ifile = '/projects/GEOCLIM/wenchang/MODEL_OUT/AM4/tiger3/CTL1990_tiger3_intel24ifort_openmpi_768PE/POSTP/03000101.atmos_month.nc'
ds = xr.open_dataset(ifile)
ds = ds[['zsurf']]
cd tigress/analysis/
cd people/
mkdir Yifan
cd Yifan/
ds.to_netcdf('AM4.zsurf.nc')