[Comment on “A turning point in auroral physics”] Origin of auroral arcs



In an article in Eos (57(39), 403, 26 September 2006), Duncan Bryant claimed “a turning point in auroral physics.” He credited the polar aurora to waves generated when positive tail ions interact with flanks of the magnetosphere. Unfortunately, auroral arcs need a stronger energy source, and electrons from the tail have a hard time penetrating the loss cone. The process could perhaps contribute to the electrons of 500–1000 eV in the plasma sheet, where their gradual escape creates the diffuse aurora observed by satellites, but not create the bright auroral arcs seen from the ground.