HF Radar and Auroral Absorption

A description is given of a method, based on riometer observations, for the calculation of auroral absorption of HF radio waves propagating over high‐latitude paths. Emphasis is on HF radar, but the method is appropriate for use in predicting circuit performance of high‐latitude HF communications. The assumptions made and the approximations used are stated explicitly so that, when better information becomes available, explicit corrections can be made. The calculations have been programmed for digital computer and the output for a given set of conditions consists of a map on which are shown contours of median auroral absorption of radio waves returned (by ground backscatter) to the radar site. For the present, only the points on the earth that are reached by one‐hop E‐layer and/or F‐layer propagation are considered.