On the use of ELF/VLF emissions triggered by HAARP to simulate PLHR and to study associated MLR events

A spectrogram of Power Line Harmonic Radiation (PLHR) consists of a set of lines with frequency spacing corresponding exactly to 50 or 60 Hz. It is distinct from a spectrogram of Magnetospheric Line Radiation (MLR) where the lines are not equidistant and drift in frequency. PLHR and MLR propagate in the ionosphere and the magnetosphere and are recorded by ground experiments and satellites. If the source of PLHR is evident, the origin of the MLR is still under debate and the purpose of this paper is to understand how MLR lines are formed. The ELF waves triggered by High-frequency Active Auroral Research Program (HAARP) in the ionosphere are used to simulate lines (pulses of different lengths and different frequencies). Several receivers are utilized to survey the propagation of these pulses. The resulting waves are simultaneously recorded by ground-based experiments close to HAARP in Alaska, and by the low-altitude satellite DEMETER either above HAARP or its magnetically conjugate point. Six cases are presented which show that 2-hop echoes (pulses going back and forth in the magnetosphere) are very often observed. The pulses emitted by HAARP return in the Northern hemisphere with a time delay. A detailed spectral analysis shows that sidebands can be triggered and create elements with superposed frequency lines which drift in frequency during the propagation. These elements acting like quasi-periodic emissions are subjected to equatorial amplification and can trigger hooks and falling tones. At the end all these known physical processes lead to the formation of the observed MLR by HAARP pulses. It is shown that there is a tendency for the MLR frequencies of occurrence to be around 2 kHz although the exciting waves have been emitted at lower and higher frequencies. Graphical Abstract

WHISTLER-TRIGGERED VLF EMISSIONS RECORDED AT JAMMU DURING DAY TIME

Whistler-triggered VLF emissions recorded at low latitude station Jammu (Geomagnetic latitude = 220 26/ N; L = 1.17) during day time period on 19th February 1999 at 14:35 hrs. IST. The recorded data have been analyzed. Based on whistler-triggered VLF emissions spectrum, the VLF waves propagate along the path with L – values lying between L = 4.4 and 4.38. During the observation period, magnetic activity was very high. Mostly these types of emissions recorded at mid latitudes. These whistler-triggered emission waves propagate along the geomagnetic field lines either in a ducted mode or in a pro-longitudinal mode. Relative amplitude of whistlers waves is almost equal to relative amplitude of triggered emissions. The proposed generation mechanism explains through the dynamic spectra of the whistler-triggered emissions.

Unexpected high-frequency “birds”-type VLF emissions.

The new typeof daytime natural VLF whistler mode emissions of the magnetospheric origin was recently found in the VLF observations at Kannuslehto station (L ~ 5.5) in Northern Finland.These VLF events occurred at the frequencies above 4-5 kHzeven up to 15 kHz. Here we present the different spectra of this peculiar daytime high-frequency VLF emissions observed under quiet geomagnetic conditions at auroral latitudes at Kannuslehto (Finland) and Lovozero (Russia) stations. These high-frequency waves cannot be attributed to typical well known VLF chorus and hiss. They became visible on the spectrograms only after the filtering out sferics originating by the lightning discharges and hiding all natural high-frequency signals. After this filtering, it was found a large collection of different natural VLF signals observed as a sequence of right-polarized short (less than 1-2 minutes) patches at frequencies above 4-5 kHz, i.e. at higher frequencythan a half the equatorial electron gyrofrequency at the L-shell of Kannuslehto and Lovozero. These emissions were called “birds” due to their chirped sounds. It was established that the “birds” are typically occur during the daytime only under quiet space weather conditions. But in this time, small magnetic substorms were could be observed in the night sector of the Earth. Here we also show the recently observed series of the “bird-mode” emissions with various bizarre quasi-periodic dynamic spectra, sometimes consisting of two (and even more) frequency bands. The “birds” occur simultaneously at Kannuslehto and Lovozero with similar spectral structure demonstrating their common source. It seems that the “birds” emissions are generated deep inside the magnetosphere at the low L-shells. But the real nature, the generation region and propagation behavior of these VLF emissions remain still unknown. Moreover, nobody can explain how the waves could reach the ground at the auroral latitudes like Kannuslehto and Lovozero as well as which magnetospheric driver could generate this very complicated spectral feature of the emissions.