Convection in Neptune's magnetosphere

We assume that nonthermal escape from Triton's atmosphere produces a co‐orbiting torus of un‐ionized gas (presumably nitrogen and hydrogen) that subsequently becomes ionized by electron impact to populate a partial Triton torus analogous to the Io plasma torus in Jupiter's magnetosphere. Centrifugal and magnetic‐mirror forces confine the ions to a plasma sheet located between the magnetic and centrifugal equators. The ionization rate, and the torus ion concentration, is strongly peaked at the two points (approximately 180° apart in longitude) at which Triton's orbit intersects the plasma equator. During the course of Neptune's rotation these intersection points trace out two arcs roughly 75° in longitudinal extent, which we take to be the configuration of the resulting (partial) plasma torus. The partial ring currents produce a quadrupolar (four‐cell) convection system that provides rapid outward transport of from the arcs. Ring‐current shielding, however, prevents this convection system from penetrating very far inside the plasma‐arc distance. We suggest that this convection/shielding process accounts for the radial confinement of ≳150 keV trapped particles within L ≈ 14.3 as observed by the Voyager LECP instrument.