Assessing the uncertainty in the global distribution of atmospheric methane using AQUA/AIRS and the Global Modeling Initiative's CTM

Global observations from space will help to reduce the large uncertainties in the global budget of methane. In our work we identify the major areas of agreement and disagreement between global methane data collected from the Atmospheric Infrared Sounder (AIRS) instrument aboard NASA's AQUA satellite and NASA's Global Modeling Initiative's chemical transport model (GMI CTM). Our goal is to help in the evaluation of this relatively new data product and to identify its strengths and limitations for constraining the methane budget. We found major discrepancies between the model and observations in regions of deep convection, such as in South Asia, the Tibetan Plateau and the entire ITCZ, which may indicate a model deficiency in simulating convective transport or a retrieval issue with clouds. In addition, areas of high surface albedo with low cloud cover also show greater than 5% differences between model and observations. Examples of this issue are most obvious in northern high latitudes during boreal winter (snow) and east and west of South America over open ocean.