Schematic representation of a convective element seen in the inertial frame S_O (origin at the point O) and in the co-moving frame S₁ (origin at the point O′). The element is represented as a spherical body for simplicity. The center of the sphere indicated as O′ also corresponds to the position of the element in S₀. The generic dimension of the convective element as seen in S₁ is indicated by ξ_e. Reproduced from Pasetto et al. (2016).