5B.6 Highlights of GMAO Hybrid 4dEnVar System

Tuesday, 24 January 2017: 11:45 AM
Conference Center: Tahoma 4 (Washington State Convention Center )
Ricardo Todling, NASA, Greenbelt, MD; and A. El Akkraoui

For about two years now, the NASA Global Modeling and Assimilation Office (GMAO) has been using a

Hybrid 3dVar assimilation system in its quasi-operational suite. This system supports various NASA

missions as well as it serves as the sanity check for updates that eventually make up the bulk of

a system to be promoted to supporting enhanced reanalysis efforts at GMAO. An upgraded parallel version of

this system has been running since mid-2016 that has as its main highlights an increased horizontal resolution

and an upgrade from hybrid 3dVar to a hybrid 4d ensemble-variational (4dEnVar) procedure. The GMAO

hybrid assimilation systems entail the following components: (i) a central, high-resolution,

forecast (background) using the GEOS-5 (FV3-based) general circulation model; (ii) a

hybrid 4dEnVar analysis, using the Gridpoint Statitical Interpolation (GSI) system; (iii) an ensemble of

low resolution GEOS-5 model background integrations; and (iv) an ensemble analysis produced using

a square-root ensemble Kalman filter (EnKF) procedure. The upcoming system, running in the parallel

suite, increases the effective resolution of its central forecasts from 28 km to roughly 12.5 km; its

hybrid 4d GSI analysis is performed at 28 km (in constrast to the quasi-operational 50 km hybrid 3dVar analysis);

and it brings in an increased ensemble horizontal resolution from roughly 100 km in the present

quasi-operational system to 50 km.

The increased model and analysis resolutions combined with the advanced assimilation strategy results in

non-negligeable improvements in different aspects of the system. As expected, the most direct benefit from

increased horizontal resolution is seen when analyzing and predicting tropical storms, with improvements in both

track and intensity forecasts. Less obvious is the considerable reduction in tropical forecast errors

brought about by the upgraded system, with tests indicating those to be due to the four-dimensional aspect of

the analysis.

Our presentation will provide multiple illustrations of improvements in the upcoming GMAO four-dimensional

system, as well as provide a view for further develop.

- Indicates paper has been withdrawn from meeting
- Indicates an Award Winner