Ih. Cairns et Pa. Robinson, FIRST TEST OF STOCHASTIC GROWTH THEORY FOR LANGMUIR-WAVES IN EARTHS FORESHOCK, Geophysical research letters, 24(4), 1997, pp. 369-372
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.