1 / 29

Tracers in Ocean and Climate Models

This article explores the importance of using tracers in ocean and climate models, including model validation, diagnosing circulation mechanisms, studying the ocean carbon cycle, data assimilation, and paleoceanographic considerations.

svaughn
Download Presentation

Tracers in Ocean and Climate Models

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Tracers in Ocean and Climate Models* Matthew England CEMAP, School of Mathematics The University of New South Wales * See also www.maths.unsw.edu.au/~matthew/publications.html#MR98

  2. Possible due to: GEOSECS, TTO, SAVE, WOCE, …..

  3. Why bother with tracers in models? • Ocean model “validation” • Diagnosis of model circulation mechanisms • Studies of the ocean carbon cycle • Data assimilation studies • Paleoceanographic considerations

  4. Why bother with tracers in models? • Ocean model “validation” (e.g. CFCs, 14C) • Diagnosis of model circulation mechanisms (e.g. dye/age tracers, 39Ar) • Studies of the ocean carbon cycle (carbon compounds, oxygen, phosphate, nitrate,…) • Data assimilation studies (e.g. CFCs, tritium) • Paleoceanographic considerations (e.g. carbon-13, oxygen-18)

  5. 100-1000 year ventilation 10-100 year ventilation

  6. Observed 14C Robust diagnostic Supressed convection and vertical motion Prognostic Robust diagnostic:T-S restored to observed in the interior Prognostic experiment:Interior T-S free to evolve Toggweiler et al. [1989]

  7. Chlorofluorocarbons

  8. Plate 2. Distribution of CFC-12 on isopycnal surfaces corresponding to maximum NADW outflow in 1988 in the Redler and Dengg [1999] simulations. (a) In the 4/3° model, and (b) in the 1/3° model. The color bar indicates CFC concentrations in pmol/kg, with iso­pycnal layer depths contoured (meters).

  9. Ajax section in the South Atlantic AAIW CDW AABW CDW

  10. Forcing functions for tracers ? 14C CFC CFC 14C CFC CFC CFC 14C 14C sea-ice Air-sea gas flux = f (k, ice, a) CFC 14C CFC k = piston velocity ~ wind speed, U2 or U3 14C a = solubility ~ SST, (SSS) 3He 3He

  11. Tracers in coupled climate models: • How to compute gas uptake: • Use model-generated ice, winds, T-S? • Use observed ice, winds, T-S? Both approaches can give an apparently good tracer simulation but for the wrong reason (see England and Maier-Reimer 2001 for details)

  12. Case 1:

  13. Case 2: Spurious convection

  14. Other tracer techniques: • Age/Dye tracers • Tracer data assimilation • Off-line tracer models (Cox, 1989, England 1995, O’Farrell 2000….) (Haine 1999, Schlitzer 1996, …) (Aumont 1998, Sen Gupta & England 2003)

  15. Off-Line Tracer Model • Interannual • Seasonal • Intraseasonal OGCM Horizontal Velocity Fields Continuity Equation u , v w Source Terms Mixing Terms Tracer Conservation Equation • Water-mass source regions • CFCs, 14C, 3He • Radioactive waste • T, S • Pollution, etc…. • Eddy statistics • Isopycnal mixing • GM (1990) • Convective ML • Wind Driven ML Tracer Concentration T (x, y, z, t) T, S, CFCs, 14C,….

  16. Example: CFC simulations in a ¼ degree model Integrated CFC content below 2000m Year = 1980 PhD project: Alex Sen Gupta

  17. Integrated CFC content below 2000m Year = 2000 PhD project: Alex Sen Gupta

  18. Integrated CFC content below 2000m Year = 2020 PhD project: Alex Sen Gupta

  19. Integrated CFC content below 2000m Year = 2040 PhD project: Alex Sen Gupta

  20. Summary – Tracers in climate models • Advantages: • Independent assessment of model (complements T-S) • Can validate within ocean-only component • Complements GBC and carbon cycle modelling • Drawbacks: • Extra CPU (especially 14C) • Can manipulate outcome to some extent • Uncertainties: • Tracer source functions • Sparse data • How to formalise assessment?

More Related