Hydrogen ENA

1. Saturn’s 10.8 hour periodicity—relationship between cold, sub-corotating plasma and hot ring current particlesDon MitchellPontus BrandtAbi RymerJim Carbary

2. Carbary, J. F., D. G. Mitchell, P. Brandt, E. C. Roelof, and S. M. Krimigis (2008), Statistical morphology of ENA emissions at Saturn, J. Geophys. Res. Mapped to ionosphere SOI to 222, 2007 Hydrogen ENA Not this talk: ENA emissions show the same local time dependence and radial displacement as that caused by the convection pattern suggested by Roussos et al., and Thomsen. And, they map to the lower bounds of the auroral zone.

3. The reference frame: Saturn’s cold plasma sub-corotates

4. Gurnett et al., 2007 Science BUT! Cold plasma density (here in the 3 – 5 Rs range) is ordered by the SKR corotation period, not the plasma rotation period.

5. Burch, J. L., A. D. DeJong, J. Goldstein, and D. T. Young (2009), Periodicity in Saturn's magnetosphere: Plasma cam, GRL. And the cold plasma appears to describe a spiral form in the SLS3 coordinate system. (SKR peaks as 100° passes noon).

6. Hydrogen ENA Protons SOI to 222, 2007 Furthermore, ENA emission as well as in situ energetic protons are also organized in SLS3. Carbary, J. F., D. G. Mitchell, P. Brandt, E. C. Roelof, and S. M. Krimigis (2008), Statistical morphology of ENA emissions at Saturn, J. Geophys. Res.

7. The SLS3 ordering of energetic ions depends on energy (gradient and curvature drift effects). Yet even for those ions with significant azimuthal drifts, ordering in SLS3 remains. Average 6 to 12 Rs

8. Average 6 to 12 Rs

9. In periodic sequences, ENA emission “jumps” forward as a new event replaces the previous one. Saturn Titan’s orbit SKR

10. Concept based on observations. Cold plasma (light and dark blue) propagates outward, driven by centrifugal acceleration. Plasma is released on the night side when the current sheet becomes too loaded--Vasyliunas reconnection. Slightly asymmetric system Spontaneous plasmoid release (Vasyliunas)

11. If plasma loading was very fast, such that in one rotation a segment that had just spawned a plasmoid was again unstable and ready to spawn another, then the steady state pattern might look something like this: But then plasmoid release would be continuous, and the sense of the spiral is the reverse of what is observed

12. But if the plasma loading is slower, it looks like this

13. (Or this…) It doesn’t matter whether the cold plasma leaves in a block—ie, a plasmoid—or as “drizzle”. The important thing is that it only leaves when it is sufficiently loaded, and that turns on and off because any particular longitudinal sector does not load to instability in only one rotation.

14. For simplicity, I’ll stick to the big plasmoid picture. The difference between the pictures may depend on solar wind pressure, and/or may bear on the behavior of the ring current (big plasmoid--strong more impulsive ring current injection; drizzle--weaker, less impulsive ring current injection).

15. So add a partial ring current to the picture. We assume this occurs during large plasmoid release. (The difference between this and the Kivelson/Jia picture is the role of the ring current. Otherwise, they are effectively similar.)

16. 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).

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. 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.

25. 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.

26. 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.

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

28. This conforms pretty closely with the picture drawn by Vasyliunas in 1983. Vasyliunas, 1983

29. What about the SKR? The field aligned current system associated with the partial ring current generated as the field dipolarizes following plasmoid release would be in about the right place. Release 1/2 rotation 1/4 rotation 3/4 rotation SKR SKR

30. Role of ionosphere and coupling Titan’s orbit, 20 Rs 8.5 Rs 6 Rs • A FAC structure set up by the plasmoid/flux rope release rotates with the ionosphere. The early stages of this can be seen in the INCA/UVIS/SKR movie from day 129, 2008. Clearly there is enhanced conductance in the ionosphere, and that extends down to ~70° latitude. It appears to rotate near rigid corotation.

32. B A A spiral pattern (quasi-wave) is a natural quasi-stable end state to a rotating, mass loaded, triggered-release system. Do we see the plasmoids? Jackman et al., 2011 does, and so does INCA (under special conditions…). Mass loading (generation + transport) is constant and radial. The plasma rotation period is ~14 hours; A full cycle (plasmoid to plasmoid) is significantly less than the plasma rotation period. D C

33. ENA Movie of Tail Reconnection Event During Saturn Eclipse

34. Reconnection begins…

35. Plasmoid release…

36. Plasmoid moves tailward, dawnward; current sheet rotates

37. Plasmoid further tailward, current sheet rotating…

38. Plasmoid disappearing tailward and dawnward…

39. Plasmoid gone from FOV; current sheet intensifying, rotating.

40. One driver: the natural development of a plasma spiral. Yellow represents the partial ring current, which is assumed to couple with the ionosphere through FACs. The red contour represents a stability limit. When the blue exceeds the red boundary, it breaks off back to its inner boundary (plasmoid release). This can happen in a block (large plasmoid), or a dribble (more like dusk tailward cold plasma flow). Blue represents plasma loading in the outer magnetosphere. Think of it more as mass content than a boundary. Cold plasma (blue) rotates at 14 hour period. As the ring current moves forward (10.8 hour period), it “pushes out” the cold plasma (representing the destabilizing effect of the current system). Conceptual model with ionospheric feedback

41. The natural development of a plasma spiral. Yellow represents the partial ring current, which is assumed to couple with the ionosphere through FACs. The red contour represents a stability limit. When the blue exceeds the red boundary, it breaks off back to its inner boundary (plasmoid release). This can happen in a block (large plasmoid), or a dribble (more like dusk tailward cold plasma flow). Blue represents plasma loading in the outer magnetosphere. Think of it more as mass content than a boundary. Cold plasma (blue) rotates at 14 hour period. As the ring current moves forward (10.8 hour period), it “pushes out” the cold plasma (representing the destabilizing effect of the current system). Conceptual model with ionospheric feedback

42. The natural development of a plasma spiral. Yellow represents the partial ring current, which is assumed to couple with the ionosphere through FACs. The red contour represents a stability limit. When the blue exceeds the red boundary, it breaks off back to its inner boundary (plasmoid release). This can happen in a block (large plasmoid), or a dribble (more like dusk tailward cold plasma flow). Blue represents plasma loading in the outer magnetosphere. Think of it more as mass content than a boundary. Cold plasma (blue) rotates at 14 hour period. As the ring current moves forward (10.8 hour period), it “pushes out” the cold plasma (representing the destabilizing effect of the current system). Conceptual model with ionospheric feedback

43. The natural development of a plasma spiral. Yellow represents the partial ring current, which is assumed to couple with the ionosphere through FACs. The red contour represents a stability limit. When the blue exceeds the red boundary, it breaks off back to its inner boundary (plasmoid release). This can happen in a block (large plasmoid), or a dribble (more like dusk tailward cold plasma flow). Blue represents plasma loading in the outer magnetosphere. Think of it more as mass content than a boundary. Cold plasma (blue) rotates at 14 hour period. As the ring current moves forward (10.8 hour period), it “pushes out” the cold plasma (representing the destabilizing effect of the current system). Conceptual model with ionospheric feedback

44. The natural development of a plasma spiral. Yellow represents the partial ring current, which is assumed to couple with the ionosphere through FACs. The red contour represents a stability limit. When the blue exceeds the red boundary, it breaks off back to its inner boundary (plasmoid release). This can happen in a block (large plasmoid), or a dribble (more like dusk tailward cold plasma flow). Blue represents plasma loading in the outer magnetosphere. Think of it more as mass content than a boundary. Cold plasma (blue) rotates at 14 hour period. As the ring current moves forward (10.8 hour period), it “pushes out” the cold plasma (representing the destabilizing effect of the current system). Conceptual model with ionospheric feedback

45. The natural development of a plasma spiral. Yellow represents the partial ring current, which is assumed to couple with the ionosphere through FACs. The red contour represents a stability limit. When the blue exceeds the red boundary, it breaks off back to its inner boundary (plasmoid release). This can happen in a block (large plasmoid), or a dribble (more like dusk tailward cold plasma flow). Blue represents plasma loading in the outer magnetosphere. Think of it more as mass content than a boundary. Cold plasma (blue) rotates at 14 hour period. As the ring current moves forward (10.8 hour period), it “pushes out” the cold plasma (representing the destabilizing effect of the current system). Conceptual model with ionospheric feedback

46. The natural development of a plasma spiral. Yellow represents the partial ring current, which is assumed to couple with the ionosphere through FACs. The red contour represents a stability limit. When the blue exceeds the red boundary, it breaks off back to its inner boundary (plasmoid release). This can happen in a block (large plasmoid), or a dribble (more like dusk tailward cold plasma flow). Blue represents plasma loading in the outer magnetosphere. Think of it more as mass content than a boundary. Cold plasma (blue) rotates at 14 hour period. As the ring current moves forward (10.8 hour period), it “pushes out” the cold plasma (representing the destabilizing effect of the current system). Conceptual model with ionospheric feedback

47. The natural development of a plasma spiral. Yellow represents the partial ring current, which is assumed to couple with the ionosphere through FACs. The red contour represents a stability limit. When the blue exceeds the red boundary, it breaks off back to its inner boundary (plasmoid release). This can happen in a block (large plasmoid), or a dribble (more like dusk tailward cold plasma flow). Blue represents plasma loading in the outer magnetosphere. Think of it more as mass content than a boundary. Cold plasma (blue) rotates at 14 hour period. As the ring current moves forward (10.8 hour period), it “pushes out” the cold plasma (representing the destabilizing effect of the current system). As the lower stability sector beneath the ionospheric enhancement reaches the night side, the absence of the confining force of the magnetopause allows the unstable plasma to break free

48. The natural development of a plasma spiral. Yellow represents the partial ring current, which is assumed to couple with the ionosphere through FACs. The red contour represents a stability limit. When the blue exceeds the red boundary, it breaks off back to its inner boundary (plasmoid release). This can happen in a block (large plasmoid), or a dribble (more like dusk tailward cold plasma flow). Blue represents plasma loading in the outer magnetosphere. Think of it more as mass content than a boundary. Cold plasma (blue) rotates at 14 hour period. As the ring current moves forward (10.8 hour period), it “pushes out” the cold plasma (representing the destabilizing effect of the current system). As the lower stability sector beneath the ionospheric enhancement reaches the night side, the absence of the confining force of the magnetopause allows the unstable plasma to break free

49. The natural development of a plasma spiral. Yellow represents the partial ring current, which is assumed to couple with the ionosphere through FACs. The red contour represents a stability limit. When the blue exceeds the red boundary, it breaks off back to its inner boundary (plasmoid release). This can happen in a block (large plasmoid), or a dribble (more like dusk tailward cold plasma flow). Blue represents plasma loading in the outer magnetosphere. Think of it more as mass content than a boundary. Cold plasma (blue) rotates at 14 hour period. As the ring current moves forward (10.8 hour period), it “pushes out” the cold plasma (representing the destabilizing effect of the current system). New reconnection and current sheet disruption driven by the plasma release reinforces the parallel currents and regenerates the high ionospheric conductance in the same sector

50. The natural development of a plasma spiral. Yellow represents the partial ring current, which is assumed to couple with the ionosphere through FACs. The red contour represents a stability limit. When the blue exceeds the red boundary, it breaks off back to its inner boundary (plasmoid release). This can happen in a block (large plasmoid), or a dribble (more like dusk tailward cold plasma flow). Blue represents plasma loading in the outer magnetosphere. Think of it more as mass content than a boundary. Cold plasma (blue) rotates at 14 hour period. As the ring current moves forward (10.8 hour period), it “pushes out” the cold plasma (representing the destabilizing effect of the current system). New reconnection and current sheet disruption driven by the plasma release reinforces the parallel currents and regenerates the high ionospheric conductance in the same sector