The dawn and dusk electrojet response to substorm onset

We have investigated the time delay between substorm onset and related reac tions in the dawn and dusk ionospheric electrojets, clearly separated from the nightside located substorm current wedge by several hours in MLT. We lo oked for substorm onsets occurring over Greenland, where the onset was iden tified by a LANL satellite and DMI magnetometers located on Greenland. With this setup the MARIA magnetometer network was located at dusk, monitoring the eastward electrojet, and the IMAGE chain at dawn, for the westward jet. In the first few minutes following substorm onset, sudden enhancements of the electrojets were identified by looking for rapid changes in magnetogram s. These results show that the speed of information transfer between the re gion of onset and the dawn and dusk ionosphere is very high. A number of ev ents where the reaction seemed to preceed the onset were explained by eithe r unfavorable instrument locations, preventing proper onset timing, or by t he inner magnetosphere's reaction to the Earthward fast flows from the near -Earth neutral line model. Case studies with ionospheric coherent (SuperDAR N) and incoherent (EISCAT) radars have been performed to see whether a conv ection-induced electric held or enhanced conductivity is the main agent for the reactions in the electrojets. The results indicate an imposed electric field enhancement.