NetCDF file requirements

The Climate Explorer will accept netCDF files provided they are
reasonably CF-compliant and adhere to the following extra restrictions.
- There is exactly one variable called 'lon*' or 'x' with units 'degree[s]_e*'.
- There is exactly one variable called 'lat*' or 'y' with units 'degree[s]_n*'.
- There is exactly one variable called 'time*' or 't' with consecutive days/months/years. If there are missing data please include these time steps. (Note that the ASCII time series representation does allow holes in the time axis.)
- There is exactly one variable not called 'time*' or 't' that depends at least on time and possibly on the x, y and (optionally) z-axes. Missing values are indicated by _FillValue or missing_value, valid_min/valid_max or not considered.