Properties, Structure and Dynamics of the Stagnant Exterior Cusp on February 19th, 2001: CLUSTER Multi-Instrument and Multi-Spacecraft Results.

Since the CLUSTER constellation launch during summer 2000, many different magnetospheric regions have been crossed. In particular, the data provided by the CIS (Cluster Ion Spectrometry) and FGM (FluxGate Magnetometer) experiments have permitted to highlight an important dayside region: the Stagnant Exterior Cusp (SEC). Indeed, on February 19, 2001, the CLUSTER fleet had both stable and transient encounters with this region. We will mainly show that this region has some major characteristics: a strong isotropy of the ion distribution functions and a very weak magnetic field (due to diamagnetic effect), that seems to present a vortex-like shaped structure. We will also present a dynamical study, showing both that this region is highly dynamic and rather stable, since it seems to be in equilibrium with the surrounding media (except for some boundary layers).