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Because of their intense incident stellar irradiation and likely tidallylocked spin states, hot Jupiters are expected to have wind speeds that approachor exceed the speed of sound. In this work we develop a theory to explain themagnitude of these winds. We model hot Jupiters as planetary heat engines andshow that hot Jupiters are always less efficient than an ideal Carnot engine.Next, we demonstrate that our predicted wind speeds match those fromthree-dimensional numerical simulations over a broad range of parameters.Finally, we use our theory to evaluate how well different drag mechanisms canmatch the wind speeds observed with Doppler spectroscopy for HD 189733b and HD209458b. We find that magnetic drag is potentially too weak to match theobservations for HD 189733b, but is compatible with the observations for HD209458b. In contrast, shear instabilities and/or shocks are compatible withboth observations. Furthermore, the two mechanisms predict different wind speedtrends for hotter and colder planets than currently observed. As a result, wepropose that a wider range of Doppler observations could reveal multiple dragmechanisms at play across different hot Jupiters.

Atmospheric Circulations of Hot Jupiters as Planetary Heat Engines