Notebook
np.max(np.ma.masked_where(tmask[0,:,:]==0,fP.variables['ATF_NO3'][0,0,:,:]/fP.variables['AFILTNO3'][0,0,:,:])),np.min(np.ma.masked_where(tmask[0,:,:]==0,fP.variables['ATF_NO3'][0,0,:,:]/fP.variables['AFILTNO3'][0,0,:,:]))