Coherent whistler emissions in the magnetosphere – Cluster observations

Abstract

Abstract. The STAFF-SC observations complemented by the data from other instruments on Cluster spacecraft were used to study the main properties of magnetospheric lion roars: sporadic bursts of whistler emissions at f ∼0.1−0.2f e where f e is the electron gyrofrequency. Magnetospheric lion roars are shown to be similar to the emissions in the magnetosheath while the conditions for their generation are much less favorable: the growth rate of the cyclotron temperature anisotropy instability is much smaller due to a smaller number of the resonant electrons. This implies a nonlinear mechanism of generation of the observed wave emissions. It is shown that the observed whistler turbulence, in reality, consists of many nearly monochromatic wave packets. It is suggested that these structures are nonlinear Gendrin's whistler solitary waves. Properties of these waves are widely discussed. Since the group velocity of Gendrin's waves is aligned with the magnetic field, these well guided wave packets can propagate through many magnetic "bottles" associated with mirror structures, without being trapped.

Beam-excited whistler waves at oblique propagation with relation to STEREO radiation belt observations

“…In particular, it means, that the wavelength is specified by kc/ω e ∼ 1, which is clear evidence of Gendrin mode waves and their importance for whistler wave emission. This aspect has also been discussed in the paper by Dubinin et al (2007).…”

Whistler-Langmuir oscillitons and their relation to auroral hiss

“…An important lesson we have learned is that the predictions of linear instability theory say very little about the wave characteristics under the conditions of nonlinear saturation and may even be misleading. Our main finding is that Gendrin modes and related oscillitons seem to play an essential role in characterizing the final nonlinear state of the system (Sydora et al, 2007;Dubinin et al, 2007;Stenzel et al, 2008;Verkhoglyadova and Tsurutani, 2009;Sauer and Sydora, 2010). In this respect many further applications (such as electron and ion cyclotron harmonic waves, multi-ion waves etc.)…”

“…Up to now, the most compelling measurements have been done using the whistler wave branch. In the paper by Dubinin et al (2007) the appearance of wave packets in the Earth's magnetosphere has been explained in terms of whistler oscillitons driven by temperature anisotropy. Subsequent kinetic simulations by Sydora et al (2007) have shown that during the nonlinear saturation of the temperature anisotropy instability a significant wave number shift (from large k values) to the Gendrin point (where phase and group velocity coincide) takes place accompanied by the formation of whistler oscillitons.…”

Three dimensional character of whistler turbulence

“…Therefore, evolution of electromagnetic turbulence is important to both space and laboratory plasmas and has been a topic of intense research for decades. Electromagnetic whistler turbulence in the intermediate frequency range, ⍀ i Ӷ Ӷ⍀ e , where ⍀ i͑e͒ are ion ͑electron͒ gyrofrequency, continues to be of interest to ionospheric, 1,2 magnetospheric, and solar wind plasmas [3][4][5] as well as to laboratory plasmas. 6,7 The purpose of this article is to show that the dominant nonlinear ͑NL͒ effect makes whistler turbulence in a low ␤ plasma, similar to that found in the near-earth space environment, a three-dimensional ͑3D͒ phenomenon in which the evolution of the turbulence is characterized by induced NL scattering.…”