Propagation pattern of low frequency waves in the terrestrial magnetosheath

Abstract. Propagation pattern (distribution of phase velocities) is determined in three dimensions in the terrestrial magnetosheath on a statistical basis using Cluster spacecraft observations. It is found that the anti-sunward propagation dominates and that the propagation direction is toward the magnetosheath flank at smaller zenith angles, while it is toward the magnetopause at larger angles. This pattern is axially symmetric regardless of the interplanetary magnetic field direction and agrees qualitatively with the density gradient directions in a hydromagnetic flow model of the magnetosheath, suggesting that the wave refraction mechanism is more significant than the wave drift effect.