In situ multi-satellite detection of coherent vortices as a manifestation of Alfvénic turbulence

Turbulence in fluids1 and plasmas2,3,4,5 is a ubiquitous phenomenon driven by a variety of sources—currents, sheared flows, gradients in density and temperature, and so on. Turbulence involves fluctuations of physical properties on many different scales, which interact nonlinearly to produce self-organized structures in the form of vortices2,3,4,5. Vortex motion in fluids and magnetized plasmas is typically governed by nonlinear equations2,3,4,5, examples of which include the Navier–Stokes equation1,2, the Charney–Hasegawa–Mima equations2,3,4,5 and their numerous generalizations6,7,8,9. These nonlinear equations admit solutions2,3,4,5 in the form of different types of vortices that are frequently observed in a variety of contexts: in atmospheres, in oceans and planetary systems2,4, in the heliosphere10,11, in the Earth's ionosphere and magnetosphere12,13,14,15,16,17, and in laboratory plasma experiments18. Here we report the discovery by the Cluster satellites19 of a distinct class of vortex motion—short-scale drift-kinetic Alfvén (DKA) vortices8,9—in the Earth's magnetospheric cusp region. As is the case for the larger Kelvin–Helmholtz vortices observed previously17, these dynamic structures should provide a channel for transporting plasma particles and energy through the magnetospheric boundary layers.