Testing and Evaluation of the GSI Data Assimilation System

The Gridpoint Statistical Interpolation (GSI) 3D-Var system is part of NOAA/NCEPs operational Global Forecast System (GFS), North American Mesoscale (NAM) model, as well as the WRF Rapid Refresh (RR) system. It will also be operational at the Air Force Weather Agency (AFWA) in the near future. The Developmental Testbed Center (DTC) is conducting extensive testing and evaluation of the GSI system. This testing involves GSI v2.0 and subsequent revisions, coupled with WPS and WRF-ARW v3.2 in order to determine the capability and robustness in regional applications. Full six-hour cycling and cool-start extended tests during a one month period over a subtropical domain were conducted. These extended tests involve impact studies on a variety of existing and proposed operational data types including conventional prepBUFR data, GPS Radio Occultation (RO) data, radiance data (AMSU-A, AMSU-B, and AIRS), surface and sounding data. The extended tests use global background errors (BE), however, regional BEs have been tested, and the impact of ARW specified BE will be tested and subsequently tuned.

Preliminary results have shown improvement in the wind fields over the tropical regions using the updated GPS RO QC and observation errors, and neutral improvements in the AMSU-A radiance assimilation using the updated community radiative transfer model (CRTM). All extended tests have been verified against prepBUFR observations as well as the ECMWF analysis for temperature, moisture, and wind parameters. Additionally, extensive testing on the observation impacts, QC procedures, and analysis sensitivity will be presented. Finally, verification of precipitation accumulation and hurricane track, intensity, and maximum winds that assess the impact of GSI on regional phenomena will be shown.