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Beyond QuikSCAT

Explore the essential parameters and limitations in utilizing satellite data for predicting tropical cyclone intensity. Requirements include high accuracy, finer resolution, reduced rain interference, and timely data availability.

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Beyond QuikSCAT

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  1. Beyond QuikSCAT TPC/NHC Requirements for Satellite Retrievals of Ocean Surface Vector Winds Richard Knabb 6 June 2006

  2. Needs vs Wants

  3. Key Forecast Parameters • Tropical Cyclone Intensity: Maximum sustained surface wind (1 minute average, 10 m altitude, unobstructed exposure), associated with the circulation of the tropical cyclone at a given point in time. • Tropical Cyclone Wind Radius: Largest distance from the center of the tropical cyclone of a particular sustained surface wind speed threshold (e.g., 34, 50, 64 kt) somewhere in a particular quadrant (NE, SE, SW, NW) surrounding the center and associated with the circulation at a given point in time.

  4. Advisory Forecast Cycle

  5. Advisory Forecast Cycle

  6. HOW DO WE ESTIMATE INTENSITY? • Aircraft reconnaissance • flight-level winds • GPS dropsondes • Stepped Frequency Microwave Radiometer (SFMR) • Airborne doppler radar • Satellites • Geostationary IR and VIS (Dvorak technique) • AMSU • QuikSCAT • Surface observations • ships, buoys, land stations (limited) • WSR-88D (near land)

  7. 90 kt 95 kt 105 kt 90 kt RECON FLIGHT-LEVEL WINDS HURRICANE GEORGES 9/20/98 20-23Z

  8. QuikSCAT Limitations • Rain contamination • Rain-induced bias in retrieved wind speeds that varies with rain rate and actual wind speeds • Lack of collocated rain rate data • Inability to measure max winds in most hurricanes • Rain attenuation, signal saturation, resolution • Directional ambiguities • TC center fixing and identification • Availability and timeliness

  9. Requirements • Greatly reduced or even non-existent sensitivity to rain • Provide accurate wind speed and direction retrievals regardless of rain rate (no rain, light rain, or heavy rain)

  10. Requirements • Capability to measure entire range of sustained surface wind speeds in TCs • 0 to 165 kt, accurate to within 1-2 kt • Finer horizontal resolution (1-4 km), and increased sensitivity at extreme wind speeds • Fill in some gaps left by aircraft recon • Does not fly into every major hurricane (e.g., east Atlantic, east Pacific) • Provides data only along a line during each flight leg • Recon gaps even in “well-sampled” storms

  11. Requirements • Elimination of the directional ambiguity problem • Need much more accurate position fixing for TCs • Determining if closed circulation exists (key factor in determining if cyclogenesis has occurred)

  12. Requirements • More timely data • Reduce time between satellite overpass and receipt of data to a few minutes

  13. Requirements • More continuous monitoring of systems • Especially needed in the Tropics where gaps in POES data are largest • Increase frequency of retrievals over each system of interest • At least 3-hourly to ensure data is timely for next advisory

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