= Solution
Three observational signatures constrain <exoplanet atmospheric dynamics>:
* \b[A displaced maximum of the <exoplanet thermal phase curve>.] If the thermal maximum precedes <exoplanet secondary eclipse>, the hottest region is displaced east of the substellar longitude in the usual synchronously rotating geometry. The observed offset for <HD 189733 b> is consistent with eastward heat advection and <atmospheric superrotation>; https://doi.org/10.1038/nature05782[the early infrared phase-curve measurement] established this effect.
* \b[Warm nightside emission and a reduced day-night contrast.] The amplitude of an <exoplanet thermal phase curve> constrains <day-night heat redistribution>. For <HD 189733 b>, the same $8\,\mu\mathrm m$ observations found hemisphere brightness temperatures roughly $970$ and $1210\,\mathrm{K}$, supporting substantial transport to the nightside instead of purely local reradiation.
* \b[Atmospheric line shifts after orbital motion is removed.] A residual <Doppler shift> measures winds projected along the <line of sight>. A <carbon monoxide> signal blueshifted by roughly $2\,\mathrm{km\,s^{-1}}$ in <HD 209458 b> was interpreted as day-to-night winds in https://doi.org/10.1038/nature09111[high-resolution transit spectroscopy]. Rotational broadening and different limb velocities can supply additional dynamical information.
<Opacity>, <exoplanet cloud> distributions, and pressure-dependent <brightness temperature> affect the phase-curve interpretation. These measurements constrain circulation through atmospheric models; a single offset or line shift does not uniquely determine a three-dimensional wind field.
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