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Verification of Tropical Cyclone Forecasts

Verification of Tropical Cyclone Forecasts. Beth Ebert (BOM) Barb Brown (NCAR) Laurie Wilson (RPN) Tony Eckel (ERT) 8 th TIGGE Working Group Meeting 22-24 February 2010, Geneva. What kind of TC forecasts?. Ensemble Track distribution strike prob., cone of uncertainty

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Verification of Tropical Cyclone Forecasts

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  1. Verification of Tropical Cyclone Forecasts Beth Ebert (BOM) Barb Brown (NCAR) Laurie Wilson (RPN) Tony Eckel (ERT) 8th TIGGE Working Group Meeting 22-24 February 2010, Geneva

  2. What kind of TC forecasts? Ensemble • Track distribution • strike prob., cone of uncertainty • Intensity distribution • mean / median • spread • 90th percentile • Prob (wind > threshold) • Prob (precip > threshold) • Prob (surge > threshold) • Temporal consistency Deterministic • TC track • Intensity • maximum wind • central pressure • temporal trend (rapid intensification) • Wind field / radii • Precipitation • Storm surge • Temporal consistency

  3. Different users need different kinds of verification information • Public and emergency managers • Simple, graphical • Focus on impact • Forecasters • Information on how to interpret forecasts • Timing errors • Modellers • Systematic errors • How to improve the model • How to improve ensemble distribution / spread

  4. Quality of deterministic forecasts • What are the track errors (along-track, cross-track)? • What are the intensity errors? • Are temporal intensity trends correctly predicted? • What is the error in timing of landfall? • What is the error in forecast maximum wind (rain)? • Multi-day total precipitation • Is the spatial distribution of wind (rain) correct?

  5. Quality of ensemble forecasts • Does the ensemble enclose the observed track? • Are the ensemble probabilities skillful and reliable predictions for • strike probability (track) • intensity (max wind, central pressure) • wind • precipitation • Does the ensemble produce an appropriate spread for these variables?

  6. Data issues • Verification data • Data sources • Best track, Dvorak, surface instruments, radar, … • Problems measuring in extreme conditions • Forecast data • Size of ensemble • Model grid resolution • Details of cyclone tracker • Reference forecasts • Statistical forecast (e.g., CLIPER)

  7. Verification methods for deterministic TC forecasts • Example 1 – visual comparison Analysis Model Track/intensity verification Courtesy Noel Davidson, BOM

  8. Verification methods for deterministic TC forecasts • Example 2 – along-track and cross-track errors Courtesy James Franklin, NHC

  9. Verification methods for deterministic TC forecasts • Example 3 – cumulative distribution of track errors Courtesy James Franklin, NHC

  10. Verification methods for deterministic TC forecasts • Example 4 – distribution of intensity errors HFIP High-Resolution Hurricane Test – DTC Final Report Sept 2009

  11. AOML / WRF – 69 cases Observed High resolution model Low resolution model Count Hours since onset of observed RI Verification methods for deterministic TC forecasts • Example 5 – rapid intensification HFIP High-Resolution Hurricane Test – DTC Final Report Sept 2009

  12. Verification methods for deterministic TC forecasts • Example 6 – rain intensity distribution Marchok et al. 2008

  13. Verification methods for ensemble TC forecasts • Example 1 – visual comparison

  14. fake ^ MOGREPS 120 h forecast for strike probability (within 120 km) TC Anja, November 2009 Verification methods for ensemble TC forecasts • Example 2 – probabilistic scores and methods

  15. Verification methods for ensemble TC forecasts • Example 3 – spread of track and intensity forecasts track track intensity intensity 20-member FIM ensemble

  16. New approaches for verifying TCs • Spatial verification methods • Precipitation and • wind fields • Storm characteristics • location • size • intensity • shape, etc.

  17. New approaches for verifying ensemble TC forecasts • Minimum spanning tree • multi-variate rank histogram • Ensemble of object properties • ensemble mean object properties • distributions – use standard methods for ensembles and probability forecasts • relationship of TC genesis to the number of ensemble members predicting the TC at day 1+? • correspondence ratio observation ensemble forecast ensemble forecast

  18. Reporting guidelines • Provide all relevant information • Model(s), grid, range of dates, forecast lead times, verification data source, etc. • Aggregation and distribution of results • Confidence intervals / uncertainty

  19. Verification tools for TCs • US Developmental Testbed Centre (DTC) • Tracker (Marchok) • Code for verification of TC track and intensity • Other international tool sets??

  20. Document on TC verification – commented literature review to be written this year Contents Introduction Verification strategy Reference data Verification methods Reporting guidelines Summary References Appendices: a. Brief description of scores b. Guidelines for computing aggregate statistics c. Confidence intervals for verification scores d. Examples of graphical verification products

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