On Signal Decrease in HF Circuits During PCA Events.

摘要

The principal morphological features of ionospheric absorption of cosmic radio noise at vertical incidence -due to influx into the polar ionosphere of solar protons with particle energy near 10MeV,and as measured by ground-based riometers operated usually at 30MHz-are reviewed with figures and brief descriptions. HF signal-intensity observations in two oblique-incidence circuits, Thule to College and Pt. Barrow to Kenai (Alaska),are compared with riometer measurements for several PCA events. It is suggested that a 'stand-by'propagation mode,involving a combination of scattering and ducting of HF radio waves near the ionospheric-bottom-boundary,comes into play. It is also suggested that,during disturbed inospheric conditions, diminutions in ionospheric electron density -in addition to,or in conjunction with,increased ionospheric absorption-is an important contributing cause to HF radio blackouts. (Modified author abstract)