Multi-spacecraft observations of magnetopause surface waves: ISEE 1 and 2 determinations of amplitude, wavelength and period

The multi-spacecraft ISEE mission allowed us for the first time to study propagation of surface waves on the magnetopause. One case which we have studied in detail was near local noon at a latitude of 24.4°. The inferred instantaneous magnetopause normal vectors oscillated about the model magnetopause normal vector in a manner expected for a wave propagating along the magnetopause from the subsolar region. By assuming a model monochromatic wave and a constant magnetopause thickness, we determine the best-fit that yields the three wave parameters; amplitude, wavelength and period. We do this by using the four inferred normal vectors and eight positions of the inner and outer edges of the magnetopause current sheet observed by ISEE 1 and 2 going into and out of the magnetopause as the surface wave moves by. The results show that the amplitude is 0.5 R e, the wavelength is 12 R e, and the period is 7.3 minutes. According to IMP 8 solar wind data, this surface wave was generated by a transient variation of solar wind dynamic pressure.