Probing the Multiscale Structure and Evolution of Field-aligned Currents, Potentials and Plasma During Substorms Using Multipoint Cluster In-situ Observations and Auroral Images

We present auroral imaging data in combination with multipoint Cluster observations within and just above the auroral acceleration region (at or below 3 Re altitude) during substorms. Particular emphasis is on the spatial structuring and dynamical evolution of field-aligned currents, plasma constituents, and potentials. Of interest is to better establish the relative importance of and/or to explore interrelationships between inverted-V and Alfvenic acceleration processes that occur during key stages of substorm development. We show that, in addition to playing active roles in driving substorm aurora, inverted-V and Alfvenic acceleration processes are causally linked. This is exemplified by the observation of the gross intensification and filamentation of a preexisting quasistatic arc current system to smaller-scale/dispersive Alfven waves during the initial onset period of a substorm. We also show examples that indicate Alfvenic variations may be an important precursor and over time may dissipate to form large-scale inverted-V structures characteristic of the quasi-static aurora. We will discuss key features such as the geometry, motion and scales of evolving field-aligned currents, electron distribution signatures, Alfvenic Poynting flux, and interrelationships between the electric and magnetic fields (e.g., E-B ratios, coherence, and phase response) that occur.