TY - JOUR
T1 - TransCom model simulations of methane
T2 - Comparison of vertical profiles with aircraft measurements
AU - Saito, Ryu
AU - Patra, Prabir K.
AU - Sweeney, Colm
AU - Machida, Toshinobu
AU - Krol, Maarten
AU - Houweling, Sander
AU - Bousquet, Philippe
AU - Agusti-Panareda, Anna
AU - Belikov, Dmitry
AU - Bergmann, Dan
AU - Bian, Huisheng
AU - Cameron-Smith, Philip
AU - Chipperfield, Martyn P.
AU - Fortems-Cheiney, Audrey
AU - Fraser, Annemarie
AU - Gatti, Luciana V.
AU - Gloor, Emanuel
AU - Hess, Peter
AU - Kawa, Stephan R.
AU - Law, Rachel M.
AU - Locatelli, Robin
AU - Loh, Zoe
AU - Maksyutov, Shamil
AU - Meng, Lei
AU - Miller, John B.
AU - Palmer, Paul I.
AU - Prinn, Ronald G.
AU - Rigby, Matthew
AU - Wilson, Christopher
PY - 2013/5/16
Y1 - 2013/5/16
N2 - To assess horizontal and vertical transports of methane (CH4) concentrations at different heights within the troposphere, we analyzed simulations by 12 chemistry transport models (CTMs) that participated in the TransCom-CH4 intercomparison experiment. Model results are compared with aircraft measurements at 13 sites in Amazon/Brazil, Mongolia, Pacific Ocean, Siberia/Russia, and United States during the period of 2001-2007. The simulations generally show good agreement with observations for seasonal cycles and vertical gradients. The correlation coefficients of the daily averaged model and observed CH4 time series for the analyzed years are generally larger than 0.5, and the observed seasonal cycle amplitudes are simulated well at most sites, considering the between-model variances. However, larger deviations show up below 2 km for the model-observation differences in vertical profiles at some locations, e.g., at Santarem, Brazil, and in the upper troposphere, e.g., at Surgut, Russia. Vertical gradients and concentrations are underestimated at Southern Great Planes, United States, and Santarem and overestimated at Surgut. Systematic overestimation and underestimation of vertical gradients are mainly attributed to inaccurate emission and only partly to the transport uncertainties. However, large differences in model simulations are found over the regions/seasons of strong convection, which is poorly represented in the models. Overall, the zonal and latitudinal variations in CH4 are controlled by surface emissions below 2.5 km and transport patterns in the middle and upper troposphere. We show that the models with larger vertical gradients, coupled with slower horizontal transport, exhibit greater CH4 interhemispheric gradients in the lower troposphere. These findings have significant implications for the future development of more accurate CTMs with the possibility of reducing biases in estimated surface fluxes by inverse modeling.
AB - To assess horizontal and vertical transports of methane (CH4) concentrations at different heights within the troposphere, we analyzed simulations by 12 chemistry transport models (CTMs) that participated in the TransCom-CH4 intercomparison experiment. Model results are compared with aircraft measurements at 13 sites in Amazon/Brazil, Mongolia, Pacific Ocean, Siberia/Russia, and United States during the period of 2001-2007. The simulations generally show good agreement with observations for seasonal cycles and vertical gradients. The correlation coefficients of the daily averaged model and observed CH4 time series for the analyzed years are generally larger than 0.5, and the observed seasonal cycle amplitudes are simulated well at most sites, considering the between-model variances. However, larger deviations show up below 2 km for the model-observation differences in vertical profiles at some locations, e.g., at Santarem, Brazil, and in the upper troposphere, e.g., at Surgut, Russia. Vertical gradients and concentrations are underestimated at Southern Great Planes, United States, and Santarem and overestimated at Surgut. Systematic overestimation and underestimation of vertical gradients are mainly attributed to inaccurate emission and only partly to the transport uncertainties. However, large differences in model simulations are found over the regions/seasons of strong convection, which is poorly represented in the models. Overall, the zonal and latitudinal variations in CH4 are controlled by surface emissions below 2.5 km and transport patterns in the middle and upper troposphere. We show that the models with larger vertical gradients, coupled with slower horizontal transport, exhibit greater CH4 interhemispheric gradients in the lower troposphere. These findings have significant implications for the future development of more accurate CTMs with the possibility of reducing biases in estimated surface fluxes by inverse modeling.
KW - TransCom Methane
KW - CH4 vertical profile
KW - vertical
KW - horizontal gradient
KW - CHEMICAL-TRANSPORT MODEL
KW - ATMOSPHERIC CO2
KW - TROPOSPHERE
KW - STRATOSPHERE
KW - VARIABILITY
KW - SENSITIVITY
KW - VERSION
KW - OZONE
KW - FLUX
KW - AIR
U2 - 10.1002/jgrd.50380
DO - 10.1002/jgrd.50380
M3 - Article
SN - 2169-897X
VL - 118
SP - 3891
EP - 3904
JO - Journal of Geophysical Research: Atmospheres
JF - Journal of Geophysical Research: Atmospheres
IS - 9
ER -