The energetic ion signature of an O-type neutral line in the geomagnetic tail

Abstract

An energetic ion signature is presented which has the potential for remote sensing of an O-type neutral line embedded in a current sheet. A source plasma with a tailward flowing Kappa distribution yields a strongly non-Kappa distribution after interacting with the neutral line: sharp jumps, or ridges, occur in the velocity space distribution function ƒ(ν ⊥, ν ∥) associated with both increases and decreases in ƒ. The jumps occur when orbits are reversed in the x-direction: a reversal causing initially earthward particles (low probability in the source distribution) to be observed results in an decrease in ƒ, while a reversal causing initially tailward particles to be observed produces an increase in ƒ. The reversals, and hence the jumps, occur at approximately constant values of perpendicular velocity in both the positive ν ∥ and negative ν ∥ half planes. The results were obtained using single particle simulations in a fixed magnetic field model.