e-folding lifetimes of various low-frequency modes for a viscous diffusivity (a) ν = 10¹¹ cm² s⁻¹ and (b) ν = 10¹² cm² s⁻¹. We note that all the modes selected here are stable modes (ℑ[ω]< 0). Different colors represent different types of inertial modes. The horizontal black dashed line shows the length of the SDO/HMI observational record (T_obs ≈ 12 yr as of today). In both cases, rotation is uniform and the stratification is adiabatic. The lifetimes of the convective modes and high-latitude modes are very sensitive to the radial and latitudinal entropy gradients, a point that is discussed in Sects. 5 and 6.2.