Net influence of an internally–generated QBO on modeled stratospheric climate and chemistry

A Goddard Earth Observing System Chemistry–Climate Model (GEOSCCM) simulation with realistic tropical non–orographic gravity wave drag (GWD) is compared to an otherwise identical simulation with near–zero tropical non–orographic GWD. The GEOSCCM generates a quasi–biennial oscillation (QBO) zonal wind signal in response to realistic tropical GWD. The modeled QBO has a frequency and amplitude that closely resembles observations. In the annual mean, the modeled QBO improves the simulation of tropical zonal winds and enhances tropical and sub–tropical stratospheric variability.

Inclusion of the QBO slows the meridional overturning circulation, resulting in a generally older stratospheric mean age–of–air. Slowing of the overturning circulation, changes in stratospheric temperature and enhanced sub–tropical mixing all affect the mean stratospheric distributions of ozone, methane, nitrous oxide and water vapor.

Inclusion of the QBO enhances polar stratospheric variability in winter. Because tropical zonal winds are generally easterly in the simulation without a QBO, there is a relative increase in tropical zonal winds in the simulation with a QBO. Extra–tropical differences between the simulations with and without a QBO thus reflect a bias toward the westerly phase of the QBO: a relative strengthening of the polar stratospheric jet, polar stratospheric cooling and a weak reduction in Arctic lower stratospheric ozone.