The question is, what is creating those files?
ncdump generates a text representation of a specified netCDF file on standard output. The text representation is in a form called CDL (‘‘network Common Data form Language’’) that can be viewed, edited, or serve as input to ncgen. ncgen is a companion program that can generate a binary netCDF file from a CDL file. Hence ncgen and ncdump can be used as inverses to transform the data representation between binary and text representations. See ncgen for a description of CDL and netCDF representations.