ga-> d atot(const(temp,1,-a),global)
   Result value = 12.5664`
   The answer we get is 4*pi, and the unit of the result is steradians.

2. Suppose you have a data variable sea ice concentration (named 'sic') which is given as a % in each grid box, and you would like to calculate the total area in the Arctic covered by sea ice. To calculate the sea ice coverage in millions of km^2, we multiply the `atot` result by the square of the radius of the Earth in km:

   `ga-> d atot(sic/100,lon=0,lon=360,lat=40,lat=90)*6371*6371*1e-6
   Result value = 11.289`