Conductivity relates the ionospheric currents to the electric field. The figure shows
the variation of Pedersen, Hall and direct conductivity as a function of altitude.
(The direct conductivity is the conductivity parallel to the magnetic field.) The Hall conductivity
maximises at 90-120 km altitude. Here the ion-neutral collision frequency is greater than the ion
gyrofrequency but where the electron collison frequency is much less than the electron gyrofrequency.
In this case the electrons E x B drift but the ions cannot.
The Hall and Pedersen conductivities also vary as a function of latitude and longitude
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