1. Possible North Atlantic extratropical cyclone activity in a warmer climate Lanli Guo William Perrie Zhenxia Long Montreal 2012 Bedford Institute of Oceanography, Dartmouth N.S.

2. Motivation To evaluate estimates of surface fields over North Atlantic from Canadian Regional Climate Model-CRCM3.7.1 (CRCM) dynamically downscaled outputs from Coupled Global Climate Model-GCM3.1(T47) (CGCM3). To evaluate estimates of surface fields over North Atlantic from Canadian Regional Climate Model-CRCM3.7.1 (CRCM) dynamically downscaled outputs from Coupled Global Climate Model-GCM3.1(T47) (CGCM3). To investigate the impact of greenhouse gas- induced global warming on the North Atlantic storm climate by using CRCM dynamically downscaled fields. To investigate the impact of greenhouse gas- induced global warming on the North Atlantic storm climate by using CRCM dynamically downscaled fields.

3. CGCM3.1(T47) (1970-1999 20C3M, 2040-2069 A1B) CGCM3.1(T47) (1970-1999 20C3M, 2040-2069 A1B) Atmospheric component: resolution T47L31 Atmospheric component: resolution T47L31 ~ 3.75° L31 levels ~ 3.75° L31 levels Oceanic component: resolution 1.85×1.85°L29 Oceanic component: resolution 1.85×1.85°L29 CRCM version 3.7.1: 45 km L29 (1970-1999, 2040-2069) CRCM version 3.7.1: 45 km L29 (1970-1999, 2040-2069) QSCAT/NCEP blended wind (0.5 °) QSCAT/NCEP blended wind (0.5 °) ERA40 and NCEP reanalysis data ERA40 and NCEP reanalysis data CFSR reanalysis data (~ 38 km) CFSR reanalysis data (~ 38 km) For Autumn (September and October) For Autumn (September and October) Models and Data

4. Storm detection methodology Step 1: Potential storm identification Local SLP minimum is less than 1010 hPa within a radius of 225 km; Local SLP minimum is less than 1010 hPa within a radius of 225 km; SLP increases by at least 4 hPa from the cyclone center within a radius of 1000 km with at least one closed isobar. SLP increases by at least 4 hPa from the cyclone center within a radius of 1000 km with at least one closed isobar. There is a relative vorticity maximum of 850hPa which is located within the 1000 km  1000 km area, and within 225 km of the SLP minimum. There is a relative vorticity maximum of 850hPa which is located within the 1000 km  1000 km area, and within 225 km of the SLP minimum. Step 2: Storm tracking If a cyclone falls within 800 km of a cyclone from a preceding time step, it is assumed to be a continuation of the previous cyclone. Otherwise it is a new cyclone. If a cyclone falls within 800 km of a cyclone from a preceding time step, it is assumed to be a continuation of the previous cyclone. Otherwise it is a new cyclone. A candidate storm must have a lifetime of at least 24 h. A candidate storm must have a lifetime of at least 24 h.

5. Present climate CFSRNCEPERA-40 CGCM3CRCM The storm track densities

6. Present climate CFSR ERA-40 CRCM Seasonal mean of 6hourly 10m wind speed QSCAT/NCEPNCEP

7. Present climate CFSR ERA-40 The mean of 10% strongest 6hourly 10m wind speed QSCAT/NCEPNCEP CRCM

8. Frequency of minimum SLP for cyclones Frequency of maximum 10m wind speed for cyclones Present climate Frequency of cyclones as a function of minimum MSLP/maximum 10m wind speed for current (1970-1999) cyclones

9. CFSRNCEPERA-40 CGCM3CRCM Present climate The densities of strong extratropical cyclones (minimum mean sea level pressure The densities of strong extratropical cyclones (minimum mean sea level pressure < 970 hPa)

10. Minimum MSLP The distribution of the future (2040- 2069) and current (1970-1999) total storms populations CGCM3 based on minimum MSLP CRCM based on minimum MSLP CRCM based on maximum wind speed Future climate

11. Difference in total storm track densities between future climate minus present climate Difference in intense storm densities between future climate minus present climate for minimum MSLP<970 hPa CRCMCGCM3 Future climate

12. CRCMNCEP Northwest Atlantic Northeast Atlantic Spatial distributions for (a) 1000-hPa wind speed (m/s) (shaded) and (b) mean sea level pressure (hPa) (contour) averaged on the 100 most intense cyclones (present climate data) over 2500 km  2500 km near the cyclone center Present climate

13. CRCMNCEP Northwest Atlantic Northeast Atlantic Vertical wind profiles (m/s) along transects passing through the storm center and the region of maximum winds Present climate

14. Northwest Atlantic Northeast Atlantic Future climate of the 1000-hPa wind speeds (shaded) and mean sea level pressure (contour) FUTURE CURRENT Future climate

15. Northwest Atlantic Northeast Atlantic Future climate of vertical wind profile (m/s) along transect for Northwest and Northeast Atlantic cyclones Future climate FUTURE CURRENT

16. Summary CRCM can capture the general characteristics of the storm tracks and wind fields suggested by the reanalysis data for the current climate over the North Atlantic (NA) area. CRCM can capture the general characteristics of the storm tracks and wind fields suggested by the reanalysis data for the current climate over the North Atlantic (NA) area. In terms of storm structure, composite analyses of the most intense cyclones show that they tend to become larger and more intense in the A1B climate change scenario. In terms of storm structure, composite analyses of the most intense cyclones show that they tend to become larger and more intense in the A1B climate change scenario.