Mass and electron densities in the inner magnetosphere during a prolonged disturbed interval

The equatorial plasma density and composition at L = 2.5 were studied during an extended disturbed interval using field line resonance measurements (yielding plasma mass density), naturally and artificially stimulated VLF whistlers (electron number density) and IMAGE EUV observations (plasmapause position and line-of-sight He⁺ intensity). During the storm the plasmapause moved to L < 2.5 and at least one density notch and drainage plume formed. These features were evident in all the data sets for some days. One notch extended from 2.4–4.5 R E and spanned <4 hours in MLT. Plume mass and electron densities were enhanced by a factor of about 3. In the plasmasphere and plasmatrough the H⁺: He⁺: O⁺ composition by number was ∾82:15:3. However, just outside the plasmapause the O⁺ concentration exceeded 50%, suggesting the presence of an oxygen torus.