Solar Applications of the Space Weather Modeling Framework
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Transcript of Solar Applications of the Space Weather Modeling Framework
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
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
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
5
Base of Chromosphere
Loop Top
Base of Corona
Rebekah M. Evans October 14, 2014 SWMF User Meeting
€
Z Gravitational acceleration
New Initial Conditions
6
€
Z
Rebekah M. Evans October 14, 2014 SWMF User Meeting
Tchromo
Tcorona
Lchromo
Lcorona
Specify:Bz
New Initial Conditions
7
€
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
8Rebekah M. Evans October 14, 2014 SWMF User Meeting
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
10Rebekah 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
€
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
12Rebekah M. Evans October 14, 2014 SWMF User Meeting
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