https://spdf.gsfc.nasa.gov/pub/data/imp/imp6/plasma_lanl/solarwind_2min/
00readme.txt

       readme.txt for IMP6

The "data" subdirectory contains solar wind flow parameters,
based on proton and alpha particle measurements, given at
approximately 2-min resolution.  Data believed to have been
Earthward of the Earth's bow shock were excluded by the LANL
team.  The data are in ASCII and each data file contains one
month of data.

More detailed information on the contents and format of the data
records is available at
https://spdf.gsfc.nasa.gov/pub/documents/old/miscellaneous_documents_from_nssdc/b46485.txt

Further information from NSSDC's Master Catalog is available from
http://nssdc.gsfc.nasa.gov/database/MasterCatalog?ds=71-019A-11D