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


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

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

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Impact of Satellite Observations on

Tropical Cyclone Track Forecasts

James S. Goerss

NRL Monterey

March 5, 2008


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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.


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191

154

124

98

72

2005 Atlantic (July-October)

Homogeneous TC Forecast Error (nm)

Number of Forecasts


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Atlantic Results


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287

236

193

149

112

Atlantic 2005-2006

TC Forecast Error (nm)

Number of Forecasts


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Atlantic 2005-2006

Percent Improvement

* Significant at the 90% level

*

*

*

*

*

*

*

*

*

*

*


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287

236

193

149

112

Number of Forecasts

Atlantic 2005-2006

TC Forecast Error (nm)


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Atlantic 2005-2006

Percent Improvement


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Global Results


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737

603

473

345

253

Global (2005-2006)

TC Forecast Error (nm)

Number of Forecasts


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Global (2005-2006)

Percent Improvement

* Significant at the 90% level

*

*

*

*

*

*

*

*

*

*

*

*

*


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737

603

473

345

253

Global (2005-2006)

TC Forecast Error (nm)

Number of Forecasts


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Global (2005-2006)

Percent Improvement


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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.


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Questions?


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376

312

243

177

128

Number of Forecasts

Global (July-September 2005)

TC Forecast Error (nm)


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