A wide range of lower F region irregularity scale sizes (75 m to 150 km) at high northern latitudes during the spring and summer of 1978 has been studied. The morphology and intensity distribution of the irregularities suggest that particle precipitation is the primary source of the larger-scale density fluctuations, with second-order effects (e.g., plasma instabilities) contributing to the smaller scale sizes. Under conditions of moderate geomagnetic activity (Kp~2-3, AE~100), the most intense density enhancements (~106 cm-3) occur in the auroral oval. Large- (L>7.5 km) and small-scale (7.5 km>L>75 m) irregularities are most prominent in the dayside auroral oval, including the region of the polar cusp. Density enhancements within the polar cap have been detected principally toward the duskward side. These polar cap enhancements are similar to auroral oval enhancements, suggesting that polar cap precipitation is the source. The altitude range (170-200 km) of the observations implies that chemical recombination is the primary decay mode of the irregularities. The decay rate of the irregularities is sufficiently fast that convection cannot transport the observed irregularities far from their source regions.