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Standing sausage modes are important in interpreting quasi-periodicpulsations in the lightcurves of solar flares. Their periods and damping timesplay an important role in seismologically diagnosing key parameters like themagnetic field strength in regions where flare energy is released. Usually suchapplications are based on theoretical results neglecting unresolved finestructures in magnetized loops. However, the existence of fine structuring issuggested on both theoretical and observational grounds. Adopting the frameworkof cold magnetohydrodynamics (MHD), we model coronal loops as magnetizedcylinders with a transverse equilibrium density profile comprising a monolithicpart and a modulation due to fine structuring in the form of concentric shells.The equation governing the transverse velocity perturbation is solved with aninitial-value-problem approach, and the effects of fine structuring on theperiods $P$ and damping times $\tau$ of global, leaky, standing sausage modesare examined. A parameter study shows that fine structuring, be it periodicallyor randomly distributed, brings changes of only a few percent to $P$ and $\tau$when there are more than about ten shells. The monolithic part, its steepnessin particular, plays a far more important role in determining $P$ and $\tau$.We conclude that when measured values of $P$ and $\tau$ of sausage modes areused for seismological purposes, it is justified to use theoretical resultswhere the effects due to fine structuring are neglected.

Periods and damping rates of fast sausage oscillations in multi-shelled coronal loops