An atmospheric chemist in search of the tropopause.

Prather, M.J., X. Zhu, Q. Tang, J. Hsu and J.L. Neu (2011), An atmospheric chemist in search of the tropopause, J. Geophys. Res., 116, D04306, doi: 10.1029/2010JD014939

To those interested in atmospheric composition and chemistry, the tropopause is a somewhat fuzzy, porous boundary between two chemically distinct regions: the stratosphere and the troposphere. The stratosphere has high ozone levels and short-wave ultraviolet photochemistry that destroys refractory greenhouse gases like nitrous oxide and chlorofluorocarbons; whereas the troposphere has precipitation and hydroxyl chemistry that rids the atmosphere of pollution and gases like methane. By introducing a tracer into a well formed computer model of the atmosphere, a group of ESS scientists provides insight into the chemistry, physics, and location of the tropopause. A tracer that decays in 90 days was chosen to measure the age of air since last contact with the surface. The atmospheric model simulations monitor the chemical aging and circulation patterns of the tracer as shown in the figure. Analysis of this data indicates that the elusive tropopause is subject to seasonal and geographic variability, but can be accurately identified with this tracer. By focusing on time scales that separate stratosphere from troposphere, Dr. Prather’s research group identified the oldest air in the troposphere, the cause of ozone seasonality at the midlatitude tropopause, and a previously unidentified north-south difference in the age of air of the lowermost stratosphere.