Experiments and theory on parametric instabilities excited in HF heating experiments at HAARP

Abstract

Parametric instabilities excited by O-mode HF heater and the induced ionospheric modification were explored via HAARP digisonde operated in a fast mode. The impact of excited Langmuir waves and upper hybrid waves on the ionosphere are manifested by bumps in the virtual spread, which expand the ionogram echoes upward as much as 140 km and the downward range spread of the sounding echoes, which exceeds 50 km over a significant frequency range. The theory of parametric instabilities is presented. The theory identifies the ionogram bump located between the 3.2 MHz heater frequency and the upper hybrid resonance frequency and the bump below the upper hybrid resonance frequency to be associated with the Langmuir and upper hybrid instabilities, respectively. The Langmuir bump is located close to the upper hybrid resonance frequency, rather than to the heater frequency, consistent with the theory. Each bump in the virtual height spread of the ionogram is similar to the cusp occurring in daytime ionograms at the E-F2 layer transition, indicating that there is a small ledge in the density profile similar to E-F2 layer transitions. The experimental results also show that the strong impact of the upper hybrid instability on the ionosphere can suppress the Langmuir instability. V C 2014 AIP Publishing LLC.

First observations of electron gyro-harmonic effects under X-mode HF pumping the high latitude ionospheric F-region

“…while the electric field of the X-mode pump wave is perpendicular to the magnetic field 76 (Robinson, 1989;DuBois et al, 1990;Stubbe, 1996;Gurevich, 2007;Kuo et al 2014). …”

A theoretical investigation on the parametric instability excited by X‐mode polarized electromagnetic wave at Tromsø

“…While the pump wave with ordinary polarization (O-mode) has been extensively studied to explain the excitation of parametric instability in the past decades [Perkins et al, 1974;Fejer, 1979;Fejer and Leer, 1972;Kuo, 1996Kuo, , 2002Kuo, , 2015Kuo et al, 1983Kuo et al, , 2014Bryers et al, 2013], the extraordinary polarized (X-mode) pump wave has been considered not to be able to excite Langmuir wave near its reflection height due to the frequency matching condition not being satisfied [Kuo, 2015]. The issue with the excitation of Langmuir parametric decay instability (PDI) and Langmuir oscillating two-stream instability (OTSI) by X-mode heating is due to the fact that the plasma frequency near X-mode pump wave reflection height is less than the heater frequency, thus not satisfying the frequency matching condition.…”

A numerical study of large‐scale ionospheric modulation due to the thermal process by powerful wave heating

“…Parametric instabilities are the principal mechanisms for most of the nonlinear ionospheric heating phenomena, including mode conversion, anomalous absorption, enhanced plasma line, SEEs, enhanced airglow, Langmuir turbulence, and small‐scale FAIs (meter scale and less) [ Kuo , , and references therein]. Different from ohmic absorption and self‐focusing instability, parametric instability is a nonthermal process prevailing in the reflection region, where electrodynamics and electrostatic processes dominate at all the stages [ Perkins et al ., ; Fejer , ; Gurevich et al ., , ; Kuo et al ., ]. The time scale of parametric instability is much less than the thermal process in ionospheric heating [ Eliasson and Thidé , ; Eliasson et al ., ; Eliasson , ].…”