A Lagrangian Particle Perspective of Tropopause Folds

Tropopause folds, which frequently occur on the poleward side of the subtropical and subpolar jets, are often associated with enhanced stratosphere-troposphere exchange. On a global scale, they account for an important fraction of the total downward transport of stratospheric air into the troposphere. Thus, it is useful to understand the processes involved in their formation. To that end, backward and forward trajectory analyses are produced for a variety of historical examples using regional Weather Research and Forecasting (WRF) model simulations and global GFS model simulations. The trajectories suggest a basic conceptual model for the formation of tropopause folds which more accurately corresponds to their average structure than solutions to the Sawyer-Eliassen equation.