This function returns the Y location of maximum grid value over a spatial domain. The syntax is:
 amaxlocy(expr, xdim1, xdim2, ydim1, ydim2)
where:
expr    any valid GrADS grid expression xdim1   starting X or LON dimension expression xdim2   ending X or LON dimension expression ydim1   starting Y or LAT dimension expression ydim2   ending Y or LAT dimension expression For the Y location of the global maximum, a shorthand may be used:
amaxlocy(expr, global) or amaxlocy(expr, g)
amaxlocy(expr, lon=0, lon=360, lat=-90, lat=90)
maxloc and max functions. 
amaxlocx will return the X  location of the maximum grid value. 
amax function to retrieve the maximum value over the grid.  
amin, aminlocx, and aminlocy.
amax.