Xin Liu MOP 2011 1

The growth of plasma convection in Saturn’s inner magnetosphere X. Liu; T. W. Hill; R. A. Wolf; Y. Chen

Physics & Astronomy Department, Rice University, Houston, TX

Xin Liu MOP 2011 2

Outline

Rice Convection Model (RCM)

3 plasma source models

Simulation results

comparison with observations

Xin Liu MOP 2011 3

Magnetosphere

Ionosphere

|| sini i ij I �

||| | i e

eij j

B B

0

( )

E B

E

v 2

||

2

e e

ee s n

e

ej

B

J

BJ r v r v v

Coupling

new || : field-aligned Birkeland

current at magnetosphere

ej

|| : field-aligned Birkeland

current at ionosphere

ij

: electrostatic potential

: plasma velocityv

The Rice Convection Model (RCM)Described by Liu et al. [JGR, doi:10.1029/2010JA015859]

ds

B

Xin Liu MOP 2011 4

Saturn’s inner magnetosphere: 2<L<12

Modeling region: 2<L<40

(Boundary condition: L=2: ; L=40: )

Ionospheric conductance: P = constant, H = 0

Inner plasma source models:

J06 = [Johnson et al., Ap. J., 2006]

S10 E3 = [Smith et al., JGR, 2010, doi:10.1029/2009JA015184], “E3” version.

CJ10 = [Cassidy & Johnson, Icarus, 2010, doi:10.1016/j.icarus.2010.04.010]

0 0L

RCM setup

Xin Liu MOP 2011 5

S10 E3150 kg/s

CJ10 160 kg/s

J0624 kg/s

Comparison of 3 source models

Mass loading rate

Locations of charge-exchange

/ionization cross-over, and of

ionization peak.

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Comparison of 3 source models(Ionization rate only)

S10 E3150 kg/s

CJ10 160 kg/s

J0624 kg/s

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Simulation results of J06 model

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Convection pattern at quasi steady state

Slow, wide and dense outflow channels alternating with fast, narrow and tenuous inflow channels.

Xin Liu MOP 2011 9

Mass flux of J06 model

Xin Liu MOP 2011 10

Inflow longitudinal width ratio of J06 model

[Observation data from Yi et al., JGR, 2010]

Xin Liu MOP 2011 11

Inflow and outflow channel velocities of J06 model

[Observation data from Yi et al., JGR, 2010]

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Recall the mass loading rates of 3 source models

J06 = 24 kg/sS10 E3 = 150 kg/sCJ10 = 160 kg/s

What about scaling J06 model up to 150 kg/s mass loading rate?(Also scaling up P with the same ratio to confine the radial velocities)

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Model: J06Global ionization: 24 kg/s

Pedersen conductance: 0.3 S

Model: J06*150/24Global ionization: 150 kg/s

Pedersen conductance: 0.3*150/24 S

Mass flux

Outflow velocity

Inflow velocity

Inflow width ratio

Scale up

Xin Liu MOP 2011 14

Model: S10 E3Global ionization: 150 kg/s

Pedersen conductance: 0.3*150/24 S

Mass fluxOutflow velocityInflow velocityInflow width ratio

Xin Liu MOP 2011 15

Model: CJ10Global ionization: 160 kg/s

Pedersen conductance: 0.3*160/24 S

Mass fluxOutflow velocityInflow velocityInflow width ratio

Xin Liu MOP 2011 16

Conclusions

The radial distribution of plasma source plays a key role in plasma

convection pattern.

The higher plasma mass loading rate can be compensated by higher

ionospheric Pedersen conductance.

Simulations with more recent plasma source models are different from

simulation with Johnson’s 06 model, and in disagreement with CAPS

observations in some aspects.

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Thank you

Xin Liu MOP 2011 18

Supporting material

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Observed result of corotation lag Simulated result of corotation lag

Corotation lag of J06 model

Xin Liu MOP 2011 20

Longitudinal width and radial velocity

0t

B

E

Faraday’s law for steady state:

inflow

outflow

out

in

w

w

v

v

0 E v B

and

w is the longitudinal width

Xin Liu MOP 2011 21

Test particles tracking of J06 model