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Enhanced Tropical Cyclone Wind Retrievals for Accurate Intensity Estimation

This study evaluates requirements for satellite retrievals of ocean surface vector winds, focusing on key forecast parameters like tropical cyclone intensity and wind radius. Limitations of QuikSCAT data are analyzed, and recommendations are made for improved sensitivity and accuracy in measuring extreme wind speeds. The need for more timely and continuous monitoring systems, along with enhanced position fixing for tropical cyclones, is emphasized to advance forecasting capabilities.

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Enhanced Tropical Cyclone Wind Retrievals for Accurate Intensity Estimation

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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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