Langmuir turbulence in moderately magnetized space plasmas*

Beam-driven Langmuir turbulence is studied in two moderately magnetized (Ωe≊ωe) space-plasma regimes: regions of the lower solar corona and the Earth’s auroral ionosphere. The turbulence is modeled using modified Zakharov equations, which are employed in two-dimensional numerical simulations. For coronal parameters, highly anisotropic coherent wave packets form and collapse when Ωe<ωe. By contrast, the turbulence is phase incoherent when Ωe≳ωe, as a result of change in the topology of the Langmuir dispersion relation. In the auroral ionosphere, intense Langmuir waves (up to 500 mV/m) have been measured, in conjunction with field-aligned electron streams and nonthermal electron tails. Approximate agreement with high-time-resolution electric-field measurements, is found in the simulations. However, because of strong damping on nonthermal electrons, wave collapse is inhibited, irrespective of the ordering of Ωe and ωe.