Gurnett, 2010 BqBq B tot Ring Current and Asymmetric Ring Current Magnetospheres of the Outer Planets - Boston, MA July 13, 2011 BRBqBfBtBRBqBfBt dB q

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Ring Current and Asymmetric Ring Current

Magnetospheres of the Outer Planets - Boston, MAJuly 13, 2011

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Regions of Interest

Sergis et al, 2010


We divided Saturn’s equatorial ring current into 3 radial regions based on their magnetic and plasma properties.

Determining the Rotation Rate

ccf=0.68

ccf=0.03


We chose a rotation rate and assigned the data a longitude () assuming that rotation rate. A sinusoidal fit of the form

A sin ( + B) + C

was performed on the organized data. The rate that gave the highest correlation coefficient was chosen.

w=799.2deg/day

w=814 deg/day

Poor fit

Better fit

Introduction to Format of Results

ccf=0.58

The left panel plots the correlation coefficient of each fit between 790 deg/day and 820 deg/day, taken every 0.1 degree. The shaded gray region indicates 85% of the highest peak. The horizontal line is at 50% correlation coefficient, the cutoff for inclusion. The vertical lines indicate the best fits.

On the right, the data are organized by the rotation rate with the highest correlation coefficient and are plotted versus phase. The sinusoidal fit is drawn in black on top of the data, and the correlation coefficient is shown.


6 < R < 9

9 < R < 12

12 < R < 15

2005-2006 Magnetic Perturbation Pressure

ccf=0.58ccf=0.68

ccf=0.68


ccf=0.58

ccf=0.57

9 < R < 12

12 < R < 15

Total Ion Pressure (MIMI + CAPS)

ccf=0.35

6 < R < 9


CAPS Ion Effective Temperature was only well organized in the region between 6 and 9 Saturn radii. Regions outside of 9 Rs had correlation coefficients below 0.5.

CAPS Ion Effective Temperature [P/n]


ccf=0.71

July 13, 2011 Magnetospheres of the Outer Planets - Boston, MA

D A Gurnett et al. Science 2007;316:442-445

RPWS Electron Density – 3 to 5 Rs

July 13, 2011

Gurnett, et al. have shown that the RPWS electron density data inside of 5 Rs tracks the SLS3 longitude. This is very close to the SLS4 South rotation rate.

Outside of 5 Rs, there is no organization of the particle density in either the RPWS electron data or the CAPS Ion data. The correlation coefficient is less than 0.5.

Thermal Ion Perturbation Pressure

Magnetic Perturbation Pressure

ddBth (Persoon)

RPWS Electron Density (Persoon)

RPWS Electron Density (Gurnett)

CAPS Ion Temperature

Equatorial Rotation Rates 2005-2006


Phase Relation Between Temperature and Pressure


Magnetic Pressure and CAPS Ion Effective Temperature, organized at a rotation rate of 800 deg/day, are out of phase between 6 and 9 Rs.

Density is not organized by the rotation rate of 800 deg/day. CAPS Ion Pressure appears to be in quadrature with the other parameters, but as the correlation coefficient with the fit is 0.38, a conclusive statement cannot be made.

Why might this be - CAM Model

• There is a pressure peak in the range 5 to 10 RS and the peak rotates at the SKR period.

•The Jia et al. model shows that inside of 5 Rs the density varies azimuthally (not illustrated), in accord with the electron density data described by Gurnett et al. data.

• Outside of 5 Rs, the model predicts no azimuthal dependence on density, as we have found.

•This implies that the azimuthal pressure variation arises through an azimuthal temperature variation.

• Outside of ~10 Rs, there is no temperature variation, as seen in both the data and this simulation.

Jia, Kivelson, and Gombosi, Submitted, 2011.


Why might this be - Vortex Model

13

K. K. Khurana et al. PSG 2011D. A. Gurnett et al. Science 2007;316:442-445P. C. Brandt et al, GRL 2010

The inflow region would act like a giant suction hose which gathers and funnels hotter plasma of the middle magnetosphere towards the inner magnetosphere.

At the mouth of the inflow region (8-12 Rs), the plasma is hot and tenuous. In the outflow region, the plasma is cold and dense forming a partial ring current.

The plasma in the ring current region may not be corotational but the pressure peak would be.


805.7805.9 806.

5

d(Magnetic Pressure) 2009 284-365


2005-2006

2009

S

S N S N

d(Magnetic Pressure): Change Over Time


Conclusions

Statistically significant rotation rates in ranges near SKR frequencies that organize the plasma parameters in late 2005 through early 2006 were not found.

Some rotation rates (preferred) stood out above the background by 15%.

In this “meta-analysis” perspective, the preferred frequencies cluster near the SLS4 North and South frequencies.

Magnetic pressure oscillates in late 2005 through early 2006 at the SLS4 South and the SLS4 North frequencies.

CAPS Ion Energy and the Magnetic Perturbation Pressure are in anti-phase in the equatorial plane between 6 and 9 Rs.

The 2009 magnetic pressure does not show two distinct peaks at the north and south SLS frequencies, but shows a broadened peak over the interval containing both.


Inertial Contribution

Thermal Particle Pressure

Magnetic Perturbation Pressure

Curvature Force

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Force Balance in Equatorial Ring Current


RadiusRadius

Magnetic Pressure 2010 001-120

Orbits are ~17-20 days long. Is big peak result of orbits?

Magnetospheres of the Outer Planets - Boston, MA

Ran out of steam. Will work on the rest tomorrow.

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Gurnett, 2010 BqBq B tot Ring Current and Asymmetric Ring Current Magnetospheres of the Outer Planets - Boston, MA July 13, 2011 BRBqBfBtBRBqBfBt dB q