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1: Purpose of this document

This document describes at a high level the underlying OMNI2 data contained in the OMNIWeb system at NASA/GSFC's Space Physics Data Facility. A companion file at http://omniweb.gsfc.nasa.gov/html/omni2_doc.html gives significantly more details about OMNI 2 Preparation.

2: Data availability

The table below identifies the dates for which different parameters of OMNI data are available.

YYYY DDD - YYYY DDD

1963 331 - 2014 081 (IMF)
1963 331 - 2014 096 (Plasma)
1967 150 - 2014 100 (Energetic Proton Fluxes)

1963 001 - 2014 090 (Kp,ap indexes, Sunspot Number, f10.7 index )

1963 001 - 2009 365 (Dst indices)
2010 001 - 2011 365 (Provisional Dst indices)
2012 001 - 2014 100 (Quick Look : 2009- .. Dst-index)

1963 001 - 1988 182 (AE, AL,AU-index)
1990 001 - 2014 031 (Provisional AE-index)

1975 001 - 2014 100 (PCn index) 

See below for differences among final, provisional and quick look Dst and AE indices

3: Magnetic field and Plasma coverage

For a plot/table of annual coverages for the entire OMNI time span, click HERE.

4: Description of records and words

This section lists all the words in the records of the OMNI data set, and various notes and units as appropriate. The format for each word is as contained in the ftp-accessible annual ASCII files. The format underlying OMNIWeb is Common Data Format (CDF), and is typically invisible to users. Subsetted ASCII data files created during OMNIWeb sessions are accompanied by their own format statements. Each record contains 55 words as described below.

   WORD      TYPE       MEANING                UNITS/COMMENTS

     1       I4         Year                   1963,1964,1965...
     2       I4         Decimal Day            Day of year (Jan 1 = Day 1)
     3       I3         Decimal Hour           (0, 1, ...23; average for "1" is from
                                                01:00 to 02:00)
     4       I5         Bartels Rotation Number
     5       I3         ID for IMF SC          See table in section 6
     6       I3         ID for SW Plasma SC    See table in section 6
     7       I4         # of fine time scale
                        points in IMF Avgs
     8       I4         # of fine time scale
                        points in Plasma Avgs
     9       F6.1       Field Magnitude Avg, 
                              <F>               nT
    10       F6.1       Magnitude of Average    nT
                        Field vector, |<B>|
    11       F6.1        Lat. Angle of avg.      Deg (GSE Coords)
                        Field vector
    12       F6.1        Long. Angle of avg.     Deg (GSE Coords)
                        Field vector
    13       F6.1        Bx,GSE                 (nT)
    14       F6.1        By,GSE                 (nT)
    15       F6.1        Bz,GSE                 (nT)
    16       F6.1        By,GSM                 (nT)
    17       F6.1        Bz,GSM                 (nT)
    18       F6.1        sigma-|B|              RMS Standard deviation in avg
                                               magnitude (wd. 10), nT
    19       F6.1        sigma-B                RMS Standard deviation in field
                                               vector, in nT; see footnote 3
    20       F6.1        sigma-Bx               RMS Standard deviation in GSE X
                                               comp. av, nT
    21       F6.1        sigma-By               RMS Standard deviation in GSE Y
                                               comp, av, nT
    22       F6.1        sigma-Bz               RMS standard deviation in GSE Z
                                               comp, av, nT
    23       F9.0        Proton temperature     Degrees Kelvin
    24       F6.1        Proton density          #N/cm**3
    25       F6.0        Bulk speed             Km/sec.
    26       F6.1        Bulk flow longitude    phi-V, degrees. phi-V increases positively/negatively
                                                from zero as the flow direction changes from being along
                                                the -Xgse axis toward the +Ygse/-Ygse axis;
                                                see footnote 1)
  
    27       F6.1        Bulk flow latitude    theta-V, degrees. theta-V increases positively/negatively 
                                                from zero as the flow direction changes from being in 
                                                the Xgse-Ygse plane toward the +Zgse/-Zgse axis;
                                                see footnote 1)

    28       F6.3         Na/Np                 Alpha/Proton ratio 
    29       F6.2        Flow Pressure          P (nPa) = (1.67/10**6) * Np*V**2 * (1+ 4*Na/Np)
                                                for hours with non-fill Na/Np ratios and
                                                P (nPa) = (2.0/10**6) * Np*V**2
                                                for hours with fill values for Na/Np more 
   
    30       F9.0        sigma-T                Degrees Kelvin
    31       F6.1        sigma-n                cm -3
    32       F6.0        sigma-V                km/sec
    33       F6.1        sigma-phi-V            deg
    34       F6.1        sigma-theta-V          deg
    35       F6.3        sigma-ratio   

    36       F7.2        Electric field         mV/m, -V(km/s) * Bz (nT; GSM) * 10**-3 
    37       F7.2        Plasma beta            Beta = [(T*4.16/10**5) + 5.34] * Np / B**2, more 
    38       F6.1        Alfven mach number     Ma = (V * Np**0.5) / 20 * B , more  

    39       I3          Kp*10                  3-hr Kp index from NGDC
                                                (See footnote 2)
    40       I4          R                      daily Sunspot Number from NGDC
    41       I6          DST Index              nT, from Kyoto
    42       I5          AE-index               nT, from Kyoto

    43       F10.2       PROT Flux              1/(cm^2 sec ster), >1 MeV
    44       F9.2        PROT Flux              1/(cm^2 sec ster), >2 MeV
    45       F9.2        PROT Flux              1/(cm^2 sec ster), >4 MeV
    46       F9.2        PROT Flux              1/(cm^2 sec ster), >10 MeV
    47       F9.2        PROT Flux              1/(cm^2 sec ster), >30 MeV
    48       F9.2        PROT Flux              1/(cm^2 sec ster), >60 MeV
    49       I3          M'SPH Flux Flag        = 6: No m'spheric contribution
                                               = 5: M'sph contrib in lowest
                                                     energy channel
                                               = 4: M'sph c in lowest 2 chnls
                                                ...
                                               = 1: M'sph c in lowest 5 chnls
                                               = 0: M'sph c in all channels
                                               =-1: Not checked for M'sph c:
                                                  relevant after 88/306
                                                (See footnote 4)

    50       I4                                  ap-index, nT, from NGDC
    51       F6.1                                f10.7_index, (10**-22) Watts/meter sq/hertz, from NGDC
                                                 adjusted to 1AU 
    52       F6.1                                PC(N) index, Data Center for Geomagnetism, Copenhagen 
    53       I6                                  AL-index, nT, from Kyoto                     
    54       I6                                  AU-index, nT, from Kyoto
    55       F5.1     Magnetosonic mach number  =V/Magnetosonic_speed 
                                                Magnetosonic speed = [(sound speed)**2 + (Alfv speed)**2]**0.5
                                                The Alfven speed = 20. * B / N**0.5 
                                                The sound speed = 0.12 * [T + 1.28*10**5]**0.5 
                                                For details click HERE  

--------------------------------------------------------------------------
FORMAT(2I4,I3,I5,2I3,2I4,14F6.1,F9.0,F6.1,F6.0,2F6.1,F6.3,F6.2,
F9.0,F6.1,F6.0,2F6.1,F6.3,2F7.2,F6.1,I3,I4,I6,I5,F10.2,5F9.2,I3,I4,2F6.1,2I6,F5.1)
Note that for missing data, fill values consisting of a blank followed by 9's which together constitute the Ix or Fx.y format are used.

Footnote 1:
Flow-vector cartesian components in GSE coordinates may be derived from the given speed and angles as
Vx = - V * cos(theta) * cos(phi)
Vy = + V * cos(theta) * sin(phi)
Vz = + V * sin(theta)

Footnote 2:
The standard Kp values look like 0, 0+, 1-, 1, 1+, 2-, ... but are stored as Kp = 0, 3, 7, 10, 13, 17, ... in the OMNI data set. We have mapped 0+ to 3, 1- to 7, 1 to 10, 1+ to 13, 2- to 17, etc.

Footnote 3:
Sigma-B is computed as: SQRT [(sigma(Bx))**2 + (sigma(By))**2 + (sigma(Bz))**2]. Note that this is the length of the vector formed from the standard deviations of component averages. It is not the standard deviation in the length of the vector formedfrom the average components.

Footnote 4:
This data set also contains fluxes of energetic protons above 1, 2, 4, 10, 30 and 60 MeV from JHU/APL instruments on IMP spacecraft for 1967/150 to 2005/365 and fluxes of protons above 10, 30, and 60 MeV from NOAA instruments on GOES spacecraft, spanning 2006/001 to near- current.

5: Daily and 27-day Averages

We have computed daily and 27-day average values for all the OMNI2 parameters, and have made them accessible via OMNIWeb and via anon/ftp. Only arithmetic averaging was done. (No averaging of logarithms.) No threshold numbers of finer scale points were required. See special note on IMF angles below.

The daily averages are taken over OMNI's basic hourly values, and the 27- day averages are taken over the daily averages. The corresponding standard deviations relate only to these averagings and do not capture the variances in the higher resolution data.

The 27-day averages are for discrete Bartels rotation numbers. Thus the first such average fully within 1999 spans January 9 through February 4.

The record format for the daily and 27-day averages is the same as for the hourly data, although certain fields have special meanings.

The time words (year, day, hour) correspond to the first hour of the averaging period (day or 27-day interval).

The ID's for the magnetic field and plasma spacecraft are set to zero, since the daily and 27-day averages frequently involve data from multiple spacecraft.

The numbers of fine scale points in the plasma and field averages are counts of (1) hourly values contributing to daily averages or (2) daily values contributing to 27-day averages. NOTE THAT WE HAVE NOT REQUIRED ANY MINIMUM NUMBER OF POINTS TO COMPUTE AN AVERAGE. For cases where there was only one point, the standard deviations were set to zero.

Kp was treated specially. After determining daily or 27-averages from basic values such as 10 (1), 13 (1+), 17 (2-), 20 (2), the average was rounded to the nearest "standard value" of Kp (i.e., 10, 13, 17, 20, ...). For cases where the average was exactly in the middle between standard values (e.g., 15), the higher standard value (17 in this case) was used.

On December 6, 2004, words 10-12 (magnitude and direction angles of vector-averaged IMF), which had been determined by simple averaging over finer scale values of these words, were replaced in OMNI by values computed from daily (or 27-day) averaged IMF Cartesian components.

6: Spacecraft identifiers

The following spacecraft identifiers have been used:
Spacecraft name         Spacecraft ID
---------------         -------------
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 MAG and Plasma/MIT
IMP 7 (Expl 47)                44 Plasma/LANL

IMP 8 (Expl 50)                50 MAG and Plasma/MIT
IMP 8 (Expl 50)                45 Plasma/LANL

AIMP 1 (Expl 33)               33
AIMP 2 (Expl 35)               35
HEOS 1 and HEOS 2               1
VELA 3                          3
OGO 5                           5
Merged LANL VELA speeds        97
Merged LANL IMP-6,-7,-8 T,N,V  98
ISEE 3                         13
ISEE 1                         11
PROGNOZ 10                     10
WIND                           51
ACE                            71
Geotail                        60 

7: Activity Indices

The OMNI2 data set has, since its creation, contained daily sunspot numbers and three geomagnetic activity indices: Kp (3-hr), AE (1-hr), and Dst (1-hr). In 2009, additional indices were added: F10.7, ap, AL, AU and PCI(N). These latter indices are grouped as "ancillary parameters" near the bottom of the OMNIWeb page providing plots and list capabilities. Multi-hour indices are distributed into the relevant 1-hour OMNI records.

Hourly AE, AL, AU and Dst values have been computed at WDC for Geomagnetism at U. Kyoto for many years now. See the pre-Kyoto and Kyoto era histories at http://swdcwww.kugi.kyoto-u.ac.jp/dstae/index.html. This page, and those it links to, give full accounts of the derivations of final, provisional and quick-look AE and Dst values. Briefly, the levels are distinguished by the different levels of completeness of ground observatory network contributing to the indices and the extent of cleaning of the input data (zero level determinations, despiking, etc.) In particular, the U.Kyoto team notes that the quick look data are derived mainly for monitoring purposes, and that any use of such indices in publications should clearly indicate that the indices are quick-look. In general, there is the hope, constrained by available resources, that quick look indexes will be replaced by provisional values, and provisional values by final values. The AE and Dst values in OMNI will be extended and upgraded as those at U. Kyoto are.

The Kp, ap, F10.7 and Rz indices are explained at, and obtained electronically from, NOAA's National Geophysical Data Center. See ftp://ftp.ngdc.noaa.gov/STP/GEOMAGNETIC_DATA/INDICES/. Note footnote 2 in section 4 above, about OMNI's mapping of standard Kp values of 0, 0+, 1-, 1, 1+, ..., 9-, 9 to 0, 3, 7, 10, 13, ... 87, 90. Kp and ap are 3-hour indices, while F10.7 and Rz are daily indices.

PC(N) is the Polar Cap Index determined from the North polar cap station at Thule, Greenland. The index is basically a 15-min index that we have averaged up to hourly for inclusion in OMNI. PC(N) is taken from ftp://ftp.space.dtu.dk/WDC/indices/pcn/, World Data Center for Geomagnetism, National Space Institute, Copenhagen

8: Contact and General Information

For questions or comments about the OMNI data contents, please contact Dr. Natalia Papitashvili, Natalia.E.Papitashvili@gsfc.nasa.gov, Code 672, Goddard Space Flight Center, Greenbelt, MD, 20771.

9: Detailed documentation from Data Books

Detailed documentation on data sources for the original data set, cross comparisons and normalizations of contributing source-specific data sets, time shifting of ISEE 3 data, etc. are available by clicking HERE.

10: Acknowledgement

Acknowledgement to the SPDF OMNIWeb database as the source of data used in publications is requested: "The OMNI data were obtained from the GSFC/SPDF OMNIWeb interface at http://omniweb.gsfc.nasa.gov". Further, for recent years when few sources (IMP 8, Wind, ACE, Geotail) contributed to OMNI, it would be appropriate to also cite the PI's who provided the data to OMNI. Copies of preprints or reprints of OMNI-based publications sent to Natalia Papitashvili (address below) would be appreciated for tracking purposes.

The best citable reference to OMNI data is J.H. King and N.E. Papitashvili, Solar wind spatial scales in and comparisons of hourly Wind and ACE plasma and magnetic field data, J. Geophys. Res., Vol. 110, No. A2, A02209, 10.1029/2004JA010804.

 

If you have any questions/comments about OMNI/OMNIWEB data and service, contact: Dr. Natalia Papitashvili, Space Physics Data Facility, Mail Code 672, NASA/Goddard Space Flight Center, Greenbelt, MD 20771

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