Stability diagrams of Earth-sized tidally locked planets hosting Earth-like (left panels) and pure CO₂ (right panels) atmospheres, with turbulent diffusion (TD, four bottom panels) and without turbulent diffusion (NTD, four top panels), superimposed on the maps of various quantities. From bottom to top: day-night advection timescale with turbulent diffusion, day-night advection timescale with turbulent diffusion over the lower bound estimated analytically by Koll & Abbot (2016) using the heat engine theory, ratio of day-night advection timescales with and without turbulent diffusion, and nightside surface temperature difference between the cases with and without turbulent diffusion. The curves and symbols are the same as in Fig. 3.