The latitude dependence of auroral roar


  • J. M. Hughes,

  • J. LaBelle


LF/MF/HF radio receivers at many sites which extend from 66.5° to 79.9° invariant allow a statistical study of the variation of 2ƒce and 3ƒce auroral roar with latitude. At each of the sites, the frequency distribution is found to be approximately Gaussian, and the center frequencies of the distributions increase with the magnitude of the local geomagnetic field, as expected if the waves are associated with electron gyroharmonics. Furthermore, peak occurrence rates of 2ƒce auroral roar are found at 75°–76° invariant and show a strong correlation with Kp, including a 27-day periodicity. These data establish that auroral roar is associated with electron gyrofrequency harmonics and suggest that 2ƒce auroral roar originates near 275 km if it is generated at the second gyroharmonic.