Tests of Time Evolutions in Deterministic Models, by Random Sampling of Space Plasma Phenomena

Abstract

We discuss general ideas, which can be used for estimating models for coherent time-evolutions by random sampling of data. They turn out to be particularly useful for interpreting data from instrumented spacecraft. These “new methods” are applied to examples of localized bursts of lower-hybrid waves and correlated density depletions observed on the FREJA satellite. In particular, lower-hybrid wave collapse is investigated. The statistical arguments are based on three distinct elements. Two are purely geometric, where the chord length distribution is determined for given cavity scales, together with the probability of encountering those scales. The third part of the argument is based on the actual time variation of scales predicted by the collapse model. The cavities are assumed to be uniformly distributed along the spacecraft trajectory, and it is assumed that they are encountered with equal probability at any time during the dynamical evolution. Cylindrical and ellipsoidal cavity models are discussed. It turns out that the collapsing cavity model can safely be ruled out on the basis of disagreement of data with the predicted cavity lengths and evolution time scales. Application to Langmuir wave collapse is suggested in order to check its reality and relevance.