OMNI and COHOWeb Data Bases Extended

NSSDC continues to update its multisource OMNI and COHOWeb data bases of heliospheric data. The OMNI data base, containing hourly solar wind magnetic field and plasma data and selected solar and geomagnetic activity indices reaching back to 1963 and IMP 8 energetic proton data reaching back to 1973, was extended with IMP 8 data to the end of 1995 during April 1996 for field and particle data and into 1996 for plasma data and activity indices. Updates are performed at approximately three-month intervals. Currently, the most convenient access path to these OMNI data is OMNIWeb (http://nssdc.gsfc.nasa.gov/omniweb/ow.html).

In contrast to OMNI data, which are obtained from geocentric and other near-Earth spacecraft, COHOWeb contains data from most spacecraft exploring the distant heliosphere. The table below lists the source spacecraft and the time spans for which data from each are now available.

SPACECRAFT	MAGNETIC FIELD	PLASMA
	Time Span	Time Span
Helios 1	74/12-81/06	74/12-80/12
Helios 2	76/01-80/03	76/01-80/03
OMNI_M	64/01-95/12	64/01-96/02
Pioneer 10	72/03-75/11	72/03-94/11
Pioneer 11	73/04-92/08	73/04-92/05
Pioneer Venus	78/12-88/08	78/12-92/09
Ulysses	90/10-93/09	90/11-94/12
Voyager 1	77/09-89/12	77/09-80/11
Voyager 2	77/09-88/12	77/09-95/11

Whereas OMNI has data from only one spacecraft for any one hour, COHOWeb has independent time series for each contributing spacecraft. The record for each spacecraft and hour contains spacecraft position and ambient magnetic field and plasma parameters. All position data have been cast into a common heliocentric inertial coordinate system, and all magnetic field vector data have been cast into a common "RTN" coordinate system to facilitate multipoint analyses of large scale heliospheric phenomena.

The OMNI_M source in the table above is a version of OMNI cast into the same format and coordinate systems as for other COHOWeb data, including the heliocentric position of the Earth. OMNI_M was included to add one more location for multipoint heliospheric analyses.

COHO data more generally are native-format, multiresolution data files as provided by each of several principal investigators and include some energetic particle data. These files from which the COHOWeb data base is built via coordinate transformations, parameter mergings, etc., are FTP-accessible from URL http://nssdca.gsfc.nasa.gov/htbin/htdir/anon_dir/coho/?/anon_dir.

COHOWeb is accessible at http://nssdc.gsfc.nasa.gov/cohoweb/cw.html. It is expected that NSSDC will issue a second heliospheric CD-ROM, a successor to its 1993 heliospheric CD-ROM, later in 1996 with the latest then-available data.

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