Atmospheric Tracer Transport Model Intercomparison Project (TransCom) Data Sets

The Atmospheric Tracer Transport Model Intercomparison Project (TransCom) was created to quantify and diagnose the uncertainty in inversion calculations of the global carbon budget that result from errors in simulated atmospheric transport, the choice of measured atmospheric carbon dioxide data used, and the inversion methodology employed. TransCom was conceived at the Fourth International CO2 Conference in Carqueiranne, France in 1993. The project is part of a larger International Geosphere-Biosphere Programme (IGBP), Global Analysis, Interpretation, and Modeling (GAIM) research program which aims to develop coupled ecosystem-atmosphere models that describe time evolution of trace gases with changing climate and changes in anthropogenic forcing.

Initially coordinated by Peter Rayner at the Commonwealth Scientific and Industrial Research Organization (CSIRO), TransCom is now being coordinated by Scott Denning and Kevin Gurney at the Department of Atmospheric Sciences, Colorado State University. Three distinct phases of the TransCom have now been completed. Investigators are currently in the process of planning and coordinating a new future for the TransCom community.

The first phase of TransCom (TransCom 01) compared the model output of two different components of the carbon cycle: the fossil CO2 source and the seasonal aspect of the biospheric CO2 source.

The second phase of TransCom (TransCom 02) examined the transport of sulfur hexafluoride (SF6) emissions using 10 tracer transport models. Comparison was made among the models and among observed concentrations at monitoring locations around the globe. The comparison allowed investigators to isolate aspects of the model transport that gave rise to systematic differences in the simulated results. The first segment of results from TransCom 2 have been published (Denning et al., 1999).

TransCom 03 involved a CO2 inversion calculation intercomparison. Investigators have completed the control inversion for Level I (the annual mean inversion) under TransCom 3 (Gurney et al., 2002). Data sensitivity analysis, model-to-model analysis and other annual mean sensitivity work has been performed (Gurney et al., 2003; Law et al., 2003) and the Level 2 cyclostationary control inversion intercomparison has been completed (Gurney et al., 2004).

Two new Transcom experiments (TransCom 4) have been initiated. The first involves a comparison of upper-air model output. The second is a simulation of hourly CO2, radon and SF6 for 2002-2003 using prescribed fluxes.

References:

Denning, A. S., M. Holzer, K. R. Gurney, M. Heimann, R. M. Law, P. J. Rayner, I. Y. Fung, S.-M. Fan, S. Taguchi, P. Friedlingstein, Y. Balkanski, J. Taylor, M. Maiss, and I. Levin. 1999. Three-dimensional transport and concentration of SF6: A model intercomparison study (TransCom 2). Tellus 51B: 266-297.

Gurney, K. R., R. M. Law, A. S. Denning, P. J. Rayner, D. Baker, P. Bousquet, L. Bruhwilerk, Y-H. Chen, P. Ciais, S. Fan, I. Y. Fung, M. Gloor, M. Heimann, K. Higuchi, J. John, E. Kowalczyk, T. Maki, S. Maksyutov, P. Peylin, M. Prather, B. C. Pak, J. Sarmiento, S. Taguchi, T. Takahashi, and C-W. Yuen. 2003. TransCom 3 CO2 inversion intercomparison: 1. Annual mean control results and sensitivity to transport and prior flux information. Tellus 55B: 555-579.

Gurney, K. R., R. M. Law, A. S. Denning, P. J. Rayner, D. Baker, P. Bousquet, L. Bruhwilerk, Y-H. Chen, P. Ciais, S. Fan, I. Y. Fung, M. Gloor, M. Heimann, K. Higuchi, J. John, E. Kowalczyk, T. Maki, S. Maksyutov, P. Peylin, M. Prather, B. C. Pak, J. Randerson, J. Sarmiento, S. Taguchi, T. Takahashi, and C-W. Yuen. 2002. Towards robust regional estimates of CO2 sources and sinks using atmospheric transport models. Nature 415: 626-630.

Gurney, K. R., R. M. Law, A. S. Denning, P. J. Rayner, B. C. Pak, D. Baker, P. Bousquet, L. Bruhwilerk, Y-H. Chen, P. Ciais, I. Y. Fung, M. Heimann, J. John, T. Maki, S. Maksyutov, P. Peylin, M. Prather, and S. Taguchi. 2004. Transcom 3 inversion intercomparison: Model mean results for the estimation of seasonal carbon sources and sinks. Global Biogeochemical Cycles 18, GB1010, doi:10.1029/2003GB002111.

Law, R. M., Y-H. Chen, K. R. Gurney, and TransCom 3 modelers. 2003. TransCom 3 CO2 inversion intercomparison: 2. Sensitivity of annual mean results to data choices. Tellus 55B: 580-595.