H. E. Laakso

Identifying the source region of plasmaspheric hiss

The presence of the plasmaspheric hiss emission around the Earth has been known for more than 50 years but its origin has remained unknown in terms of source location and mechanism. The hiss, made of whistler mode waves, exists for most of the time in the plasmasphere and is believed to control the radiation belt surrounding the Earth which makes its understanding very important. This paper presents direct observational evidence that the plasmaspheric hiss originates in the equatorial region of the plasmaspheric drainage plumes. It shows that the emissions propagate along the magnetic field lines and away from the equator in the plumes but towards the equator at lower L shells inside the plasmasphere. The observations also suggest that the hiss waves inside the plasmasphere are absorbed as they cross the equator.

Shall we carry sounders onboard future magnetospheric missions? Lessons learned from Cluster

Since 2000, the four ESA/NASA Cluster satellites orbit the Earth from 20 Re down to 1 Re. Each spacecraft is equipped with the same set of 11 plasma instruments, among which a relaxation sounder named WHISPER. Scientific highlights, where WHISPER data played a key role, will be first presented with an emphasis on plasmaspheric wave research [1]. Then, we will illustrate how WHISPER is key to estimate the electron density in various regions (sometimes unforeseen) of the magnetosphere, on its own and in conjunction with other plasma instruments [2]. These lessons learned from Cluster will help to answer the following question: shall we carry sounders onboard future magnetospheric missions?