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We develop the power spectral density (PSD) model to explain the nature ofthe X-ray variability in IRAS 13224-3809, including the full effects of theX-ray reverberation due to the lamp-post source. We utilize 16 XMM-Newtonobservations individually as well as group them into three different luminositybins: low, medium and high. The soft (0.3-1 keV) and hard (1.2-5 keV) PSDspectra are extracted and simultaneously fitted with the model. We find thatthe corona height changes from h ~ 3 $\ r_{\rm g}$ during the lowest luminositystate to ~ $25 \ r_{\rm g}$ during the highest luminosity state. This providesfurther evidence that the source height from the reverberation data issignificantly larger than what constrained by the spectral analysis.Furthermore, as the corona height increases, the energy spectrum tends to besofter while the observed fractional excess variance, $F_{\rm var}$, reduces.We find that the PSD normalization is strongly correlated with $F_{\rm var}$,and moderately correlated with the PSD bending index. Therefore, thenormalization is dependent on accretion rate that controls the intrinsic shapeof the PSD. While the intrinsic variability of the disk is manifested by thereverberation signals, the disk and corona may evolve independently. Ourresults suggest that, during the source height increases, the disk itselfgenerates less overall variability power but more high-frequency variabilityresulting in the PSD spectrum that flattens out (i.e. the inner disk becomesmore active). Using the luminosity-bin data, the hint of Lorentzian componentis seen, with the peak appearing at lower frequencies with increasingluminosity.

Mapping the X-ray corona evolution of IRAS 13224-3809 with the power spectral density