Remote sensing the state of the inner magnetosphere

Summary form only given. The terrestrial magnetosphere is a plasma filled cavity carved out of the solar wind by the Earth´s magnetic field. This plasma originates from both the upper atmosphere and the solar wind, and its presence has a significant effect of the topology of the magnetospheric magnetic field. Particularly at high geomagnetic latitudes, electrons and protons of magnetospheric origin precipitate into the upper atmosphere, producing the aurora. Auroral optical emissions are a direct result of this precipitation. In the inner magnetosphere, conservation of the first adiabatic invariant, and short bounce periods relative to typical convection times, lead to a population of stable bounce trapped protons. At larger geocentric distances, some combination of field line curvature, magnetic turbulence, and wave-particle interactions lead to violation of adiabaticity, resulting in a full proton loss cone, and to the proton aurora. The equatorward boundary of the proton aurora marks the transition from stable bounce trapping to a full proton loss cone. The latitude of this transition, as identified in proton auroral observations, correlates extremely well with the inclination of the magnetic field in the vicinity of geosynchronous orbit. In this talk, I describe work based on in situ and groundbased observations that demonstrates this correlation between the latitude of the equatorward boundary of the proton aurora and the stretching of the magnetic field in the near-Earth magnetotail, and sheds light on the mechanism(s) responsible for the proton auroral precipitation.