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introduction
The "Methane" experiment was proposed during the TransCom 2008 meeting in Utrecht. The first protocol was discussed during the post-ICDC8 TransCom meeting in Jena, followed by the final protocol in 2010. Since then 16 models or model variants have performed the simulations. Previous TransCom experiments focused on chemically non-reactive species (SF6, CO2, 222Rn). A CH4 intercomparison requires introduction of atmospheric chemistry, which means a significant new model development for the traditional TransCom participants. However, to focus on model transport properties, the CH4 chemistry is reduced to offline radical (OH, O1D, Cl) only, which means the full-chemistry modellers have to scale down chemistry. During discussion at Jena, methyl chloroform (CH3CCl3) was included for tracking tropospheric OH abundance in the models, as well as SF6 and 222Rn for model transport evaluations. Prescribed fluxes are input to a transport model and 20 years of simulation is run with meteorological forcing appropriate for 1988-2007. Hourly concentrations of all species are output for 280 locations. At 115 locations, species profiles, surface fluxes and meteorological variables are also output.
protocol
The protocol (version 7) . It details the input fluxes, regridding instructions and lists of the output sites and required file formats (similar to TransCom continuous experiment). Instructions are included for accessing the ftp site for downloading input files and uploading model submissions.
model output
The model output is freely available for research purposes but please note the "conditions of use" . The data are available in two formats: the original model submissions containing output for all sites. Output files can be downloaded from ftp fxp.nies.go.jp (refer to the Protocol files for access information). In an effort towards ease of access, time series at a subset of surface sites are archived at the WMO World Data Centre for Greenhouse Gases (http://gaw.kishou.go.jp/)
publications and presentations
Patra, P. K., S. Houweling, M. Krol, P. Bousquet, L. Bruhwiler, and D. Jacob (2010), Protocol for TransCom CH4 intercomparison, Version 7, April (available online at transcom.project.asu.edu/pdf/transcom/T4.methane.protocol_v7.pdf ).
Patra, P. K., S. Houweling, M. Krol, P. Bousquet, D. Belikov, D. Bergmann, H. Bian, P. Cameron-Smith, M. P. Chipperfield, K. Corbin, A. Fortems-Cheiney, A. Fraser, E. Gloor, P. Hess, A. Ito, S. R. Kawa, R. M. Law, Z. Loh, S. Maksyutov, L. Meng, P. I. Palmer, R. G. Prinn, M. Rigby, R. Saito, C. Wilson, TransCom model simulations of CH4 and related species: Linking transport, surface flux and chemical loss with CH4 variability in the troposphere and lower stratosphere, Atmos. Chem. Phys. Discuss., Submitted, 2011.
presentations at the 10th TransCom workshop, University of California, Berkeley, 2010, (Saturday Session) are available on the TransCom-CH4 FTP server at NIES.
for more information
Please contact one of the experiment coordinators: Prabir Patra , Sander Houweling , Maarten Krol and Philippe Bousquet
 
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