Scale Sizes of Intense Auroral Electric Field Structures

The scale sizes of intense (> 0.15 V/m, mapped to the ionosphere), high-altitude (4-7 earth radii geocentric distance) auroral electric fields (measured by the Cluster EFW instrument) have been determined in a statistical Study. Monopolar and bipolar electric fields, and converging and diverging events, are seperated. The relation between the scale size and the potential variation is investigated. The calculated electric field scale sizes are compared with the scale sizes of the associated filed-aligned currents (FACs). The influence of, or relation between, other parameters (proton gyroradius, particle tempratures, plasma density gradients, ionospheric conductivity and geomagnetic activity), and the E-field scale sizes are considered. Early results indicate that the typical scale sizes of these auroral electric field structures (4 km) are similar to the scale sizes of the associated FACs (3 km), the size of the density gradients (4 km) and the proton gyroradius at these times and locations (2 km). (All values mapped to the ionosphere.)