机械温室：Turbulence在热木星大气中的热量埋藏
The Mechanical Greenhouse: Burial of Heat by Turbulence in Hot Jupiter Atmospheres
摘要：
热彗星受到的强烈辐射抑制了其大气层外层的对流，降低了其冷却速度。“膨胀的”热蒸发器，即，具有非常大的通过半径的那些需要额外的热源或抑制冷却。我们考虑了辐射层中强迫湍流混合的影响，它可能是由大气环流或其他机制驱动的。由于大气层的稳定分层，强迫湍流驱动向下的热通量。微弱的湍流混合减缓了这一过程的冷却速度，就好像行星受到了更强烈的辐射。较强的湍流混合将热量埋入对流内部，只要湍流延伸到辐射-对流边界。这使地球膨胀，直到埋在内部的热量和从内部辐射的热量之间达到平衡。我们还包括由于湍流耗散或其他效应而直接注入的热量。这种加热已经被认为可以减缓行星的冷却。我们发现，耗散也增强了热埋从混合降低阈值湍流混合驱动热进入内部。强湍流混合的重分子物种，如TiO可能是必要的解释平流层的热逆温。我们表明，通过我们的机制，发射TiO所需的混合量可能会使地球过度膨胀。TiO假说的这种可能的反驳值得进一步研究。我们的膨胀机制需要一个很深的分层层，只有当吸收的恒星通量大大超过本征发射通量时才存在。因此，对于更明亮的褐矮星和更长周期的气体巨星，包括木星和土星，它的效率会降低。
英文摘要：
The intense irradiation received by hot Jupiters suppresses convection in the outer layers of their atmospheres and lowers their cooling rates. "Inflated" hot Jupiters, i.e., those with anomalously large transit radii, require additional sources of heat or suppressed cooling. We consider the effect of forced turbulent mixing in the radiative layer, which could be driven by atmospheric circulation or by another mechanism. Due to stable stratification in the atmosphere, forced turbulence drives a downward flux of heat. Weak turbulent mixing slows the cooling rate by this process, as if the planet was irradiated more intensely. Stronger turbulent mixing buries heat into the convective interior, provided the turbulence extends to the radiative-convective boundary. This inflates the planet until a balance is reached between the heat buried into and radiated from the interior. We also include the direct injection of heat due to the dissipation of turbulence or other effects. Such heating is already known to slow planetary cooling. We find that dissipation also enhances heat burial from mixing by lowering the threshold for turbulent mixing to drive heat into the interior. Strong turbulent mixing of heavy molecular species such as TiO may be necessary to explain stratospheric thermal inversions. We show that the amount of mixing required to loft TiO may overinflate the planet by our mechanism. This possible refutation of the TiO hypothesis deserves further study. Our inflation mechanism requires a deep stratified layer that only exists when the absorbed stellar flux greatly exceeds the intrinsic emitted flux. Thus it would be less effective for more luminous brown dwarfs and for longer period gas giants, including Jupiter and Saturn.
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