Energy cascades in the troposphere and stratosphere

Atmospheric circulation spans a wide range of scales from Ο(10⁴) km down to scales Ο(1) cm, all of which are nonlinearly coupled and can exchange energy. Energy transfer and conversion at various length scales can play important roles in shaping weather patterns and the global circulation regulating Earth’s climate. In this work, we apply a coarse-graining (CG) scale-analysis framework to atmospheric reanalysis data (ERA5) derived from satellites and high-resolution models, which enables us to create global geographic maps of the KE cascade at any scale. In addition to an upscale cascade, we find the existence of a significant down-scale KE cascade at scales smaller than synoptic scales. While theoretically expected, such downscale transfer was not measured in previous analyses, which relied on a spherical harmonics framework and were restricted to the toroidal (non-divergent) atmospheric circulation. While the toroidal (non-divergent) component dominates the KE, the potential (divergent) component plays a central role in facilitating down-scale cascades. We show that the transition from up-scale to down-scale kinetic energy cascade occurs at different flow scales for different pressure levels in the troposphere and stratosphere.