Mean ages of stratospheric air derived from in situ observations of CO₂, CH₄, and N₂O

Abstract

Abstract. Accurate mean ages for stratospheric air have been derived from a spatially and temporally comprehensive set of in situ observations of CO2, CH4, and N20 obtained from 1992 to 1998 from the NASA ER-2 aircraft and balloon flights. Errors associated with the tropospheric CO2 seasonal cycle and interannual variations in the CO2 growth rate are ( 0.5 year throughout the stratosphere and ( 0.3 year for air older than 2 years (N20 < 275 ppbv), indicating that the age spectra are broad enough to attenuate these influences over the time period covered by these observations. The distribution of mean age with latitude and altitude provides detailed, quantitative information about the general circulation of the stratosphere. At 20 km, sharp meridional gradients in the mean age are observed across the subtropics. Between 20 and 30 km, the average difference in mean age between the tropics and midlatitudes is -2 years, with slightly smaller differences at higher and lower altitudes. The mean age in the midlatitude middle stratosphere (-25-32 km) is relatively constant with respect to altitude at 5 _ 0.5 years. Comparison with earlier balloon observations of CO2 dating back to the 1970s indicates that the mean age of air in this region has remained within _+1 year of its current value over the last 25 years. A climatology of mean age is derived from the observed compact relationship between mean age and N20. These characteristics of the distribution of mean age in the stratosphere will serve as critically needed diagnostics for models of stratospheric transport.

Constraints on inorganic gaseous iodine in the tropical upper troposphere and stratosphere inferred from balloon-borne solar occultation observations

“…Upward transport of air masses from the TTL into the tropical stratosphere is controlled by the large-scale dynamics of the Brewer-Dobson circulation implying comparatively slow ascent that leaves time for horizontal mixing and for processing of organic source gases to inorganic product gases. Ascent velocities in the tropical lower stratosphere are estimated to a few tenths of a mm/s implying that the mean time since air masses around 20 km (∼475 K) entered the stratosphere is several months (Andrews et al, 2001;Schoeberl et al, 2008). We concede that our observations in the tropical tropopause layer might be affected by local variability of air masses.…”

Variability of stratospheric mean age of air and of the local effects of residual circulation and eddy mixing

“…For completeness, we compare the CLaMS simulated mean age of air with this data set. Figure A1 compares latitudinal profiles of CLaMS simulated mean age of air at 20 km, AoA based on MIPAS observations of SF 6 [Haenel et al, 2014] and on airborne in situ observations of SF 6 and CO 2 (same data as shown in Waugh and Hall [2002], based on various measurements, [Boering et al, 1996;Andrews et al, 2001;Elkins et al, 1996;Ray et al, 1999;Harnisch et al, 1996]). The shadings show the range of monthly mean values for CLaMS and MIPAS, while the error bars show the range between minimum and maximum in situ observations in each latitude bin.…”

The Total Carbon Column Observing Network

“…Stratospheric CO 2 profiles are generated from the age of air relationship derived by Andrews et al [53]. The H 2 O a priori profiles come from the NCEP/NCAR analysis for that day, interpolated to local noon, with stratospheric VMRs based on MkIV balloon profiles.…”