Proton cyclotron echoes and spurs observed on Alouette II and ISIS II


  • R. E. Horita


Proton cyclotron echoes and spurs observed on the topside sounder ionograms on the Canadian Alouette and ISIS satellites are phenomena related to the proton cyclotron frequency. They appear on the ionograms at apparent ranges which lead to a frequency close to the proton cyclotron frequency; the frequency is calculated by taking the reciprocal of the time elapsed between the transmission of the sounder pulse and the reception of the signal at the satellite. Most proton cyclotron echoes and spurs occur at frequencies below the electron plasma frequency, ƒN; the echoes occur predominantly at frequencies slightly above the electron cyclotron frequency, ƒH, while the spurs occur predominantly when a harmonic of ƒH is near ƒN. Over 1000 ionograms exhibiting proton cyclotron echoes and/or spurs were examined and were classified depending on apparent range and shape of the echoes or spurs. The major classifications were echoes only, spurs only, and spur-echo combinations. The subclassifications include one new type of spur which occurs at frequencies above ƒN. The classifications also reveal the absence of echoes with apparent ranges less than those corresponding to the calculated proton gyroperiod in the vicinity of the satellite. These results are compared with theories for the generation mechanism for proton cyclotron echoes and spurs.