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

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

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

Downflow network breaks up with depth but NS lanes remain

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?

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

Differential Rotation W (nhz) r/R

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

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)

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

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

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

Tachocline promotes more organized fields W Magnetic Energy density

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

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