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arXiv 1402.0814astro-ph.EP
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热木星全球环流模式中辐射方案的精度检验

Accuracy tests of radiation schemes used in hot Jupiter global circulation models

David Skålid Amundsen, Isabelle Baraffe, Pascal Tremblin, James Manners, Wolfgang Hayek, N. J. Mayne, David M. Acreman

摘要:

全球环流模式(GCM)中辐射输运的处理对于正确描述地球和系外行星的大气动力学过程至关重要。双流近似和相关k方法是目前应用于地球和热木星GCM辐射方案的最先进的近似方法,以便于快速计算通量和加热率。他们的准确性已经过广泛的测试,类似地球的条件下,但验证的方法的适用性,以热的类超导体的条件是缺乏文献。我们正在适应英国气象局的GCM,统一模型(UM),为研究热对流层,并在这项工作中提出的适应爱德华-斯林戈辐射计划的基础上的双流近似和相关k方法。我们讨论了高温谱线的吸收系数的计算,并强调了压力加宽谱线宽度的大的不确定性。我们比较通量和加热速率与我们的适应计划,更准确的离散纵坐标(DO)线的线(LBL)计算忽略散射的影响。我们发现,在大多数情况下,误差保持在10%以下的加热速率和通量使用~ 10 k系数在每个波段和扩散系数D = 1.66。双流近似和相关k方法都对总误差有不可忽略的贡献。我们还发现,使用带平均吸收系数,这是以前使用的热木星的辐射流体动力学模拟,可能会产生约100%的误差,因此应谨慎使用。

英文摘要:

The treatment of radiation transport in global circulation models (GCMs) is crucial to correctly describe Earth and exoplanet atmospheric dynamics processes. The two-stream approximation and correlated-k method are currently state-of-the-art approximations applied in both Earth and hot Jupiter GCM radiation schemes to facilitate rapid calculation of fluxes and heating rates. Their accuracy have been tested extensively for Earth-like conditions, but verification of the methods' applicability to hot Jupiter-like conditions is lacking in the literature. We are adapting the UK Met Office GCM, the Unified Model (UM), for the study of hot Jupiters, and present in this work the adaptation of the Edwards-Slingo radiation scheme based on the two-stream approximation and the correlated-k method. We discuss the calculation of absorption coefficients from high temperature line lists and highlight the large uncertainty in the pressure-broadened line widths. We compare fluxes and heating rates obtained with our adapted scheme to more accurate discrete ordinate (DO) line-by-line (LbL) calculations ignoring scattering effects. We find that, in most cases, errors stay below 10 % for both heating rates and fluxes using ~ 10 k-coefficients in each band and a diffusivity factor D = 1.66. The two-stream approximation and the correlated-k method both contribute non-negligibly to the total error. We also find that using band-averaged absorption coefficients, which have previously been used in radiative-hydrodynamical simulations of a hot Jupiter, may yield errors of ~ 100 %, and should thus be used with caution.

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