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

The wave-particle interactions involved in the generation of narrowband ele ctrostatic noise (NEN) are discussed in the context of plasma waves and pla sma measurements by Geotail spacecraft. NEN is characterized by its frequen cy spectrum which ranges from f(pi) to f(pe), where f(pi) and f(pe) represe nt the ion and electron plasma frequencies, respectively. For this frequenc y 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 correla tion between NEN emissions and the occurrence of "structures" in the electr on pitch angle distributions. Our observation results indicate that NEN is excited by the electron velocity space hole mode and support the results ba sed on the collaboration between electron measurements and computer simulat ions which were presented by Yin et al. [1999].