The role of ducted whistlers in the precipitation loss and equilibrium flux of radiation belt electrons

Abstract

New experimental evidence suggests that every ducted whistler component may precipitate bursts of radiation belt electrons into geomagnetically conjugate ionospheric regions. Strong spatial and temporal associations are seen between transient ionospheric disturbances observed in conjugate regions and ducted whistlers monitored at Palmer Station, Antarctica. The ionospheric disturbances were detected by their characteristic perturbing effects (“Trimpi events”) on subionospheric VLF, LF, and MF signals recorded at Palmer Station and at northern hemisphere sites. Of 74 such events examined on four different days, all were time‐associated with ducted whistlers. In no case was the arrival azimuth or dispersion of the associated whistlers inconsistent with the locations of the conjugate ionospheric disturbances, which were inferred from the configuration of perturbed signal paths. Other whistlers occurring independently of detected disturbances were found to be either weak or to have arrived from regions where a disturbance would not have been detected for lack of monitored signal paths. Signal perturbation onset behavior was consistent with multiple regions of precipitation induced by components of multipath whistlers and with theoretical predictions for ducted whistler‐induced precipitation. The results not only support the hypothesis that ducted whistlers are responsible for burst precipitation of energetic electrons but imply that such bursts may be induced by every ducted whistler component. Since radio energy from a lightning discharge can excite whistler ducts located 2500 km or more away from the flash, every ducted whistler observed at Palmer Station may indicate the presence of precipitation bursts associated one‐to‐one with excited whistler ducts distributed over a 5000‐km‐wide portion of the Earth's surface, and over its geomagnetic conjugate as well. The estimated effect of this precipitation on 70‐ to 200‐keV radiation belt electron populations for 2 < L < 3 is comparable to that predicted as a result of plasmaspheric hiss, indicating that ducted whistlers may contribute as significantly as hiss to radiation belt equilibrium at those electron energies.