Temporal evolution of a synthetic umbral flash in Ca II 8542 Å. Panel a: vertical velocity (black solid line, left axis), temperature perturbation (black dashed line, right axis), and density perturbation (red dashed line, red right axis) as a function of time. The blue-shaded area denotes the times when the core of the line is in emission. Vertical dotted lines indicate the time steps plotted in panels b–s. Bottom panels: Stokes I (left column), Stokes V (middle column), and response functions of the intensity to velocity (solid line) and temperature (dashed line) as a function of geometrical height (right column). Each row corresponds to the time shown in the left column and indicated by vertical dotted lines in panel a.