Title: Diagnosing the small-scale and large-scale structured winds of hot, massive stars

Abstract:
It is observationally as well as theoretically well-established that the winds of hot, massive stars are highly structured on a 
broad range of spatial scales. This talk first discusses consequences of the small-scale structures associated with the strong 
instability inherent to the line-driving of these winds. We demonstrate the importance of a proper treatment of such wind 
clumping (including effects of optically thick clumps and a non-monotonic velocity field) to accurately interpret wind 
diagnostics and obtain reliable estimates of mass-loss rates. But a growing subset of massive stars has also been found to 
possess strong surface magnetic fields, which may channel the star's wind outflow and so induce also large-scale structures 
and cyclic behaviour of spectral diagnostics. The talk concludes by presenting our recent result showing that 
multi-dimensional magneto-hydrodynamical wind simulations together with detailed radiative-transfer modeling remarkably 
well reproduce the periodic Balmer emission observed in slowly rotating magnetic O stars.