Presentation on theme: "Late 20th Century (and Future) Simulations of Western Atlantic Winter Storms in Several CMIP5 Models and other Regional Climate Ensembles Brian A. Colle,"— Presentation transcript:
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 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 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?
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 ~2004, 6-hourly Rcp8.5 - high emissions scenario, 2006~2098, 6-hourly
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.
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.
Cyclone Center Total Centers Centers Missed False Alarm numbers rate/7.9%4.5% Verification – 11 Januaries of CFSR from (every other January) Lon 90-40°W, Lat 20-60°N
Some Results Cool Season November – March, 5 months Historical part 1979 – 2004 (26 cool seasons) 3 Future parts Early 21 st Century Middle 21 st Century Late 21 st Century Large blue box: for spacial density plot Small dashed box: for statistical analysis
CycloneTrack Density CFSR_ Higher Resolution Members Cyclone numbers per cool season per 2.5° x 2.5° CMIP5_Mean/Spread Lower Resolution Members
Cyclone Intensity Distribution 8 Lower Resolution Members
Cyclone Intensity Distribution 7 Higher Resolution Members
Genesis Density Cyclone numbers per 5 cool seasons per 2.5° x 2.5° Best 8 members CFSR_ CMIP5_ CMIP5_ CMIP5_ CMIP5_
Cyclone Density from 50-km NARCCAP North American Regional Climate Change Assessment Program (DJF ) forced by NCEP2 analysis
Challenges: Sensitivity of Regional Climate Models to Physics (20-km WRF forced by NCEP2 reanalysis) Number of DJF cyclones per 2.5x2.5deg ( ) CFSRWRF-mean WRF-KF/YSU WRF-BM/YSU WRF-KF/MYJWRF-BM/MYJWRF-GR/YSU WRF-GR/QNSE
Summary The 15 CMIP5 models can realistically predict the 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 ( ) 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 % uncertainties in predicted cyclone climatology related to model physics uncertainties.