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The strategy:

3) read the data with fraction land caverage from which the land/sea mask will be created. Regrid the fraction to the 5-deg grid, create land and sea masks.

4) create sst/tas variables masked with ocean/land maskes .

# extract a land/sea mask and regrid it to our desired 5 degree grid
# (these data are percent land coverage [0-100])
file4 = os.path.join(sys.prefix, 'sample_data/geo.1deg.ctl')
c = cdms.open(file4) 
fraction=c('sftlf',squeeze=1)
c.close() 
# plot the fraction field
y=vcs.init()
y.setcolormap('default')
y.plot(fraction)

# get grid for regridding 
grid3=fraction.getGrid() 
# etup regrid function 
regridfunc=Regridder(grid3,grid1)
# regrid mask values 
fraction=regridfunc(fraction) 
  
# create land and sea masks.
# 50% or more coverage in a box is defined as land 
# and less than or equal to 50% coverage is ocean.
# All other values in the arrays are zeros.
land=Numeric.where(Numeric.greater(fraction.filled(),50.),1.,0.)
ocean=Numeric.where(Numeric.less_equal(fraction.filled(),50.),1.,0)

masked_sst=Numeric.multiply(sst_new.filled(),ocean)
masked_tas=Numeric.multiply(tas_new.filled(),land)

Plot 'masked_sst' and 'masked_tas'

x=clear() 
x.plot(masked_sst) 

y=clear() 
y.plot(masked_tas)

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