= Stellar activity Rossby number
{title2=$\operatorname{Ro}_*=P_{\rm rot}/\tau_c$}
For a convective star, the activity convention compares its <rotation> period with a convective turnover time. It differs by fixed factors from the <fluid> <Rossby number> estimated from speed, <length> and angular <velocity>. Small $\operatorname{Ro}_*$ denotes strong rotational influence on <convection>. Magnetic activity usually rises as this ratio decreases in the unsaturated regime, but levels off in a saturated rapid-rotation regime.
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