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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/amt-2017-470
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
05 Feb 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).
Chemical modeling of the reactivity of short-lived greenhouse gases: a model inter-comparison prescribing a well-measured, remote troposphere
Michael J. Prather1, Clare M. Flynn1, Xin Zhu1, Stephen D. Steenrod2,3, Sarah A. Strode2,3, Arlene M. Fiore4, Gustavo Correa4, Lee T. Murray5, and Jean-Francois Lamarque6 1Department of Earth System Science, University of California, Irvine, CA 92697-3100, USA
2NASA Goddard Space Flight Center, Greenbelt, MD, USA
3Universities Space Research Association (USRA), GES TAR, Columbia, MD, USA
4Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, USA
5Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627-0221, USA
6Atmospheric Chemistry, Observations and Modeling Laboratory, National Center for Atmospheric Research, Boulder, CO 80301, USA
Abstract. We develop a new protocol for merging in situ measurements with 3-D model simulations of atmospheric chemistry with the goal of integrating over the data to identify the most reactive air parcels in terms of tropospheric production and loss of the greenhouse gases ozone and methane. Presupposing that we can accurately measure atmospheric composition, we examine whether models constrained by such measurements agree on the chemical budgets for ozone and methane. In applying our technique to a synthetic data stream of 14,880 parcels along 180 W, we are able to isolate the performance of the photochemical modules operating within their global chemistry-climate and chemistry-transport models, removing the effects of modules controlling tracer transport, emissions, and scavenging. Differences in reactivity across models are driven only by the chemical mechanism and the diurnal cycle of photolysis rates, which are driven in turn by temperature, water vapor, solar zenith angle, clouds, and possibly aerosols and overhead ozone, which are calculated in each model. We evaluate six global models and identify their differences and similarities in simulating the chemistry through a range of innovative diagnostics. All models agree that the more highly reactive parcels dominate the chemistry (e.g., the hottest 10 % of parcels control 25–30 % of the total reactivities), but do not fully agree on which parcels comprise the top 10 %. Distinct differences in specific features occur, including the regions of maximum ozone production and methane loss, as well as in the relationship between photolysis and these reactivities. Unique, possibly aberrant, features are identified for each model, providing a benchmark for photochemical module development. Among the 6 models tested here, 3 are almost indistinguishable based on the inherent variability caused by clouds, and thus we identify 4, effectively distinct, chemical models. Based on this work, we suggest that water vapor differences in model simulations of past and future atmospheres may be a cause of the different evolution of tropospheric O3 and CH4, and lead to different chemistry-climate feedbacks across the models.

Citation: Prather, M. J., Flynn, C. M., Zhu, X., Steenrod, S. D., Strode, S. A., Fiore, A. M., Correa, G., Murray, L. T., and Lamarque, J.-F.: Chemical modeling of the reactivity of short-lived greenhouse gases: a model inter-comparison prescribing a well-measured, remote troposphere, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-470, in review, 2018.
Michael J. Prather et al.
Michael J. Prather et al.
Michael J. Prather et al.

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Short summary
A new protocol for merging in situ atmospheric chemistry measurements with 3-D models is developed. This technique can identify the most reactive air parcels in terms of tropospheric production/loss of O3 & CH4. It also shows differences in 6 global chemistry models even with specified composition. Thus in situ measurements from, eg, NASA's ATom mission can be used to develop a chemical climatology of, not only the key species, but also the rates of key reactions in each air parcel.
A new protocol for merging in situ atmospheric chemistry measurements with 3-D models is...
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