Steven Pawson, NASA Goddard Space Flight Center, GMAO

Abstract: The Modern-Era Retrospective Analysis for Research and Applications (MERRA) provides space-time information about the atmospheric structure between the surface and the stratopause. This work examines the integrity of the upper troposphere and the stratosphere in MERRA. Evaluations of the quality of MERRA fields are provided by comparisons with other reanalyses (such as ERA-Interim), independent observations (such as the EOS-MLS), and from the internal statistics of the system (the “observation minus analysis” residuals). These comparisons show a robustness of analyses in the lower stratosphere, with increasing uncertainty in the upper stratosphere. Difficulties in producing accurate meteorological analysis when only deep-layer thermal information from nadir sounders (AMSU and SSU) will be discussed along with the additional complications of model biases in the upper stratosphere. The balance between physical forcing mechanisms and the “incremental analysis update” forcing added to the model in order to drive it towards the observations will be discussed. In particular, the impact of this balance on long-term changes in the stratosphere will be emphasized. Finally, impacts of long-term changes in tropospheric circulation on the structure of the tropopause region will be discussed.