Determining the wavelength of Langmuir wave packets at the Earth's bow shock
- 1Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, UMR 6115 CNRS and University of Orléans, 3A avenue de la Recherche Scientifique, 45071 Orléans, France
- 2Physics Department and Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450, USA
Abstract. The propagation of Langmuir waves in plasmas is known to be sensitive to density fluctuations. Such fluctuations may lead to the coexistence of wave pairs that have almost opposite wave-numbers in the vicinity of their reflection points. Using high frequency electric field measurements from the WIND satellite, we determine for the first time the wavelength of intense Langmuir wave packets that are generated upstream of the Earth's electron foreshock by energetic electron beams. Surprisingly, the wavelength is found to be 2 to 3 times larger than the value expected from standard theory. These values are consistent with the presence of strong inhomogeneities in the solar wind plasma rather than with the effect of weak beam instabilities.