...
common_retrieve_params = ( type : "fc", levtype : "ml", step : 12, grid : [1.5,1.5] )
tmod = retrieve(
...
param : "t",
...
levelist : [1, 'to', 91],
...
common_retrieve_params)
lnsp = retrieve( param : "lnsp",
...
levelist : 1,
...
common_retrieve_params)
# interpolate onto a list of pressure levels
...