Data obtained by the Chatanika, Alaska, incoherent scatter radar have been used to study ionospheric electric fields, conductivities, and currents associated with three sudden commencements (sc) of geomagnetic activity which occurred on August 4, 1972. Each se appears to have had a different ionospheric response. The first se, which began at 0119 UT (1519 Alaskan Standard Time (AST)), showed a small rise in the electric field several minutes aftr se onset. No change in the local ionospheric conductivity was noted. The second se at 0220 UT (1620 AST) was inked to a large increase in the electric field and a small increase in particle precipitation. Both effects appear to have resulted from an equatorward shift of the auroral oval in response to the initiaion of a se-triggered aurorl substorm. The third se at 2054 UT (1054 AST) came with an abrupt burst of 30- to 40-keV electrons which increased the ionospheric Hall conductivity by a factor of 2. This se was accompanied by a Pc 5 pulsation event. The H component variations of this event are well reproduced by the local ionospheric currents. The D component pulsations, however, show substantial desagreement. A large equatorward displacement of the midday auroral oval took place following this se with intense particle impact ionization to altitudes as low as 60 km. Throughout the third se, substantial ionization was present in the D region arising from solar proton precipitation. No changes in the D region electron densities were seen at se onset, implying that the solar proton flux was not appreciably affected by the magnetospheric disturbance.