  Context. The atmosphere of exoplanets has been studied extensively in recent
years, using numerical models to retrieve chemical composition, dynamical
circulation or temperature from data. One of the best observational probes in
transmission is the sodium doublet, due to its large cross section. However,
modelling the shape of the planetary sodium lines has proven to be challenging.
Models with different assumptions regarding the atmosphere have been employed
to fit the lines in the literature, yet statistically sound direct comparisons
of different models are needed to paint a clear picture. Aims. We will compare
different wind and temperature patterns and provide a tool to distinguish them
driven by their best fit for the sodium transmission spectrum of the hot
Jupiter HD 189733b. We parametrise different possible wind patterns already
tested in literature and introduce the new option of an upwards driven vertical
wind. Methods. We construct a forward model where the wind speed, wind geometry
and temperature are injected into the calculation of the transmission spectrum.
We embed this forward model in a nested sampling retrieval code to rank the
models via their Bayesian evidence. Results. We retrieve a best-fit to the HD
189733b data for vertical upward winds
$|\vec{v}_{\mathrm{ver}}(\mathrm{mean})|=40\pm4$ km/s at altitudes above
$10^{-6}$ bar. With the current data from HARPS, we cannot distinguish wind
patterns for higher pressure atmospheric layers. Conclusions. We show that
vertical upwards winds in the upper atmosphere are a possible explanation for
the broad sodium signature in hot Jupiters. We highlight other influences on
the width of the doublet and explore strong magnetic fields acting on the lower
atmosphere as one possible origin of the retrieved wind speed.
