1. Solar Applications of the Space Weather Modeling Framework R. M. Evans 1,2, J. A. Klimchuk 1 1 NASA GSFC, 2 GMU February 2014 SDO AIA 171 Å

2. Bart, Igor, Chip, Rona, Gabor, Meng, Ofer, Noé, Zhenguang, Darren, Rich, Lars, and Tamas Thank you! February 2014 SDO AIA 171 Å

3. Introduction The formation and disruption of current sheets Applies to many domains and problems in heliophysics Coronal loops are bright structures in EUV and X ray images –A variety of observations indicate that both loops and the diffuse emission between loops are heated by impulsive bursts of energy, called nanoflares 3 What are the critical onset conditions for current sheet disruption, and are they different in the chromosphere and corona? How does the coupling between the chromosphere and corona affect the disruption? At what height in the atmosphere is the disruption likely to occur? Rebekah M. Evans October 14, 2014 SWMF User Meeting July 2012 SDO/AIA

4. Approach: leverage experience and existing problem type 4 REGIONAL Flux Emergence Model (ModUserEe) Rebekah M. Evans October 14, 2014 SWMF User Meeting GLOBAL Solar Corona Model (ModUserScChromo) REGIONAL Coronal Loop Model with Chromosphere (ModUserTbd) Fang et al. 2012

5. g Schematic of a semicircular loop, straightened out with a modified profile for gravity. Simulation Set Up 5 Base of Chromosphere Loop Top Base of Corona Rebekah M. Evans October 14, 2014 SWMF User Meeting Gravitational acceleration

6. New Initial Conditions 6 Rebekah M. Evans October 14, 2014 SWMF User Meeting T chromo T corona L chromo L corona Specify: B z

7. New Initial Conditions 7 Rebekah M. Evans October 14, 2014 SWMF User Meeting Steady State Atmosphere Calculate Q* and N corona using static equilibrium loop scaling laws; ρ corona from ideal gas law Calculate Q* and N corona using static equilibrium loop scaling laws; ρ corona from ideal gas law Hydrostatic extrapolation using P corona and T chromo (H~500 km) to find base pressure P chromo *Q is the background volumetric heating. We use density- dependent heating for T<T chromo T chromo T corona Specify: B z L chromo L corona

8. Existing capabilities ModEquationMhd (single fluid) Optically thin radiative energy loss User-defined loss function Field-aligned collisional heat flux User-defined source terms to energy, momentum equations –Gravity and Volumetric heating function AMR –Static atmosphere and Current sheet formation 8 Rebekah M. Evans October 14, 2014 SWMF User Meeting Radiative loss function Radiative Loss Function Klimchuk, Raymond Simulation time increases significantly Temperature

9. Challenge: Boundary conditions I Desired features for top/bottom plasma BCs: force balance across the boundary (no mass flow) BATSRUS options for BCs base of chromosphere: –‘reflect’, ‘float’, ‘fixed’, ‘linetied’ Implemented user BC –Hydrostatic extrapolation of pressure into ghost cells using Temp. in first internal cell. Density calculated from p, Temp –As the simulation approaches SS, pressure increases somewhat at the boundary and total mass of system increases 9 k=-1 Rebekah M. Evans October 14, 2014 SWMF User Meeting k=1 k=0 k=2 Future – solve for the actual force balance (may be too complicated) Sides are periodic

10. Challenge: Boundary conditions II 10 Rebekah M. Evans October 14, 2014 SWMF User Meeting Desired features for top/bottom BCs: create a current sheet by adding energy into the system via a shear flow at the boundary BATSRUS options for shearing BCs: –‘shear’: instructions to only use for specific problem type (shock tube) –Eruptive event, breakout - not clear how to easily work into generic ModUser Implemented BC: No magnetic flux transport through boundary - Shearing speed U 0 =0.01v A,corona - Current sheet half width w=0.001L y - Ramp up time - Apply in both ghost cells w/Ly=0.01 w/Ly=0.001 X [km] U y [km/s]

11. Simulation at the end of the ramp up (t=10 minutes) 11 w ~200 km Uy By Jz At the lower boundary: Velocity and magnetic shear, and the resulting current sheet At the lower boundary: Shear profile and resulting magnetic field Rebekah M. Evans October 14, 2014 SWMF User Meeting

12. Required feature - AMR Currently using: –Static atmosphere (4 AMR levels) dz= 24 km in TR ~4 million cells –Current sheet (5 AMR levels) > 10 million cells 12 Rebekah M. Evans October 14, 2014 SWMF User Meeting Using AMR to refine TR Cell Number Z (km) Cell Size (km) corona TR 24 km 375 km

13. Required feature - AMR Currently using: –Static atmosphere (4 AMR levels) dz= 24 km in TR ~4 million cells –Current sheet (5 AMR levels) > 10 million cells Desire – flexible AMR criteria to give length scales for any quantity 13 Rebekah M. Evans October 14, 2014 SWMF User Meeting Desire – AMR criteria selection in PARAM.in normalized to the maximum value in the simulation Using AMR to refine TR Cell Number Z (km) Cell Size (km) corona TR

14. Challenge: Grid Optimization Direction-specific AMR –Current capability: one direction, must be specified during configure – we are still thinking about how to take advantage of this –Desire: variable during runtime Aspect ratio of cells –Current capability: can be stretched, but fixed from grid initialization –Desire: variable in time, and in the domain 14 Rebekah M. Evans October 14, 2014 SWMF User Meeting CoronaTR Chromo. Early times As current sheet forms As current sheet disrupts

15. Needs for the future Short term: –3d file saving issue (Tecplot) may be resolved Field lines, domain –Energy balance issue (Jim will discuss more) –Need S>10,000, CS aspect ratio >100 –Assistance w/ higher order schemes (spatially fifth-order MP5 limiter) –Subcycling and Part-Steady scheme may be useful Long term: –Neutrals (multi-fluid) – Jim will discuss more –Resistivity: T-dependent, B-dependent, Pederson (cross-field) General feedback –Tecplot output is used –Easier way to make user-defined plot variables (ex: source terms in En. Eq) –Making the code run faster is always good 15 Rebekah M. Evans October 14, 2014 SWMF User Meeting