Modulating Mass Unloading in Saturn's Magnetosphere and the Role of SKR Periods (ISSI Update)

1. The Clock at Saturn: How mass unloading may be modulated at the SKR periods, and how those periods may be imposed throughout the magnetosphere(slight update, ISSI)Don MitchellPontus BrandtSasha UkhorskiyAbi Rymer+ ideas influenced by many others, especially V. Vasyliunas, K. Khurana, J. Burch, T. Hill,J. Carbary, M. Kivelson, D. Gurnett, D. SouthwoodK.C. Hansen, T. Gombosi

2. How does Saturn’s magnetosphere modulate so many phenomena at so many latitudes/radial distances with the same modulation period? (SKR, magnetic field, current sheet, magnetopause, energetic particles, plasma density, etc.) We present a conceptual model addressing the following: • Mechanism for very regular unloading via Vasyliunas reconnection • Role of ionosphere and coupling • 3. Mechanism for inner magnetosphere modulation. • Ionospheric coupling, driving separately from northern and southern hemispheres (time permitting)

3. First, a reminder: Saturn’s magnetosphere seriously sub-corotates! Thomsen et al., 2010, JGR

4. Saturn’s magnetospheric plasma completes a rotation in between 12.7 and 15.4 hours (70%-85% of SKR period) Wilson, R. J., R. L. Tokar, M. G. Henderson, T. W. Hill, M. F. Thomsen, and D. H. Pontius Jr. (2008), Cassini plasma spectrometer thermal ion measurements in Saturn’s inner magnetosphere, J. Geophys. Res., 113, A12218, doi:10.1029/2008JA013486.

5. In spite of the much longer cold plasma rotation period, Saturn ring current activity shows well defined periodicity at about the SLS3 period (Carbary et al., 2008)

6. Generated at high latitude by a field aligned current-driven mechanism, Saturn Kilometric Radiation (SKR) is modulated. Gurnett et al., 2007 Science And closer to Saturn (mapping to much lower latitudes), magnetic field components and plasma density are both modulated at the SKR period

7. The plasma Clock-Weight—the driving force Unloading of excess Enceladus-source plasma is generally accepted to take place down the magnetotail. As suggested by Vasyliunas, this can be continuous or intermittent, by generation of classical plasmoids, or by what has been termed “dribble” down the dusk flank (still reconnection). Vasyliunas, 1983

8. In our model, we can demonstrate that a spiral pattern is a natural quasi-stable end state to a rotating, mass loaded, triggered-release system. (More on this later if time allows—for now, please take the existence of the spiral on faith.) B A In our model, mass loading (generation + transport) is strictly radial, and for the sake of simplicity, constant. The plasma rotation period is ~14 hours.

12. Now, add a partial ring current to the picture. This occurs during large plasmoid release.

13. Through gradient and curvature drift, the ring current enhancement has period closer to the SKR period. The plasma period is 13 to 15 hours, energetic particles 8 to 12 hours (energy dependent).

14. Note that the ring current, through gradient and curvature drift, moves prograde relative to the cold plasma, and therefore under the oldest, most loaded sector.

15. Note that the ring current, through gradient and curvature drift, moves prograde relative to the cold plasma, and therefore under the oldest, most loaded sector.

16. Note that the ring current, through gradient and curvature drift, moves prograde relative to the cold plasma, and therefore under the oldest, most loaded sector.

17. Note that the ring current, through gradient and curvature drift, moves prograde relative to the cold plasma, and therefore under the oldest, most loaded sector.

18. Note that the ring current, through gradient and curvature drift, moves prograde relative to the cold plasma, and therefore under the oldest, most loaded sector.

19. Note that the ring current, through gradient and curvature drift, moves prograde relative to the cold plasma, and therefore under the oldest, most loaded sector.

20. Note that the ring current, through gradient and curvature drift, moves prograde relative to the cold plasma, and therefore under the oldest, most loaded sector.

21. Note that the ring current, through gradient and curvature drift, moves prograde relative to the cold plasma, and therefore under the oldest, most loaded sector.

22. Note that the ring current, through gradient and curvature drift, moves prograde relative to the cold plasma, and therefore under the oldest, most loaded sector.

23. Note that the ring current, through gradient and curvature drift, moves prograde relative to the cold plasma, and therefore under the oldest, most loaded sector.

24. The previous ring current enhancement facilitates the next plasmoid (or it could equally be continuous plasma) release.

25. Flows in Saturn’s night side magnetosphere McAndrews et al., Planet. Space Sci. (2009) Kane et al., Fall 2009 AGU

26. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

27. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

28. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

29. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

30. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

31. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

32. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

33. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

34. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

35. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

36. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

37. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

38. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

39. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

40. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

41. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

42. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

43. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

44. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

45. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

46. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

47. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

48. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

49. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).

50. The ring current actually gradient and curvature drifts at different rates according to particle energy. We therefore depict it to be spreading and fading through the rotation. Field aligned currents connect it with the ionosphere, and the associated ionospheric conductance enhancement is more likely to rotate with a fixed period (~10.6 to 10.8 hours).