Effects on the geomagnetic tail at 60REof the geomagnetic storm of April 9, 1971

A geomagnetic storm beginning with a sc occurred on April 9, 1971. During the storm the charged particle lunar environment experiment at the Apollo 14 site, the solar wind spectrometer experiment at the Apollo 12 site, and the Ames magnetometers on Explorer 35 took data in the magnetosheath, at the magnetopause, in the plasma sheet, and in the high-latitude geomagnetic tail. The MIT Faraday cup and Ames magnetometers on-board Explorer 33 monitored the solar wind. The data show that the storm was caused by a corotating tangential discontinuity in the solar wind, the magnetopause position is strongly dependent on the attack angle of the solar wind, and the tail field strength was indirectly measured to increase from 10 to 14 γ after the sc. During the main phase the field strength in the tail was observed to increase to between 28 and 34 γ. This increase is consistent with a thermal and magnetic compression of the tail radius from ∼26 to ∼16 RE. The data also show that plasma sheet electrons were observed to drift into the magnetosheath, the thickness of the magnetopause was measured by spatially separated instruments to be >3000 km, and the plasma and magnetic field data are consistent with a model for currents flowing along magnetic field lines in the boundary.