Evaluation of CO Distribution and Variation in the UTLS from GMI and GEOS-Chem Simulations by Using Aura MLS Observations

Previous studies have investigated the distribution and transport of carbon monoxide (CO) in the troposphere using both model simulations and satellite observations. However, how model performs in the upper troposphere and lower stratosphere (UTLS) is still not clear. The Global Modeling Initiative (GMI) and GEOS-Chem are two global 3-D chemical transport models (CTMs) driven by assimilated meteorological observations. This study evaluates the simulations of CO during 2004-2012 in the UTLS region from these two models by using the latest version (V4.2) of Aura Microwave Limb Sounder (MLS) data. The spatial distributions, temporal variations and tape recorder of CO in the UTLS region are compared between model simulations and MLS observations. We also investigate the combined impacts of surface emission and deep convection on CO concentration in the UTLS over different regions using both model simulations and satellite observations. Results show that GMI and GEOS-Chem simulations of CO are similar in spatial distribution and magnitude. However, the CO peak values are smaller than MLS observations, with ~50% underestimation at 100 hPa. Besides, the seasonal cycles of CO in the UTLS are not well simulated over most regions where high CO centers are located above. The two models are capable to reproduce the emission-convection-CO relationships as observed by MLS over some regions at 215 hPa and 147 hPa.