Radio echoes from auroral ionization detected at relatively low geomagnetic latitudes

High-frequency radio echoes from ionization associated with the Aurora Borealis have been identified at Stanford University (geomagnetic latitude
43.75\deg
). The echoes occur at ranges between 1400 km and 4700 km corresponding to reflection from ionization in the zone of maximum auroral occurrence located far to the north of Stanford. The formation of the ionization is attributed to the bombardment of the upper atmosphere by high-speed charged particles emitted from the sun. The echoes have great amplitudes with duration times between one second and one hour. Their appearance and disappearance is quite similar to the behavior of visual auroras; the occurrence of the echoes has been found to be related to geomagnetic disturbances. The heights of reflection appear to be between 100 km and 1200 km above the surface of the earth. The paths which the auroral signals travel over the relatively enormous distance from Stanford to the auroral zone (and back) are greatly influenced by the presence of the normal ionospheric layers. The echoes have been observed at ranges and bearings which indicate reflection from ionization at points along the auroral zone all the way from eastern Canada to Alaska.