The geometry of auroral communications

As early as 1939, radio amateurs found auroral ionization useful for communication purposes. Such ionization makes hf and vhf propagation possible over paths as great as several hundred kilometers when other more normal ionospheric propagation modes do not exist. The geometry of reflection is investigated for a variety of transmitter locations based upon the assumption of specular reflection from columnar ionization aligned with the earth´s magnetic field lines. The results of the investigations outline the region of useful auroral ionization and the regions on the earth within which the auroral propagation is possible. The probability has been determined of obtaining propagation from a particular transmitter location to any receiver location within the region of propagation. These geometrical studies allow the communicator to predict the most useful transmitter and receiver locations in utilizing auroral ionization for communication purposes. The studies also may suggest methods of minimizing the effects of auroral propagation when it is considered a detrimental propagating mode, for example, when it results in undesirable multipath effects.