Atlas Rachel, Podglajen Aurélien, Wilson Richard, Hertzog Albert, Plougonven Riwal
Laboratoire de Météorologie Dynamique/Institut Pierre Simon Laplace, École Normale Supérieure- Paris Sciences et Lettres Université, École Polytechnique- Institut Polytechnique de Paris, Sorbonne Université, CNRS, Paris 91128, France.
Laboratoire Atmosphères et Observations Spatiales/Institut Pierre Simon Laplace (LATMOS/IPSL), Sorbonne Université, Paris 75005, France.
Proc Natl Acad Sci U S A. 2025 Jan 14;122(2):e2409791122. doi: 10.1073/pnas.2409791122. Epub 2025 Jan 8.
The tropical stratosphere is the gateway to the global stratosphere and a commonly proposed location for solar geoengineering. The dynamics of this remote and difficult to observe region are poorly understood, particularly at turbulent length scales. Existing observational estimates of turbulence frequency and strength vary widely. Furthermore, the sources of turbulence and the relationship between turbulence and the mean flow are largely unknown. We assembled a 21-y database of high vertical resolution (10 m) radiosonde data from four equatorial sites in two ocean basins to study tropical stratospheric turbulence frequency, variability, and sources. Turbulent layers thicker than 200 m are identified using subcritical Richardson number as a proxy for turbulence. We show that the turbulent fraction of the tropical stratosphere is strongly modulated by the quasi-biennial oscillation (QBO). Turbulence is enhanced during the QBO phase shifts, and the atmosphere is most turbulent right before the QBO phase switches from negative to positive, where turbulent instabilities typically occur within specific phases of Kelvin waves. Turbulence is less common when the QBO phase is well established, and the atmosphere is least turbulent during the negative phase of the QBO. The turbulent fraction of the equatorial lower stratosphere varies over a factor of ten depending on QBO phase. This relationship provides a robust observational constraint on the multiscale dynamics within this region, which is useful for evaluating atmospheric models, studying wave-mean flow interactions in the context of the QBO, and informing the operation of stratospheric aircraft and the injection of aerosol for geoengineering.
热带平流层是通往全球平流层的通道，也是太阳地球工程中一个常被提议的实施地点。这个偏远且难以观测的区域的动力学情况鲜为人知，尤其是在湍流长度尺度方面。现有的对湍流频率和强度的观测估计差异很大。此外，湍流的来源以及湍流与平均流之间的关系在很大程度上尚不清楚。我们收集了来自两个大洋盆地四个赤道站点的21年高垂直分辨率（10米）探空仪数据数据库，以研究热带平流层的湍流频率、变异性和来源。使用亚临界理查森数作为湍流的代理指标来识别厚度超过200米的湍流层。我们表明，热带平流层的湍流比例受到准两年振荡（QBO）的强烈调制。在QBO相位转换期间，湍流增强，并且在QBO相位从负向正转换之前，大气最为湍流，此时湍流不稳定通常发生在开尔文波的特定相位内。当QBO相位稳定时，湍流较少见，并且在QBO的负相位期间大气湍流最少。赤道低平流层的湍流比例根据QBO相位变化达十倍之多。这种关系为该区域内的多尺度动力学提供了一个有力的观测约束，这对于评估大气模型、在QBO背景下研究波-平均流相互作用以及为平流层飞机的运行和气溶胶注入地球工程提供参考很有用。
