Effects of the quasi‐biennial oscillation on the zonally averaged transport of tracers

Abstract

Abstract. The influence of the quasi-biennial oscillation (QBO) on the transport of long-lived tracers out of the tropics and the mechanism responsible for the QBO in subtropical ozone and its dependence on the seasonal cycle are examined with a two-dimensional model. The modeled QBO induces a meridional circulation which modulates transport of long-lived tracers out of the tropics. The induced circulation also produces a QBO in ozone in the subtropics by advection of ozone out of the tropics and down from higher altitudes. In agreement with observations, the subtropical anomalies in ozone are greatest in the winter season. This seasonal synchronization of the subtropical anomalies occurs because the induced circulation is stronger always in the winter hemisphere as a result of nonlinear momentum advection in the tropics and subtropics. Meridional transport in the model is enhanced by the QBO through an "upper" and a "lower" transport regime, in agreement with the analysis by Hitchman et al. [ 1994]. When there are descending westerly winds in the tropics in the model, transport out of the tropics is enhanced in the lower stratosphere. When there are descending easterlies, transport out of the tropics is enhanced in the middle stratosphere. This modulation of transport out of the tropics significantly influences the stratospheric distribution of long-lived tracers. Depending on the phase of the QBO, mixing ratio surfaces of long-lived tracers (such as N20 ) in the extratropics can be displaced poleward by more than 10 ø.

Spatiotemporal variation of the ozone QBO in MLS data by wavelet analysis

“…These results agree well with our results. On the other hand, the amplitude (4%) obtained from model simulation (Chipperfield et al, 1994;Jones et al, 1998;McCormack et al, 2007) is much less than the amplitude obtained from satellite data.…”

“…The anomalies at these levels are out of phase and indicate a node at 28 km. From model simulations Chipperfield et al (1994) and Jones et al (1998) reported similar double peak structure (with two maxima of about 4% centered at about 24 and 32 km). Using HALOE data from 1992 to 2000 and numerical simulation, Yuejuan et al (2002) reported that in the tropical region, the phase of the ozone QBO changes many times with increase in height.…”

“…Subsequent observational (Soukharev, 1997;Kondratiyev, 1990;Stolarski et al 1991;Chandra and McPeters 1994) as well as numerical simulations (Mayr et al, 2003;Lee and Smith, 2003;McCormack, 2003;Yuejuan et al, 2005;Cordero and Nathan, 2005) have reported various features of the QBO. The influence of the QBO on many trace gases including methane, water vapor, ozone, NO 2 , HCl, volcanic aerosol have been reported in the past (Dunkerton, 2001;Jones et al, 1998;Fleming et al, 2002;Yuejuan et al, 2005;Fadnavis et al, 2007).…”

Analysis of residual mean transport in the stratosphere: 1. Model description and comparison with satellite data

“…It is shown further that subtropical tracer gradients are generated as a natural consequence of the difference between the timescale for advection in the tropics and the timescale for diffusion in the extratropics. The location and the steepness of the gradients are modulated by changes in the tropical circulation resulting, for example, from the quasi-biennial oscillation (QBO) [Jones et al, 1998]. …”

“…Transport within the tropics and across the subtropics is completely advective in nature and consistent, within the TEM framework, with the large-scale diffusion specified in the extratropics. (2) The nonlinear momentum advection terms are included in the dynamics module and have a significant effect on the circulation in the vicinity of the equator [Jones et al, 1998]. (3) Frictional drag in the lower stratosphere is assumed to be small except for the region immediately above the tropopause.…”