  A key factor in determining the potential habitability of synchronously
rotating planets is the strength of the atmospheric boundary layer inversion
between the dark side surface and the free atmosphere. Here we analyse data
obtained from polar night measurements at the South Pole and Alert Canada,
which are the closest analogues on Earth to conditions on the dark sides of
synchronously rotating exoplanets without and with a maritime influence,
respectively. On Earth, such inversions rarely exceed 30 K in strength, because
of the effect of turbulent mixing induced by phenomena such as so-called
mesoscale slope winds, which have horizontal scales of 10s to 100s of km,
suggesting a similar constraint to near-surface dark side inversions. We
discuss the sensitivity of inversion strength to factors such as orography and
the global-scale circulation, and compare them to a simulation of the planet
Proxima Centauri b. Our results demonstrate the importance of comparisons with
Earth data in exoplanet research, and highlight the need for further studies of
the exoplanet atmospheric collapse problem using mesoscale and eddy-resolving
models.
