论文标题
光化学雾化产生的系外行星的传输光谱中的超雷利坡度
Super-Rayleigh Slopes in Transmission Spectra of Exoplanets Generated by Photochemical Haze
论文作者
论文摘要
系op云大气的光传输光谱中的光谱斜率封装了有关外来云的性质的信息。坡度通常归因于微小的气溶胶颗粒引起的瑞利散射，而最近的检索研究表明，斜坡通常比规范的雷利斜坡陡峭。在这里，我们建议在剧烈混合气氛中形成的光化学雾化可以解释这种超射线斜坡。我们首先在分析上表明，光谱斜率可以通过垂直不透明度梯度陡峭，其中大气不透明度随海拔高度增加。使用微物理模型，我们证明了这种不透明度梯度可以由光化学雾化自然产生，尤其是当涡流混合具有基本效率时。朦胧大气的传播光谱可以从雾质质量通量和涡流扩散系数方面划分为四个典型的机制。我们发现，如果涡流扩散系数足够高，并且雾质质量通量降至中等值，则传输光谱可以比雷利斜坡陡峭2--4倍。基于最近对大气环流的研究提出的涡流扩散系数，我们建议光化学雾度优先生成平衡温度为1000--1500 K的行星上的超射线斜坡，这可能与最近检索研究的结果一致。我们的结果将有助于从雾霾形成的角度来解释光谱斜率的观察结果。
Spectral slopes in optical transmission spectra of exoplanetary atmospheres encapsulate information on the properties of exotic clouds. The slope is usually attributed to the Rayleigh scattering caused by tiny aerosol particles, whereas recent retrieval studies have suggested that the slopes are often steeper than the canonical Rayleigh slopes. Here, we propose that photochemical haze formed in vigorously mixing atmospheres can explain such super-Rayleigh slopes. We first analytically show that the spectral slope can be steepened by the vertical opacity gradient in which atmospheric opacity increases with altitude. Using a microphysical model, we demonstrate that such opacity gradient can be naturally generated by photochemical haze, especially when the eddy mixing is substantially efficient. The transmission spectra of hazy atmospheres can be demarcated into four typical regimes in terms of the haze mass flux and eddy diffusion coefficient. We find that the transmission spectrum can have the spectral slope 2--4 times steeper than the Rayleigh slope if the eddy diffusion coefficient is sufficiently high and the haze mass flux falls into a moderate value. Based on the eddy diffusion coefficient suggested by a recent study of atmospheric circulations, we suggest that photochemical haze preferentially generates super-Rayleigh slopes at planets with equilibrium temperature of 1000--1500 K, which might be consistent with results of recent retrieval studies. Our results would help to interpret the observations of spectral slopes from the perspective of haze formation.
