GEM: Influence of Solar Wind and Modes of Geomagnetic Activity on Plasma Sheet Turbulence

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A description of how electromagnetic energy stored in the magnetotail is transferred to plasma energy is critical to our understanding of the magnetosphere. Turbulence is known to be an effective mechanism for the heating of fluids and for the transfer of momentum and energy, but the role of turbulence in heating Earth's plasma sheet (PS) has not been well studied. Without measurements to characterize spatial and temporal variations independently, the existence of PS turbulence and its role in energy transport remain uncertain. This project will examine spacecraft data from PS crossing to determine the fluctuations in the magnetic field and assess the level of turbulence that is present. The project will examine how the strength of the turbulence correlates with geomagnetic activity. The project will empirically determine the effective magnetic Reynolds number and the energy transfer rate associated with the turbulent cascade. This study will use the multi-spacecraft aspect of the Cluster-II mission to partially separate temporal and spatial properties of turbulent PS fluctuations. To determine when the magnetic fluctuations are turbulent, the fluctuation amplitude will be compared to the mean field and the shape of the probability distribution functions. Turbulent fields are characterized by non-Gaussian probability distribution functions (PDFs). Scaling exponential functions and PDFs of the fluctuations at different spatial and temporal separations will be constructed to determine when intermittent turbulence is present. The correlation between the intensity of the turbulent fluctuations and the geomagnetic activity will be investigated. A similar study will be done with the solar wind parameters and the turbulent fluctuations. The overall importance of PS turbulence will be assessed by comparing the energy transfer rate with the total magnetospheric energy. In addition to correlating the turbulent fluctuations with the solar wind and geomagnetic activity, all the observations of each PS traversal observed by Cluster will be made available to the space physics community over the internet.