Generation of the narrowband electrostatic noise in the geomagnetic tail: Geotail observations

The wave‐particle interactions involved in the generation of narrowband electrostatic noise (NEN) are discussed in the context of plasma waves and plasma measurements by Geotail spacecraft. NEN is characterized by its frequency spectrum which ranges from ƒpi to ƒpe, where ƒpi and ƒpe represent the ion and electron plasma frequencies, respectively. For this frequency range, no standard electrostatic plasma wave mode exists that propagates in the direction parallel to the ambient magnetic field. The present paper shows the early results from our examination of the correlation between the simultaneously observed NEN and plasmas. We demonstrate the strong correlation between NEN emissions and the occurrence of “structures” in the electron pitch angle distributions. Our observation results indicate that NEN is excited by the electron velocity space hole mode and support the results based on the collaboration between electron measurements and computer simulations which were presented by Yin et al. [1999].