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

Outline

A.Convective patterns

B.Mean Flows (DR & MC)

C.Dynamo processes

Achievements Challenges Helioseismic

implications

What might giant cells look like?

Radial velocityr=0.98R

The ASH Code

QuickTime™ and aNone decompressor

are needed to see this picture.

Look for Vorticity and Divergence in SSW maps?

QuickTime™ and aCinepak decompressor

are needed to see this picture.

dv/d at r = 0.98R

(d = 14.6 Mm)

A better way to find NS downflow

lanes?

Summary: Convection StructureWhat might we look for in SSW maps?

Miesch Oct, 2006

• 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 <vv>?

– Spectra, pdfs, etc

• Evolution– Correlation timescales of days to weeks

– Prograde propagation of NS lanes

– Shearing and fragmentation of cellular flows

QuickTime™ and aCinepak decompressor

are needed to see this picture.

QuickTime™ and aNone decompressor

are needed to see this picture.

Differential Rotation

r/R

(nhz)

Meridional Circulation

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v(m s-1)

r/R

60

30

equatorward

poleward

v(m s-1)

latitud

e

Maintenance of Mean Flows: Dynamical balances

• Statistically steady• Neglect LF, VD• Rapid rotation CF >> RS• Ideal gas• Hydrostatic, adiabatic

background

(1) Meridional circulation = Reynolds stresses

Coriolis-induced tilting of

convective structures

(2) Thermal Wind balance (Taylor-Proudman

theorem)

DR, MC, RS, S are tied together by (1), (2)

Warm poles!S=constant

Lower BCS=S()

Lower BC

Thermal wind balance and coupling to the tachocline

Summary: Mean FlowsGuidance for helioseismology, dynamo

modeling

Miesch Oct, 2006

• 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

Dynamo Action in Global Convection Simulations

Sustained Toroidal/Poloidal field generationComplex spatial and temporal dependence

MagneticEnergy density

Tachocline promotes more organized fields

Pumping, amplification, and organization of toroidal fields

Mid-CZ Overshoot region/tachocline

Summary: Dynamo ProcessesWhere do global convection simulations

stand?

Miesch Oct, 2006

• 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