Simulations of the trend and annual cycle in stratospheric CO2

Abstract

In our general circulation model, CO2 enters the stratosphere primarily through the tropical tropopause, where air parcels are effectively labeled in time by their CO2 values (although not uniquely because of the cycles in tropospheric concentration). Parcels of differing ages are subsequently mixed in the stratosphere. Only when the growth is purely linear can the CO2 offset in a parcel relative to the troposphere be interpreted as the average time since stratospheric air was last in contact with the troposphere, i.e., the "age' of the stratosphere. Our model is in qualitative agreement with multiyear averages of balloon soundings at northern mid- and high latitudes; the stratosphere at 30 km at mid-latitudes is about 4 years (6 ppm of CO2) behind the troposphere. We predict significant propagation of the CO2 annual cycle into the lower stratosphere, an effect which must be accounted for when interpreting observations. -from Authors