The influence of the stratospheric Quasi-Biennial Oscillation on trace gas levels at the Earth’s surface

Abstract

The Quasi-Biennial Oscillation (QBO) of tropical zonal wind is one of the most important modes of interannual variability in the stratosphere. It is well established that the QBO influences the distribution of trace gases throughout the global stratosphere. What has not been clearly shown thus far is whether the stratospheric QBO has a consistent and significant impact on tropospheric trace gases. Here we clearly demonstrate that the effects of QBO variability in stratospheric transport and trace gas distributions regularly and persistently extend into the troposphere, which influences the interannual variability of long-lived trace gas mole fractions at the Earth’s surface. We show that the variability in the surface mole fractions on one- to five-year timescales is primarily driven by the QBO. The QBO influence on tropospheric constituent mole fractions arises from the modulation of the stratosphere to troposphere mass flux and is apparent in surface measurements, as well as throughout the stratosphere and troposphere in chemistry–climate model simulations of chlorofluorocarbon-11, chlorofluorocarbon-12 and nitrous oxide. The global total emissions estimated from measured changes in the global mean surface mole fractions of these ozone-depleting species, as well as other long-lived trace gases, will be improved by accurately accounting for the QBO-driven variability. Interannual variations of long-lived trace gas mole fractions at the Earth’s surface are primarily driven by the stratospheric Quasi-Biennial Oscillation, according to surface measurements and model simulations. Ignoring this variability may induce errors in estimating emissions of trace gases.