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Amplitude and phase of nonlinear magnetospheric wave growth excited by the HAARP HF heater

2010; American Geophysical Union; Volume: 115; Issue: A2 Linguagem: Inglês

10.1029/2009ja014610

2156-2202

Mark Gołkowski, U. S. Inan, M. B. Cohen, A. R. Gibby,

Solar and Space Plasma Dynamics

The High Frequency Active Auroral Research Program (HAARP) HF ionospheric heater is used to inject ELF/VLF signals into the magnetosphere to study wave‐particle interactions that lead to nonlinear amplification. HAARP‐generated whistler mode “echoes” are observed after twice crossing the equatorial plane in magnetospheric ducts. The magnetospheric paths traversed by the signals are determined to be in the range 5.06 < L < 5.19 with associated cold plasma densities of 177 cm −3 < N eq < 185 cm −3 . The amplitude and phase of the echoes are observed to exhibit exponential temporal increase. A decrease in input amplitude by 14 dB is observed to yield a delay in onset of nonlinear growth by ∼1 s. Nonlinear theory of cyclotron resonant currents formed by electrons phase trapped in the potential well of the input wave is used to analyze the simultaneous evolution of amplitude and phase of the observations. The average nonlinear resonant current vector is found to rotate in relation to the input wavefields during growth, and the magnetospheric linear growth rate is estimated to be 31–45 dB/s.