Chorus and chorus‐like emissions seen by the ionospheric satellite DEMETER

Abstract

A lot of different emissions have been detected by the low‐altitude satellite DEMETER (Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions), and the aim of this paper is to study extremely low frequency (ELF) electromagnetic waves with elements drifting in frequency. It is shown that only some of them can be considered as usual chorus. These chorus elements are emitted in the equatorial plane, and their propagation analysis indicates that they are going downward at low altitudes in the ionosphere to be detected by the satellite. The study of one remarkable event recorded along the same orbit in both the Northern and the Southern Hemispheres on 8 May 2008 indicates that this propagation mechanism is reinforced at the location of the ionospheric trough, which corresponds to the plasmapause at higher altitudes. It has been observed that usual chorus elements at low frequencies are always in a frequency band which overlaps with a hiss band limited by a frequency cutoff close to the proton gyrofrequency. Other drifting elements can be attributed to emissions triggered by PLHR (power line harmonic radiation). It means that without a high‐resolution spectral analysis, chorus‐like elements triggered by PLHR can be wrongly considered as natural chorus. These drifting elements can also appear as filamentary structures emerging at the upper frequencies of a hiss band or quasiperiodic emissions. There are events where the elements even have certain similarities to quasiperiodic emissions. The difference between these elements and the chorus emissions will be emphasized.

EMIC Waves Converted From Equatorial Noise Due to M/Q = 2 Ions in the Plasmasphere: Observations From Van Allen Probes and Arase

“…The spectral matrix is estimated from the frequency analysis of the EFW waveform data. In this study, the singular value decomposition (SVD) method (Parrot et al, ; Santolik et al, ; Santolik & Gurnett, ) is used to derive the wave propagation characteristics. The polarization, wave normal angles, and magnetic planarity are derived from the magnetic spectral matrix.…”

“…Considering that the local crossover frequency depends on the L‐shell (Horne & Throne, ; Matsuda et al, ), it is expected that the RH polarization of EN emissions should readily change to LH polarization during its radial propagation toward Earth inside the plasmasphere (Parrot et al, ; Santolik & Parrot, , ). In fact, Santolík et al () reported that the polarization reversal of the whistler is decoupled from the low‐frequency magnetosonic branch at low‐altitudes from the DEMETER observations.…”

Simultaneous Observations of ELF/VLF Rising‐Tone Quasiperiodic Waves and Energetic Electron Precipitations in the High‐Latitude Upper Ionosphere

“…The high‐latitude ionosphere (geomagnetic latitudes over ~50°) is a highly dynamic region because of the energetic particle precipitation from the radiation belts and a variety of intense electromagnetic emissions, especially the whistler‐mode waves in the extremely/very low frequency (ELF/VLF) range (e.g., Materassi et al, 2018 ; Parrot et al, 2014, 2016; Santolík et al, 2006). The most common and typical ELF/VLF whistler‐mode waves in the high‐latitude ionosphere include ionospheric hiss waves (Chen et al, 2017; Xia et al, 2019; Zhima et al, 2017), chorus waves (which occasionally appear) (Cao et al, 2005; Parrot et al, 2016; Santolík et al, 2006; Yang et al, 2008; Zhima et al, 2013), and quasiperiodic (QP) waves (e.g., Hayosh et al, 2014, 2013; Němec, Hospodarsky, et al, 2016, Němec, Bezděková, et al, 2016). In this paper, we studied the QP whistler‐mode waves in the ELF/VLF range based on the observations from the China Seismo‐Electromagnetic Satellite (CSES) satellite, which was launched in 2018 at an altitude of 507 km in the upper ionosphere.…”

Co-Existance of Lightning Generated Whistlers, Hiss and Lower Hybrid Noise Observed by e- POP (SWARM-E) –RRI

“…Whistler mode waves have been observed on the ground as well as on satellites [16,28,[36][37][38][39][40].…”