Spatio-temporal development of large scale auroral electrojet currents relative to substorm onsets

The electric currents flowing in the ionosphere change rapidly and a large amount of energy is dissipated in the auroral ionosphere during auroral substorms. An important part of the auroral current system are the auroral electrojets whose profiles can be estimated from magnetic field measurements from low Earth orbit satellites. We have combined electrojet data derived from the Swarm satellite mission of ESA with the substorm database derived from the SuperMAG ground network data. We organize the electrojet data in relation to the location of the onset and obtain statistics for the development of the integrated current and latitudinal location for the auroral electrojets relative to the onset. Especially we show that just after the onset the latitudinal location of the maximum of the westward electrojet determined from Swarm satellite data is mostly located close to the onset latitude in the local time sector of the onset regardless of where the onset happens.