A peculiar type of daytime absorption in the auroral zone

By means of a chain of riometers with antennas pointed in different directions along the magnetic meridian at College, Alaska, a peculiar type of daytime radio-wave absorption has been identified in the auroral zone. Unlike the typical auroral absorption which varies in an irregular manner in space and time, the peculiar daytime absorption shows little fluctuation with time and is usually much stronger to the north of College than to the south. It is shown that the characteristics of the absorption event can be explained in terms of the ionizing effects of a steady beam of primary auroral particles that slowly moves from the north of College to the south and whose intensity undergoes a pronounced decrease with its southward motion.