Density modulated whistler mode emissions observed near the plasmapause

Abstract

Electron density fluctuations are regularly observed near the plasmapause together with electromagnetic waves below the electron cyclotron frequency (usually called hiss or chorus). Instruments on board CLUSTER spacecraft often observe two such emission bands with fluctuating wave intensities that suggest wave ducting in density enhancements as well as troughs. Near perigee the CLUSTER density measurements are usually limited to the electron density from 0.2 to 80 cm-3. To establish a correlation between density and wave intensity deeper inside the outer plasmasphere, we extrapolate the electron density from the spacecraft potential after fitting a relationship between observed plasma frequency and spacecraft potential. During a plasmapause crossing on June 5, 2001 (near the geomagnetic equator, L = 4 - 6, afternoon sector), density fluctuations up to hundreds cm-3 are found while whistler mode waves are observed in two separate frequency bands, at 100-500 Hz (correlated to the density fluctuations) and 3-6 kHz (anti-correlated).