Preliminary results of 400-MC radar investigations of auroral echoes at college, Alaska

Results of radar investigations of auroral ionization at a frequency of 398 mc are described. The radar detected auroral echoes at College, Alaska (near Fairbanks), even when the line of sight from the transmitter does not intersect the earth\´s magnetic field lines at perfect perpendicular incidence. The auroral echoes were observed with off-perpendicular intersection angles as great as . The requirement for near-perpendicular intersection of the radar beam with the earth\´s magnetic field is therefore met. The auroral echoes at 398 mc were seen frequently. Occasionally they were very strong; those of highest amplitude were as much as 27 db above the receiver noise level. The echoes were detected over a relatively large echoing region corresponding to bearings within of geomagnetic north, and elevation angles of . Two types of auroral echoes were observed-discrete and diffuse. The discrete echoes corresponded roughly to reflections from visual auroral forms seen at night. The diffuse echoes corresponded to reflections from a large echoing region that apparently existed most often during daylight hours. Estimates of the wavelength, , dependence of auroral echo power, although quite crude, are deduced as for the radar site at College, Alaska, and for sites where perpendicular reflection can be obtained.