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Magnetically Self-Consistent Simulations of Ring Current with Implications for Diffuse Aurora and PIXIE Data Interpretation. Margaret W. Chen 1 and Michael Schulz 2 1 The Aerospace Corporation, Los Angeles, CA 2 Lockheed Martin Advanced Technology Center, Palo Alto, CA.

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Magnetically Self-Consistent Simulations of Ring Currentwith Implications for Diffuse Auroraand PIXIE Data Interpretation

Margaret W. Chen1 and Michael Schulz2

1The Aerospace Corporation, Los Angeles, CA

2Lockheed Martin Advanced Technology Center, Palo Alto, CA

 2007 The Aerospace Corporation


Previously we have simulated diffuse aurora by using a static axisymmetric B-field model with no ring current.We have studied effects of convective transport and variations in plasmasheet distributions for various scattering models.

2

Fig 12 of Chen et al. [JGR, 110, A03210, 15 March 2005]


3 static axisymmetric


19 October 1998 Storm (min static axisymmetric Dst ~ –110 nT)

Solar-wind dynamic pressure was very low during the main phase of this storm.

We use AMIE model results (courtesy of G. Lu) to specify total potential drop DV across the polar cap.

from Fig 1 of Chen et al. [JGR, 110, A03210, 15 March 2005]

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Ring Current Particle Dynamics static axisymmetric

Hamiltonian:H = MBm + qVE(L,;t)

M = first adiabatic invariant, Bm = mirror-point field, q = particle charge, and VE = electrostatic scalar potential

Euler Potentials: = E/La ;  = 

Geomagnetic Dipole Moment:mE = 0.305G-RE3

Drift Equations:d/dt = H/; d/dt = +H/

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from Figs 2 & 3 of static axisymmetric Chen et al. [JGR, 111, A11S15, 23 Nov 2006]

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from Figs 2 & 4 of static axisymmetric Chen et al. [JGR, 111, A11S15, 23 Nov 2006]

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Kinetic Energy: static axisymmetric

E = [2/(g + 1)]MBm

p2 = 2m0MBm

Particles gain energy less efficiently from inward radial transport when the magnetic field produced by the ring current itself is taken into account.

Fig 7 of Chen et al. [JGR, 111, A11S15, 23 Nov 2006]

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from Figs 2 & 6 of static axisymmetric Chen et al. [JGR, 111, A11S15, 23 Nov 2006]

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Magnetic perturbation static axisymmetric DB(0)at “center of Earth”

DB(0) from self-consistent model is about 75% of DB(0) from non-self-consistent model during main phase of 19 Oct 1998 storm.

Fig 9 of Chen et al. [JGR, 111, A11S15, 23 Nov 2006]

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Comparison of Simulated and Observed Proton Energy Flux static axisymmetric

At ring current energies the simulated energy flux agrees better (especially so at E = 57 keV) with measured (Polar/CAMMICE) energy flux when model is magnetically self-consistent.

Fig 10 of Chen et al. [JGR, 111, A11S15, 23 Nov 2006]

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Application to plasmasheet electron transport (previously based on static axisymmetric B-field model with no ring current) for comparison with UVI and PIXIE data

Fig 12 of Chen et al. [ JGR, 110, A03210, 15 March 2005]

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Plasmasheet Electron Dynamics based on static axisymmetric

Fourth Adiabatic Invariant: p3

Flux-Tube Volume: (1/B) ds

Hamiltonian:

H = [(/)2/3c2+ m02c4]1/2m0c2 + qVE(L, ; t)

Strong-Diffusion Lifetime:  = 2Bh (1 – )(m/p)

where Bh is the magnetic intensity at altitude h = 128 km,  (= 0.25) is a backscatter coefficient, and p/m is the particles’ common speed.

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14 based on static axisymmetric


15 based on static axisymmetric


16 based on static axisymmetric


17 based on static axisymmetric


based on static axisymmetric = 

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Fig 1 of based on static axisymmetric Chen et al. [JGR, 111, A11S15, 23 Nov 2006]

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20 based on static axisymmetric


Schulz & Chen [ based on static axisymmetric JASTP, in press, 2007]

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22 based on static axisymmetric


23 based on static axisymmetric


Model [based on based on static axisymmetric Søraas and Davis, NASA Report GSFC X-612-68-328, 1968] of equatorial magnetic-field perturbation produced by ring current

Fig 1 of Schulz [JGR, 102, 14149–14154, 1997]

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Asymptotic radius of tail lobe, scaled radius of equatorial neutral line, and angular radius of boundary between closed and open mag-netic field lines on Earth’s surface as func-

tions of B01 = (2/3)Dst.

Fig 3 of Schulz [JGR, 102, 14149–14154, 1997]

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Summary
SUMMARY neutral line, and angular radius of boundary between closed and open mag-netic field lines on Earth’s surface as func-

  • Use of self-consistent magnetic field (produced by ring current) in simulations “stretches” field lines outward and mitigates particle energization associated with inward radial transport.

  • Particular intensities of diffuse auroral precipitation thus occur at lower latitudes than in Dungey’s model magnetosphere as the stormtime ring current develops.

  • As an example, self-consistency reduced the latitude of the midnight mapping from geosynchronous altitude to the ionosphere by about 2 during the main phase of the storm that began 19 Oct 1998.

  • A magnetically self-consistent model thus yields significant effects for the diffuse aurora, even though L values of diffuse auroral features are typically almost twice as high as the L values at which the ring current is most intense.

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