1. An update on convection zone modeling with the ASH code
Mark Miesch
HAO/NCAR
Sacha Brun, Juri Toomre, Matt Browning, Marc DeRosa,
Ben Brown, Nick Featherstone, Kyle Augustson
Oct, 2006

2. Outline Convective patterns Mean Flows (DR & MC) Dynamo processes
Achievements
Challenges
Helioseismic implications

3. What might giant cells look like?
The ASH Code
Discuss ASH code
granulation-like cells but much bigger
Asymmetry between upflows + downflows
Vorticity in downflow lanes
NS lanes
Nearly a million node hours: that’s 128 CPUs running nonstop for nearly a year
Radial velocity
r=0.98R

4. Look for Vorticity and Divergence in SSW maps?
Replace this with Vr, rvort, hdiv?

5. Downflow network breaks up with depth but NS lanes remain

6. A better way to find NS downflow lanes?
dvj/dj at
r = 0.98R
(d = 14.6 Mm)
A better way to find NS downflow lanes?

7. Summary: Convection Structure What might we look for in SSW maps?
Coherent Structures
Downflow network
Persistent NS lanes (Lisle et al 2004)
Correlations & Statistics
Cyclonic vorticity/horizontal convergence
(Gizon 2006, Komm et al 2006)
Cool, vortical downflows
Reynolds stresses <vqvj>?
Spectra, pdfs, etc
Evolution
Correlation timescales of days to weeks
Prograde propagation of NS lanes
Shearing and fragmentation of cellular flows
Miesch
Oct, 2006

8. Differential Rotation
W (nhz)
r/R

9. Meridional Circulation
vq (m s-1)
equatorward vq
(m s-1)
60o
latitude
Note of caution: boundary layer effects
30o
poleward
r/R

10. Maintenance of Mean Flows: Dynamical balances
(1) Meridional circulation = Reynolds stresses
(2) Thermal Wind balance
(Taylor-Proudman theorem)
Coriolis-induced tilting of convective structures
Add thermal wind balance figure?
Statistically steady
Neglect LF, VD
Rapid rotation CF >> RS
Ideal gas
Hydrostatic, adiabatic background
DR, MC, RS, S are tied together by (1), (2)

11. Thermal wind balance and coupling to the tachocline
S=constant
Lower BC
S=S(q)
Lower BC
Warm poles!

12. Summary: Mean Flows Guidance for helioseismology, dynamo modeling
Differential rotation
Reynolds stresses
Latitudinal entropy/temperature variations
Tachocline may play an important role in maintaining global profile
Meridional Circulation
Delicate balance between large forces
Large fluctuations in space and time
Poleward circulation in the Sun may be a surface effect - we need deeper inversions!
DR, MC, RS, S are tied together by dynamical balances
Miesch
Oct, 2006

13. Dynamo Action in Global Convection Simulations
Sustained Toroidal/Poloidal field generation
Complex spatial and temporal dependence

14. Tachocline promotes more organized fieldsW
Magnetic
Energy density

15. Pumping, amplification, and organization of toroidal fields
Mid-CZ
Overshoot region/tachocline

16. Summary: Dynamo Processes Where do global convection simulations stand?
Achievements
Sustained field generation by turbulent convection (0-1)
Pumping downward into a tachocline (2)
Amplification by rotational shear (3)
Challenges
Formation of toroidal bands (4)
Flux destabilization and emergence (4-7)
Activity cycle (8)
Tachocline dynamics
Instabilities
Penetrative Convection
Waves & Oscillations
Confinement
Miesch
Oct, 2006