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arXiv 2402.17697astro-ph.EP
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测试热木星大气的近似红外散射辐射传输方法

Testing approximate infrared scattering radiative-transfer methods for hot Jupiter atmospheres

Elspeth K. H. Lee

AI总结:

本文针对热木星大气辐射传输计算瓶颈,测试了吸收近似和变分迭代法两种近似长波散射方法,发现四流VIM在保证出射通量误差约1%的同时具有优异速度,适合用于GCM和反演建模。

摘要:

内部大气(长波)通量的计算是任何需要辐射传输(RT)计算的系外行星大气模型的关键组成部分。对于包含强散射成分(如云粒子)的大气,大多数一维多散射RT方法通常涉及数值上昂贵的矩阵求逆。当需要大量RT计算时,例如在通用环流模型(GCM)和反演方法中,这一计算瓶颈会更加严重。为了在不牺牲太多精度的情况下提高RT计算的速度,我们研究了为地球科学界发展的近似长波散射方法对热木星大气的适用性。我们以64流DISORT计算作为参考解,测试了应用于典型多云热木星场景的吸收近似(AA)和变分迭代法(VIM)。我们发现四流VIM变体是一种非常有前景的方法,可用于热木星GCM和反演建模,显示出优异的速度特性,出射通量的典型误差约为1%,垂直加热率的典型误差在约50%以内,但在深层云层测试用例中误差较大。本研究中探索的其他方法通常在垂直加热率方面表现出类似的误差特征。

英文摘要:

The calculation of internal atmospheric (longwave) fluxes is a key component of any model of exoplanet atmospheres that requires radiative-transfer (RT) calculations. For atmospheres containing a strong scattering component such as cloud particles, most 1D multiple-scattering RT methods typically involve numerically expensive matrix inversions. This computational bottleneck is exacerbated when multitudes of RT calculations are required, such as in general circulation models (GCMs) and retrieval methods. In an effort to increase the speed of RT calculations without sacrificing too much accuracy, we investigate the applicability of approximate longwave scattering methods developed for the Earth science community to hot Jupiter atmospheres. We test the absorption approximation (AA) and variational iteration method (VIM) applied to typical cloudy hot Jupiter scenarios, using 64 stream DISORT calculations as reference solutions. We find the four-stream VIM variant is a highly promising method to explore using for hot Jupiter GCM and retrieval modelling, showing excellent speed characteristics, with typical errors $\sim$1\% for outgoing fluxes and within $\sim$50\%, but with larger errors in the deep cloud layer test case, for vertical heating rates. Other methods explored in this study were found to typically produce similar error characteristics in vertical heating rates.

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