Articles | Volume 17, issue 20
Atmos. Chem. Phys., 17, 12743–12778, 2017

Special issue: The SPARC Reanalysis Intercomparison Project (S-RIP) (ACP/ESSD...

Atmos. Chem. Phys., 17, 12743–12778, 2017

Research article 26 Oct 2017

Research article | 26 Oct 2017

Assessment of upper tropospheric and stratospheric water vapor and ozone in reanalyses as part of S-RIP

Sean M. Davis1,2, Michaela I. Hegglin3, Masatomo Fujiwara4, Rossana Dragani5, Yayoi Harada6, Chiaki Kobayashi6,7, Craig Long8, Gloria L. Manney9,10, Eric R. Nash11, Gerald L. Potter12, Susann Tegtmeier13, Tao Wang14, Krzysztof Wargan11,15, and Jonathon S. Wright16 Sean M. Davis et al.
  • 1Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, USA
  • 2Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado at Boulder, Boulder, CO 80309, USA
  • 3Department of Meteorology, University of Reading, Reading, RG6 6BX, UK
  • 4Faculty of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan
  • 5European Centre for Medium-Range Weather Forecasts, Reading, RG2 9AX, UK
  • 6Japan Meteorological Agency, Tokyo, 100-8122, Japan
  • 7Climate Research Department, Meteorological Research Institute, JMA, Tsukuba, 305-0052, Japan
  • 8Climate Prediction Center, National Centers for Environmental Prediction, National Oceanic and Atmospheric Administration, College Park, MD 20740, USA
  • 9NorthWest Research Associates, Socorro, NM 87801, USA
  • 10Department of Physics, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA
  • 11Science Systems and Applications, Inc., Lanham, MD 20706, USA
  • 12NASA Center for Climate Simulation, Code 606.2, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  • 13GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, 24105, Germany
  • 14NASA Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA 91109, USA
  • 15Global Modeling and Assimilation Office, Code 610.1, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  • 16Department of Earth System Science, Tsinghua University, Beijing, 100084, China

Abstract. Reanalysis data sets are widely used to understand atmospheric processes and past variability, and are often used to stand in as "observations" for comparisons with climate model output. Because of the central role of water vapor (WV) and ozone (O3) in climate change, it is important to understand how accurately and consistently these species are represented in existing global reanalyses. In this paper, we present the results of WV and O3 intercomparisons that have been performed as part of the SPARC (Stratosphere–troposphere Processes and their Role in Climate) Reanalysis Intercomparison Project (S-RIP). The comparisons cover a range of timescales and evaluate both inter-reanalysis and observation-reanalysis differences. We also provide a systematic documentation of the treatment of WV and O3 in current reanalyses to aid future research and guide the interpretation of differences amongst reanalysis fields.

The assimilation of total column ozone (TCO) observations in newer reanalyses results in realistic representations of TCO in reanalyses except when data coverage is lacking, such as during polar night. The vertical distribution of ozone is also relatively well represented in the stratosphere in reanalyses, particularly given the relatively weak constraints on ozone vertical structure provided by most assimilated observations and the simplistic representations of ozone photochemical processes in most of the reanalysis forecast models. However, significant biases in the vertical distribution of ozone are found in the upper troposphere and lower stratosphere in all reanalyses.

In contrast to O3, reanalysis estimates of stratospheric WV are not directly constrained by assimilated data. Observations of atmospheric humidity are typically used only in the troposphere, below a specified vertical level at or near the tropopause. The fidelity of reanalysis stratospheric WV products is therefore mainly dependent on the reanalyses' representation of the physical drivers that influence stratospheric WV, such as temperatures in the tropical tropopause layer, methane oxidation, and the stratospheric overturning circulation. The lack of assimilated observations and known deficiencies in the representation of stratospheric transport in reanalyses result in much poorer agreement amongst observational and reanalysis estimates of stratospheric WV. Hence, stratospheric WV products from the current generation of reanalyses should generally not be used in scientific studies.

Short summary
Ozone and water vapor in the stratosphere are important gases that affect surface climate and absorb incoming solar ultraviolet radiation. These gases are represented in reanalyses, which create a complete picture of the state of Earth's atmosphere using limited observations. We evaluate reanalysis water vapor and ozone fidelity by intercomparing them, and comparing them to independent observations. Generally reanalyses do a good job at representing ozone, but have problems with water vapor.
Final-revised paper