Magnetic data used
in CMP3 model
The near-Earth magnetic
field is due to sources in Earth's core, ionosphere, magnetosphere, lithosphere
and from coupling currents beyween ionosphere and magnetosphere and between
hemispheres. Traditionally the main field (low degree internal field) and
magnetospheric field have been modeled simultaneously and field from other
sources modeled separately. Making the separation intruduces spuriousfeatures.
A new model, designated
CMP3 (Comprehensive Model:Phase 3) has been derived from quiet time
Magsat and POGO satellite measurements and observatory hourly and annual
means measurements as part of an effort to coestimate fields from all of
these sources.as part of an attempt to represent fields from all of these
sources. The initial phase of this work were first reported in Sabaka and
Baldwin (1993) and the second phase in Langel and al. (1996). In this third
phase the model of the dominant sun-synchronous, local-time morphology
of the ionospheric field is now supplemented with non-local-time modes.
Since many ionospheric features follow lines of dip latitude in equatorial
regions and of the auroral oval in polar latitudes, quasi-dipole (QD) latitude
special harmonic functions have been introduced, including terms accounting
for seasonal variation and variation with annual solar activity.
The new model also accounts
for low conductivity levels in the low and mid-latitude regions of the
nightime ionosphere via special constraints on the QD functions. Both local
and non-local-time terms, with seasonal modulations, are included in a
spherical harmonic representation of the field of magnetospheric origin.
The dipole terms in this external expansion include variation with respect
to the Dst index in order to account for variations in the intensity of
the ring current. Because the time varying ionospheric and magnetospheric
fields induce currents in the earth, a transfer function between the primary
and induced fields is introduced under the assumption of an apriori radially-varying
conductivity model. The fields produced by coupling currents (field aligned,
meridional) residing in the satellite sampling region have been explicitly
modeled under the assumption that they are primarily radial in direction
in the sampling region. This radial current model, including seasonal variation,
is accomplished via toroidal stream functions separately for dawn and dusk
Magsat data. Finally, the internal spherical harmonics are extended to
degree 65 in order to account for fields from the earth's lithosphere as
measured at satellite altitude. The results of this effort is a model whose
fits to the data are superior and whose parameter states for the various
constituent sources are very reasonable.
Magnetic data used
in CMP3 model
Forward modeling
code (CMP3.f subroutine) which predicts the various
CMP3 source fields
Lithospheric Field lithospheric contribution (degrees 15 to 42 ) to Z and
Br (alt=400km)
