Morphology of HF electrostatic turbulence sites in the Earth's foreshock: case events observations from the four points CLUSTER constellation
Abstract
High frequency fluctuating electric field upstream from the Earth bowshock at frequencies near the local electron plasma frequency Fpe but varying within a considerable range sim 0 1 to 1 3 Fpe have been observed in situ by several plasma wave instruments Referred to as Langmuir waves when found near the plasma frequency as upshifted or downshifted oscillations when found above or below Fpe they are associated with the flux of electrons which move upstream from the bowshock in the foreshock region The Cluster constellation offers a unique opportunity to perform a spatial-temporal analysis of the active sites of such electrostatic emissions We present case events taken at various sizes of the Cluster constellation 100 km 1000 km and 10 000 km spacecraft separation over a few minutes time interval in the foreshock region Although the emissions are quite sporadic in term of amplitude variations the global characteristics in term of frequency signatures can persist over a few seconds We can thus define regions or active sites of a given class of frequency signatures Changes from a given global signature to another are seen as temporal variations from the small size constellation all spacecraft being placed in the same site at the same time They appear as spatial variations from the large size constellation We shall present and discuss an analysis of a detailed properties of the spectral signatures frequency shift amplitude distribution spin modulation compared in particular with measured electron distribution b the
- Publication:
-
36th COSPAR Scientific Assembly
- Pub Date:
- 2006
- Bibcode:
- 2006cosp...36.2471D