Modelling the high-latitude ionosphere

The solar wind plasma, as it flows past the low-density cavity generated by the Earth´s magnetic field, the magnetosphere, generates a large scale electric field which causes circulation of plasma in the outer magnetosphere. This is mapped down the magnetic field lines into the high-latitude ionosphere. This so-called `convection´ of high-latitude ionospheric plasma is now known to control the three-dimensional distribution of plasma and its variations. Its influence is greatest at high latitudes but extends to cover the globe. Because HF systems make use of ionospheric reflections to give over-the-horizon propagation, the operations of HF communication, radar and navigation systems worldwide will therefore be influenced by convection. The paper discusses how departures from steady-state convection should be allowed for in numerical models of the high-latitude ionosphere