Future changes in extratropical storm tracks in the CMIP5 models from a cyclone perspective Robert Lee Supervisors: Kevin Hodges, Tim Woollings European Meteorological Society 13 th Annual Meeting Session CL8 | September 9 th 2013 Image acquired June 14, 2012 using MODIS | © NERC Satellite Receiving Station / University of Dundee

Introduction Key aims - assess the extratropical storm track density and intensity: – biases in the current generation of climate models – future projections under RCP scenarios Motivated by importance of assessing and understanding: – future changes consequences for large populations and economy – model biases help to improve models and future predictions Slide 2 of 14Robert Lee | 13 th EMS | September 2013

Methodology Data: – CMIP5 historical ( ) – 29 models AMIP ( ) – 22 models RCP4.5, RCP8.5 ( ) – 29 models – ERA-Interim Reanalysis for comparison ( ) reanalysis uncertainty (Hodges, Lee and Bengtsson, 2011) TRACK algorithm (Hodges 1994, 1995, 1996, 1999): –ξ 850hPa at 6-h frequency, filtered to T42 Main plots: – track density – intensity distributions (T42 vorticity, 850hPa winds, MSLP, precip) Large scale analysis (investigation of causes) Slide 3 of 14Robert Lee | 13 th EMS | September 2013

All CMIP5 models with 6-hourly data: 29 ModelResolutionModelResolution ACCESS ° x 1.9°, L38 GFDL-ESM2M 2.0° x 2.5°, L24 ACCESS ° x 1.9°, L38 HadGEM2-CC 1.3° x 1.9°, L60 bcc-csm ° x 2.8°, L26 HadGEM2-ES 1.3° x 1.9°, L38 bcc-csm1-1-m 1.0° x 1.0°, L26 inmcm4 1.5° x 2.0°, L21 BNU-ESM 2.8° x 2.8°, L26 IPSL-CM5A-LR 1.9° x 3.8°, L39 CanESM2 2.8° x 2.8°, L35 IPSL-CM5B-LR 1.9° x 3.8°, L39 CCSM4 0.9° x 1.3°, L26 IPSL-CM5A-MR 1.3° x 2.5°, L39 CMCC-CM 1.1° x 1.1°, L31 MIROC5 1.4° x 1.4°, L40 CNRM-CM5 1.4° x 1.4°, L31 MIROC-ESM 2.8° x 2.8°, L80 CSIRO-Mk ° x 1.9°, L18 MIROC-ESM-CHEM 2.8° x 2.8°, L80 EC-EARTH 1.1° x 1.1°, L62 MPI-ESM-LR 1.9° x 1.9°, L47 FGOALS-g2 3.0° x 2.8°, L26 MPI-ESM-MR 1.9° x 1.9°, L95 FGOALS-s2 1.7° x 2.8°, L26 MRI-CGCM3 1.1° x 1.1°, L95 GFDL-CM3 1.8° x 1.8°, L48 NorESM1-M 1.9° x 2.5°, L26 GFDL-ESM2G 2.0° x 2.5°, L24 (ERA-Interim) (0.7° x 0.7°, L60) Slide 4 of 14Robert Lee | 13 th EMS | September 2013

Image acquired April 7, 2013 using Meteosat-10 | © NERC Satellite Receiving Station / University of Dundee Northern Hemisphere

NH Storm track climatology Extratropical cyclone track density climatology based on ERA-Interim (1986–2005) Winter (NH DJF) Summer (NH JJA) Slide 5 of 14Robert Lee | 13 th EMS | September 2013 North Atlantic North Pacific Mediterranean fewer cyclones

NH Storm tracks biases 29 member multi-model mean historical experiment – ERA-Interim ( ) Stippling shows where at least 90% of models agree on the sign of the bias Winter (NH DJF)Summer (NH JJA) Slide 6 of 14Robert Lee | 13 th EMS | September – – + – – – – – –

NH Storm tracks future projections Multi-model mean RCP ( ) – historical ( ) Winter (NH DJF) Summer (NH JJA) Slide 7 of 14 RCP8.5 – historical RCP4.5 – historical stippling where ≥ 90% model agreement on sign of change – – – – – – – –

Winter storm intensities (NH DJF) Intensity distribution of cyclone minimum sea level pressure Slide 8 of 14Robert Lee | 13 th EMS | September 2013 medium intensityweakstrong

Southern Hemisphere Image acquired April 7, 2013 using Meteosat-10 | © NERC Satellite Receiving Station / University of Dundee

SH Climatology (from ERA-Interim ) Winter (SH JJA) Summer (SH DJF) Slide 9 of 14Robert Lee | 13 th EMS | September 2013 primary genesis regions spiral towards coast final lysis regions more zonally symmetric

SH Storm tracks biases Multi-model mean historical experiment – ERA-Interim ( ) stippling where model agreement on sign of change is at least 90% Winter (SH JJA)Summer (SH DJF) Robert Lee | 13 th EMS | September 2013 Slide 10 of 14 – + – – – – +

SH Storm tracks future projections Multi-model mean RCP ( ) – historical ( ) Winter (SH JJA) Summer (SH DJF) RCP8.5 – historical RCP4.5 – historical stippling where ≥ 90% model agreement on sign of change Slide 11 of 14 – – – – – – – – – + + – – –

Winter storm intensities (SH JJA) Intensity distribution of cyclone minimum sea level pressure Robert Lee | 13 th EMS | September 2013 Slide 12 of 14 medium intensityweakstrong

Northern Hemisphere (extratropics: 30° to 90°) Southern Hemisphere (extratropics: -30° to -90°) Cyclone Frequency Changes DJF (Winter)MAM (Spring)JJA (Summer)SON (Autumn) ExperimentRCP4.5RCP8.5RCP4.5RCP8.5RCP4.5RCP8.5RCP4.5RCP8.5 Percentage change relative to historical -2.88%-5.68%-2.42%-5.15%-2.93%-6.47%-3.46%-6.88% 29 model standard deviation 1.32%2.00%1.18%2.43%2.96%4.34%1.52%2.49% DJF (Summer)MAM (Autumn)JJA (Winter)SON (Spring) ExperimentRCP4.5RCP8.5RCP4.5RCP8.5RCP4.5RCP8.5RCP4.5RCP8.5 Percentage change relative to historical -2.53%-5.00%-2.62%-4.97%-2.54%-5.39%-2.34%-5.68% 29 model standard deviation 1.04%1.85%1.09%1.38%1.26%1.80%1.11%1.45% Slide 13 of 14 Robert Lee | 13 th EMS | September 2013

Conclusions from CMIP5 models Biases: – zonal bias in latitudinal tilt of modelled storm tracks – most models underestimate storm intensity (SH) / too few storms (NH) Projected changes : – decreases on equatorward flanks – some smaller increases on poleward flanks of storm tracks, mostly in the Southern Hemisphere – decrease in medium intensity storms, small increase in SH strong storms – decrease in the number of storms of up to ~ 6 % globally under RCP8.5 – storm track response: RCP8.5 ≈ x 2 RCP4.5 Storm track plots online at: Slide 14 of 14 Robert Lee | 13 th EMS | September 2013