American Journal for Young Scientists · ISSN 3068-9015
Atmospheric Circulation Change in a Warming Climate: Hemispheric Asymmetry, ENSO Variability, and Polar Vortex Weakening
Authors: Anish Dhamija
Published: June 2, 2026
Category: Environmental Science
Abstract
Large-scale atmospheric circulation moves heat from the tropics toward the poles and plays a major role in shaping regional climate. I examine multidecadal changes in tropo- spheric overturning cells, winter stratospheric variability, and tropical Pacific dynamics using ERA5 reanalysis data and nonlinear dimensionality-reduction methods. From 1979 to 2025, the Hadley cell widens at a statistically significant rate, mainly due to shifts in the South- ern Hemisphere. During the same period, the Polar cell contracts, again primarily in the Southern Hemisphere, while the Ferrel cell shows no clear long-term trend. These results show that recent circulation changes are not evenly distributed between hemispheres. In the winter stratosphere, diagnostics at 10 hPa and 60◦N, including zonal wind, polar-cap geopo- tential height, and planetary wave-1 amplitude, display strong year-to-year variability but no statistically significant long-term trend. This suggests that internal variability remains the dominant influence on Arctic winter stratospheric behavior over this time range. For the tropics, I construct a low-dimensional nonlinear representation of ENSO using principal com- ponent analysis followed by autoencoder embedding. The reconstructed structure broadens and shifts over time, indicating changes in both ENSO strength and spatial pattern