AMPTE observations of mirror mode waves in the magnetosheath: Wavevector determination

A unique method has been developed to completely determine the wavevector o f a mirror mode wave using data from two closely spaced (separation less th an wavelength/2) spacecraft;. The method is based on the fact that mirror m ode waves are linearly polarized and have zero frequency in the plasma rest frame. The method has been tested using Active Magnetospheric Particle Tra cer Explorers United Kingdom Subsatellite (AMPTE UKS) and Ion Release Modul e (AMPTE IRM) high-resolution magnetic field data from an interval of mirro r mode waves observed in the middle magnetosheath on September 21, 1984. Th e results are also compared to those obtained using other methods of waveve ctor determination. The wavevectors estimated during the event are highly o blique to the ambient magnetic field direction as is expected from mirror w ave theory. The application of the wavevector determination technique to fu rther studies, such as studying the effect of finite electron temperature o n mirror wave characteristics, is discussed.