Magnetospheric amplification and emission triggering by ELF/VLF waves injected by the 3.6 MW HAARP ionospheric heater

Abstract

The HF dipole array of the High Frequency Active Auroral Research Program (HAARP) in Gakona, Alaska, was recently upgraded to 180 elements, facilitating operations at a total radiated power level of 3.6 MW and an effective radiated power of ∼575 MW. In the first experiments at the new power level, the HAARP array is used for magnetospheric wave injection. Modulated heating of auroral electrojet currents in the ionosphere yields radiation in the ELF/VLF frequency range. The HAARP-generated signals are injected into the magnetosphere, where they propagate in the whistler mode in field-aligned "ducts," allowing them to be observed at the conjugate point on a ship-borne receiver and on autonomous buoy platforms. The observation of the 1-hop signals is accompanied by the observation of associated 2-hop components in the northern hemisphere, which have reflected from the ionospheric boundary in the southern hemisphere. The observed signals are accompanied by triggered emissions and exhibit temporal amplification of 15-25 dB/s and bandwidth broadening to ∼50 Hz. Amplification occurs at injected signal frequencies selected in near real time on the basis of observations of natural emission activity, and only certain components of the frequency-time formats transmitted are amplified. Observations at multiple sites and dispersion analysis show that the signals are injected into the magnetosphere directly above the HF heater. The duration of echo observation and the prevalence of 1-hop observations are consistent with statistics from 1986 Siple Station experiments. The particle-trapping wave amplitude near the magnetic equator is estimated in the range 0.1-0.4 pT and gyroresonance with 10 keV-100 keV electrons. Copyright 2008 by the American Geophysical Union.