Electron circulation in Saturn's magnetosphere.
J GEOPHYS RES-SPACE
, Article A01201. 10.1029/2007JA012589.
We present a model wherein electrons produced in Saturn's inner magnetosphere circulate through a combination of outward and inward motions driven by the centrifugal interchange instability and azimuthal motion through gradient and curvature drifts. Cool (< 100 eV) electrons produced inside L similar to 12 move slowly outward. To balance outflowing flux, inward transport occurs in small scale injection events. Electrons in these inwardly moving flux tubes are heated adiabatically to energies greater than 100 eV and their pitch angle distributions evolve from isotropic to "pancake'' ( peaked at 90 degrees). We show that this evolution is observed, and that the pitch angle distributions observed inside a plasma injection are consistent with loss free inward adiabatic transport from L similar to 11. As the flux tube moves inward the warm electrons undergo energy dependent gradient and curvature drifts out of the inwardly moving flux tube and find themselves superposed on cold, locally produced, plasma. At this point they turn around and are transported along with the cold plasma back toward the outer magnetosphere. With reasonable assumptions about scattering and loss this motion can naturally lead to the "butterfly'' electron pitch angle distributions ( with local minima at both 90 degrees and 0/180 degrees) that are observed in the warm electron plasma component. We note that we cannot reproduce the butterfly distributions using loss free outward adiabatic transport alone. This is to be expected because there exist pitch angle dependent losses in the form of Saturn's neutral gas cloud and E-ring.
|Title:||Electron circulation in Saturn's magnetosphere|
|Keywords:||MIDDLE MAGNETOSPHERE, JUPITERS INNER, PLASMA, INJECTIONS, DIFFUSION, DYNAMICS|
|UCL classification:||UCL > School of BEAMS
UCL > School of BEAMS > Faculty of Maths and Physical Sciences
Archive Staff Only