Dynamic meteorology at the photosphere of HD 209458b

We calculate the meteorology of the close-in transiting extrasolar planet HD 209458h using a global, three-dimensional atmospheric circulation model. Dynamics are driven by perpetual irradiation of one hemisphere of this tidally locked planet. The simulation predicts global temperature contrasts of ∼500 K at the photosphere and the development of a steady superrotating jet. The jet extends from the equator to midlatitudes and from the top model layer at 1 mbar down to 10 bar at the base of the heated region. Wind velocities near the equator exceed 4 km s^-1 at 300 mbar. The hottest regions of the atmosphere are blown downstream from the substellar point by ∼60° of longitude. We predict from these results a factor of ∼2 ratio between the maximum and minimum observed radiation from the planet over a full orbital period, with peak infrared emission preceding the time of the secondary eclipse by ∼14 hr.