Spectral features of lightning‐induced ion cyclotron waves at low latitudes: DEMETER observations and simulation

Abstract

[1] We use a comprehensive analysis of 6-component ELF wave data from the DEMETER satellite to study proton whistlers, placing emphasis on low-latitude events originating from lightning strokes in the hemisphere opposite to the hemisphere of observation. In this case, the formation of proton whistlers does not involve mode conversion caused by a strong mode coupling at a crossover frequency, although a polarization reversal remains an important element in formation of the phenomenon. DEMETER measurements of the six electromagnetic field components in the frequency band below 1000 Hz make it possible to determine not only the dynamic spectrum, but also the wave polarization, the wave normal angle, and the normalized parallel component of the Poynting vector. This permits us to address fine features of proton whistlers, in particular, we show that the deviation of the upper cutoff frequency from the equatorial cyclotron frequency is related to the Doppler shift. Experimental study of proton whistlers is supplemented by an investigation of ion cyclotron wave propagation in a multicomponent magnetoplasma and by numerical modeling of spectrograms, both in the frame of geometrical optics.

Ionospherically reflected proton whistlers

“…The values of the wave refractive index for the first signal are ∼ 200–300, while for the second one N ∼ 600–800, which is consistent with the fact that proton cyclotron waves forming proton whistlers turn into resonance regime of propagation very fast, already after one hop, becoming quasi‐electrostatic and therefore strongly attenuating [see, e.g., Shklyar et al , ].…”

“…For oblique ion cyclotron wave propagation in collisionless plasma, the mode conversion is inessential, but it may become significant if the collisions are taken into account; this question has been studied by Jones []. More detailed account of experimental and theoretical developments related to proton whistlers may be found in Shklyar et al [] where the authors returned to the problem of proton whistlers using a comprehensive analysis of six‐component ELF wave data from the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite.…”

“…In this paper, we present the first experimental observation of IRPW found in ELF data from DEMETER. We perform the wave data analysis similar to that of Shklyar et al [], which permits to determine, along with the spectral intensity of electromagnetic field, several additional wave characteristics such as the wave normal angle, polarization, wave refractive index, and parallel component of the Poynting flux. The analysis of experimental data is based on consideration of ion cyclotron wave propagation and is supplemented by numerical modeling of all wave properties displayed on real spectrograms.…”

Propagation of equatorial noise to low altitudes: Decoupling from the magnetosonic mode

“…Propagation of this type of waves has been analyzed in detail from the DEMETER data previously [Santolík et al, 2008[Santolík et al, , 2009Shklyar et al, 2012]. A structure of strong electromagnetic spectral lines is well seen in the first part of the time interval before 03:33 UT at frequencies of 150-250 Hz, with a lowintensity emission spanning up to 400 Hz.…”

Circulation of Heavy Ions and Their Dynamical Effects in the Magnetosphere: Recent Observations and Models

“…Recently, a new mechanism of ion energization due to interaction with lightning-induced emission has been considered (Shklyar and Kuzichev 2014). A part of the electromagnetic energy induced by lightning in the ELF frequency band penetrates into the low-altitude magnetosphere and starts propagating there as slow ion cyclotron waves (see, e.g., Shklyar et al 2012, and references therein). A feature of these waves is that they propagate almost along the geomagnetic field lines, and they have resonance at the gyrofrequency of each sort of ions at which the wave refractive index N = kc/ω goes to infinity.…”