Evaluation of UTLS carbon monoxide simulations in GMI and GEOS-Chem chemical transport models using Aura MLS observations

摘要

This study evaluates the distribution and variation of carbon monoxide (CO)in the upper troposphere and lower stratosphere (UTLS) during 2004–2012 assimulated by two chemical transport models, using the latest version of AuraMicrowave Limb Sounder (MLS) observations. The simulated spatialdistributions, temporal variations and vertical transport of CO in the UTLSregion are compared with those observed by MLS. We also investigate theimpact of surface emissions and deep convection on CO concentrations in theUTLS over different regions, using both model simulations and MLSobservations. Global Modeling Initiative (GMI) and GEOS-Chem simulations ofUTLS CO both show similar spatial distributions to observations. The globalmean CO values simulated by both models agree with MLS observations at 215and 147 hPa, but are significantly underestimated by more than 40 % at100 hPa. In addition, the models underestimate the peak CO values by up to70 % at 100 hPa, 60 % at 147 hPa and 40 % at 215 hPa, withGEOS-Chem generally simulating more CO at 100 hPa and less CO at 215 hPathan GMI. The seasonal distributions of CO simulated by both models are inbetter agreement with MLS in the Southern Hemisphere (SH) than in theNorthern Hemisphere (NH), with disagreements between model and observationsover enhanced CO regions such as southern Africa. The simulated verticaltransport of CO shows better agreement with MLS in the tropics and the SHsubtropics than the NH subtropics. We also examine regional variations in therelationships among surface CO emission, convection and UTLS COconcentrations. The two models exhibit emission–convection–CO relationshipssimilar to those observed by MLS over the tropics and some regions withenhanced UTLS CO.