Abstract
Abstract. We present the results of a statistical analysis of low-frequency fluctuations in the high latitude regions of the dayside magnetosheath using CLUSTER as a wave telescope. Magnetic field observations are used to determine wave propagation directions and wave numbers for selected frequencies. Using observations of the plasma flow velocity we correct for the Doppler shift, in order to calculate frequencies and phase velocities in the plasma rest frame. This provides us with the possibility to perform a statistical dispersion analysis and to investigate various wave properties, such as the phase velocity and the propagation angle between k and B. The analysis of dispersion distributions and Friedrichs diagrams results in the identification of different wave populations. We find a multiplicity of standing structures (mirror modes) convected with the plasma flow and a large number of Alfvénic waves. The results confirm previous magnetosheath wave studies, such as ISSE or AMPTE spacecraft observations, but we also find a small number of mirror mode-like waves that have propagation speeds up to the local Alfvén velocity, quasi-perpendicular to the magnetic field.
Highlights
The terrestrial magnetosheath constitutes the interface between the interplanetary medium and the magnetosphere of the Earth
We have analyzed 407 frequencies and have identified 516 wave vectors, i.e. in some cases we find more than one wave vector at a given frequency
The (ω, k)-distributions found are displayed in Fig. 7 for both frequencies in the spacecraft, as well as in the plasma rest frame
Summary
The terrestrial magnetosheath constitutes the interface between the interplanetary medium and the magnetosphere of the Earth. Low-frequency fluctuations are dominating the magnetosheath plasma driven by solar wind dynamic pressure variations, plasma instabilities and other effects It is generally accepted, that in the linearized Vlasov theory, Alfven-proton-cyclotron mode and mirror mode are the predominant low-frequency wave modes in the magnetosheath (Schwartz et al, 1996), whereas the nonlinear treatment and fluid picture can lead to a variety of slow and Alfven modes (Stasiewicz, 2005). Mirror modes are linear polarized and non-propagating waves, or standing structures, in the plasma rest frame The growth of these modes is mainly affected by the temperature anisotropy T⊥,p>T ,p and different values of the plasma β (Denton, 2000), where T⊥,p and T ,p are the proton temperatures perpendicular and parallel to the background magnetic field B. The extension and compression of the magnetic field adjacent to the magnetosphere can lead to temperature anisotropies (Crooker and Siscoe, 1977)
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