Low Frequency Waves Upstream and Downstream of the Terrestrial Bow Shock

The thesis makes use of the four point measurements provided by the Cluster spacecraft mission and determines not only wave vectors but also dispersion relations, propagation patterns, and wave number spectra in the upstream and the downstream regions of the terrestrial bow shock. Furthermore, those wave properties are determined in a proper frame of reference, the plasma rest frame, by correcting the Doppler shift. In the upstream region the dispersion relation exhibits two branches which correspond to the right-hand polarized magnetosonic/whistler mode and the ion beam resonant mode, respectively. The upstream waves exhibit phase velocities oriented toward upstream along the magnetic field in the plasma rest frame. In the downstream region the dispersion relations show a transition to the mirror mode whose properties are frequently detected in the statistical study, too. Interestingly, the mirror modes have finite propagation speeds, possibly coupled to the background inhomogeneities known as the drift mirror mode. While the upstream waves propagate nearly parallel to the background magnetic field, the downstream waves propagate nearly perpendicular. On a statistical average there is an organization of wave propagation pattern: outward divergent in the upstream region; toward the magnetosheath flank region aligned with the plasma flow direction in the downstream region; and inward convergent in the magnetosheath flank. The wave number spectra are also directly determined for the magnetic field fluctuations in the shock upstream region and they are interpreted in light of turbulence. The fluctuations exhibit properties of not fully developed turbulence but intermittency, suggesting that there is not enough time for turbulence to become fully developed.