ISEE 1 & 2 observations of the oscillating magnetopause

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Abstract
Examination of multiple magnetopause crossings observed with the magnetometers on ISEE 1 and 2 has allowed us to determine the amplitude of the oscillation of surface waves on the magnetopause with periods greater than about 2 minutes and its dependence on latitude, local time and direction of the interplanetary magnetic field (IMF). The magnetopause is more oscillatory for southward IMF than for northward IMF. When the IMF is southward, the amplitude of the oscillation increases with increasing angle from the subsolar point, which suggests that reconnection‐related phenomena can generate surface waves on the magnetopause. When the IMF is northward, the oscillation does not grow with distance from the subsolar point, which is contrary to the expected growth of the Kelvin‐Helmholtz (K‐H) instability. A study of the spectrum of the solar wind dynamic pressure shows that solar wind pressure fluctuations may cause all of the observed boundary oscillations for northward IMF. Thus the K‐H instability plays at most a very minor role in causing the surface waves on the dayside magnetopause with periods longer than about 2 minutes.