Atmospheric dynamics of Pegasi planets

We present three-dimensional numerical simulations of the atmospheric dynamics of close-orbiting planets such as HD209458b. Our simulations show that winds of several km/sec and day-night temperature differences reaching 500-1000 K are possible at and above the photosphere. The circulation takes the form of a broad superrotating (eastward) equatorial jet. At 0.1-1 bar, the superrotation blows the hottest regions of the atmosphere downwind by 60 degrees of longitude, but at lower pressures the temperature pattern tracks the stellar illumination. We predict factors of several variation in the infrared flux received at Earth throughout an orbital cycle; if the photosphere is deep enough (>50-100 mbar pressure), the peak infrared emission should lead the time of secondary eclipse by 10 hours or more. Dynamics plays a key role in shaping the spectrum, clouds, chemistry, and long-term planetary evolution.