'reinit'

'open  pre.ctl'
'set grads off' 
'set lon 20 60'
'set lat 0 20'

'set t 1'

'define prca=ave(aa,t+1,t=24)'
'define prca1=ave(aa,t=1,t=12)'
'define prca2=ave(aa,t=13,t=24)'

'define fcy=(prca-prca1)*(prca-prca1)+(prca-prca2)*(prca-prca2)'

'define fc=fcy/2'

'd smth9(sqrt(fc))'