Vorticity field after 20, 200, 400 and 600 rotations (from left to right, respectively) in a 2D disk with thermal relaxation with a cooling time τ = 160. Top row: stable stratification (p = 1.5, q = 0.5). Bottom row: unstable stratification (p = 1, q = 0.5). Vortices are rapidly decaying in the case of a stable stratification while they are slowly but systematically amplified in the case of an unstable stratification.