Properties of UFs in a simulation with a chromospheric resonant cavity. Panel a: wavelength shift of the center of the emission core (Δv) as a function of the vertical velocity at log τ = −5.1 (v_z). Panel b: maximum intensity of the emission feature as a function of the temperature fluctuation at log τ = −5.1. Panels a and b: blue dots represent upflowing UFs and red dots correspond to downflowing UFs. Panel c: histogram illustrating the duration of upflowing (blue bars) and downflowing (bars filled with red lines) UF events. Panel d: relation between the duration of the upflowing UFs and the preceding downflowing UFs. The color bar indicates the number of occurrences of UFs with the corresponding durations.