Artistic representation of temporal evolution of a convective element. The star is a superposition of m layers in hydrostatic equilibrium. The generic layer, L_n, is defined by the hydrostatic pressure, density, and temperature (p,ρ,T)_Ln. These values are assumed to be time-independent and far away from the convective element, i.e., for every layer . Vice versa, each convective element is never in hydrostatic equilibrium with its medium, and the pressure, temperature, and density at the surface of a convective element are {p_e(t),ρ_e(t),T_e(t)}≠{p^∞,ρ^∞,T^∞}. Upper and lower borders of a layer are indicated by ∂L_n = ∂L_n(x). Data are from Pasetto et al. (2019).