Through 1996, the magnetics group at the Goddard Space Flight Center (GSFC) undertook a project to produce a near-comprehensive main field model. In the course of research, several variant models were developed which differed in such things as truncated levels of spatial and temporal basis functions describing ionospheric and magnetosphere fields, and fields associated with the meridional current system. Much of this project was advanced during the collaboration with Nils Olsen (Department of Geophysics, Copenhagen University, Denmark) in February and December of 1996.
Some model variations utilized groups of physical indices in an attempt to parameterize complex behavior of certain magnetic sources. Two such indices, describing solar activity, were added to each record. The first of these was the 10.7 cm solar radio flux adjusted to 1 AU. This is a measure of the radio energy emitted from the sun in units of 10 to the -22 Joules/second/square meter/Hertz collected daily in Ottawa, Canada at local noon (1700 GMT). The values were corrected for antenna gain, atmospheric absorption, bursts in progress, background sky temperature, changing sun-Earth distance, and waves reflected from the ground. Daily values were copied off the CD ``Solar Variability Affecting Earth'' from the National Geophysical Data Center (NGDC) then averaged over one year intervals. Yearly averages were calculated separately for each month (ie all values in January 1960 were assigned F10.7 averages from July 15, 1959 to July 15, 1960).
The second solar indicator was the angle between the dipole axis and the Earth-sun line. The program to calculate these values was obtained from Mauricio Peredo (Hughes STX) at GSFC. This program calculates the angles based on the day of the year and universal time in hours.
For this project, data was used from the following sources:
Observatory Annual Means (obsan) (see Section 3.2)Observatory Hourly Means (obshr) (see Section 3.1)
Magsat Dawn (dwn)
Magsat Dusk (dsk)
POGO Pass Data (pogopc) (see Section 3.7)
POGO Decimated Data (pogodc) (see Section 3.7)
The number of points in each of these datasets, as well as in their original dataset can be found in Table 3.2. All of the final datasets and most preliminary datasets described can all be found on the CDROM entitled SQOBS002 located in the Magnetics CD Library at the Goddard Space Flight Center. All final datasets are in IEEE binary in SQ format.
Unless otherwise indicated, points were rejected if the difference between the observed value and the value computed using the AA_1 model was greater than the residual limit. The AA_1 model is comprised of a degree 13 main field model with a cubic B-spline secular variation basis, an ionospheric model with maximum latitudinal wavenumber of 7 for local time terms and 3 for non-local time terms, a degree 5 magnetospheric model with local time terms only, and no F10.7 dependence on the ionosphere. The POGO datasets also used selection criteria based on the QnnlF10.7 model and the 21X3030 model. The QnnlF10.7 model is similar to the AA_1 model but with an ionospheric component linearly dependent upon F10.7 per the formulation outlined by Niles Olsen. The 21X3030 model is also similar to the AA_1 model but with an ionospheric model having maximum latitudinal wavenumber of 30 for both the local and non-local time terms and with the POGO input data weighted heavily (21 times that used in AA_1).
Number of points in the original and final dataset used in the Sq modeling project. The residual limits used to reject points are also displayed:
Number in Original Residual Limit Number in Final
dskB.iee
B 11419 25 nT 11404
dskXZ.iee
X 9384 25 nT 9381
Z 9386 25 nT 9382
dskY.iee
Y 9387 25 nT 9321
dskpXY.iee
X 8081 100 nT 7985
Y 8081 100 nT 7988
dwnB.iee
B 12460 25 nT 12441
dwnXZ.iee
X 10595 25 nT 10570
Z 10595 25 nT 10588
dwnY.iee
Y 10595 25 nT 10537
dwnpXY.iee
X 8558 100 nT 8483
Y 8558 100 nT 8445
obsan.iee
X 4047 4047
Y 4047 4047
Z 4047 4047
obshr.iee
X 122494 150 nT 122414
Y 122535 150 nT 122503
Z 121315 150 nT 121208
pogodc.iee
B 57434 10, 30 nT (21x3030)
12 nT (21x3030)
25 nT 22685
pogopc.iee
B 6779 15 nT (QnnlF10.7)
25 nT 6754
The Magsat dusk dataset was copied from CD:SURVEYMISC1 files /sat/su5006/su5006.016-22. This data was NOT corrected for the difference between the Dawn and Dusk models. The Magsat dawn dataset was not recreated at this time; however, it is thought that the file corresponds to files /sat/su5006/su5006.011-15. There is a full description of these datasets in ``Geodynamics Branch Data Base for Main Magnetic Field Analysis'' [Langel and Baldwin, 1991]. Both datasets were then reformatted to accommodate the fitting program and split into files of XZ values, Y values, and B values. Points were rejected when the observed values differed from the AA_1 model computed values by more than 25 nT. The values were actually retained in the dataset, but their quality code (BQ) was changed to a `3' to indicate that the data should not be used by the Fit software. The individual components (X Y Z B) were checked and changed separately. The final files are named dskxz.iee, dwnxz.iee, dsky.iee, dwny.iee, dskb.iee, and dwnb.iee.
The Magsat dusk files do not contain vector data poleward of 50 degrees dipole latitude. Investigator B data, from CD:MAGSATINB01 files mgstinvb.001-mgstinvb.003, was used to add this information back into the file. The times of scalar data poleward of 50 degrees dipole latitude were compared with the times on the Investigator B data. Vector observations (XY only) that were within 100 msec of each other were written out to a separate file to be used in the modeling process. A residual limit of 150 nT was placed on the data using the AA_1 model resulting in the final file dskpxy.iee.
The Magsat dawn data had approximately 200 special vector pole points above 50 degrees diplatitude. Additional vector points were added to the data using Investigator B data similar to the procedure used to create the dusk polar dataset above. Care was taken; however, not to duplicate the times of the special vector points that were already in the dataset. The new points were then compared with computed values from the AA_1 model. All points with residuals greater than 150 nT were rejected. The final file is dwnpxy.iee.