Radio wave absorption in the auroral ionosphere

The temporal and spatial morphology of the aurorally associated ionospheric absorption of cosmic radio noise is described, using the results of an analysis of the riometer data collected in Alaska over a 5-yr period. The observed daytime and winter maximums of absorption are interpreted as reflecting the temporal variation of the bombardment of the upper atmosphere by primary auroral particles. On the basis of the observed latitude variation of absorption, the auroral absorption zone defined with a maximum at College (geomagnetic 64.65 deg ) was found to be south of the analogous visual auroral zone. The absorption zone is believed to represent the latitude variation of the energy flux of the incoming stream of auroral particles. The temporal and spatial characteristics of auroral absorption are related to magnetic activity and to the luminous aurora. (auth) incoming stream of auroral particles. The temporal and spatial characteristics of auroral absorption are related to magnetic activity and to the luminous aurora. (auth)