dset ch4.dat title ch4 data options big_endian undef -999.0 xdef 1 linear -1 1 ydef 37 levels -90.0 -85.0 -80.0 -75.0 -70.0 -65.0 -60.0 -55.0 -50.0 -45.0 -40.0 -35.0 -30.0 -25.0 -20.0 -15.0 -10.0 -5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0 70.0 75.0 80.0 85.0 90.0 zdef 86 linear 0 1 tdef 1 linear 15jan1000 1mo vars 1 ch4 86 99 zonal mean methan mixing ratio (ppmv) endvars