The meteorology of hot Jupiters has been characterized primarily with thermal measurements, but recent observations suggest the possibility of directly detecting the winds by observing the Doppler shift of spectral lines seen during transit. Motivated by these observations, we show how Doppler measurements can place powerful constraints on the meteorology. We show that the atmospheric circulation—and Doppler signature—of hot Jupiters splits into two regimes. Under weak stellar insolation, the day-night thermal forcing generates fast zonal jet streams from the interaction of atmospheric waves with the mean flow. In this regime, air along the terminator (as seen during transit) flows toward Earth in some regions and away from Earth in others, leading to a Doppler signature exhibiting superposed blueshifted and redshifted components. Under intense stellar insolation, however, the strong thermal forcing damps these planetary-scale waves, inhibiting their ability to generate jets. Strong frictional drag likewise damps these waves and inhibits jet formation. As a result, this second regime exhibits a circulation dominated by high-altitude, day-to-night airflow, leading to a predominantly blueshifted Doppler signature during transit. We present state-of-the-art circulation models including non-gray radiative transfer to quantify this regime shift and the resulting Doppler signatures; these models suggest that cool planets like GJ?436b lie in the first regime, HD?189733b is transitional, while planets hotter than HD?209458b lie in the second regime. Moreover, we show how the amplitude of the Doppler shifts constrains the strength of frictional drag in the upper atmospheres of hot Jupiters. If due to winds, the ~2 km s–1 blueshift inferred on HD?209458b may require drag time constants as short as 104-106?s, possibly the result of Lorentz-force braking on this planet's hot dayside.
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机译：热木星的气象学主要是通过热测量来表征的，但是最近的观察表明，可以通过观察在运输过程中看到的谱线的多普勒频移直接检测风。基于这些观察，我们展示了多普勒测量如何对气象学施加强大的约束。我们表明，热木星的大气环流和多普勒特征分为两个区域。在弱恒星日照下，昼夜热强迫通过大气波与平均流量的相互作用产生快速的纬向射流。在这种情况下，沿着终结器的空气（在运输过程中看到）在某些区域流向地球，而在另一些区域则远离地球，从而导致多普勒信号表现出叠加的蓝移和红移分量。但是，在强烈的恒星日照下，强大的热强迫会减弱这些行星尺度的波，从而抑制其产生射流的能力。强烈的摩擦阻力同样会衰减这些波并抑制射流的形成。结果，第二种方案表现出以高空，昼夜气流为主的循环，导致在运输过程中多普勒信号明显偏蓝。我们提出了最先进的循环模型，包括非灰色辐射转移，以量化这种状态偏移和由此产生的多普勒信号。这些模型表明，像GJ？436b这样的凉爽行星处于第一状态，HD？189733b是过渡状态，而比HD？209458b更热的行星处于第二状态。此外，我们显示了多普勒频移的幅度如何限制了热木星高层大气中摩擦阻力的强度。如果是由于风，在HD？209458b上推断出的〜2 km s–1蓝移可能需要短至104-106？s的拖曳时间常数，这可能是在地球炎热的白天洛伦兹力制动的结果。
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