Atmos., 116, D20115,, 2011. 2 there) and about 1 year older air than kinematic mean age. For both K z cases, the effect of depletion is stronger than the diffusive separation by more than 1 order of magnitude. Since the AoA is derived as a difference of the SF6 mixing ratios, whereas depletion introduces multiplicative change to the SF6 abundance, the effect of the sink on apparent SF6 AoA is unsteady in time (Fig. All authors participated in the final preparation of the text. None of the model setups are capable of reproducing the observations above 40 km.
4 as a function of time and altitude. 5b, but three years later. Along with setting the equilibrium state with the bulk of a heavy admixture being in the lower layers, molecular diffusion provides additional means for transport to the upper layers where the destruction occurs. The reanalysis uses a 12 h data assimilation cycle, and the forecasts are stored with a 3 h time step. Res., 106, 32295–32314,, 2001. a, b, c. Bhandari, N., Lal, D., and Rama, D. : Stratospheric circulation studies based on natural and artificial radioactive tracer elements, Tellus, 18, 391–406,, 1966. a. Boering, K., Wofsy, S., Daube, B., Schneider, H., Loewenstein, M., Podolske, J., and Conway, T. : Stratospheric mean ages and transport rates from observations of carbon dioxide and nitrous oxide, Science, 274, 1340–1343,, 1996. a. Brinkop, S. and Jöckel, P. : ATTILA 4. Our estimate is also slightly above the range given by Kovács et al. As mentioned in Sect. B) How many grams of NH3 are needed to provide the same number. Regardless of depletion, stronger K z reduces the effect of the gravitational separation; however, the latter is still non-negligible if precisions of the order of a month for AoA are required. Simulations of the AoA as defined above have been performed with Lagrangian transport models. For heavy admixtures, such as SF6 ( kg mol −1) the equilibrium gradient of a mixing ratio is substantial. The simulations for different K z have been initialized with the same state obtained from a separate spin-up simulation with 0. 001-Kz profile in Fig. The WACCM profiles match very well with the observations below 17 km but turn nearly constant above, thus under-representing the depletion of SF6 inside the polar vortex.
Note the slight increase of the model bias after 2009, which is likely caused by our overestimating of the emission rates since that time (see Sect. Dissertation or Thesis. However, in the simulations by Kovács et al. This profile is likely to over-mix the lower stratosphere and under-mix the upper stratosphere and the mesosphere. For SF6, the effect of its loss on the AoA was evaluated by Stiller et al. The latter makes the age derived from the passive tracer equivalent to the age derived from the ideal-age tracer. 2 ECMWF ERA-Interim reanalysis. Phys., 17, 883–898,, 2017. a, b, c, d, e, f, g, h, i, j, k. Krol, M., de Bruine, M., Killaars, L., Ouwersloot, H., Pozzer, A., Yin, Y., Chevallier, F., Bousquet, P., Patra, P., Belikov, D., Maksyutov, S., Dhomse, S., Feng, W., and Chipperfield, M. : Age of air as a diagnostic for transport timescales in global models, Geosci. 5 year per decade in the altitude range of 15–30 km with a profile that varies across altitudes.
The decrease of the atmospheric SF6 content after the emission stop is given in the inset in Fig. This discrepancy is in line with the comparisons in Fig. 1), we used two intermediate profiles obtained by scaling the reference one with factors 0. The error bars show 95% confidence intervals calculated as if a model of linear trend with uncorrelated Gaussian noise was applicable to the time series. The simulated profiles agree quite well with the observed profiles, except for the most diffusive case that gave notably smoother profiles and somewhat overstated SF6 mixing ratios due to too strong upward transport by diffusion through the tropopause and in the lower stratosphere. 5 years were run without the SF6 emissions to evaluate its destruction rate.
1 hPa, which is below the altitude of the SF6 destruction. To minimize the inconsistency between the tracer transport and air-mass fluxes caused by the dimension split at finite time step, the splitting sequence has been inverted at each time step. The vertical profile of molecular diffusivity in the U. S. Standard Atmosphere (NOAA et al., 1976) is shown in (Fig. ERA-Interim and ERA5 reanalyses datasets are available from the European Centre for Medium-Range Weather Forecasts (Dee et al., 2011; Copernicus Climate Change Service, 2017).
A, b. Sofiev, M., Vira, J., Kouznetsov, R., Prank, M., Soares, J., and Genikhovich, E. : Construction of the SILAM Eulerian atmospheric dispersion model based on the advection algorithm of Michael Galperin, Geosci. Destruction of atmospheric SF6 occurs at altitudes above 60 km (Totterdill et al., 2015) that fall within the topmost layer of the ERA-Interim data. These errors are of the order of 4% (below 30 km) up to 10% (at 60 km). A substantial disagreement, however, exists with the ages derived from the MIPAS satellite observations (Stiller et al., 2012; Haenel et al., 2015). Expectedly, the effect of gravitational separation is most pronounced for the case of low eddy diffusivity (0. The remaining differences are caused by spatial inhomogeneities of near-surface mixing ratio of the passive tracer due to variations in the near-surface air density. In the current study, we use an updated version of the SF6 data (compared to the one described in Haenel et al., 2015) called V5H/R_SF6_21/224/225. Atmos., 107, 8285,, 2002. a. Ray, E. L., Rosenlof, K. H., Davis, S. M., Sweeney, C., Tans, P., Wang, T., Elkins, J. W., Bönisch, H., Engel, A., Sugawara, S., Nakazawa, T., and Aoki, S. : Improving stratospheric transport trend analysis based on SF6 and CO 2 measurements, J. 6 pmol mol −1 higher SF6 mixing ratios in the upper part of the stratosphere (above 30 km) than the old versions and is closer to independent reference data. 5 m 2 s −1 for the upper troposphere and 0. It is non-zero for an admixture of a molecular mass different from the one of air. Phys., 10, 10305–10320,, 2010. a, b, c, d, e. Schoeberl, M. R., Sparling, L. C., Jackman, C. H., and Fleming, E. : A Lagrangian view of stratospheric trace gas distributions, J.
12 over 1990–2018 (Fig. The effect of the mesospheric sink is clearly visible above 15–20 km at all latitudes (Fig. Similar to the case in Fig. Phys., 12, 3311–3331,, 2012. a, b, c, d, e, f, g, h, i, j. Strunk, M., Engel, A., Schmidt, U., Volk, C. M., Wetter, T., Levin, I., and Glatzel-Mattheier, H. : CO 2 and SF 6 as stratospheric age tracers: Consistency and the effect of mesospheric SF6-loss, Geophys. This increase of the bias does not appear in Fig.
1) and (6), one can obtain a steady-state distribution of the mass-mixing ratio, ξ, of SF6 due to destruction in the mesosphere at any point where both Eqs. 2017) and the current evaluation are the following. The latter assumption implies that the diffusive vertical flux overwhelms the advective one. Besides, the reduction has a noticeable inter-annual variability that poses substantial difficulties for applying a consistent correction to the apparent AoA. As expected, after July 2016 the content of passive SF6 stays constant, while the others begin to decrease at a rate that depends on the transport properties in the stratosphere with the faster removal for the stronger eddy diffusivity. We could not find any reliable observations of vertical diffusion in a range of 30–50 km. This increase might be caused by issues with retrievals as the systematic errors of the retrievals increase with altitude.
The model was suggested by Hall and Plumb (1994) as an illustration for the concept of the age spectrum.