P. Schmoldt, PhD - MTNet - DIAS

2. Sources for magnetotelluric recording
Fig. 2.10.: Top: possible interaction between field-aligned currents with convection electrojets and cross-polar cap current flow the
sunlit polar ionosphere; from [Zanetti et al., 1983]. Bottom: Schematic representation of a substorm current system intrusion into
the convection electrojets system for a dark ionosphere (left) causing vibrations of the Hall current system (right) represents fieldaligned
currents into the ionosphere, out of it; from Mareschal [1986].
Polar electrojets
The exact mechanisms of current flow in the Polar Regions are not yet fully understood,
but different models have been presented in order to explain certain aspects of the present
current system: e.g. Birkeland and Pedersen field align currents generating Hall currents
in the polar region that flow towards the Harang discontinuity at local midnight [e.g. Kisabeth
and Rostoker, 1977; Rostoker et al., 1982; Baumjohann, 1983; Zanetti et al., 1983]
(Fig. 2.10). As polar electrojets (PEJ) are an important contributor to local polar MT
signals, a great deal of effort has been spent on investigating their characteristics in terms
of height above the surface, length and the related pulsation structure, e.g. Walker and
Greenwald [1981]; Andre and Baumjohann [1982]; Baumjohann [1983]; Pirjola [1998].
This led to the conclusion that the PEJ is usually constrained to a height of 100 – 120 km
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