Statistical and case studies of radio emissions observed near 2ƒce and 3ƒce in the auroral zone

Abstract

Receivers located at Two Rivers, Alaska (64.9°N, 146.9°W), and Circle Hot Springs, Alaska (65.5°N, 144.7°W), have been used to monitor the spectrum between 0.05‐4.8 MHz for extended periods. Seasonal and diurnal effects of auroral roar, a weak narrow band radio emission near 2 and 3 times the ionospheric electron cyclotron frequency (ƒce), have been determined. Many individual auroral roar events correlate with magnetic activity, and superposed epoch analysis using planetary K indices shows a correlation between magnetic activity and auroral roar commencement. For a 3ƒce roar event on March 23, 1992, riometer, magnetometer, photometer, and all‐sky camera data are available and show that individual bursts of 3ƒce auroral roar are associated with intensifications of the aurora, as was known previously for 2ƒce roar. Finally, two possible generation mechanisms are investigated in detail: nonlinear interaction between lower hybrid and electrostatic upper hybrid waves producing electromagnetic waves, and the feasibility of a lower ionospheric decameter maser for direct generation of X mode waves at harmonics of ƒce.