Quoted from: https://ccmc.gsfc.nasa.gov/modelweb/ionos/auroral_absorp.html

Parameter: Probability that absorption at 30 MHz exceeds 1dB; median absorption

Brief Description:
This model provides information for HF propagation calculations at high latitudes. It is based on the long record of worldwide riometer measurements. The model describes the probability Q1 that the HF absorption exceeds 1dB. Q1 is a parameter important for long term predictions. Simple empirical expressions are given for the dependence on corrected geomagnetic latitude, longitude, and local time, solar activity (12 months smoothed sunspot number), and season. Assuming a log-normal distribution for the cumulative absorption probability, the authors deduce a simple linear relationship between Q1 and the median absorption.

Availability: PC software may be available from the authors.

References:
A. J. Foppiano and P. A. Bradley, Prediction of Auroral Absorption of High-Frequency Waves at Oblique Incidence, Telecomm. J. 50, 547, 1983.

A. J. Foppiano and P. A. Bradley, Day-to-Day Variability of Riometer Absorption, J. Atmos. Terr. Phys. 46, 689, 1984.