Probability Distributions of Langmuir Waves in Type II and III sources

Type II and III Solar radio bursts involve streaming electrons that produce Langmuir waves that then couple wave energy into radio emission. These Langmuir waves can be driven to large enough amplitudes that they undergo electrostatic (ES) decay into a backward propagating Langmuir wave and forward propagating ion acoustic wave. The forward and backwards propagating Langmuir waves can then 'beat' together to produce characteristic Langmuir waveforms and spectra, plus radio emission. Stochastic growth theory (SGT) predicts that the probability distribution of the Langmuir wave electric field strength should be lognormal, with known modifications if non-linear processes like ES decay are occurring. Other analyses suggest Pearson distributions may be relevant. Here, previous work on Langmuir waves in type II and III source regions is generalized and tested by analysing the probability distributions of the waveforms of Langmuir waves observed by the STEREO spacecraft. The Nelder-Mead fitting technique is used with various appropriate goodness of fit tests to assess the statistical significance of the fits. The results for the Langmuir wave probability distributions are compared with previous work on Langmuir wave spectra that identified periods with ES decay. The results to date show that the type II and III Langmuir events for which spectral analyses provide evidence of ES decay also show probability distributions consistent with the combination of SGT and a nonlinear process like ES decay. Fits to Pearson distributions and comparisons with pure and nonlinear SGT are ongoing, as are the statistics and interpretations of events with and without evidence for SGT and/or nonlinear processes.