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 Method Data - 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. ModelsTotal GridsLAT GridsLON Grids CESM55296192288 EC-EARTH51200160320 MRI-CGCM351200160320 CNRM-CM532768128256 MIROC532768128256 HadGEM2-ES27840145192 HadGEM2-CC27840145192 INMCM421600120180 IPSL-CM5A-MR20592143144 MPI-ESM-LR1843296192 NorESM11382496144 GFDL-ESM2M1296090144 IPSL-CM5A-LR921696 BCC-CSM1819264128 MIROC-ESM-C819264128 High Resolution: 7 Models Low Resolution: 8 Models Total Grids = LatGrids × LonGrids CMIP5 _ 15 models

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. Cyclone Center Total Centers Centers Missed False Alarm numbers2286181103 rate/7.9%4.5% 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 21 st Century 2009-2038 Middle 21 st Century 2039-2068 Late 21 st Century 2069-2098 Large blue box: for spacial density plot Small dashed box: for statistical analysis

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

10. Cyclone Intensity Distribution 8 Lower Resolution Members

11. Cyclone Intensity Distribution 7 Higher Resolution Members

13. CMIP5 Cyclone Ranking Rank (red – high resolution) Models Combined Rank Track Density Correlation Intensity Distribution Resolution EC-EARTH2.514160x320 MPI-ESM-LR4.02696x192 HadGEM2-ES4.545145x192 MRI-CGCM35.091160x320 CESM5.583192x288 CNRM-CM55.538128x256 HadGEM2-CC6.0102145x192 NorESM18.07996x144 BCC-CSM19.011764x128 GFDL-ESM2M9.061290x144 IPSL-CM5A-MR9.5513143x144 MIROC-ESM-CHEM12.0141064x128 INMCM413.01511120x180 MIROC513.01214128x256 IPSL-CM5A-LR14.0131596x96

14. Future Cyclone Density Change Best 8

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

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

18. 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) CFSRWRF-mean WRF-KF/YSU WRF-BM/YSU WRF-KF/MYJWRF-BM/MYJWRF-GR/YSU WRF-GR/QNSE

19. 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.