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Motivation

Late 20th Century (and Future) Simulations of Western Atlantic Winter Storms in Several CMIP5 Models and other Regional Climate Ensembles Brian A. Colle, Zhenhai Zhang, Ping Liu, Kelly Lombardo, Edmund Chang, and Minghua Zhang, Stony Brook University - SUNY. Motivation.

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Motivation

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  1. Late 20th Century (and Future) Simulations of Western Atlantic Winter Storms in Several CMIP5 Models and other Regional Climate Ensembles Brian A. Colle, Zhenhai Zhang, Ping Liu, Kelly Lombardo, Edmund Chang, and Minghua Zhang, Stony Brook University - SUNY

  2. Motivation • Determine how well the CMIP5 models can simulate the Western Atlantic extratropical cyclones (density, intensity, genesis, deepening, etc…) for the cool season (Nov-March) for 1979-2004 historical period. • What is the impact of model resolution and weighting the CMIP ensemble members based on past performance? • Is there any indication of future cyclone change? Frequency, intensity, or spatial distribution?

  3. Data and MethodData - Mean Sea Level Pressure (MSLP) • CFSR: Climate Forecast System Reanalysis from NCEP, 1979~2004, 6-houly (Also tried ERA-Interim) • CMIP5: Coupled Model Intercomparison Project Phase 5, new set of climate model experiments for IPCC AR5. Historical - 1979~2004, 6-hourly Rcp8.5 - high emissions scenario, 2006~2098, 6-hourly

  4. CMIP5 _ 15 models High Resolution: 7 Models Low Resolution: 8 Models Total Grids = LatGrids × LonGrids

  5. Methods Tracker Procedure - Hodges TRACK Scheme (A General Method For Tracking Analysis And Its Application To Meteorological Data; Hodges, 1994) Step I: Spectral Bandpass Filter Remove planetary scale background and truncate too small scales, and get MSLP anomaly field. Step II: Cyclone Tracking Separate the data points into object and background points, locate the minimum pressure; Use a constrained optimization of a cost function to determine the next potential cyclone center position; Label these connected cyclone centers with a unique storm ID.

  6. Main Parameters • Wavelength (600 – 10000km) • removing the planetary scales and too small scales • Minimum Lifetime (24 hours) • Minimum moving distance (1000km) • filtering centers exist for too short time or remain too stationary • Also compared with the Hodges 850 hPa Vorticity Tracking Approach Too many non-cyclones.

  7. Verification – 11 Januaries of CFSR from 1980-2000 (every other January) Lon 90-40°W, Lat 20-60°N

  8. Some Results Cool Season November – March, 5 months Historical part 1979 – 2004 (26 cool seasons) 3 Future parts Early 21st Century 2009-2038 Middle 21st Century 2039-2068 Late 21st Century 2069-2098 Large blue box: for spacial density plot Small dashed box: for statistical analysis

  9. CFSR_1979-2004 CMIP5_Mean/Spread1979-2004 CycloneTrack Density Cyclone numbers per cool season per 2.5° x 2.5° 8 Lower Resolution Members 7 Higher Resolution Members

  10. Cyclone Intensity Distribution 8 Lower Resolution Members

  11. Cyclone Intensity Distribution 7 Higher Resolution Members

  12. CMIP5 Cyclone Ranking Rank (red – high resolution)

  13. Future Cyclone Density Change “Best 8”

  14. CFSR_1979-2004 CMIP5_1979-2004 GenesisDensity Cyclone numbers per 5 cool seasons per 2.5° x 2.5° Best 8 members CMIP5_2009-2038 CMIP5_2039-2068 CMIP5_2069-2098

  15. Cyclone Density from 50-km NARCCAP North American Regional Climate Change Assessment Program (DJF 1979-1999) forced by NCEP2 analysis

  16. Challenges: Sensitivity of Regional Climate Models to Physics (20-km WRF forced by NCEP2 reanalysis) Number of DJF cyclones per 2.5x2.5deg (1985-2004) WRF-GR/QNSE WRF-KF/YSU CFSR WRF-mean WRF-BM/MYJ WRF-KF/MYJ WRF-GR/YSU WRF-BM/YSU

  17. Summary • The 15 CMIP5 models can realistically predict the 1979-2004 winter cyclone density distribution over the western Atlantic and U.S. East Coast; however, most of the CMIP5 models underpredict the magnitude. • The “higher resolution” CMIP5 models better simulate the cyclone density and intensity, but most models underpredict the relatively deep cyclones (< 980 hPa). • The cyclone numbers decrease gradually over western Atlantic and U.S. East Coast in the future period (2009-2098) for Rcp8.5 experiment. There is a reduction in cyclone genesis along East Coast. • A diverse set of physics (or multi-models) is required for regional ensembles (plus ensemble weighting) given the 20-30% uncertainties in predicted cyclone climatology related to model physics uncertainties.

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