Why do simulated solar convection speeds exceed helioseismic limits?
In plain words
Computer models of the Sun's churning outer layer predict large-scale flows much faster than sound waves inside the Sun appear to allow, and models with solar parameters tend to rotate the wrong way at the equator.
Precise statement
Global convection simulations at solar luminosity and rotation give large-scale velocities (spherical-harmonic degree below $\sim 30$) above some helioseismic upper limits, and tend toward anti-solar differential rotation (slow equator). Identify the missing physics: low effective Prandtl number, non-local surface-driven convection (entropy rain), a weakly subadiabatic deep layer, or magnetic feedback. Answer: a simulation matching both the helioseismic convective power spectrum and the observed rotation profile.
What would settle it
Convergent helioseismic measurements of deep convective velocities by independent methods, matched by a simulation that also reproduces solar differential rotation.
Status in the literature
Helioseismic estimates of deep convective velocities from different methods (2012 and 2015) disagree by more than an order of magnitude.