Waveforms of Langmuir turbulence in inhomogeneous solar wind plasmas

Abstract

Modulated Langmuir waveforms have been observed by several spacecraft in various regions of the heliosphere, such as the solar wind, the electron foreshock, the magnetotail, or the auroral ionosphere. Many observations revealed the bursty nature of these waves, which appear to be highly modulated, localized, and clumped into spikes with peak amplitudes typically 3 orders of magnitude above the mean. The paper presents Langmuir waveforms calculated using a Hamiltonian model describing self-consistently the resonant interaction of an electron beam with Langmuir wave packets in a plasma with random density fluctuations. These waveforms, obtained for different profiles of density fluctuations and ranges of parameters relevant to solar type III electron beams and plasmas measured at 1 AU, are presented in the form they would appear if recorded by a satellite moving in the solar wind. Comparison with recent measurements by the STEREO and WIND satellites shows that their characteristic features are very similar to the observations.

Statistics of electric fields' amplitudes in Langmuir turbulence: A numerical simulation study

“…[ Krafft et al , ]. Recently, the dynamical model was used to study the resonant interaction of an electron beam with Langmuir wave packets in plasmas with random density fluctuations, under conditions typical of solar type III bursts regions [ Volokitin et al , ; Krafft et al , , ]. Comparison of the waveforms of the Langmuir waves obtained with recent measurements by the STEREO and Wind satellites showed that their characteristic features are very similar [ Krafft et al , ].…”

“…Recently, the dynamical model was used to study the resonant interaction of an electron beam with Langmuir wave packets in plasmas with random density fluctuations, under conditions typical of solar type III bursts regions [ Volokitin et al , ; Krafft et al , , ]. Comparison of the waveforms of the Langmuir waves obtained with recent measurements by the STEREO and Wind satellites showed that their characteristic features are very similar [ Krafft et al , ]. Moreover, the model was used to study the statistics of Langmuir waves when the decay instability is developed as well as particle acceleration and diffusion processes at work in the fluctuating plasma [ Krafft and Volokitin , ; Volokitin and Krafft , ].…”

Electron Acceleration by Langmuir Waves Produced by a Decay Cascade

“…In previous papers (Krafft et al 2015a(Krafft et al , 2015bKrafft & Volokitin 2016), the authors discussed the influence of the random density inhomogeneities of the background solar wind plasma on the Langmuir decay processes. In particular, it was shown thatif several aspects of the weak turbulence theory in uniform plasmas could be used to describe the phenomena (as, for example, the values of the wavenumbers of the product waves), some important differences were evidenced compared to the case of homogeneous or quasi-homogeneous plasmas.…”

Spatial distribution of Langmuir waves observed upstream of Saturn's bow shock by Cassini

“…These complicated spectra often have the form of the superposition of two or more spectral peaks. It is believed that these spectra result from the Doppler shift of back‐scattered waves, plasma density inhomogeneities [ Smith and Sime , ; Krasnoselskikh et al , ; Krafft et al , ; Voshchepynets et al , ], or nonlinear three‐wave interactions of two Langmuir waves with ion acoustic or transverse electromagnetic waves [ Robinson , ; Bale et al , ; Soucek et al , ; Graham and Cairns , , , and reference therein]. The presence of Langmuir waves has been reported in the upstream region of all planets from Venus to Neptune observed by a number of spacecraft including Voyager 1 and 2 [ Gurnett et al , ; Scarf et al , ; Gurnett et al , , ], Galileo [ Hospodarsky et al , ], Cassini [ Hospodarsky et al , ; Píša et al , ], Cluster [ Soucek et al , ; Sigsbee et al , ], Wind [ Bale et al , ], and STEREO [ Malaspina et al , ].…”