Wave properties near the subsolar magnetopause: Pc 1 waves in the sheath transition layer

We study the waves in the frequency range of Pc 1 in the sheath transition layer of the magnetopause from the ISEE 1 and 2 observations. The waves are enhanced in the sheath transition layer, although they are scattered into the magnetosheath when the outer edge of the sheath transition layer is not sharp. A statistical study of 16 cases shows that the wave frequency is proportional to and equal to about 44% of the ion gyrofrequency. The wave amplitude is much greater when the interplanetary magnetic field (IMF) is southward than when the IMF is northward. The waves are left‐handed polarized when the IMF is southward but are linearly polarized for northward IMF. The direction of maximum variation is perpendicular to both the background field and the gradients of the field and density when the IMF is northward. For southward IMF, the waves are more turbulent. The wave generation mechanisms apparently depend on the IMF orientations rather than the shock geometry. To investigate the free energy to generate the waves for northward IMF, a method is developed combining the measurements from the fast plasma experiment and Lepedea to obtain a high time resolution estimate of the temperature anisotropy when the IMF is strongly northward. The estimated ion temperature anisotropy is enhanced, up to a factor of 2, within the sheath transition layer for northward IMF.