Dr. Pierrette Décréau (LPCE-CNRS, Orléans, France)
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The electron foreshock region is the part of the solar wind connected magnetically to the terrestrial bow shock, under a plasma regime characterized by the presence of reflected electrons moving sunward, upstream of the bow shock. Such conditions create plasma instabilities resulting in bursts of electrostatic waves at or near the electron plasma frequency Fp, as discovered with the OGO 5 spacecraft. The so called down-shifted emissions (at frequencies below Fp) and up-shifted emissions (at frequencies above Fp) have been studied using data from the ISEE-1 mission, in relation with the electron populations observed simultaneously. These studies, as well as simulations efforts published later, indicate that local properties of electron populations and wave emissions are evolving according to the observer position in a map of the electron foreshock region. After a short review of fundamental studies, I will present a series of CLUSTER observations in the electron foreshock region, and show progresses made in the knowledge of this region, in particular due to the multipoint capabilities of CLUSTER and to the high resolution of available measurements. I will discuss pending questions still unresolved, like the exact nature of wave- particle interactions at work, and whether local properties could be used as remote sensing the foreshock boundaries and its global morphology. Another region of dayside magnetosphere, the magnetosheath, display bursts of electrostatic emissions discovered with CLUSTER HF wave instruments, at frequencies always larger than Fp. As a first step to a search of a possible generation mechanism, I will present detailed properties of those emissions, which, compared to the up-shifted foreshock emissions, show significant differences in the wave signatures, as well as in associated global plasma conditions. |
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