[论文解读] Atmosphere and Greenhouse Gas Primer

W. A. van Wijngaarden, W. Happer|arXiv (Cornell University)|Mar 1, 2023

Atmospheric Ozone and Climate被引用 4

一句话总结

本文解释了CO₂和H₂O等温室气体如何在地球大气中产生热阻，导致对流层的对流和辐射驱动的平流层。通过基本热力学和辐射传输理论，表明CO₂增加会通过增强大气不透明度来提高地表温度，模型与卫星观测的一致性证实了辐射传输计算的准确性，尽管光谱特征复杂。

ABSTRACT

We discuss how greenhouse gases affect radiation transfer in Earth's atmosphere. We explain how greenhouse gases like water vapor or carbon dioxide, differ from non-greenhouse gases like nitrogen or oxygen. Using simple thermodynamics and fluid mechanics, we show that a planet with sufficiently high concentrations of greenhouse gases must develop a convecting troposphere. The planet must also develop a non-convecting stratosphere above the tropopause. In the simplest approximation of an atmosphere that is transparent to sunlight and has frequency-independent opacity for thermal radiation, one can find simple formulas for the tropopause altitude, and for the altitude profiles of pressure and temperature. The troposphere is nearly isentropic and the stratosphere is nearly isothermal. Earth's real atmosphere is much more complicated but it does have a troposphere and a stratosphere. Between the surface and the tropopause the entropy per kilogram of real tropospheric air increases slowly with altitude. The entropy increases much more rapidly with altitude in the stratosphere. The stratosphere has a nearly isothermal lower part and a hotter upper part due to absorption of solar ultraviolet radiation by ozone. The thermal opacity of the real atmosphere has a complicated frequency dependence due to the hundreds of thousands of vibration-rotation transitions of its greenhouse molecules. Unlike the simple model where nearly all radiation to space originates at the tropopause altitude, radiation to space from Earth's real atmosphere originates from both the surface and all altitudes in the troposphere. A small additional amount of radiation originates in the stratosphere. When these complications are taken into account, model calculations of the thermal radiation spectrum at the top of the atmosphere can hardly be distinguished from satellite observations.

研究动机与目标

• 解释温室气体如何通过基本物理机制改变地球大气中的辐射传输和大气结构。
• 阐明温室气体通过对流和辐射过程在形成对流层和平流层中的作用。
• 证明模型计算的红外辐射谱与卫星观测一致，验证了尽管大气复杂，其基本物理原理的可靠性。
• 评估CO₂增加对地表温度的影响，强调反馈机制的作用，并指出缺乏观测支持强正反馈。

提出的方法

• 使用基本热力学和流体力学推导对流层对流和非对流平流层形成的条件。
• 应用Schwarzschild方程，通过频率相关的不透明度建模大气中的辐射传输。
• 采用局域热动平衡和Boltzmann分布的概念，描述大气中分子能级状态。
• 将模型预测的地球大气顶层红外辐射谱与干涉仪实测的卫星数据进行比较。
• 使用简化的灰体大气模型，推导对流层顶高度、温度和压力分布的解析表达式。
• 分析水汽、云和臭氧在改变辐射通量和反照率方面的作用，特别是在红外窗口区域。

Figure 1: The three vibrational modes of the CO 2 from Fermi’s classic paper on mode mixing [ 5 ] . For the most abundant isotopolgue, 16 O 12 C 16 O, the mode frequencies are: symmetric stretch (b) $\nu_{1}=1388$ cm -1 ; (c) bending $\nu_{2}=667$ cm -1 ; and (d) asymmetric stretch, $\nu_{3}=2349$ c

实验结果

研究问题

• RQ1 CO₂和H₂O等温室气体与N₂和O₂等非温室气体在大气辐射效应上有何不同？
• RQ2 在温室气体浓度足够高的行星上，哪些物理机制导致对流层和平流层的形成？
• RQ3 真实大气复杂的光谱不透明度在多大程度上影响了地球向外空间辐射的起源高度？
• RQ4 简化的辐射传输模型在多大程度上能准确再现地球向外热辐射的卫星观测光谱？
• RQ5 CO₂增加对地表温度的定量影响是什么？反馈机制如何影响这一效应？

主要发现

• 在简化的灰体大气模型中，对流层接近等熵，平流层接近等温，对流层顶高度由辐射与对流平衡决定。
• 在真实大气中，地球向外空间的热辐射来自对流层的多个高度，以及平流层的少量贡献，而不仅限于对流层顶，如简化模型所示。
• 模型计算的大气顶层红外光谱与卫星观测结果高度一致，即使在水汽差异显著的区域（如撒哈拉、地中海和南极）也成立。
• 在考虑所有反馈机制后，CO₂浓度加倍导致的地表温度上升估计约为1 °C，且无观测证据支持存在大的正反馈。
• 云和反照率变化（如北极海冰融化）仅具有区域影响，不会显著改变全球能量平衡。
• 大气作为热机运行，温室气体作为热阻，促进能量的垂直输送，驱动天气和气候动力学。

Figure 2: To calculate greenhouse effects in detail, one must include the opacity of hundreds of thousands of individual line intensities, shown here as colored dots from the HITRAN data base. More details of how line intensities are used can be found in references [ 6 , 7 ] .