From combined STARE and magnetometer observations during a moderately disturbed period, it is deduced that the conductivity rather than the electric field is the prime agent responsible for the long-period variations of both the ground magnetic signatures and the backscatter cross section. At times, there is an almost linear dependence between backscatter amplitude and conductivity suggesting that, within the framework of a nonlinear saturation mechanism, it is the relative amplitude Δn/n of the plasma wave irregularities rather than the absolute amplitude Δn that must be limited. In addition to backscatter amplitude modulation, there is also a modulation observed in the E field direction which is interpreted as being due to secondary east-west polarization electric fields controlled by conductivity modifications in the region.