Panel a): temporal evolution of the temperature; panel b): magnitude of the heating terms relating to collisional coupling at x = 0 for a timescale that follows the transition from the initiation to the weak coupling regimes (see Sect. 4.2). The normalisation of the power is . Because the temperatures cross at t ~ 3.5τ the thermal damping term become 0 at this point then reverse sign (i.e. the ionised fluid is losing heat to the neutral fluid before this time, but gaining heat from the neutral fluid after this point).