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1: Introduction

The Low Resolution OMNI (LRO) data set is primarily a 1963-to-current compilation of hourly-averaged, near-Earth solar wind magnetic field and plasma parameter data from several spacecraft in geocentric or L1 (Lagrange point) orbits. The data have been extensively cross compared, and, for some spacecraft and parameters, cross-normalized. Time-shifts of higher resolution data to expected magnetosphere-arrival times are done for data from spacecraft in L1 orbits (ISEE 3, Wind, ACE), prior to taking hourly averages.

LRO also provides other widely accessed data that are frequently used with solar wind data. In particular, LRO provides fluxes of protons with energies above 1, 2, 4, 10, 30, and 60 MeV from several IMP and GOES spacecraft, and provides a wide range of geomagnetic and solar activity indices. The data are made available at daily and 27-day resolutions, in addition to hourly resolution. They are made accessible with a variety of functionalities from http://omniweb.gsfc.nasa.gov/ow.html.
High Resolution OMNI (HRO) data set include 1-min and 5-min bow-shock-nose- shifted solar wind magnetic field and plasma data from IMP 8, Geotail, Wind and ACE see: http://omniweb.gsfc.nasa.gov/ow_min.html

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 253 (IMF)
1963 331 - 2014 274 (Plasma)
1967 150 - 2014 273 (Energetic Proton Fluxes)

1963 001 - 2014 243 (Kp,ap indexes, Sunspot Number, f10.7 index )

1963 001 - 2009 365 (Dst indices)
2010 001 - 2011 365 (Provisional Dst indices)
2012 001 - 2014 279 (Quick Look : 2009- .. Dst-index)

1963 001 - 1988 182 (AE, AL,AU-index)
1990 001 - 2014 181 (Provisional AE-index)

1975 001 - 2014 277 (PCn index) 

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

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

3: Description of records and words

The format for each word is as contained in the ftp-accessible annual ASCII files. 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 below
     6       I3         ID for SW Plasma SC    See table below
     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 Flux)

    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:
The flow OMNI "phi" angle is opporite GSE "phi" angle, threrfore, 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.

4: 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.

5: 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 

6: Activity Indices

The OMNI2 data set has, since its creation, contained daily sunspot numbers (Rz) assigned to each hour of the relevant day and three geomagnetic activity indices: Kp (3-hr), AE (1-hr), and Dst (1-hr). In 2009, additional indices were added: F10.7 (daily) , ap (3-hr), AL, AU and PCN.

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.

Hourly AE, AL, AU Dst indices are computed at and obtained from the World Data Center for Geomagnetism, operated by the Data Analysis Center for Geomagnetism and Space Magnetism at Kyoto University, Japan. See 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. Definitive time series of AE, Dst and other indices reach back to 1957 on the Kyoto web site. There are provisional values of AE and Dst also available from Kyoto for periods after the definitive time series that end in mid-1988 (AE) and mid-2002 (Dst). Definitive hourly values of AE and Dst are included in OMNI 2 from 1963 to their ends and are extended when possible. We thank Drs. T. Iyemori and T. Kamei for permission to include these indices in OMNI 2.

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

7: Energetic Particles Fluxes

Energetic particle data sources: Fluxes of protons above 6 energy thresholds (1, 2, 4, 10, 30, 60 Mev) from the IMP 7 and IMP 8 Charged Particle Measurement Experiment (CPME; Principal Investigator S.M. Krimigis, then R.B. Decker) are included in OMNI and OMNI 2 for the period January 1, 1973, through the end of 2005 shortly after which IMP 8 operations terminated. The data were prepared and provided by CPME Co- Investigator T.P. Armstrong and colleagues at U. Kansas and Fundamental Technologies, LLC. The instrument and data are further described at http://sd-www.jhuapl.edu/IMP/imp_index.html and at http://imp.ftecs.com/

Fluxes of protons above 1, 10, 30 and 60 MeV for mid-1967 through the end of 1972, from the JHU/APL Solar Proton Monitoring Experiment (SPME) on IMP 4 (1967/150 - 1969/123) and IMP 5 (1969/172 - 1972/358) were added to OMNI 2 shortly after its creation. The fluxes were computed at NSSDC from count rates provided on tape to NSSDC decades earlier. The values are not reliable absolute measures of quiet time galactic fluxes, but are good for solar and shock- accelerated particles. cf. Williams and Bostrom, J. Geophys. Res.,74, 3019, 1969.

Fluxes of protons above 10, 30 and 60 MeV, as measured by NOAA's geosynchronous GOES 11 spacecraft for 2006-2010 and from GOES 13 for 2011 and later (cf. http://satdat.ngdc.noaa.gov/sem/goes/data/new_avg/), were added to OMNI 2. (The GOES 13 data added to OMNI 2 are actually averages over the fluxes given at NGDC for eastward- looking and westward looking sensors.) Principal Investigator for the GOES energetic particle instruments is currently T. Onsager, and key responsible NGDC person is D. Wilkinson. Comparisons of IMP 8, GOES 10 and GOES 11 proton flux values obtained between 1999 and 2005 show reasonably good agreement during solar particle flux events; see http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/flux_ogg.html.

Spacecraft prioritizations

A new prioritization on which spacecraft to use for hours with multiple sources. Previously, we prioritized Wind over ACE through the end of 1999, and prioritized ACE thereafter.

  
 Now, we have spacecraft priorities for 7 intervals:
     1. 1995/001-1998/180 Wind, ACE, IMP8, Geotail
     2. 1998/181-1999/129 ACE, Wind, IMP8, Geotail
     3. 1999/130-1999/228 Wind, ACE, IMP8, Geotail
     4. 1999/229-2002/333 ACE, Wind, IMP8, Geotail
     5. 2002/334-2003/222 Wind, ACE
     6. 2003/223-2004/119 ACE, Wind,   
     7. 2004/120-current    Wind, ACE 
These ACE-prioritized intervals are when Wind either makes several magnetospheric incursions or is unusually far (e.g., >200 Re) from the magnetosphere.

IMF data sources:

Table 1 shows the sources of LRO magnetic field data. The parentheses after the spacecraft names show our numeric spacecraft identifiers.
As of 2014, Wind and ACE data were being periodically added to LRO. The current latest date of magnetic field data in LRO is given at http://omniweb.gsfc.nasa.gov/html/ow_data.html.

Table 1
-----------
Spacecraft	Key persons		Data time span	References	
----------    -----------          -----------------    ----------------
IMP 1 (18)         Ness            11/27/63-02/15/64    Ness et al, 1964
IMP 3 (28)         Ness            06/01/65-01/29/67    Ness et al, 1964
AIMP 1 (33)        Ness            07/04/66-07/13/68    Behannon et al, 1968
IMP 4 (34)         Ness            05/26/67-12/27/68    Fairfield, 1969
AIMP 2 (35)        Ness            07/26/67-11/10/69    Ness et al, 1967
HEOS (1)           Hedgecock       12/11/68-10/28/75	Hedgecock, 1975
IMP 5 (41)         Ness            06/21/69-10/26/72    Fairfield & Ness, 1972
IMP 6 (43)         Ness            03/14/71-07/21/74    Fairfield, 1974
IMP 7 (47)         Ness            09/26/72-04/03/73    Mish & Lepping, 1976
IMP 8 (50)         Ness, Szabo     10/30/73-05/12/00    Mish & Lepping, 1976
ISEE 3 (13)        E.Smith         08/14/78-12/21/82    Frandsen et al, 1978
Prognoz 10 (10)    Yeroshenko      04/27/85-11/04/85    Styazhkin et al, 1985
Wind (51)          Lepping, Szabo  11/21/94-current     Lepping et al, 1995
ACE (71)           Smith           02/06/98-current     Smith et al, 1998.
Geotail (60)       Nagai           05/08/95-12/31/06       
-----------        ------           -----------------    ------------------ 
Full citations for these references are given at: http://omniweb.gsfc.nasa.gov/html/omni2_doc_old.html#references.
Hourly resolution versions of data from these magnetometers are available from:
http://omniweb.gsfc.nasa.gov/ftpbrowser/ and
ftp://spdf.gsfc.nasa.gov/pub/data/

The web pages of the IMP 8, Geotail, Wind and ACE magnetometer teams are to be found at:
IMP 8: http://wind.gsfc.nasa.gov/imp8/
Wind: http://wind.gsfc.nasa.gov/mfi/
ACE: http://www.srl.caltech.edu/ACE/ASC/level2/index.html
Geotail: http://cdaweb.gsfc.nasa.gov/

Of special relevance to LRO preparation is an FTPBrowser-accessible merged hourly IMP8-Geotail-Wind-ACE IMF data set at http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/mag_iwa.html from which one may make overlapping time-series plots. A second interface at http://omniweb.gsfc.nasa.gov/ftpbrowser/mag_iwa_s2.html enables one to make scatter plots and linear regression fits of user-selected parameter pairs and time span. Results of analyses of these data, with this latter tool, are reported below. A third interface at http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/mag_iwa_d.html enables one to determine distributions, means and their standard deviations, and medians of any IMF parameter from any of the spacecraft named, for any time span.

Plasma data sources:

Most of the solar wind plasma data used in LRO are from the MIT Faraday Cups ( PI is Bridge in Table 2) or the Los Alamos National Laboratory (LANL) electrostatic analyzers ( PI is Bame in Table 2). The data were mainly provided to NSSDC or SPDF and used in OMNI as 1-hour averages. Exceptions are:
1. The IMP 1, Vela and HEOS data which were provided as 3-hour averages and were assigned to each of three successive one-hour records in OMNI,
2. The ISEE 3, Wind and ACE data whose 1-hour averages were computed at SPDF from time-shifted higher-resolution and
3. The LANL IMP 6, 7 and 8 data whose 1-hour averages were computed at SPDF from higher-resolution data.

At present time, Wind and ACE data were being periodically added to OMNI.
Information on current latest date of plasma data in OMNI is given at http://omniweb.gsfc.nasa.gov/html/ow_data.html

Table 2
--------
Spacecraft	  Key persons		Time span		Comments, Reference
----------      -----------        ----------------     --------------------
IMP 1 (18)           Bridge        11/27/63-02/22/64    Bridge et al, 1965
Merged Vela (97)     Bame          07/21/64-03/18/71    Bame et al, 1971
Vela 3 (3)           Bame          07/26/65-11/13/67    Hundhausen et al, 1967
AIMP 1 (33)          Bridge        07/06/66-09/23/69    Lyon et al, 1968
IMP 4 (34)           Ogilvie       06/03/67-12/16/67    Ogilvie et al, 1968
AIMP 2 (35)          Bridge        07/28/67-07/03/68    Lyon et al, 1967
OGO 5 (5)            Neugebauer    03/05/68-04/29/71    Neugebauer, 1970
HEOS 1 (1)           Bonetti       12/11/68-04/15/70    Bonetti et al, 1969
IMP 6 (43)           Bame          03/18/71-07/21/74    Feldman et al, 1973	
IMP 7 (44)           Bame          10/06/72-09/29/78    Asbridge et al, 1976
IMP 7 (47)           Bridge        01/03/75-09/20/78    Lazarus et al, 1998
IMP 8 (45)           Bame          11/04/73-07/16/00    Asbridge et al, 1976
IMP 8 (50)           Bridge        12/05/73-07/26/01	Lazarus et al, 1998
ISEE 1 (11)          Bame          10/30/77-12/19/79    Bame et al, 1978b
ISEE 3 (13)          Bame          08/16/78-10/12/82    Bame et al, 1978a
Wind (51)      Lazarus and Kasper  01/01/95-current     Kasper, 2002
ACE (71)	 McComas, R. Skoug   02/05/98-current     McComas et al, 1998
Geotail (60)  	L.Frank       05/08/95-12/07/06       
Additional key scientists contributing to IMP 8 plasma data are have been J. Gosling and J. Steinberg at LANL and A. Lazarus, K. Paularena and J. Richardson at MIT.
All citations may be found at: http://omniweb.gsfc.nasa.gov/html/omni2_doc_old.html#references.
The plasma parameters included in the early-period OMNI-input data sets (i.e., the first 8 rows of data sets of Table 2) are identified in the original OMNI documentation, available through OMNIWeb, and will not be repeated here. For the middle and later periods, we have used the following in OMNI 2 from the various input data sets:

			N	V	T      phi-V  theta-V   alpha/prot

IMP 6 			x	x	x	x		    x
IMP7 (LANL)		x	x	x	x		    x
IMP7 (MIT)			x
IMP8 (LANL)		x	x	x	x		    x
IMP8 (MIT)		x	x	x	x	x
ISEE 1				x
ISEE3 (protons)		x	x	x	x
ISEE3 (electrons)	x	x
Wind/SWE		x	x	x	x	x	    x
ACE/SWEPAM		x	x	x	x	x 	    x
Geotail  		x	x	x	x	x
Wind SWE plasma parameter data are available in three separate data sets created by the Principal Investigator team.
These are:
1. KP- key parameter data determined by taking linear fits of assumed-isotropic convecting Maxwellian distribution functions,
2. NLF- parameters based on on anisotropic non-linear fitting of bimaxwellian convecting distributions,
3. MOM - parameters based on taking moments of observed distributions.

The Wind/SWE/NLF plasma data set was chosen as the baseline was the result of analysis at MIT (Kasper, 2006, see http://omniweb-dev.sci.gsfc.nasa.gov/html/HROdocum.html#6) and discussed in details in the "Data set intercomparisons and parameter normalizations" section below

Previously we used definitive NLF through November 2004, and we used cross-normalized Wind/SWE KP data thereafter. Now, owing to their greater "robustness," we use for 1995-current the cross-normalized SWE KP data. (SWE KP cross-normalization is to the SWE/NLF.)

92s proton and alpha particle NLF parameters, and proton MOM parameters, are available for solar wind intervals only, at

http://omniweb.gsfc.nasa.gov/ftpbrowser/wind_swe_2m.html, and  at
http://omniweb.gsfc.nasa.gov/ftpbrowser/wind_swe_2mp.html for all orbit phases.
Protons-only KP data are available for solar wind intervals only, at 
http://omniweb.gsfc.nasa.gov/ftpbrowser/wind_swe_kp.html (graphical interface) 
and at ftp://spdf.gsfc.nasa.gov/pub/data/wind/swe/ascii/swe_kp_unspike/ 

The ACE/SWEPAM parameters provided by the SWRI/LANL plasma team were 
determined by taking moments over distribution functions. 

Additional interfaces for comparing MIT Wind/SWE NLF and KP data to each other 
and to ACE/SWEPAM (LANL), IMP 8 (LANL and MIT) and Geotail are at 
http://omniweb.gsfc.nasa.gov/ftpbrowser/pla_iwa.html     time series plots, lists
http://omniweb.gsfc.nasa.gov/ftpbrowser/pla_iwa_s2.html  2-spacecraft scatter plots
http://omniweb.gsfc.nasa.gov/ftpbrowser/pla_iwa_s3.html  sctr plots, log N&T
http://omniweb.gsfc.nasa.gov/ftpbrowser/pla_iwa_d.html   statistics w. filtering
Readers interested in the differences between the Wind moments-based and NLF-fits-based parameter-determination approaches may access http://omniweb.gsfc.nasa.gov/ftpbrowser/wind_swe2m_s.html

The LANL plasma instruments on ISEE 3 measured ions and electrons separately. The ion instrument failed February 19, 1980. Electron-based flow speeds and densities were used in OMNI 2 after the ion instrument failure until late 1982, but neither electron-based temperatures nor flow direction angles were included into OMNI 2. (This was also done for OMNI years ago.) It should be noted that on two days (July 4,1979, and July 31, 1979), ISEE 3 measured densities so low that for each of several hours, the hourly averaged density was less than 0.05/cc. Given OMNI's use of F6.1 format for densities, this yields an apparent density of 0.0 in OMNI for these few hours.

Only flow speeds are provided from IMP 7 (MIT) and from ISEE 1. In the former case, this limitation to flow speed was at the suggestion of A. Lazarus at MIT. In the case of ISEE 1, there were too few hours (<240) when ISEE 1 data were used in OMNI 2 (only when no other data were available) to prioritize doing new density and temperature normalizations.

Web pages of the primary contributors of recent plasma data to LRO are at:

IMP8/MIT: ftp://space.mit.edu/pub/plasma/imp/www/imp.html
IMP8/LANL: http://imp8.lanl.gov/
Wind/SWE/MIT: http://web.mit.edu/space/www/wind/wind.html
ACE/SWEPAM: http://swepam.lanl.gov/
Geotail: http://cdaweb.gsfc.nasa.gov/
As with the magnetometer data addressed earlier, hourly and higher resolution plasma data are available via multiple pathways, mostly cited on the foregoing web pages. They are available via ftp from ftp://spdf.gsfc.nasa.gov/pub/data/ and with display and subsetting capabilities via FTPBrowser and/or CDAWeb at http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/ and http://cdaweb.gsfc.nasa.gov/cdaweb/sp_phys Several multiple-source hourly data sets were created at NSSDC or SPDF to aid in data checking and cross-normalization. These are discussed in the "Data cleaning" section to follow and at http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/merged.html.

Cleaning of source data

It is desirable that LRO data be as free of "bad data" as possible. Extensive checking of 1971-current magnetic field and plasma data was carried out at NSSDC and SPDF as part of creating the LRO data set. Several web-based tools were created and used to review input data sets individually and as compared to each other.

There are two sources of "bad data" in LRO. One is "noise points" in constituent data sets that may arise from transient instrument malfunction or, in the case of plasma parameters, from the time variation of plasma during the accumulation of one distribution function whose subsequent analysis for determining bulk parameters yields meaningless values. Such noise points typically yield single-point upward or downward spikes in parameter profiles. While instrument teams have removed most such points in the data they provided to NSSDC and SPDF, it has been beneficial to seek out and eliminate such points here.

The other main source of bad data in LRO is the inappropriate inclusion of magnetosheath field or plasma data in a data set intended as solarwind-only. This is more significant, the more times the source spacecraft crosses the Earth's bow shock. Thus it is insignificant for ACE which went into an upstream libration point orbit very shortly after launch, very significant for IMP 8 in its ~12-day geocentric orbit, and significant to an intermediate extent for Wind with its more complex and time- varying orbit.

The data sets provided to NSSDC and SPDF and used in LRO were nominally for solar wind periods only. The exceptions are: IMP 8 hourly data were submitted time continuously, and solar wind portion were extracted using the bowshock data base at http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/bowshock.html. and Geotail for which we established conservative solar wind intervals.

Among the tools developed and used for concurrently screening multi-source data and summarized at http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/merged.html were:

http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/mag_iwa.html 
      for plotting magnetic field intensity or components from IMP 8, Wind and ACE for 1994-2000;
http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/pla_iwa.html 
      for plotting plasma parameters and/or variances from any pair of the 5 data sets IMP8/MIT,
      IMP8/LANL, Wind/SWE (fits-based), Wind/SWE (moments-based) or ACE/SWEPAM for 1995-2001;
http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/pla_iwa.html 
      for plotting plasma parameters and/or variances from IMP8/MIT and IMP8/LANL for 1973-2001;
http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/pla_ii.html 
     for plotting plasma parameters and/or variances from IMP8/MIT, IMP8/LANL and ISEE 3 for 1978-1982;
http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/pla_imp_678.html 
     for plotting plasma parameters and/or variances from IMP6/LANL, IMP7/LANL and IMP8/LANL for 1971-1978
These tools all work with time-shifted (see below) hourly-averaged data. They yield plots with one panel per physical parameter selected, with color-coded intensity-time profiles from each of the data sources. They make noise points visible and they make intervals visible when the apparent solar wind behavior at multiple sources differs significantly. Some cases of the latter correspond to one source being magnetosheath-contaminated while other cases may correspond to real differences in the solar wind plasma domains seen at the two spacecraft.

Another family of tools was also developed that generates scatter plots of parameter values from various pairs of plasma data sources. (These tools also determine regression fits as will be further discussed in the later data comparison and cross- normalization sections of this wtiteup.) This set of tools makes outliers very visible and has led to identification of several magnetosheath-contaminated data-hours. These tools include:

http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/mag_iwa_s2.html 
     for 1994-latest_available IMP 8, Wind, ACE and Geotail magnetic field parameters
http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/pla_iwa_s2.html 
     for 1995-2001 IMP 8, Wind and ACE plasma parameters
http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/pla_lm_s2.html 
     for 1995-latest_available IMP 8, Wind, ACE and Geotail plasma parameters
http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/pla_ii_s2.html
     for 1978-1982 IMP8/MIT, IMP8/LANL and ISEE 3 plasma parameters.
http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/pla_imp_678_s2.html
    for 1997-1998 LANL IMP 6, 7 and 8 plasma parameters.
Replacing the "s2" in these url's with "s3" in the last four of these gives a variant of the pages for working with base-10 logarithms of densities and temperatures rather than with densities and temperatures themselves. These tools allow filtering by values of any of the parameters in the relevant data records, including numbers of fine scale points in the hour-averages. The second of them also allows filtering by the impact parameter (transverse separation distance, see below) between any pair of spacecraft.

For many years, the IMP 8 spacecraft was the only LRO source, and was the dominant OMNI/LRO data source from its late-1973 launch to the mid-1978 ISEE 3 launch and again from the late-1982 departure of ISEE 3 from an L1 orbit until the late-1994 Wind launch. In its 12-day, 35-Re near-circular geocentric orbit, IMP made at least 2 and frequently 10-20 transitions into and out of the solar wind, across the Earth's time-varying bow shock.

To enable a more reliable exclusion of magnetosheath-contaminated IMP 8 field or plasma data, and a more reliable inclusion of interesting solar wind intervals (that might once have been excluded by the magnetic field or plasma teams in their SPDF and NSSDC submissions of hourly solar wind data as being magnetosheath-contaminated), a major effort was undertaken (with support from a NASA/AISRP grant) by the IMP 8 magnetic field team at GSFC and the plasma team at MIT to jointly study the field and plasma data and to identify and characterize all IMP 8 bow shock crossings. The fruits of this effort for 1973 to 2000 are visible at http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/bowshock.html. We have used this file to identify and delete magnetic field or plasma data when IMP 8 was not wholly in the solar wind. (The exception was that, for the case of LANL plasma data wherein hourly averages were created from ~2-min data previously separated at LANL as being in the solar wind vs. magnetosheath, LANL hourly averages were retained in OMNI 2 for hours in which IMP encountered shock crossings and was therefore partly in the solar wind.)

Time-shifting of data

In this section we address why, when and how we time shift data of ~minute resolution before building hourly averages for inclusion in OMNI 2.

Why and when to shift: That most of the source spacecraft contributing to LRO make IMF and plasma observations minutes upstream of the magnetosphere (e.g., <= 15 minutes for the moon-orbiting, late-1960's Explorer 35 spacecraft at ~60 Re) was not factored into the hourly averages interspersed into LRO. However, the ISEE 3, Wind and ACE spacecraft are frequently or always about an hour upstream of the magnetosphere. As their data are to be interspersed with data from much-closer-to-Earth spacecraft (e.g., IMP 8), it is appropriate to time-shift the hour-upstream data at higher resolution and to compute hourly averages "at Earth" for inclusion in LRO. Such shifting has been done for the field and plasma data of these three spacecraft, as described herein.

How to shift: Several factors determine optimal shifts: the geometry of the Earth- spacecraft separation vector; the Earth's orbital motion about the sun between observations upstream and at Earth; the geometry (shape, orientation) of the solar wind variation phase front; the solar wind flow direction; and local propagation of the phase front relative to the mean solar wind. (In the above, "Earth" can be replaced by "second spacecraft" for time shifts made for two-spacecraft comparisons.) However, for the purpose of shifting many years of upstream data for LRO, we seek a statistically optimal approach. Relative to the above factors, we assume the variation phase fronts are planar, of arbitrarily large extent normal to the Sun-Earth line and normal to the ecliptic, and that they merely convect outward with a solar wind flow assumed radial. It remains to specify the angle between the Sun-Earth line and the intersection between the phase front and the ecliptic plane.

For solar wind variation phase fronts normal to the ecliptic (no Zi-Zj dependence), geometric considerations say that the time delay equation for one spacecraft and Earth is

Delta-t = (X/V) * {[1 + (Y*W)/X]/[1 - Ve*W/V]}, 
where 
Delta-t is the time shift in seconds, 
X and Y are GSE X and Y components of the spacecraft position vector, in km, 
V is the observed solar wind speed in km/s (assumed radial),
Ve is the speed of the Earth's orbital motion (30 km/s). 
W=tan [0.5 * atan (V/428)] is parameter related to the assumed orientation of the phase front relative
  to the Earth-sun line.  It is Half-way between corotation geometry and convection geometry.

Doing the time shifts: We have shifted 1-5 min ISEE 3, Wind and ACE IMF and plasma data using the above time-shift equation, using known locations of those spacecraft and using observed solar wind flow speeds in the data sets being shifted. We then created averages over all fine scale values whose shifted time tags placed them within a given hour "at Earth." Thus all the values with shifted time tags between 00:00 and 01:00 were averaged to give the first OMNI 2 average for a day.

The upstream orbits: Let us review the ISEE 3, Wind and ACE orbits briefly. From shortly after its 8/12/78 launch until August, 1982, when it was directed towards the Earth's deep magnetotail, ISEE 3 was in an L1 libration point orbit with X in the range ~200-260 Re, Y in the range ~ +/- 100 Re, and Z in the range ~ -15 Re to + 20 Re. At its extremes (X ~ 220 Re, Y ~ +/- 100 Re, Z ~ 0), the impact parameter (IP, see above) values for ISEE 3 relative to Earth were ~ 83 Re and ~117 Re, where the asymmetry results from the Earth's motion towards -Y during the ~hour that the solar wind moves from Xisee to Xearth. Note that the time shifts for ISEE 3 could range between ~25 min for high flow speed (700 km/s) and Ygse = -100 Re and ~ 80 min for low speed (350 km/s) and Ygse = +100 km/s.

Wind has been in a variable orbit since its 11/01/94 launch. Through 1998, Wind executed a series of ~30 geocentric orbits with near-noon apogees of distances ranging between ~50 Re and ~250 Re and periods ranging between ~20 days and ~150 days. During these years, the Y component of the Wind position vector was typically in the range +/- 40 Re and almost never exceeded the range +/- 60 Re. For 1999 through the first half of 2000, Wind had three orbits reaching X values of 210, 180 and 100 Re, but otherwise many Wind apogees were of lower altitude and well away from the noon meridian. Starting in mid-2000, Wind was put into an orbit reaching extreme values of +/- 250-260 Re in the dawn-dusk meridian. After some time in this orbit, Wind was placed in an L1 orbit. Figure 4 shows the Wind-Earth impact parameter for 1994-2003.

ACE has been in a regular L1 orbit since shortly after its 08/25/97 launch, with X in the range ~218-248 Re, Y in the +/-40 Re range and Z in the +/- 24 Re range. The ACE project was assessing orbit adjustments in 2003.

The high resolution data sets that were fed into the time shift algorithm were:

ISEE 3 2-min merged IMF/plasma data at http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/isee3_merged.html.
Wind/SWE 92-s plasma data at http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/wind_swe_2m.html.
Wind 1-m IMF data at ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/wind/mag/1min_ascii/.
ACE 4-min merged IMF/plasma data at http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/ace_merge.html.
Geotail mag. data were processed from 15 sec. data, as a part of HRO preparation and they are accesiible from http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/geotail_mag15s.html
Geotail plasma data were processed from: http://cdaweb.gsfc.nasa.gov/ (GE_H0_CPI)
(for details see HRO preparation at http://omniweb.sci.gsfc.nasa.gov/html/omni_min_data.html)

For ISEE 3, a given field-plasma-merged record was given a shifted time tag only if it had a flow speed value to use in the time shift equation above. If the record had no flow speed value, then its IMF data, if present, were not shifted nor otherwise carried forward for inclusion in OMNI 2. However, for both ACE and Wind, IMF data were shifted using a flow speed interpolated to the IMF record time tag with input from the closest-before and closest-after good flow speed values, regardless of the duration between the two input points used. (The treatment of ACE data in this regard was changed from being ISEE-3-like to being Wind-like in February, 2006.) Since plasma gaps may have been over many hours, users of shifted IMF data may want to assess the goodness of their time tags by examining whether there are concurrent plasma data and, if not, how long a plasma gap (during which flow speeds might have varied significantly) there was.

For OMNI 2, we shifted each ISEE 3 electron- based density and flow speed in the LANL-provided hourly data set by one hour. No new "half-way" time shift of these electron-based parameters was done.

The hourly averages determined from the shifted field and plasma ISEE 3, Wind and ACE data are available, along with concurrent but unshifted IMP 8 data, at http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/merged.html.

Data set intercomparisons and parameter normalizations

There are random and systematic differences between hourly averages of pairs of like parameters obtained by two spacecraft. Among the reasons for the random differences may be (1) the two averages have differently time-located gaps in the averages, (2) spatial gradients in parameters being measured combined with offsets of the spacecraft locations relative to the flow direction, (3) incorrect (or no) time shifts used for one or another data set prior to hourly-average construction (see prior section), (4) etc. Among the reasons for systematic differences are differing processing approaches (e.g., taking fits vs. moments for deriving flow parameters from distribution functions), subtle calibration factors not adequately accounted for in data processing, etc.

As OMNI 2 involves the interspersal of IMF data and of plasma data from each of several spacecraft, it is desirable to understand and to compensate for the differences between pairs of sources. It is not feasible to decrease random differences between pairs of sources (except via identification and exclusion of "bad data" as discussed earlier), but it is valuable to understand their magnitude in order to understand the "accuracy" of the OMNI 2 data as representative of the nearby solar wind. It is feasible to find and compensate for systematic differences between pairs of data sets.

Magnetic field comparisons:

Using the scatter plot and regression fit interface at http://omniweb.gsfc.nasa.gov/ftpbrowser/mag_iwa_s2.html, we have done several runs of the form Bi,j = a + b * Bi,k, where i designates a field component (GSE X, Y, Z) or field magnitude ( <|B|>), where j, k designate a spacecraft pair and where a and b are intercept and slope of a linear regression fit determined by minimizing sums of squares of perpendicular distances between (Bi,j, Bi,k) data points and the best fit line. Use of the "perpdist" regression approach rather than the "delta-Y" regression approach is more appropriate to cases where the uncertainties or errors in the Y and X variables are comparable. In all the runs, we required at least half an hour's coverage in each hourly average.
All details are discussed at http://omniweb.sci.gsfc.nasa.gov/html/omni2_doc_old.html

Summarizing of the magnetic field comparisons results we have:
In the range +/- 10 nT, where most IMF values lie, the difference between an observed value and any of the values computed from the above equations is almost always within 0.2 nT of zero. 0.2 nT is much less that the natural spread of data points about the best fit regression lines so we shall not perform any cross-normalizations of magnetic field data.

It was determined that the only IMF normalization needed for Geotail and Prognoz-10 data
Magnetic field normalization for Geotail :
The Geotail magnetic field data we worked with had preliminary and incorrect Bz offset values. Accordingly, we compared Geotail data with data from the other spacecraft and derived the following "normalizations" of the Geotail data:

Bx and By, all time, all Bz:

Bx(norm) = 1.02 * Bx(obsvd)
By(norm) = 1.02 * By(obsvd)

Bz (depends on time)

19950101-19951231:  Bz(norm) = -0.490 + 1.004 * Bz(obsvd)
19960101-19991231:  Bz(norm) = -0.597 + 1.017 * Bz(obsvd)
20000101-20040401:  Bz(norm) = -0.149 + 1.019 * Bz(obsvd)
20040402-20050401 : Bz(norm) = -0.461 + 1.020 * Bz(obsvd)
20050402-20051231:  Bz(norm) = -0.663 + 1.023 * Bz(obsvd)

Bt (depends on time and on sign of Bz)

19950101-19991231, Bz<0:  Bt(norm) = 0.123 + 1.022 * Bt(obsvd)
19950101-19991231, Bz>0:  Bt(norm) = -0.180 + 1.012 * Bt(obsvd)
20000101-20040401, Bz<0:  Bt(norm) = 0.052 + 1.016 * Bt(obsvd)
20000101-20040401, Bz>0:  Bt(norm) = -0.021 + 1.014 * Bt(obsvd)
20040402-20051231, Bz<0:  Bt(norm) = 0.123 + 1.022 * Bt(obsvd)
20040402-20051231, Bz>0:  Bt(norm) = -0.180 + 1.012 * Bt(obsvd)
Magnetic field normalization for Prognoz:
The only IMF normalization needed was for the sun-pointing (spin-axis aligned) IMF component of the Prognoz 10 IMF vector. This was done for OMNI, and will be continued unchanged in OMNI 2.

Plasma parameter comparisons:

We use the same approach to comparing multi-source plasma flow speed, density and temperature values as was used for IMF parameters. For plasma we have four multi-source data sets:
1971-1978 LANL IMP6/IMP7/IMP8 data;
1973-2001 IMP8 MIT/LANL data;
1978-1982 IMP8/MIT/LANL-ISEE3/LANL data;
1995-present IMP8/MIT-IMP8/LANL; Wind/SWE/fits; ACE/SWEPAM; Geotail data.
The relevant interfaces for both scatter plots and regression fits and for overlying intensity-time profiles are at http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/merged.html It is likely that comparisons among currently active Wind/SWE and ACE/SWEPAM plasma data sources will be of most current interest.
Only the SWE/NLF ( Non-Linear Fits) set was directly compared to the ACE data, as this set is believed to be significantly more reliable by the SWE team.
Owing to the significant differences between Wind/NLF and ACE values, for both densities and temperatures, cross normalization of ACE values to equivalent Wind values were performed in creating the OMNI 2 data set. That the Wind/SWE plasma data set was chosen as the baseline was the result of analysis at MIT comparing fits-based proton densities and alpha particle densities, plus a model-based contribution for electrons from higher-Z species, with total electron content from the independent Wind/WAVES instrument. From this analysis the uncertainty in the SWE proton density was estimated as 2%.
Finally, "physics-based" tests of the goodness of the nonlinear fits (NLF)-based velocities (~0.16% in speed, ~3 deg in direction), densities (~3%)and temperatures (~8%) are discussed in (Kasper, 2006, see http://omniweb.sci.gsfc.nasa.gov/html/HROdocum.html#6).

So,for plasma comparisons, we used P(Wind/NLF) = a + b * P(2) where now P(2) might be ACE or IMP 8 or Wind/KP, and where a and b are the intercepts and slopes in the equations and NLF- nonlinear fit data

We have not systematically regressed flow direction angles (Users may make comparisons of such parameters from the http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/merged.html interface.)

While we have done both linear (the "_s2" interfaces) and logarithmic (the "_s3" interfaces) regressions ("logarithmic regression" is shorthand for "linear regressions of logs of parameters") for density (N) and temperature (T), we have normalized densities and temperatures using the results of the logarithmic regressions because densities and temperatures tend to be more log-normally distributed than linearly distributed.
The normalization parameters will be specified as pairs (a b)
(logN)norm = a + b * (logN)obsvd
(logT)norm = a + b * (logT)obsvd

We showed that, with rare exceptions, flow speed regression lines are typically within a few km/s of the Y = X line over the 300-800 km/s range, so we have not normalized any flow speed data.

Our interfaces also allow one to filter the data used in a given regression run by the numbers of fine scale points in the hourly averages and by the "impact parameter" IP for the pair of spacecraft contributing data to the run. The IP is the transverse separation of the spacecraft pair. IP's are available for IMP8-ISEE3, IMP8-Wind, IMP8-ACE and Wind-ACE from http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/impact.html and from http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/impact_ii.html. Virtually all IP-relevant runs were done with IP<60 Re to minimize basing comparisons and subsequent cross- normalizations on plasma parameters from different plasma regimes. The filtering on numbers of fine scale points enabled us to minimize the effects of hours wherein hourly averages may be based on limited and different coverages during an hour.

We note that solar wind densities are expected to decrease as 1/R**2 on average, with R the heliocentric distance. The L1 libration point at 200+ Re from Earth is close to 0.99 AU from the sun. This means the density of a plasma element measured at L1 should be decreased by ~ 2% when it reaches the Earth's magnetosphere at ~1.00 AU. We have not used this fact in our analysis, but we note that the density differences we find in comparing sources are typically greater than 2%.

The comparisons among currently active Wind/SWE and other plasma data sources gave us following results:

Normalizing Wind/SWE Kp data
 Fist we normalized SWE KP data (for 1995-current) to the SWE/NLF data (that is basic data)
 Summarized the new results are:  
     For Wind/SWE KP Np and Tp data
     For Np, for all V and time,
     LogN(Wind/KP, norm) = -0.055 + 1.037 * LogN(Wind/KP, obsvd)
     For Tp, for all V and for 1995-7,
     LogT(Wind/KP, norm) = -0.030 + 1.055 * LogT(Wind/KP, obsvd)
     For Tp, for all V and for >= 1998,
     LogT(Wind/KP, norm) = LogT(Wind/KP, obsvd)

Normalizing ACE/SWEPAM data:
 Summarizing ACE/SWEPAM Np and Tp data to the SWE/NLF we have: 
    Let t be fractional years since 1998.0. (E.g., t = 1.5 on July 1, 1999.)
    Let V = solar wind speed
    N = ACE/SWEPAM proton density as observed
    Nn = value of N as normalized to equivalent Wind/SWE nonlinear fit proton densities
    For V < 395 km/s, Nn = [0.925 + 0.0039 * t] * N
    For V > 405 km/s, Nn = [0.761 + 0.0210 * t] * N
    For 395 < V < 405, Nn = [74.02 - 0.164*V - 6.72*t + 0.0171*t*V] * N/10
    For temperature (all V), LogT(norm) = -0.069 + 1.024 * LogT(obsvd)

Normalizing Geotail/CPI data: 
For Geotail, we use:
Density (all time and all V):  LogN(norm) = -0.072 + 0.980 * LogN(obsvd)
Temperature (1995-1998, all V):  LogT(norm) = 0.166 + 0.925 * LogT(obsvd)
Temperature (1999-2005, all V):  LogT(norm) = -0.362 + 1.052 * LogT(obsvd)

 Normalizing of ACE/SWEPAM and IMP6/7/8 LANL Na/Np ratios to Wind/SWE/NLF Na/Np ratio: 

 For normalizing of ACE/SWEPAM ratio to Wind/SWE/NLF Na/Np ratio we use equation:
   Na/Np(norm) = 1.23 * Na/Np(obsvd)
 For normalizing of IMP6/7/8 LANL Na/Np ratios to Wind/SWE/NLF Na/Np ratio first 
    we found coefficient X-normalization of alpha/proton ratios for IMP 8 to Wind.  
    Analysis shows there is no need to normalizing IMP 6 or IMP 7 to IMP 8 and then to Wind
   because the Na/Np from IMP6 and IMP7 approximately [statistically] equals Na/Np from IMP 8
   (See http://omniweb.gsfc.nasa.gov/ftpbrowser/pla_imp_678_s2.html) and the equation is:
    Na/Np(norm) = 0.78 * Na/Np(obsvd)
  
Normalizing IMP8/MIT and IMP8/LANL data to Wind/SWE/NLF
IMP 8 plasma data span a 28-year, 1973-2001 interval. We report herein the results of 
comparisons of IMP8/MIT, IMP8/LANL and Wind/SWE data. We shall also use the flow speed 
bins <350 km/s, 350-450 km/s and >450 km/s in performing normalizations. Another key 
assumption is that there has been no significant time variation in IMP8/MIT density and 
temperature not previously found and compensated for by the MIT team. This enables us to 
normalize IMP-8/MIT to Wind/SWE data and then to normalize all other data sources 
(not contemporaneous with Wind/SWE) by chaining the regressions of each such data set to 
IMP 8 with the IMP8-Wind/SWE regressions. 

Normalizing IMP8/MIT Density and Temperature to Wind/SWE/NLF
Normalization coeff. a and b for IMP8/MIT  for entire time interval to Wind/SWE for different 
bins are given below:
      V<=350.    V>350 and V<=450    V>450
N:  (.020 .941)  (.033 .919)  (.019 .907)
T:  (.864 .839)  (.491 .920)  (.702 .890)
-----------------------------------------

Normalizing IMP8/LANL Density and Temperature to Wind/SWE/NLF
We obtained time dependent normalization coeff.  a and b  for IMP8/LANL 
to Wind/SWE/NLF, finding normalization coeff IMP8/LANL to IMP8/MIT for each LANL group of years:
 If a" and b" normalization coeff IMP8/MIT to IMP8/LANL:  Log(Nlan)=a"+ b"*Log(Nmit)  
( see Appendix 3 in omni2_doc_old.html) then the coeff. a' and b' for IMP8/LANL to IMP8/MIT 
will be: Log(Nmit)=a'+ b'*Log(Nlan) then we have Log(Nmit)=[Log(Nlan)-a")]/b" , 
where a'=-a"/b"; b'= 1/b";
And then we normalised obtained data  data to Wind/SWE/NLF.
The normalization coeff.  a and b  for IMP8/LANL to Wind/SWE/NLF are:
Normalization for Density
    Year           V<=350.    V>350 and V<=450    V>450
    1973-1979    (.111 .943)    (.064 .951)     (-.011 .958)
    1980-1981    (.140 1.024)   (.092 1.010)    (-.028 1.048)
    1982-1994    (.064 .965)    (-.020 1.000)   (-.085 1.006)
    1995-2001    (.040 1.007)   (-.023 1.013)   (-.093 1.022)
 Normalization for Temperature
    1973-1979    (.621 .879)  (.290 .958)    (.271 .969)
    1980-1981    (.840 .811)  (-.482 1.091)  (.207 .964)
    1982-1994    (.497 .894)  (+.044 .997)   (.130 .982)
    1995-2001    (.441 .895)  (-.044 1.008)  (-.165 1.036)
---------------------------------------------------------

Normalizations for IMP6, IMP7 to WIND/SWE/NLF
There were LANL plasma instruments on IMP 6 (1971-1974) and IMP 7 (1972-1978)
First we normalized IMP6/LANL or IMP7/LANL to IMP8/LANL with coeff Ax and Bx that we got using
 interface: http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/pla_imp_678_s3.html
and then we normalised rezults from previous step to Wind SWE using coeff. for IMP8/LANL to Wind/SWE. (with help of interface: http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/pla_iwa_s3.html) In this case our equations looks like: log(Ni)=Ax + Bx*log(Nx) where log(Nx)-Log of density of X spacecraft, X=IMP6 or IML7, or ISEE3 log(Ni)- Log of density normalized to IMP8/LANL, Ax, Bx coeff of normalization X- spacecraft to IMP8/LANL, then we normalized to Wind: log(Nw)=Ai + Bi*Log(Ni) where Ai, Bi coeff of normalization IMP8/LANL to Wind/SWE. log(Nw)- Log of density normalized to Wind/SWE, last equation can be modified: log(Nw)=Ai+Bi*(Ax + Bx*log(Nx)) or log(Nw)=Ai+Bi*Ax +Bi*Bx*Log(Nx) final: log(Nw)=Aw+Bw*Log(Nx), Aw= Ai+Bi*Ax; Bw=Bi*Bx Coeff. Aw and Bw for Density and Temperature for IMP6/LANL are given in the table: V<=350. V>350 and V<=450 V>450 Aw Bw Aw Bw Aw Bw N: (.000 1.075) (.037 1.007) (.018 .952) T: (.509 .894) (.308 .950) (.560 .910) ------------------------------------------- Coeff. Aw and Bw for Density and Temperature for IMP7/LANL are given in the table: V<=350. V>350 and V<=450 V>450 Aw Bw Aw Bw Aw Bw N: (-.050 .983) (-.053 .967) (-.099 .968) T: (.641 .872) (.359 .942) (.322 .957) -------------------------------------------- Normalizations for proton and electron from ISEE3 to WIND/SWE/NLF ISEE 3 (1978-1982) was a very significant near-Earth solar wind monitor from shortly after its 1978/08/12 launch until late 1982 when it was moved from its L1 orbit to probe the deep geomagnetic tail. The LANL plasma experiment on ISEE 3 separately measured ions and electrons. Unfortunately the ion instrument failed on February 19, 1980. We include in OMNI 2 (as we did for OMNI) ion-based density, flow speed, temperature and flow azimuth information through 1980/02/19, but only electron-based density and flow speed thereafter. Further details see Appendix 4 at http://omniweb.sci.gsfc.nasa.gov/html/omni2_doc_old.html that shows the results of comparisons of IMP 8 data with ISEE 3 ion-based and electron-based parameters. Coeff. Aw and Bw for Density and Temperature of ISEE3/Proton data to Wind/SWE/NLF: ( See previous section for calculations of Aw, Bw) V<=350. V>350 and V<=450 V>450 Aw Bw Aw Bw Aw Bw N: (.059 .855) (.097 .911) (.076 .972) T: (.348 .926) (.007 1.000) (-.053 1.016) ----------------------------------------------- The normalization equations for Density of ISEE3/Electron data to Wind/SWE: V<=350. V>350 and V<=450 V>450 N: (.019 .888) (.052 .842) (.004 .859) -------------------------------------------- Appendixes 1-5 at http://omniweb.sci.gsfc.nasa.gov/html/omni2_doc_old.html contains the some more details of comparisons across different spacecraft pairs (specially for old spacecraft).
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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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