LOW-FREQUENCY WAVES IN THE EARTHS MAGNETOSHEATH - PRESENT STATUS

The terrestrial magnetosheath contains a rich variety of low-frequency (less than or similar to proton gyrofrequency) fluctuations. Kinetic and fluid-like processes at the bow shock, within the magnetosheath pl asma, and at the magnetopause all provide sources of wave energy. The dominance of kinetic features such as temperature anisotropies, couple d with the high-P conditions, complicates the wave dispersion and vari ety of instabilities to the point where mode identification is difficu lt. We review here the observed fluctuations and attempts to identify the dominant modes. along with the identification tools. Alfven/ioncyc lotron and mirror modes are generated by T-perpendicular to/T-parallel to > 1 temperature anisotropies and dominate when the plasma beta is low or high, respectively. Slow modes may also be present within a tra nsition layer close to the subsolar magnetopause, although they are ex pected to suffer strong damping. All mode identifications are based on linearized theory in a homogeneous plasma and there are clear indicat ions, in both the data and in numerical simulations, that nonlinearity and/or inhomogeneity modify even the most basic aspects of some modes . Additionally, the determination of the wave vector remains an outsta nding observational issue which, perhaps, the Cluster mission will ove rcome.