Impact of Satellite Observations on Tropical Cyclone Track Forecasts James S. Goerss NRL Monterey March 5, 2008

1. Impact of Satellite Observations on Tropical Cyclone Track Forecasts James S. Goerss NRL Monterey March 5, 2008

2. NOGAPS Satellite Observation Impact Experiments The current operational NOGAPS/NAVDAS data assimilation system was run with different combinations of observational data over two test periods: July-October 2005 and August-September 2006. The first period was an extremely active one covering most of the record-breaking Atlantic season with 18 hurricanes (including Katrina, Rita, and Wilma), 12 typhoons, and 20 tropical storms. The second period was not nearly as active with 9 hurricanes, 7 typhoons, and 10 tropical storms. The control run used all available conventional and satellite obser-vations. The satellite observations assimilated in these experiments consisted of feature-track winds from geostationary and polar-orbiting satellites, SSM/I precipitable water and wind speeds, AMSU-A radiances, and QuikSCAT and ERS-2 scatterometer winds.A number of exper-iments were run in which one type of satellite data was excluded. A final experiment was run excluding all satellite observations.

3. 191 154 124 98 72 2005 Atlantic (July-October) Homogeneous TC Forecast Error (nm) Number of Forecasts

4. Atlantic Results

5. 287 236 193 149 112 Atlantic 2005-2006 TC Forecast Error (nm) Number of Forecasts

6. Atlantic 2005-2006 Percent Improvement * Significant at the 90% level * * * * * * * * * * *

7. 287 236 193 149 112 Number of Forecasts Atlantic 2005-2006 TC Forecast Error (nm)

8. Atlantic 2005-2006 Percent Improvement

9. Global Results

10. 737 603 473 345 253 Global (2005-2006) TC Forecast Error (nm) Number of Forecasts

11. Global (2005-2006) Percent Improvement * Significant at the 90% level * * * * * * * * * * * * *

12. 737 603 473 345 253 Global (2005-2006) TC Forecast Error (nm) Number of Forecasts

13. Global (2005-2006) Percent Improvement

14. Summary and Conclusions For the 2005-2006 test periods the assimilation of the feature-track winds from geostationary satellites had the most impact for both the Atlantic and the combined basins. For the Atlantic, the impact due to the assimilation of SSM/I precipitable water and the AMSU-A radiances was significant at 24h and 48h and that due to the assimilation of scatterometer winds and SSM/I wind speeds were significant at 24h. For the combined basins, the impact due to the assimilation of SSM/I precipitable water was significant at all forecast lengths while that due to the assimilation of AMSU-A radiances was significant at 24h, 48h, and 120h. The impact due to the assimilation of all satellite observations upon the NOGAPS TC track forecasts for the 2005-2006 test periods was similar for both the Atlantic and the combined basins resulting in a gain in skill of roughly 12h for the 48-h and 72-h forecasts and a gain in skill of roughly 24h for the 96-h and 120-h forecasts. Although the assimilation of some satellite observation types did not result in statistically significant improve- ments, their assimilation contributed additively and even multiplicatively at some forecast lengths to reduction in NOGAPS track forecast error.

15. Questions?

16. 376 312 243 177 128 Number of Forecasts Global (July-September 2005) TC Forecast Error (nm)