Equatorial noise emissions observed by the DEMETER spacecraft during geomagnetic storms

Abstract

Equatorial noise emissions are electromagnetic waves routinely observed in the equatorial region of the inner magnetosphere at frequencies between the proton cyclotron frequency and the lower hybrid frequency. Their observations are, however, typically limited to radial distances larger than about 2RE. We use the data measured by the low-altitude DEMETER spacecraft (altitude of about 700 km) to confirm that during periods of enhanced geomagnetic activity, these emissions penetrate down to low radial distances and eventually become a dominant wave emission close to the proton cyclotron frequency in the equatorial region. Wave data obtained during six intense geomagnetic storms (Dst