A non-grey analytical model for irradiated atmospheres - I. Derivation
A non-grey analytical model for irradiated atmospheres - I. Derivation
复制标题
DOI：
10.1051/0004-6361/201322342
复制
发表时间：
2013-11
影响因子：
6.5
通讯作者：
V. Parmentier;T. Guillot
中科院分区：
文献类型：
--
作者：
V. Parmentier;T. Guillot
语境。半灰色大气模型（一种可见光不透明度和一种红外光不透明度）有助于了解受辐射大气的整体结构、其动力学以及行星、褐矮星和恒星的内部结构和演化。但与受辐射系外行星的直接数值辐射传输计算相比，这些模型系统地高估了低光学深度下的温度，而与不透明度参数无关。我们希望了解为什么半灰色模型在低光学深度下失败，并通过考虑红外中的可变不透明度来提供对大气结构的更准确的近似。我们的分析辐射非灰色模型提供了与数值计算获得的温度范围一致的温度范围。我们发现，即使对于轻微的非灰色热不透明度，温度结构也与以前的半灰色模型有很大不同。对于较小的 beta 值（当线条占主导地位时预计），我们发现非灰色效果仅限于低光学深度。然而，对于大于 0.5 的 beta（适用于波长相关性较小或与普朗克函数宽度相当的波段），我们发现，由于所谓的覆盖效应，温度结构甚至会受到影响，甚至达到红外光学深度单位和更深。我们推导的表达式可用于为从光谱信息反演大气特性的算法提供适当的函数形式。由于可以直接计算完整的大气结构，因此这些表达式对于模拟这些大气的动力学和行星的热演化应该很有用。最后，它们应该用于测试完整的辐射传输模型并提高其收敛性。
Context. Semi-grey atmospheric models (with one opacity for the visible and one opacity for the infrared) are useful to understand the global structure of irradiated atmospheres, their dynamics and the interior structure and evolution of planets, brown dwarfs and stars. But when compared to direct numerical radiative transfer calculations for irradiated exoplanets, these models systematically overestimate the temperatures at low optical depth, independently of the opacity parameters. We wish to understand why semi-grey models fail at low optical depths, and provide a more accurate approximation to the atmospheric structure by accounting for the variable opacity in the infrared. Our analytical irradiated non-grey model is found to provide a range of temperatures that is consistent with that obtained by numerical calculations. We find that even for slightly non-grey thermal opacities the temperature structure differs significantly from previous semi-grey models. For small values of beta (expected when lines are dominant), we find that the non-grey effects are confined to low-optical depths. However, for beta larger than 0.5 (appropriate in the presence of bands with a wavelength-dependence smaller or comparable with the width of the Planck function), we find that the temperature structure is affected even down to infrared optical depths unity and deeper as a result of the so-called blanketing effect. The expressions that we derive may be used to provide a proper functional form for algorithms that invert the atmospheric properties from spectral information. Because a full atmospheric structure can be calculated directly, these expressions should be useful for simulations of the dynamics of these atmospheres and of the thermal evolution of the planets. Finally, they should be used to test full radiative transfer models and improve their convergence.