Spatial distribution of the compressible term Q_p∇⋅v = −p∇ ⋅ v from the internal energy equation. Left: Vertical profile indicated with a dashed black curve from the sub-surface CZ to the TR. Both the positive (heating via compression Q_comp) and negative (cooling via expansion Q_exp) contributions of this term are illustrated with a grey and solid gold line, respectively. All profiles are averaged horizontally in space and over 1 solar hour in time. The dark arrows point to the local increase in Q_p∇⋅v, due to the change in behaviour of Q_comp, resulting from upward-propagating waves that shock in the lower chromosphere. Right: Horizontal cut of Q_p∇⋅v at z = 1 Mm. Grey and gold regions illustrate heating via compression and cooling via expansion, respectively. The limits of the colour bar correspond to twice the standard deviation of this map. An animation covering 17 s (27 solar minutes) is available online.