LANGMUIR TURBULENCE IN THE AURORAL IONOSPHERE .2. NONLINEAR-THEORY AND SIMULATIONS

A theoretical interpretation of sounding rocket measurements of intense Langmuir wave fields (less-than-or-equal-to 500 mV/m) driven by a stream of 20 eV - 4 keV electrons in the lower auroral zone is developed. This interpretation is based on the ability of the 10 mus sampling rate of the wave detector to temporally resolve the structure of the Langmuir wave field envelope. A modified form of the Zakharov equations is used to numerically study beam-driven Langmuir turbulence in the presence of a moderate magnetic field (OMEGA(e) almost-equal-to omega(pe)). Strong Landau damping on observed nonthermal scattered electrons, which is treated in a companion paper (Newman et al., this issue), plays an important role by inhibiting backscatter cascade and the development of strong turbulence. A parameterized model of the linear electron stream-driven wave instability is introduced, which incorporates limited quasilinear plateau formation. A reasonable set of parameters is found that yields semiquantitative agreement between observed properties of the Langmuir fields and the results of Zakharov equation simulations, including the amplitude and characteristic frequency of the electric field envelope modulations.