NASA Atmospheric Effects of Aviation Project - Status and plans

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Abstract. Empirical age spectra for the lower tropical stratosphere (from the tropopause to --19.5 km) have been derived from in situ measurements of CO2, using information provided by the vertical propagation of the tropospheric seasonal cycle and long-term positive trend. Our method provides accurate and unambiguous mean ages for this region which are difficult to obtain by simple analysis of lag times from tracer measurements. We find that the air is 30-40% younger in northern spring than in autumn. For example, at 460 K the mean age (relative to the tropical tropopause) was 0.4 years in March and 0.6 years in September. The phase lag times and attenuation of CO2 seasonal extrema in the stratosphere are shown to depend on seasonal variations in transport rates and on the presence of harmonics in the CO2 boundary condition with frequencies higher than 2n/yr. Profiles of stratospheric water vapor, generated from the derived age spectra with a stratospheric boundary condition based on observed tropical tropopause temperatures, are consistent with in situ observations of H20.Comparison of the predicted water vapor seasonal cycle with satellite observations suggests that satellite-borne instruments underestimate the amplitude near the tropical tropopause. We relate the empirical age spectra to the analytic solution for the 1-D advection-diffusion tracer continuity equation to obtain seasonally resolved estimates of the ascent rate and the vertical diffusion coefficient. The derived age spectra provide a unique observation-based diagnostic for evaluating the simulation of tracer transport in models.

Empirical age spectra for the lower tropical stratosphere from in situ observations of CO₂: Implications for stratospheric transport

Andrews¹,

Boering²,

Daube³

et al. 1999

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The Global Modeling Initiative assessment model: Application to high‐speed civil transport perturbation

Kinnison¹,

Connell²,

Rodríguez³

et al. 2001

When compared to available NOy observations, we find that the model consistently underestimates lower stratospheric NO v. This discrepancy is consistent with the model bias toward less negative ozone impact, when cohapared to results from other models. Additional analysis also indicates that for an HSCT assessment it is equally important for a model to accurately represent the lower stratospheric concentrations of ozone and H20. The GMI model yields good agreement in comparisons to ozone data for present-day conditions, while H20 is constrained by climatology as much as possible; thus no further biases would be expected from these comparisons. Uncertainties due to discrepancies in the calculated age of air compared to that derived from measurements, and of the impact of emissions on heterogeneous and polar chemistry, are difficult to evaluate at this point.

Small‐scale chemical evolution of aircraft exhaust species at cruising altitudes

Kärcher¹,

Hirschberg²,

Fabian³

1996

The chemical transformation of exhaust trace species in aircraft plumes, both directly emitted by the airplane and generated in situ within the first few kilometers behind a single jet engine, is investigated. The chemical processes are strongly coupled to the turbulent dynamics of the hot jet which rapidly mixes with the surrounding atmospheric air. Key issues of the chemical reactions in the jet regime are worked out and the results of extensive parameter studies are presented. The evolution of hydrogen, oxygen, nitrogen, and sulfur species is discussed in detail and related to observations. Spatially resolved, two‐dimensional simulations are compared with box model calculations to point out specific features that result from the coupling between mixing and chemistry and to answer the question under which conditions box models can be applied to give a reasonable description of the jet plume chemistry. Main results concern the conversion efficiencies of primary into secondary exhaust products, the oxidation potential within young aircraft plumes to produce nitrous, nitric, and sulfuric acid, the sensitivity of these processes under variation of exit plane conditions, as well as the production of new aerosol particles. Open questions concerning chemical processing in near‐field exhaust plumes are addressed. The modeling framework presented in this study serves as a basis for further near‐field studies on the physics and chemistry in aircraft wakes.