Geoscience Reference
In-Depth Information
3 Dynamics and Electrodynamics
of the Equatorial Zone
In this chapter we study the dynamics and electrodynamics of the magnetic
equatorial zone. To a great extent our knowledge of the electrical structure of
this region comes from measurements made at the Jicamarca Radio Observatory,
located just east of Lima, Peru. This incoherent scatter radar facility was designed
to optimize measurements of plasma flow perpendicular to the earth's magnetic
field, which is nearly horizontal over the site. In the F region of the ionosphere,
κ i
and
κ e are very large, so the ion and electron velocities perpendicular to B are very
nearly equal to each other. This means that a plasma flow velocity can be uniquely
defined and related to the electric field. We deal first with the generation of electric
fields by thermospheric winds in the F region and follow with an analysis of the
E-region dynamo and the equatorial electrojet. The latter is an intense current jet
that flows in the E region at the magnetic equator. These dynamos are the primary
sources of the low-latitude electric field, but high-latitude processes also contribute
and are discussed as well. An introduction to D-region dynamics is also presented.
3.1 Motions of the Equatorial F Region: The Database
We choose first to study the equatorial F-layer dynamo, since it seems concep-
tually simpler, although it was not discovered first. Most of the data concern-
ing equatorial electrodynamics come from incoherent scatter radar observations
near the magnetic equator over Jicamarca, Peru. Details concerning Jicamarca
and several other observatories are given in Appendix A, along with a discussion
of the measurement method. The Jicamarca system is capable of determining the
plasma temperature, density, composition, and ion drift velocity as functions of
altitude and time from the backscatter due to thermal fluctuations in the plasma.
The radar can be directed perpendicular to the magnetic field, where the fre-
quency width of the backscatter spectrum is very narrow—meaning that even
small mean Doppler shifts can be detected and converted to very accurate iono-
spheric drift velocities. In practice, the radar is split into two beams, one oriented
3
to the geomagnetic east and one 3
to the geomagnetic west. The difference
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