FIRST TEST OF STOCHASTIC GROWTH THEORY FOR LANGMUIR-WAVES IN EARTHS FORESHOCK

This paper presents the first test of whether stochastic growth theory (SGT) can explain the detailed characteristics of Langmuir-like waves in Earth's foreshock. A period with unusually constant solar wind mag netic field is analyzed. The observed distributions P (log E) of wave fields E for two intervals with relatively constant spacecraft locatio n (DIFF) are shown to agree well with the fundamental prediction of SG T, that P (log E) is Gaussian in log E. This stochastic growth can be accounted for semi-quantitatively in terms of standard foreshock beam parameters and a model developed for interplanetary type III bursts. A veraged over the entire period with large variations in DIFF, the P (l og E) distribution is a power-law with index similar to -1; this is in terpreted in terms of convolution of intrinsic, spatially varying P (l og E) distributions with a probability function describing ISEE's resi dence time at a given DIFF. Wave data from this interval thus provide good observational evidence that SGT can sometimes explain the clumpin g, burstiness, persistence, and highly variable fields of the foreshoc k Langmuir-like waves.