# Presentation: 855334

## Magnetically Self-Consistent Simulations of Ring Currentwith Implications for Diffuse Auroraand 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.

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

- 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.

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

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

- 19 October 1998 Storm (min *Dst* ~ –110 nT)

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

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## Hamiltonian:  H  =  MBm + qVE(L, ; t)

- Hamiltonian:  *H*  =  *MB*m + *qV*E(*L*, ; *t*)
*M* = first adiabatic invariant, *B*m = mirror-point field, *q* = particle charge, and *V*E = electrostatic scalar potential
- Euler Potentials:   = E/*L**a *;   = 
- Geomagnetic Dipole Moment:  E = 0.305 G-*R*E3
- Drift Equations:  d/d*t* =  *H*/; d/d*t* = + *H*/

**Ring Current Particle Dynamics**

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

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

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

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

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## Kinetic Energy: 

*E*  =  [2/(*MB*m
*p*2  =  2*m*0 *MB*m
- 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 Chen et al. [JGR, 111, A11S15, 23 Nov 2006] 

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

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## Magnetic perturbation B(0) at “center of Earth” 

- *B*(0) from self-consistent model is about 75% of *B*(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 

- 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]

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

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## Flux-Tube Volume:       (1/B) ds 	

- Fourth Adiabatic Invariant:        *p*3 
- Flux-Tube Volume:      **** (1**/***B*) d*s*
- Hamiltonian:
*H*  =  [(**/**)2**/**3*c*2**  **+  *m*02*c*4]1**/**2  ****  *m*0*c*2  +  *qV*E(*L*, ; *t*)
- Strong-Diffusion Lifetime:    =  2*B**h *(1 – )(*m*/*p*)
- where *B**h* 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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##   =  

-   **=**  

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## Fig 1 of Chen et al. [JGR, 111, A11S15, 23 Nov 2006] 

- Fig 1 of *Chen et al*. [*JGR*,* 111*, A11S15, 23 Nov 2006]

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- Schulz & Chen [*JASTP*, in press, 2007]

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

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

- Model [based on *S*ø*raas and Davis*, NASA Report *GSFC X-612-68-328*, 1968] of equatorial magnetic-field perturbation produced by ring current

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

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

- 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 B**01** = (2/3)*Dst*.

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## SUMMARY

- 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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