solar applications of the space weather modeling framework r. m. evans 1,2, j. a. klimchuk 1 1 nasa...
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Solar Applications of the Space Weather
Modeling Framework
R. M. Evans1,2, J. A. Klimchuk1
1NASA GSFC, 2GMU
February 2014 SDO AIA 171 Å
Bart, Igor, Chip, Rona, Gabor, Meng, Ofer, Noé, Zhenguang,
Darren, Rich, Lars, and Tamas
Thank you!
February 2014 SDO AIA 171 Å
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
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• 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
Approach: leverage experience and existing problem type
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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
g
Schematic of a semicircular loop, straightened out with a modified profile for
gravity.
Simulation Set Up
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Base of Chromosphere
Loop Top
Base of Corona
Rebekah M. Evans October 14, 2014 SWMF User Meeting
€
Z Gravitational acceleration
New Initial Conditions
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€
Z
Rebekah M. Evans October 14, 2014 SWMF User Meeting
Tchromo
Tcorona
Lchromo
Lcorona
Specify:Bz
New Initial Conditions
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€
Z
Rebekah M. Evans October 14, 2014 SWMF User Meeting
Steady State Atmosphere
Calculate Q* and Ncorona using static equilibrium
loop scaling laws;ρcorona from ideal gas law
Calculate Q* and Ncorona using static equilibrium
loop scaling laws;ρcorona from ideal gas law
Hydrostatic extrapolation using Pcorona and Tchromo
(H~500 km) to find base pressure Pchromo
Hydrostatic extrapolation using Pcorona and Tchromo
(H~500 km) to find base pressure Pchromo
*Q is the background volumetric heating. We use density-
dependent heating for T<Tchromo
Tchromo
Tcorona
Specify:Bz
Lchromo
Lcorona
Existing capabilitiesModEquationMhd (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
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Radiative loss function Radiative loss function
Rad
iati
ve
Lo
ss F
un
ctio
n
Klim
chuk
, R
aym
ond
€
Qrad = ni neΛ Te( ) = n2Λ Te( )
€
qe = −κ 0Te5
2∇Te Simulation time increases significantly
Temperature
Challenge: Boundary conditions IDesired 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
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k=-1
Rebekah M. Evans October 14, 2014 SWMF User Meeting
k=1
k=0
k=2
€
Z
• Future – solve for the actual force balance (may be too complicated)
€
∇p
€
ρg
€
p−1 = p0 = p1
€
p0 = p1 exp zH −1( )
€
ρUz( )0
= − ρUz( )1
€
ρUz( )0
= − ρUz( )1
€
p−1 = p0 = PressBase Sides are periodic
Challenge: Boundary conditions II
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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
€
Uy (x,z = ±LZ 2 ) = ±U0 cosπx
Lx
⎛
⎝ ⎜
⎞
⎠ ⎟tanh
x
w
⎛
⎝ ⎜
⎞
⎠ ⎟
- Shearing speed U0=0.01vA,corona
- Current sheet half width w=0.001Ly
- Ramp up time - Apply in both ghost cells
w/Ly=0.01w/Ly=0.001
X [km]U
y [k
m/s
]
€
Bx( )0
=ρ 0
ρ1
Bx( )1
€
Bz( )−1,0
= Bz,input
€
By( )0
=ρ 0
ρ1
By( )1
Simulation at the end of the ramp up (t=10 minutes)
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w ~200 kmw ~200 km
UyUy
ByBy
JzJz
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
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
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Using AMR to refine TR
Cell Number
€
J 2
€
gradlogρ
Z (km)
Cel
l S
ize
(km
)C
ell
Siz
e (k
m) corona
corona
TR
TR 24 km
375 km
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
13Rebekah 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
€
BydBy
dx
€
J 2
€
gradlogρ
Z (km)
Cel
l S
ize
(km
)C
ell
Siz
e (k
m) corona
corona
TR
TR
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
14Rebekah M. Evans October 14, 2014 SWMF User Meeting
CoronaTRChromo.
Early times
As current sheet forms
As current sheet disrupts
€
Z
€
X
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
15Rebekah M. Evans October 14, 2014 SWMF User Meeting