The Earth: Plasma Sources, Losses, and Transport Processes

This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed

The annual and longitudinal variations in plasmaspheric ion density

This paper shows that at solar maximum, equatorial ion densities at L = 2.5 are substantially higher at American longitudes in the December months than in the June months. This arises because the configuration of the geomagnetic field causes a longitude-dependent asymmetry in ionospheric solar illumination at conjugate points that is greatest at American longitudes. For example, at −60°E geographic longitude the L = 2.5 field line has its foot point near 65° geographic latitude in the Southern Hemisphere but near 42° latitude in the Northern Hemisphere. We investigated the consequent effects on equatorial electron and ion densities by comparing ground-based observations of ULF field line eigenoscillations with in situ measurements of electron densities (from the CRRES and IMAGE spacecraft) and He+ densities (IMAGE) for L = 2.5 at solar maximum. Near −60°E longitude the electron and ion mass densities are about 1.5 and 2.2 times larger, respectively, in the December months than in the June months. Over the Asia-Pacific region there is little difference between summer and winter densities. Plasmaspheric empirical density models should be modified accordingly. By comparing the electron, helium, and mass densities, we estimate the annual variation in H+, He+, and O+ concentrations near −3°E longitude and −74°E longitude. In each case the He+ concentration is about 5% by number, but O+ concentrations are substantially higher at −3°E longitude compared with −74° E. We speculate that this may be related to enhanced ionospheric temperatures associated with the South Atlantic anomaly

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

The Earth: Plasma Sources, Losses, and Transport Processes

International audienceThis paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed