  When structured light is propagated through the atmosphere, turbulence
results in modal scattering and distortions. An extensively studied example is
that of light carrying orbital angular momentum (OAM), where the atmosphere is
treated as a phase distortion and numerical tools extract the resulting modal
cross-talk. This approach focuses on the light itself, perturbed by the
atmosphere, yet does not easily lend itself to physical insights, and fails to
ask a pertinent question: where did the OAM that the beam gained or lost come
from? Here, we address this by forgoing the beam and instead calculating the
OAM of the atmosphere itself. With this intuitive model we are able to draw
general conclusions on the impact of atmospheric turbulence on OAM beams, which
we confirm experimentally. Our work alters the perspective on this problem,
opening new insights into the physics of OAM in turbulence, and is easily
extended to other structured light fields through arbitrary aberrations.

Optics;Fluid Dynamics