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Developing a next generation representation of the ocean for atmospheric chemistry transport models.

Prof Mat Evans (WACL, University of York), Prof Lucy Carpenter (WACL, University of York)

Contact email: mat.evans@york.ac.uk

Computer models of the Earth system are a central tool in understanding how atmospheric processes and feedbacks impact global climate and air quality, two pressing social issues. These models need to provide sufficient detail to be able to simulate key interactions, such as that between the atmosphere and the biosphere.  The vast majority of the Earth is covered by ocean and so air-sea interactions are critical. Historically, the process level representation of this interaction has been somewhat simplistic. However, over the last decade, as observations have increased, our understanding of processes occurring between the ocean and the atmosphere has improved (see for example [Ganzeveld et al., 2009; Bell et al., 2013; Carpenter et al., 2013]) to the point where a more detailed numerical description of the processes occurring at the ocean-atmosphere interface is now warranted.

The focus of this project will be on developing a new ocean-atmosphere module representing the physics, chemistry, and biology of the ocean, together with the exchange between the top of the ocean and the bottom of the atmosphere. The initial activity will be on developing the ocean tracer transport module based on the assimilated products being produced by the Copernicus Marine project (http://marine.copernicus.eu). This model will be tested against CFC observations and models contributing the OMIP modelling effort [Griffies et al., 2016] to allow its veracity to be assessed. Subsequently the representation of the photolytic breakdown of compounds in the ocean will need to be included. Once these processes are in place the chemistry and biology of the oceans can be considered. Long lived chemical (Cl-, NO3- etc.) and biological components (chlorophyll, dissolved organic carbon etc.) will be driven by the Copernicus products. The initial chemical development will be on the ocean production, loss and emission of methyl iodide into the ocean as it is thought to be represented by a relatively simple chemistry / biological system. The ultimate goal is to understand the exchange between the atmosphere and the atmosphere of reactive compounds in general and to specifically include a much better representation of the ocean deposition of ozone and its subsequent surface chemistry. 

The atmospheric component of the modelling will use the GEOS-Chem model (www.geos-chem.org), an open source community atmospheric chemistry transport model. Prof Evans has extensive experience of using this model. The project will exploit computing resources available to the atmospheric chemistry group at the University of York. Ongoing ocean-atmospheric and ocean chemistry research from Prof Carpenter’s field and laboratory studies will be incorporated into the project analysis.

Figure 1:Surface chlorophyll concentration (left) and surface velocity (right) from the Copernicus Marine system. These and other products will be used to drive the ocean tracer-transport model.

Objectives

  1. Develop an offline ocean tracer transport model based on the Copernicus Marine outputs.
  2. Test the model against available observations of passive tracers such as CFCs and the output of other models.
  3. Add in the capability to determine photo-dissociation rates within the ocean based on pre-existing code.
  4. Add chemistry into the model to represent the chemistry of methyl iodide production
  5. Add in a representation of the uptake of ozone to the model and the subsequent reactions in the surface layer.  

Potential for high impact outcome

Over the last decade, interest in ocean-atmosphere interactions have taken a secondary role to land-atmosphere interactions. However, recent developments have shown that ocean-atmosphere interactions can play a surprisingly large role in determining the concentration of ozone in the present day and in the past with implications for climate and air quality [Saiz-Lopez et al., 2012, 2014; Sherwen et al., 2016a] and may provide a new source of atmospheric aerosols [Sherwen et al., 2016b]. We would anticipate further developments in this field over the next years.

Training

The student will be provided with training as part of the standard package from the Department of Chemistry at the University of York and as part of the NERC SPHERES Dotoral Training Partnership. The student will be expected to attend courses run by the National Centre of Atmospheric Science and though NERC funded advanced training courses. Where appropriate the student will be encouraged to develop their skills in HPC and numerical methods through other courses locally and nationally.  The student will form part of the Wolfson Atmospheric Chemistry Laboratories at the University of York which consistent of  a large and vibrant atmospheric chemistry community.

Student profile

The student should have a strong interest in global environmental problems with a strong background in a quantitative and mathematically based science (maths, physics, chemistry, engineering). The student should also have an enthusiasm for programming, numerical methods and scientific computing.

References

Bell, T. G., W. De Bruyn, S. D. Miller, B. Ward, K. Christensen, and E. S. Saltzman (2013), Air-sea dimethylsulfide (DMS) gas transfer in the North Atlantic: Evidence for limited interfacial gas exchange at high wind speed, Atmos. Chem. Phys., 13(21), 11073–11087, doi:10.5194/acp-13-11073-2013.

Carpenter, L. J., S. M. MacDonald, M. D. Shaw, R. Kumar, R. W. Saunders, R. Parthipan, J. Wilson, and J. M. C. Plane (2013), Atmospheric iodine levels influenced by sea surface emissions of inorganic iodine, Nat. Geosci., doi:10.1038/ngeo1687.

Ganzeveld, L., D. Helmig, C. W. Fairall, J. Hare, and A. Pozzer (2009), Atmosphere-ocean ozone exchange: A global modeling study of biogeochemical, atmospheric, and waterside turbulence dependencies, Global Biogeochem. Cycles, 23(4), 1–16, doi:10.1029/2008GB003301.

Griffies, S. M. et al. (2016), Experimental and diagnostic protocol for the physical component of the CMIP6 Ocean Model Intercomparison Project (OMIP), Geosci. Model Dev. Discuss., 1–108, doi:10.5194/gmd-2016-77.

Saiz-Lopez, A. et al. (2012), Estimating the climate significance of halogen-driven ozone loss in the tropical marine troposphere, Atmos. Chem. Phys., doi:10.5194/acp-12-3939-2012.

Saiz-Lopez, A., R. P. Fernandez, C. Ord????ez, D. E. Kinnison, J. C. G. Mart??n, J. F. Lamarque, and S. Tilmes (2014), Iodine chemistry in the troposphere and its effect on ozone, Atmos. Chem. Phys., doi:10.5194/acp-14-13119-2014.

Sherwen, T. et al. (2016a), Global impacts of tropospheric halogens (Cl, Br, I) on oxidants and composition in GEOS-Chem, Atmos. Chem. Phys., (May), 1–52, doi:10.5194/acp-2016-424.

Sherwen, T. M., M. J. Evans, D. V Spracklen, L. J. Carpenter, R. Chance, A. R. Baker, J. A. Schmidt, and T. J. Breider (2016b), Global modelling of tropospheric iodine aerosol, Geophys. Res. Lett., n/a--n/a, doi:10.1002/2016GL070062.

Related undergraduate subjects:

  • Chemistry
  • Engineering
  • Physics