Small-scale auroral arc distortions

摘要: Small-scale spatially periodic distortions of auroral forms have been studied utilizing low-light level television observations made at various locations in the Northern and Southern Hemispheres. The most commonly observed features were folds vortex-like curl formations. curls, identified here with Kelvin-Helmholtz instability due to fluid shear, invariably had a counterclockwise rotational shape motion when viewed direction anti-parallel Earth's magnetic field. typical measured wavelength (∼5 km) growth rate (4.2 sec−1) used evaluate dispersion relation for apparent shear ωs = ∂ νx∂y (28 sec−1). horizontal velocities both (0–5 km/sec) curls (0–22 be respect multiple arc centre antiparallel B. Consistent agreement between suggests that closely approximate actual values. If results from E×B drifts space charge field, calculated value ωs, implies an unneutralized electron density ∼0–1 cm−3 ΔE across element ∼500mV/m. velocity measurements indicate values individual elements can combine produce transient electric fields edges arcs as high 1000 mV/m.