| A numerical model has been developed to study the coupled behaviour of the thermosphere, ionosphere, and electrodynamics in the auroral oval. The model operates in a two-dimensional domain in the meridional plane and is capable of spatial resolution below one kilometre. It uses a dipole magnetic field model and a partially structured mesh, with computational nodes located on discrete magnetic field lines, but with unstructured node spacing along each field line.;The scenarios studied involve perpendicular electric fields of order 100 mV m-1 and mesoscale (order 20 km) arcs of hard (order 5 keV) electron precipitation.;The results show that a term in the ion continuity equation corresponding to Pedersen drift, which has been neglected in previous work, is essential to an understanding of E-region electrodynamics. It is found that ions can be transported up to 150 km from the precipitation region within a few minutes, and that parallel currents are established over a much wider area, but with lower peak density, than previously thought.;The model has also shown that ionosphere-thermosphere coupling is a significant feature of auroral phenomena. This coupling occurs through two means. Joule heating drives thermospheric disturbances that transport the molecular species N2 and O2 to altitudes where they are normally rare. This changes the primary production of ion species, and it affects the ion-neutral chemistry. Even without vertical mixing, the concentrations of the minor neutral species N and NO are significantly changed by auroral activity, which has a feedback on ion composition.;The inputs to the model are a perpendicular electric field imposed at the top boundary by an idealised magnetosphere, and energetic electron precipitation. The model calculates time-dependent electric fields and currents; number densities, drift velocities and temperatures of electrons and ions; electron heat flow; and neutral temperature, velocity and composition disturbances.;Keywords: upper atmosphere, auroral oval, numerical modelling, thermosphere-ionosphere coupling... |
