DESCRIPTION OF THE OMNI DATA SET:
Description of the Coordinate Systems
Cross-normalization of Parameters
The OMNI table is a part of "Heliosphere" database supported by the
Institute of Cosmophysical Research and Aeronomy SB RAS, Yakutsk, Russia. All the data in
this table and the description were taken from U.S. National Space Science Data Center.
The OMNI table contains the hourly mean values of the interplanetary magnetic field (IMF) and solar wind plasma parameters measured by various spacecraft near the Earth's orbit, as well as geomagnetic and solar activity indices, and energetic proton fluxes. Data gaps were filled with dummy numbers for the missing hours or entire days to make all files of equal length. The character '9' is used to fill all fields for missing data according to their format.
|IMF||Nov 27 1963||Nov 30 1999||1783||2271|
|Plasma||Nov 27 1963||Dec 19 1999||1783||2271|
|Geomag.Activity||Nov 02 1963||Nov 30 1999||1783||2271|
|DST indices||Nov 02 1963||Dec 31 1997||1783||2245|
|Provisional DST||Jan 01 1998||Sep 30 1999||2245||2268|
|Particle Fluxes||Jan 01 1973||Dec 16 1998||1907||2258|
All the data in this table and description were taken from U.S. National Space Science Data Center.
flag1 = 0 - No flag1 value in original data
flag1 = 1 - IMF and Plasma data, same spacecraft
flag1 = 2 - IMF and Plasma data, different spacecraft
flag1 = 3 - No Plasma data
flag1 = 4 - No IMF data
flag1 = 5 - No IMF or Plasma data
Sigma B is sqrt((sigma Bx)^2 + (sigma By)^2 +(sigma Bz)^2)
The sigma B values were not provided with HEOS IMF data, i.e. for such records the words 21-23 of the original OMNI data set (fields sigma_bx, sigma_by, sigma_bz of this table) contain sigma|B| (repeat word 19 or sigma_bmod), sigma theta B and sigma phi B in degrees respectively.
flag2 = 0 - there are no Proton Flux data, or all of the Proton Flux data are contaminated by the magnetospheric events
flag2 = 1 - then the channels >1,>2,>4,>10,>30 Mev were judged to have magnetospheric 'contamination'
flag2 = 2 - then the channels >1,>2,>4,>10 Mev were judged to have magnetospheric 'contamination'
flag2 = 3 - then the channels>1,>2,>4 Mev were judged to have magnetospheric 'contamination'
flag2 = 4 - then the channels >1,>2 Mev were judged to have magnetospheric 'contamination'
flag2 = 5 - then the channels >1 Mev channels were judged to have magnetospheric 'contamination'
flag2 = 6 - then no channel was judged to have magnetospheric 'contamination'
flag2 = -1 - then not checked for magnetospheric relevant after 88/306.
|IMP 1 (Expl 18)||18|
|IMP 3 (Expl 28)||28|
|IMP 4 (Expl 34)||34|
|IMP 5 (Expl 41)||41|
|IMP 6 (Expl 43)||43|
|IMP 7 (Expl 47)||47|
|IMP 8 (Expl 50)||50|
|AIMP 1 (Expl 33)||33|
|AIMP 2 (Expl 35)||35|
|HEOS 1 and HEOS 2||1|
|Merged LANL VELA Speed Data (July 1964 - March 1971)||99|
|Merged LANL IMP T,N,V (Including all IMP 8 LANL Plasma)||98|
DESCRIPTION OF COORDINATE SYSTEMS:
The Heliographic Inertial (HGI) coordinates are Sun-centered and inertially fixed with respect to an X-axis directed along the intersection line of the ecliptic and solar equatorial planes. The solar equator plane is inclined at 7.25 degrees from the ecliptic. This direction was towards ecliptic longitude of 74.367 degrees on 1 January 1900 at 1200 UT; because of precession of the celestial equator, this longitude increases by 1.4 degrees/century. The Z axis is directed perpendicular and northward from the solar equator, and the Y-axis completes the right-handed set. This system differs from the usual heliographic coordinates (e.g. Carrington longitudes) which are fixed in the frame of the rotating Sun.
The RTN system is fixed at a spacecraft (or the planet). The R axis is directed radially away from the Sun, the T axis is the cross product of the solar rotation axis and the R axis, and the N axis is the cross product of the R and T axes. At zero heliographic latitude, when the spacecraft is in the solar equatorial plane, the N and solar rotation axes are parallel.
Convention for Latitude and Longitude Angles:
Latitude and longitude angles of solar wind plasma flow are generally measured from the radius vector away from the Sun. In all cases, latitude angles are positive for north-going flow. The flow longitude angles have been treated differently for the near-Earth data, i.e. the OMNI, and for the deep space data. The flow is positive for the near-Earth data when coming from the right side of the Sun as viewed from the Earth, i.e. flowing toward +Y from -X GSE or opposite to the direction of planetary motion. On the other hand, the flow longitudes for the deep space spacecraft use the opposite sign convection, i.e. positive for flow in the +T direction in the RTN system.
The OMNI data set contains daily sunspot numbers and three geomagnetic activity indices: Kp (3-hr), C9 (24-hr), and Dst (1-hr). The multi-hour
indices are distributed into the relevant 1-hour OMNI records.
The Dst index is calculated at Kyoto University. Recent improvements have included quickly released provisional values. See http://swdcdb.kugi.kyoto-u.ac.jp/dstdir/index.html. OMNIweb now includes Provisional Dst values as noted in the Data Availability section above. The provisional values are replaced with the final values as soon as they become available (in one-year segments).
The Kp index is calculated at NGDC. The OMNI convention is to multiply the value by 10. This transforms, for example, 3+ to 33 and 4- to 37.
CROSS-NORMALIZATION OF PARAMETERS:
Note that, as discussed in the paper data books, cross-normalization of parameters obtained from different sources has been done to yield more
multi-source uniformity and to allow comparison of parameters. For data later than 1971, only plasma density and temperature values have been
normalized. No implication about which data set is "correct" is implied; the historical choice was to normalize to the IMP8/LANL data. For the
post-1971 period the normalization equations used were (from Table 9 of Data Book Supplement 3, NSSDC 86-04):
|For IMP8/LANL||no normalization|
|For IMP8/MIT|| (log N)norm = 0.12 + 0.89*(log N)obsvd
(log T)norm = -0.62 + 1.11*(log T)obsvd
|For ISEE3|| (log N)norm = 0.20 + 0.83*(log N)obsvd
(log T)norm = -0.55 + 1.07*(log T)obsvd
|For ISEE1|| (log N)norm = 0.18 + 0.85*(log N)obsvd
(log T)norm = (log T)obsvd
Acknowledgements to the National Space Science Data Center OMNIWeb database as the
source of data used in publications is requested. Copies of preprints or reprints of
OMNI-based publications sent to Joseph King (address below) would be appreciated for
For questions about this data set, please contact:
Dr. Joseph H. King, Code 633, Goddard
Space Flight Center, Greenbelt, MD, 20771.
Dr. Natalia Papitashvili, Code 633, Goddard
Space Flight Center, Greenbelt, MD, 20771.