The dependence of Langmuir wave amplitudes on position in Earth's foreshock

Abstract

We present the first results of Langmuir wave observations in the foreshock from the Cluster WBD Plasma Wave Receiver. When the data were binned by distance to the foreshock boundary, the Langmuir wave amplitude probability distributions followed the log-normal statistics predicted by stochastic growth theory for all regions of the foreshock. The Cluster data show for the first time that the centers of the probability distributions shift to lower amplitudes with increasing distance to the boundary, and that a spatially averaged power law distribution results from summing these distributions.