Courant Institute, NYU
Title: Assessing Stratospheric Transport in Atmospheric General Circulation Models using Age of Air
Abstract: Accurate representation of tracer transport continues to be a challenge for climate models. Differences in the resolved circulation, biases due to physical parameterizations, and differences in the numerical representation of trace gases result in large variations in transport, even among state-of-the-art climate models. These differences result in disagreement among model projections of the evolution of stratospheric ozone throughout the 21st century, particularly in the recovery of the Antarctic ozone hole.
We first propose two benchmark tests to assess stratospheric transport in four different atmospheric models. The models were developed at GFDL and NCAR and employ different numerical method to solve the underlying equations. The models are forced with identical thermal forcings and transport is quantified using age of air, an idealized tracer that quantifies transport timescales in the atmosphere. The benchmark tests reveal important differences across the models in both the resolved dynamics and transport. We further use a theoretical “leaky pipe” model of stratospheric transport to understand the impact of differences in diabatic circulation, stratospheric wave breaking and mixing, and numerical model diffusion on stratospheric transport in the stratosphere.