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

Abstract

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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10\deg</tex> . 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pm 45\deg</tex> of geomagnetic north, and elevation angles of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0\deg-17\deg</tex> . 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, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda</tex> , dependence of auroral echo power, although quite crude, are deduced as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda^{10}</tex> for the radar site at College, Alaska, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda^{5}</tex> for sites where perpendicular reflection can be obtained.