Effects of the stratospheric quasi-biennial oscillation on long-lived greenhouse gases in the troposphere

An analysis is presented of results of an extended integration with a global general circulation model that includes treatment of a long-lived tropospheric trace constituent as well as a momentum source that forces a realistic stratospheric quasibiennial oscillation (QBO) It is shown that the dynamical QBO may modulate stratosphere-troposphere exchange in such a manner as to produce a QBO in global-mean tropospheric tracer mixing ratio. For the growth rate of tropospheric methane this transport-induced QBO is expected to have a peak-to-peak amplitude of 1-2 ppbv yr(-1) which, while modest compared with the full range of observed variability in growth rate, is still significant. The observed methane growth rate time series during 1983-1999 is shown to be consistent with the predicted QBO effect,although the record is definitely dominated by other interannual variations.