  The diffuse hot medium inside clusters of galaxies typically exhibits
turbulent motions whose amplitude increases with radius, as revealed by
cosmological hydrodynamical simulations. However, its physical origin remains
unclear. It could either be due to an excess injection of turbulence at large
radii, or faster turbulence dissipation at small radii. We investigate this by
studying the time evolution of turbulence in the intracluster medium (ICM)
after major mergers, using the Omega500 non-radiative hydrodynamical
cosmological simulations. By applying a novel wavelet analysis to study the
radial dependence of the ICM turbulence spectrum, we discover that faster
turbulence dissipation in the inner high density regions leads to the
increasing turbulence amplitude with radius. We also find that the ICM
turbulence at all radii decays in two phases after a major merger: an early
fast decay phase followed by a slow secular decay phase. The buoyancy effects
resulting from the ICM density stratification becomes increasingly important
during turbulence decay, as revealed by a decreasing turbulence Froude number
$Fr \sim \mathcal{O}(1)$. Our results indicate that the stronger density
stratification and smaller eddy turn-over time are the likely causes of the
faster turbulence dissipation rate in the inner regions of the cluster.
