Shock Source Description:Large-Scale Hybrid Simulations

Dietmar Krauss-VarbanJanet Luhmann

Ilan RothYan Li

Steve Ledvina

Space Sciences Laboratory, UC Berkeley

CISM All-Hands Meeting, Boston, 9/2004

Overview• Black-box Model and

Source Description• Observations• Theory and Transport

Models• Role of Simulations in

CISM SEP model

Reames, 1999

Hybrid Simulations

• Overview and Goals/Deliverables• Scales and Extrapolation• Early Results• Limitations and Outlook

Hybrid Simulations

Overview and Goals:

• Kinetic ions, electron fluid

• Spatial scale: c/p ; time scale p-1

• Initially focus on protons; later: arbitrary masses and charge states

Primary shock parameters: , MA, Bn

Secondary parameters: absolute n, absolute T

Hybrid Simulations

SEP Shock Sources:

Hybrid Simulations

Scales and Extrapolation (conservative estimate):

Assume target energy of 1MeV.

Convected gyro radius in 6nT B-field 105 km ~ 103 c/p

Need several resonant in system in 1 direction

e.g., 10,000 x 500 c/p (assuming 2-D).

Typical time step 0.01 p-1, 2.5·106 pp/s / CPU

1 hour of real time (~transit time at MA = 5)

5 days on 40 CPUs

Power-law extrapolation

Hybrid SimulationsEarly Results - Overview

Bz and T|| ; MA = 6.0, Bn = 30o

Hybrid SimulationsIon Distributions: quasi-parallel case

Hybrid SimulationsIon Distributions: oblique case

Hybrid SimulationsIon Distributions: upstream vs. downstream

Hybrid Simulations

Fluctuations and Anisotropy

Hybrid Simulations

Velocity Distributions: quasi-parallel case

Hybrid Simulations

Velocity Distributions: oblique case

Hybrid Simulations

Limitations:

• Computational requirements/ infrastructure

• 3-D necessary for nearly-perpendicular case because of cross-field diffusion

Hybrid SimulationsParameter Space:

Hybrid Simulations

Outlook/ Tentative Deliverables

3-D Parameter space:

• result grid ~O(100) points• Deliver: peak flux, power law index, and pitch-angle

distribution both upstream and downstream

Contributions from Test Particle Studies

• Generic results• Shock surfing/ nearly perpendicular shock• Power law extrapolation• Shock crossings: Transparency and further

energization• Understand trapped particle population at

quasi-perpendicular shock• Goals and deliverables

Test Particle Contribution

Generic Results: model shock with turbulence

Example: MA = 2, Bn = 85o, shock width = 0.1 c/p

Legend: (here: shock in x-z plane)

X position vs. time Y position vs. time

X vs. Y positions Vx velocity vs. time

Vx vs. Vy velocities Z vs. y positions

Z velocity vs. time energy vs. time

Test Particle Contribution

Shock-interaction of ions:

- accelerated at another shock,

- or mirrored, e.g. ,in converging fields behind (sunward of) shock

“transparency”

MA = 3.0, Bn = 80o

Turbulent medium: sigma= 0.1, M=3, theta=80, W= 225keV

Turbulent shock –> significant effect on medium energy ions

Test Particle Contribution

• In presence of turbulence, as expected, ions can be further energized during second encounter

• Depending on level of turbulence and spectrum, very energetic particles may not be significantly affected by shock

• Transmission is strongly pitch-angle dependent

Yan Li will study observationally trapping/ pitch-angle distributions of energized ions at q-perp shocks

Energetic Storm Particle (ESP) Events

• Overview/ Relevance to CISM

• Hybrid Simulations of Spatio-Temporal Evolution

• Integration into CISM SEP Model:

- empirical model

- integration of simulation results

Energetic Storm Particle (ESP) Events

• Hybrid Simulations of Spatio-Temporal Evolution

Energetic Storm Particle (ESP) Events

• Integration into CISM SEP Model:

- empirical model

- integration of simulation results

• Yan observational study:

- when/why high energies

- distinguish bulk vs. spike

Summary

• Hybrid simulations will provide shock source description (peak flux, power-law index, pitch-angle distribution) for entire parameter space

• ESP events require to be integrated into CISM SEP model in a separate way. Hybrid simulations can directly contribute to quantifying ESP events.