Cluster observations of ELF/VLF signals generated by modulated heating of the lower ionosphere with the HAARP HF transmitter

Abstract

Abstract.It is now well known that amplitude modulated HF transmissions into the ionosphere can be used to generate ELF/VLF signals using the so-called "electrojet antenna". Although most observations of the generated ELF/VLF signals have been made on the ground, several low and highaltitude satellite observations have also been reported (James et al., 1990). One of the important unknowns in the physics of ELF/VLF wave generation by ionospheric heating is the volume of the magnetosphere illuminated by the ELF/VLF waves. In an attempt to investigate this question further, ground-satellite conjunction experiments have recently been conducted using the four Cluster satellites and the HF heater of the High-Frequency Active Auroral Research Program (HAARP) facility in Gakona, Alaska. Being located on largely closed field lines at L≈4.9, HAARP is currently also being used for ground-to-ground type of ELF/VLF waveinjection experiments, and will be increasingly used for this purpose as it is now being upgraded for higher power operation. In this paper, we describe the HAARP installation and present recent results of the HAARP-Cluster experiments. We give an overview of the detected ELF/VLF signals at Cluster, and a possible explanation of the spectral signature detected, as well as the determination of the location of the point of injection of the HAARP ELF/VLF signals into the magnetosphere using ray tracing.

HF modulated ionospheric currents

“…439-442]. This determination is consistent with previous satellite measurements of radiation detected on satellites above a modulated ionosphere Platino et al, 2004].…”

Powerful electromagnetic waves for active environmental research in geospace

“…ELF/VLF waves produced by auroral electrojet modulation with the HAARP facility were detected by the Cluster satellites at a radial distance of 27,000–29,000 km immediately outside the plasmapause [ Platino et al , 2004]. It is suggested that high magnetic activity might by necessary for the detection of HAARP‐generated ELF/VLF signals beyond L ∼ 4.…”

Generation of whistler waves by continuous HF heating of the upper ionosphere

“…The generation of electromagnetic waves in the ELF/VLF frequency range by modulated HF heating of the ionospheric plasma has been the subject of many studies. Experiments and theory revealed that three completely different physical processes control their generation: (1) electrojet current modulation, which relies on modulated HF heating of the D/E region plasma electrons in the presence of electrojet currents, capable of VLF generation up to 10-20 kHz [Rietveld et al, 1986;Barr et al, 1985;Papadopoulos and Chang, 1985;Papadopoulos et al, 1990Papadopoulos et al, , 2003Papadopoulos et al, , 2005Platino et al, 2004Platino et al, , 2006Piddyachiy et al, 2008;Cohen et al, 2011;Cohen and Golkowski, 2013]; (2) ionospheric current drive [Papadopoulos et al, 2011a[Papadopoulos et al, , 2011b, which relies on modulated heating of the electron temperature in the F region, is independent of the presence of electrojet currents and capable of ELF generation up to 60 Hz; and (3) excitation of the thermal cubic nonlinearity is an additional electrojet-independent mechanism for generating ELF/VLF waves [Moore et al, 2013].…”