The governing processes and timescales of stratosphere-to-troposphere transport and its contribution to ozone in the Arctic troposphere

Abstract

Abstract. We used the seasonality of a combination of atmospheric trace gases and idealized tracers to examine stratosphere-to-troposphere transport and its influence on tropospheric composition in the Arctic. Maximum stratosphere-to-troposphere transport of CFCs and O 3 occurs in April as driven by the Brewer-Dobson circulation. Stratosphere-troposphere exchange (STE) occurs predominantly between 40 • N to 80 • N with stratospheric influx in the mid-latitudes (30-70 • N) accounting for 67-81% of the air of stratospheric origin in the Northern Hemisphere extratropical troposphere. Transport from the lower stratosphere to the lower troposphere (LT) takes three months on average, one month to cross the tropopause, the second month to travel from the upper troposphere (UT) to the middle troposphere (MT), and the third month to reach the LT. During downward transport, the seasonality of a trace gas can be greatly impacted by wet removal and chemistry. A comparison of idealized tracers with varying lifetimes suggests that when initialized with the same concentrations and seasonal cycles at the tropopause, trace gases that have shorter lifetimes display lower concentrations, smaller amplitudes, and earlier seasonal maxima during transport to the LT. STE contributes to O 3 in the Arctic troposphere directly from the transport of O 3 and indirectly from the transport of NO y . Direct transport of O 3 from the stratosphere accounts for 78% of O 3 in the Arctic UT with maximum contributions occurring from March to May. The stratospheric contribuCorrespondence to: Q. Liang (Qing.Liang@nasa.gov) tion decreases significantly in the MT/LT (20-25% of total O 3 ) and shows a very weak March-April maximum. Our NO x budget analysis in the Arctic UT shows that during spring and summer, the stratospheric injection of NO y -rich air increases NO x concentrations above the 20 pptv threshold level, thereby shifting the Arctic UT from a regime of net photochemical ozone loss to one of net production with rates as high as +16 ppbv/month.

Using beryllium-7 to assess cross-tropopause transport in global models

“…By contrast, GEOS4-DAS tends to have too strong a residual circulation, and the age of air is too young compared to observations Schoeberl, 2004;Douglass et al, 2008). A GMI CTM simulation driven with the GEOS4-DAS meteorological fields showed the model's inadequacy in simulating upper-tropospheric ozone (Liang et al, 2009). These findings are consistent with what we illustrated in this study from a perspective of 7 Be tracers.…”

“…Terao et al (2008) examined the role of variability in the input of stratospheric ozone on the interannual variability of tropospheric ozone in the northern extratropics. Liang et al (2009) investigated the impact of stratosphere-to-troposphere transport on tropospheric ozone and NO x chemistry over the Arctic. By contrast, GEOS4-DAS tends to have too strong a residual circulation, and the age of air is too young compared to observations Schoeberl, 2004;Douglass et al, 2008).…”

Air‐mass origin as a diagnostic of tropospheric transport

“…This in turn has implications for albedo changes [e.g., black carbon, Koch and Hansen, 2005;Huang et al, 2010] and biosphere health [e.g., polychlorinated biphenyls, Malanichev et al, 2004]. Similarly, the changes in the air masses of last stratosphere contact have implications for the tropospheric distribution of ozone [e.g., Liang et al, 2009] and cosmogenic tracers such as beryllium-7 [e.g., Dibb et al, 2003;Liu et al, 2004], and for the maintenance of the tropospheric moisture budget [e.g., Waugh, 2005]. In particular, increases in the air-mass fraction of last contact with the midlatitude tropopause, where most stratosphere-to-troposphere transport takes place, imply potentially increased surface ozone of stratospheric origin (assuming no changes in chemistry), increases in beryllium-7, and drier air.…”

Analysis of ozone and nitric acid in spring and summer Arctic pollution using aircraft, ground-based, satellite observations and MOZART-4 model: source attribution and partitioning

“…This reflects the different sampling strategies between the two campaigns Brock et al, 2011). Transport from the stratosphere, which is responsible for a large enhancement of tropospheric ozone in regions of subsidence (Cooper et al, 2002;Liang et al, 2009), is the predominant source above 5 km. It becomes even larger than the sum of the tropospheric contributions above 8 km.…”