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 Mitchell Pontus Brandt Sasha Ukhorskiy Abi Rymer + ideas influenced by many others, especially V. Vasyliunas, K. Khurana, J. Burch, T. Hill, J. Carbary, M. Kivelson, D. Gurnett, D. Southwood K.C. Hansen, T. Gombosi

1.Mechanism for very regular unloading via Vasyliunas reconnection 2.Role of ionosphere and coupling 3. Mechanism for inner magnetosphere modulation. 4.Ionospheric coupling, driving separately from northern and southern hemispheres (time permitting) 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:

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

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: /2008JA Saturn’s magnetospheric plasma completes a rotation in between 12.7 and 15.4 hours (70%-85% of SKR period)

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)

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

Vasyliunas, 1983 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).

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.) A B In our model, mass loading (generation + transport) is strictly radial, and for the sake of simplicity, constant. The plasma rotation period is ~14 hours.

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

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).

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.

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

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

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

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).

A B C D Full cycle is ~3/4 cold plasma period

The partial ring current system dipolarizes the field inside the pressure enhancement, but further stretches the field outside, destabilizing it. The FAC may diminish before getting back to midnight, but the enhanced conductance may not fully dissipate. This ionospheric patch of higher conductance may increase ionosphere-magnetosphere coupling, and also promote plasmoid release in synch with the ionospheric rotation rate. 2.Role of ionosphere and coupling (cont.)

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, Clearly there is enhanced conductance in the ionosphere, and that extends down to ~70° latitude. It appears to rotate near rigid corotation. The FAC structure will want to follow the azimuthal ring current pressure gradients (ENA blobs). These move faster than local plasma velocity, via gradient/curvature drift. 2.Role of ionosphere and coupling

Now, what about the spiral shape? That seems contrived. However… Burch, DeJong, Goldstein and Young, plasma spiral, GRL, 2009 And, if time allows, I’ll show that our model generates this pattern

Release 1/4 rotation 1/2 rotation 3/4 rotation So, the ring current, and its divergence field aligned current system, may provide important coupling to the ionosphere

3. Mechanism for inner magnetosphere modulation.

Tom Hill (Mauk, Saturn Book, 2010) Flux tube interchange (simulation) The dominant process through which plasma transport is thought to proceed in Saturn’s middle magnetosphere. Hot, tenuous plasma moves planet-ward, cold dense plasma moves ~ radially outward. Chen et al find no SKR dependence.

Fresh Injection No dispersion, NO ambient cold plasma Older injections, dispersion, new ionospheric electrons, higher plasma density Older injections, dispersion, new ionospheric electrons, higher plasma density

3. Mechanism for inner magnetosphere modulation. Hot electron population transported by interchange ionizes neutral gas, enhances plasma density in the inner magnetosphere

3. Mechanism for inner magnetosphere modulation. As mass is unloaded in longitudinal chunks at the perimeter, the gradient between loaded and unloaded flux tubes is steepened, and the remaining trapped plasma is heated (in that longitudinal sector). This results in a hotter electron population being transported inward through flux tube interchange, and the interchange tubes may also penetrate to lower radii (because they are more buoyant, or lighter, than those in other sectors). This enhanced transport keeps jumping ahead of the plasma rotation speed, as the steep gradient jumps ahead by the mechanism previously described. This transport enhancement may be communicated all the way back to 3-5 Rs, where Gurnett shows the density enhancement, in synch with SLS3, not in synch with plasma rotation.

Probably NOT a Flow Pattern

Conceptual model with ionospheric feedback And now, the movie version

How Long Is the Day on Saturn? Agustín Sánchez-Lavega SCIENCE VOL FEBRUARY 2005 Discovery of a north-south asymmetry in Saturn’s radio rotation period, Gurnett et al., GRL Vol. 36, 2009

How Long Is the Day on Saturn? Agustín Sánchez-Lavega SCIENCE VOL FEBRUARY 2005 Saturn’s probable interior period S. Auroral Zone N. Auroral Zone SKR Period 2. The Role of the Ionosphere as Driver

Conceptual model with ionospheric feedback, 2 periods Two ionospheric enhancements (N and S)

Conclusions Concept reconciles slow plasma rotation rate with short modulation period (we believe this to be the ionospheric period, slipping relative to neutral winds,slowed by magnetospheric drag). Model provides framework for modulation of the inner magnetosphere via flux tube inter- change of hotter plasma in the “active” sector. Model CAN accommodate multiple periods simultaneously. Model can accommodate a range of plasma rotation periods and loading rates

Hypothesis If the ionosphere is driving at a rate much faster than the plasma rotation rate, it either has to be doing that at a location where there is very little drag imposed from the magnetosphere (but then you wouldn’t get a strong current driven), or It has to be driven through strong coupling to the lower altitude lower atmosphere.

McAndrews et al., 2009 PSS Kane et al. JGR % SLS3 75% SLS3

Conceptual model with ionospheric feedback 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 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 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 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 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 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 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 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).

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

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

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

Conceptual model with ionospheric feedback 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 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 The natural development of a plasma spiral. Much later…

3.Response to changes in mass source rate If the mass source rate increases, the outer magnetosphere will reach a critical loading rate faster. This may be compensated for by having a larger longitudinal sector break off in the tail on each rotation. The additional mass loading may slow down the plasma corotation, but the longer segment breaking off can compensate with a larger phase jump and stay in synch with the ionosphere. A lower mass loading rate would result in smaller chunks breaking off, and perhaps faster plasma rotation.

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

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).

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.

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