|
IT IS BELIEVED that these magnetic fields are generated by electric
currents flowing in the ionosphere at heights of about 110 km. The currents are
driven by emfs generated when winds blow the partly ionised atmosphere across
the Earth's main magnetic field. It is therefore expected that changes in
the observed magnetic variations should
provide information on changes in the wind systems but so far there
is scarcely any evidence for this link.
Research has been directed to modelling the current systems and their
magnetic fields by introducing various expected wind systems as input to the model.
This procedure is slightly complicated by the presence of the Hall effect in
the ionosphere. In addition to winds driven by solar heating, there is also
a component driven by lunar forces and this component can be isolated
from both the observed magnetic variations
and from the upper atmosphere winds. This provides a separate opportunity
to investigate the link between winds and magnetic fields though the
lunar variations are smaller and more difficult to accurately isolate from the raw data.
|
Recently a joint project between the Australian Geological
Survey Organisation (AGSO) and Flinders
University set up an array of more than 50 magnetometers covering
the Australian mainland. We have been investigating ways of analysing
these data to show the changes in the ionospheric currents system. The
figure below shows the currents system passing over the Australian continent.
We want to try to understand how changes in the shape of this
current system relate to changes in the winds in the upper atmosphere.
Robert Stening
|
