[gradsusr] Meridional gradient?

[Li Dong]

Hello list,

I need to calculate the meridional temperature gradient across 20 degree
latitude belt using global gridded data. Below is what I did:

'open ta.ctl'
'set t 1'
'set lev 1000'
'set lon 0 360'
'set lat -80 80'
'define Tgrad=ta(lat+10)-ta(lat-10)'

However, Grads complained "Cannot use an offset value with a varying
dimension". If I set 'lat' at a fixed value, such as 'set lat 40', the
above script did work, but the downside is that this only gives
temperature meridional gradient at the specified latitude instead of
over the entire latitude range. Any inputs would be highly appreciated!

Best,

Li