Correlations of observable K line profile properties for diagnosing vertical velocities in the chromosphere from Model 2. Panel a: the K₃ Doppler shift against the vertical velocity at the K₃ formation height is indicated. Panel b: the K₂ peak separation against the maximum vertical velocity amplitude between K₂ and K₃ formation heights is shown. Panel c: the average K₂ Doppler shift against the averaged vertical velocity at the K₂ formation heights is indicated. Panel d: the emission peak asymmetry against the mean vertical velocity between the K₂ and K₃ formation heights is shown. The panels follow the same format as Fig. 6.