Variable field-to-normal angles in the shock foreshock boundary observed by ISEE 1 and 2

Saturated ULF waves in the foreshock, with amplitudes comparable to the magnitude of the average field, are convected by the solar wind to the quasi-parallel shock where the average field-normal angle is less than, or about, 45 deg. Several examples from ISEE 1 and 2 magnetometer data show waves that defined local, instantaneous field-normal angles very different periodically from the average. Local geometric conditions at the nominally quasi-parallel shock varied from nearly parallel to nearly perpendicular, at the periods of typical upstream waves. Clear magnetic shock transitions occurred under temporarily quasi-perpendicular geometry.