Investigations of Plasma Flow Spatial Scales Using the Cluster Electron Drift Instrument

The character of the flow of plasma within the Earth's magnetosphere is of fundamental importance to the distribution and flow of energy within this system. Two dimensional fluid turbulence theory predicts that energy applied at a given scale length will cascade to larger scales whereas enstrophy will cascade to smaller scales. The uncertainty in equating two dimensional fluid theory to space plasmas arises from the limited analysis that can be performed with single spacecraft measurements. However, with multi-spacecraft measurements such as Cluster, we are able to expand our understanding of plasma flow as a directly measurable function of separation between payloads. The Electron Drift Instrument on board each Cluster satellite directly measures electron drift utilizing a test particle population. From this measurement the plasma flow velocity vector perpendicular to the ambient magnetic field is derived. To further the understanding as to the importance of flow turbulence within the magnetosphere, this study analyzes the structure within plasma flows measured in high latitude crossings. The velocities are correlated as a function of position using multi baseline payload separations and time to determine flow correlations at various scale lengths. This analysis is used to compare with two dimensional fluid turbulence theory as well as for deriving an insight into the scale lengths of flow structures within the magnetosphere. Results suggest energy deposition in a scale range of 5 - 15 km with an approximate -5/3 power law energy cascade to larger scales.