National Aeronautics and Space Administration

Preliminary Evaluation

Developments of the GEOS systems since the MERRA-2 and GEOS-FPIT version was frozen in 2015 have led to numerous improvements in the quality of the products, compared to observations and analyses from other centers. GEOS-IT captures this overall improvement to the analyzed climate when compared to the current version of FP-IT.
Aspects of significant improvement include:

• More realistic tropical temperature and humidity profiles in the middle and upper troposphere
• A better-balanced top of the atmosphere energy budget
• An improved land-ocean precipitation distribution
• Closer surface temperatures to observations over land

Despite the overall improvements, some fields in the proposed GEOS-IT system are less well represented than in the GEOS-FPIT and the GEOS-FP systems. Specifically:

• Equatorial wind and temperature structuresin the middle and upper stratosphere (QBO/SAO region, especially the QBO regime transitions near 10-20hPa.
• Polar cap upper atmosphere ozone

The GMAO continues to investigate these features, in order to trace the causes. For the ozone, potential reasons include the use of different observations than in GEOS-FPIT, as well as differences in large-scale transport. For the QBO winds, there is a potential problem with the initialization of the system and/or the manner in which the model’s background gravity wave spectrum is acting in the early stages of the assimilation. While undesirable, these degradations were not regarded as showstoppers that preclude the distribution of the sample dataset.