Interplanetary shocks, magnetopause boundary layers and dayside auroras: The importance of a very small magnetospheric region

Dayside near-polar auroral brightenings occur when interplanetary shocks im pinge upon the Earth's magnetosphere. The aurora first brightens near local noon and then propagates toward dawn and dusk along the auroral oval. The propagation speed of this wave of auroral light is similar to 10 km s(-1) i n the ionosphere. This speed is comparable to the solar wind speed along th e outer magnetosphere. The fundamental shock-magnetospheric interaction occ urs at the magnetopause and its boundary layer. Several physical mechanisms transferring energy from the solar wind directly to the magnetosphere and from the magnetosphere to the ionosphere are reviewed. The same physical pr ocesses can occur at other solar system magnetospheres. We use the Haerende l (1994) formulation to estimate the acceleration of energetic electrons to 50 keV in the Jovian magnetosphere/ionosphere. Auroral brightenings by sho cks could be used as technique to discover planets in other stellar systems .