Regional and Global NWP Observing System Data Denial Experiments using NCEP's Operational Models

The impact of in-situ and remotely-sensed observations is being studied quantitively at CIMSS via model data denial experiments, using both regional and global models supplied by NCEP. The regional work has been ongoing for several years, using NCEP's Eta Data Assimilation/Forecast System (EDAS). Recently, global studies have been initiated that use the Global Forecast System (GFS).

The impact of in-situ rawinsonde data and remotely sensed geostationary and polar orbiting satellite data routinely used in the EDAS was studied for extended length time periods during four seasons. The case studies chosen consisted of 15-day periods during Fall 2001, Winter 2001/2002, Spring 2002 and Summer 2002. The model runs included a control run, which utilized all data types routinely used in the EDAS, and three experimental runs in which either all rawinsonde, GOES or POES data was denied. Differences between the experimental and control runs were then accumulated over the 15-day periods and analyzed to demonstrate the 24 and 48-hr forecast impact of these data types in the EDAS. The diagnostics were computed over both the entire horizontal model domain, and within a subsection covering the continental United States and adjacent coastal waters (extended CONUS).

Observing System Experiments (OSEs) with NCEP's Global Forecast System (GFS) are currently being conducted to evaluate the impact of various operational observing systems on NCEP's global forecasts. Two separate six week periods are being evaluated, with the last four weeks of each period being used to generate forecast impact statistics. In this work, the NCEP Global Data Assimilation System (GDAS) is being run at the full operational resolution of T254 (55 km) and 64 levels vertically. Currently, all Advanced Microwave Sounder Unit (AMSU) and High-resolution Infrared Radiation Sounder (HIRS) observing system data are being evaluated by denying each system separately in the GDAS. Both systems for these data consist of instrumentation on NOAA-15, -16 and -17. The impact statistics computed include the percent change in root mean square (rms) for sea level pressure, and mandatory level (100-1000 hPa) relative humidity, temperature and zonal wind. In addition, geopotential height anomaly correlations at 500 and 1000 hPa for both the Northern and Southern Hemispheres are being evaluated, and tropical rms vector errors at both 200 and 850 hPa will be calculated.