Space–time maps of density (top row) and temperature (bottom row) perturbations for the three initial pulses: isochoric (left), isobaric (middle), and isentropic (right). Each panel shows the perturbation amplitude as a function of position along the loop and simulation time. Note how a centrally cooling, denser region at the apex develops for both isochoric and isobaric pulses, corresponding to the thermal instability, which is not triggered by an isentropic pulse.