how to calculate the difference between the two latitudes

[Phillip Lin]

Hi everyone,

I need to solve a problem: namely get the difference between the two
latitudes at which the mass stream function equals zero, between these two
zero values there is a maximum value usually. And the grid values about
the mass stream function phim (lat,pressure) are from a netCDF data file.
So how can I get the difference between these two latitudes with zero
stream function? Do I need to convert netCDF to the other .dat file by
using ncdump tool , and then use F90 to do the simple calculation to solve
my problem, or am I able to only use GrADS scripting language to do the
simple calculation? Or any other way to solve this?

I will appreciate any help !

Phillip