Aidi Zhang | Searcharxiv

arXiv2025

Understanding the Evolution of Global Atmospheric Rivers with Vapor Kinetic Energy Framework

Atmospheric rivers (ARs) often cause damaging winds, rainfall, and floods. However, the physical mechanisms governing their evolution remain poorly understood. To close this gap, we perform a global Vapor Kinetic Energy (VKE) budget analysis. Using two formulations of VKE, we show that ARs are governed by similar mechanisms regardless of ocean basins. ARs intensify primarily through the conversion of potential energy to kinetic energy (PE-to-KE), with horizontal convergence of vapor kinetic energy providing a secondary contribution in some regions. ARs decay mainly through condensation and turbulent dissipation, while their propagation is governed by the downstream convergence and upstream divergence of vapor kinetic energy. We also find PE-to-KE conversion varies spatially and strengthens in regions of greater baroclinic instability or enhanced topographic lifting, e.g., along North America's west coast. Collectively, these findings demonstrate that the VKE framework provides a powerful diagnostic for how physical processes shape AR evolution and regional variability.

physics.ao-ph↗

arXiv2024

Stable 3-dimensional Vortex Families Consistent with Jovian Observations Including the Great Red Spot

Detailed observations of the velocities of Jovian vortices exist at only one height in the atmosphere, so their vertical structures are poorly understood. This motivates this study that computes stable 3-dimensional, long-lived planetary vortices that satisfy the equations of motion. We solve the anelastic equations with a high-resolution pseudo-spectral method using the observed Jovian atmospheric temperatures and zonal flow. We examine several families of vortices and find that {\it constant-vorticity} vortices, which have nearly-uniform vorticity as a function of height and horizontal areas that go to zero at their tops and bottoms, converge to stable vortices that look like the Great Red Spot (GRS) and other Jovian anticyclones. In contrast, the {\it constant-area} vortices proposed in previous studies, which have nearly-uniform areas as a function of height and vertical vorticities that go to zero at their tops and bottoms, are far from equilibrium, break apart, and converge to {\it constant-vorticity} vortices. Our late-time vortices show unexpected properties. Vortices that are initially non-hollow become hollow (i.e., have local minima of vertical vorticity at their centers), which is a feature of the GRS that cannot be explained with 2-dimensional simulations. The central axes of the final vortices align with the planetary-spin axis even if they initially align with the local direction of gravity. We present scaling laws for how vortex properties change with the Rossby number and other non-dimensional parameters. We analytically prove that the horizontal mid-plane of a stable vortex must lie at a height above the top of the convective zone.

physics.flu-dyn↗