Relativistic electron precipitations in association with diffuse aurora: Conjugate observation of SAMPEX and the all-sky TV camera at Syowa Station

It has been believed that whistler mode waves can cause relativistic electron precipitations. It has been also pointed out that pitch angle scattering of ∼keV electrons by whistler mode waves results in diffuse auroras. Thus, it is natural to expect relativistic electron precipitations associated with diffuse auroras. Based on a conjugate observation between the SAMPEX spacecraft and the all-sky TV camera at Syowa Station, we report, for the first time, a case in which relativistic electron precipitations are associated with diffuse aurora. The SAMPEX observation shows that the precipitations of > 1 MeV electrons are well accompanied with those of > 150 and > 400 keV electrons. This indicates that electrons in the energy range from several keV to > 1 MeV precipitate into the atmosphere simultaneously. Our result supports the idea that whistler mode waves contribute to both generation of diffuse auroras and relativistic electron precipitations.