Evaluation of MERRA using CERES cloud objects for the 1998 El Nino - La Nina transition

Modeling of the physical climate has recently taken center focus in the international community, as the implications for future climate change must be assessed today in order to make accurate and potentially life-saving decisions for the global population. However, these models and their results cannot be accepted blindly – how can we validate the performance of the models we use? How can we know that they are accurate in their predictions? A baseline test of the robustness of the model solution is the realism of the model output when run in re-analysis mode. In a re-analysis model, past observations are incorporated into a numerical weather prediction model at specific times to produce a continuous, long-term data record of modeled atmospheric conditions. It follows that one method of validating the accuracy of a climate model is through an observational - re-analysis validation; comparing real, observed atmospheric conditions to those predicted in the re-analysis procedure.

In this presentation, one method of observational – re-analysis comparison is presented. Re-analysis data from NASA's Modern Era Retrospective-analysis for Research and Applications (MERRA) is compared with observational data obtained from NASA's CERES (Clouds and Earth's Radiant Energy System) instrument aboard the Earth Observing System's (EOS) Aqua Spacecraft. Specifically, this presentation will address the comparison of deep convective cloud objects in the equatorial Pacific Ocean during the year 1998, which was marked by a transition from a strong El Nino to a moderate La Nina. In addition to simply validating the MERRA model re-analysis, we also focus on validating the accuracy of the representation of the complex connection between El Nino, deep convective clouds, and the large-scale overturning (Walker) circulation. Though these processes have been well-observed, they are not very well represented in current climate models. Preliminary results from this investigation suggest that NASA's MERRA re-analysis model realistically represents aspects of the observed occurrence and properties of deep convection over the equatorial Pacific Ocean when compared to actual observed cloud objects in the CERES data. Analysis of several variables related to clouds and cloud physics, including cloud top temperature and height as well as liquid and ice water path indicate MERRA has utility as a re-analysis specifically tailored to capture the details of the global hydrological cycle.