在画海温图时，define 定义时无效操作，sst识别不出来

求学的双鱼

ga-> define tem=ave(sst,t+0,t=360,12)
Averaging.  dim = 3, start = 1, end = 360
Low Level I/O Error:  Read error on data file
  Data file name = c:/data/sst2.grd
  Error reading 1440 bytes at location 3110400
Data Request Error:  Error for variable 'sst'
Operation Error:  Error from ave function
  Error ocurred at column 1
DEFINE error:  Invalid expression.
ga-> modify tem seasonal
MODIFY Error: Defined grid tem not found

dset  c:/data/sst2.grd
undef 32767.00
xdef 360 linear 0 1
ydef 180 linear -89.5 1
zdef 1 linear 0 1
tdef 360 linear 00Z01JAN1971 1mo
vars 1
sst   0 -999 Monthly Means of Sea Surface Temperature
endvars

'reinit'
'open c:\data\sst2.ctl'
'set t 1 12'
'define tem=ave(sst,t+0,t=360,12)'
'modify tem seasonal'
'set t 1'
'd tem'
'draw title average'
'printim c:\1yuepingjun.gif gif white'
;