A comparison of observations of Pi B magnetic pulsations at the ground with wide-angle photometer measurements of the accompanying auroral luminosity fluctuations has found several cases of well-correlated magnetic and optical pulsations, with periods in the range 15--50 s. This finding strongly suggests that precipitation fluctuations drive at least some of those components of the Pi B signal with periods in this range. We found no luminosity fluctuations associated with the 3-s enhancement of Pi B pulsations. We modeled the magnetic perturbation under a patch of enhanced E region conductivity as it drifts or as its conductivity changes, for circular and strip patch shapes. These idealized models can reproduce some features of the Pi B signature. Most notably, a monotonic variation in the model parameters can produce a reversal in the sense of polarization rotation. A moderate enhancement in the conductivity of a 1-km-wide strip can produce magnetic perturbations with amplitudes typical of Pi B pulsations. ¿ American Geophysical Union 1995.