Possible North Atlantic Possible North Atlantic extratropical cyclone extratropical cyclone

activity in a warmer climateactivity in a warmer climate

Lanli Guo William Perrie Zhenxia LongLanli Guo William Perrie Zhenxia Long

Montreal 2012

Bedford Institute of Oceanography, Dartmouth N.S.

MotivationMotivation• To evaluate estimates of surface fields over To evaluate estimates of surface fields over

North Atlantic from North Atlantic from Canadian Regional Canadian Regional Climate Model-CRCM3.7.1Climate Model-CRCM3.7.1 (CRCM) (CRCM) dynamically downscaled outputs fromdynamically downscaled outputs from Coupled Coupled Global Climate Model-GCM3.1(T47)Global Climate Model-GCM3.1(T47) (CGCM3).(CGCM3).

• To investigate the impact of greenhouse gas-To investigate the impact of greenhouse gas-induced global warming on the North Atlantic induced global warming on the North Atlantic storm climate by using CRCM dynamically storm climate by using CRCM dynamically downscaled fields.downscaled fields.

• CGCM3.1(T47) (1970-1999 20C3M, CGCM3.1(T47) (1970-1999 20C3M, 2040-2069 2040-2069 A1BA1B))

Atmospheric component: resolution T47L31Atmospheric component: resolution T47L31 ~ 3.75° L31 levels ~ 3.75° L31 levels

Oceanic component: resolution 1.85×1.85°L29Oceanic component: resolution 1.85×1.85°L29 • CRCM version 3.7.1: 45 km L29 (1970-1999 , CRCM version 3.7.1: 45 km L29 (1970-1999 ,

2040-20692040-2069))

• QSCAT/NCEP blended wind (0.5 QSCAT/NCEP blended wind (0.5 °)°)• ERA40 and NCEP ERA40 and NCEP reanalysis data reanalysis data • CFSR reanalysis data (~ 38 km)CFSR reanalysis data (~ 38 km)

For Autumn (September and October)For Autumn (September and October)

Models and DataModels and Data

Storm detection Storm detection methodologymethodology

Step 1: Potential storm identificationStep 1: Potential storm identification• Local SLP minimum is less than 1010 hPa within a Local SLP minimum is less than 1010 hPa within a

radius of 225 km;radius of 225 km;• SLP increases by at least 4 hPa from the cyclone SLP increases by at least 4 hPa from the cyclone

center within a radius of 1000 km with at least one center within a radius of 1000 km with at least one closed isobar.closed isobar.

• There is a relative vorticity maximum of 850hPa There is a relative vorticity maximum of 850hPa which is located within the 1000 km which is located within the 1000 km 1000 km area, 1000 km area, and within 225 km of the SLP minimum. and within 225 km of the SLP minimum.

Step 2: Storm trackingStep 2: Storm tracking • If a cyclone falls within 800 km of a cyclone from a If a cyclone falls within 800 km of a cyclone from a

preceding time step, it is assumed to be a preceding time step, it is assumed to be a continuation of the previous cyclone. Otherwise it is continuation of the previous cyclone. Otherwise it is a new cyclone.a new cyclone.

• A candidate storm A candidate storm mustmust have a lifetime of at least have a lifetime of at least 24 h.24 h.

Present climate

CFSRNCEPERA-40

CGCM3 CRCM

The storm track densities

Present climate

CFSR

ERA-40

CRCM

Seasonal mean of 6hourly 10m wind speed

QSCAT/NCEP NCEP

Present climate

CFSR

ERA-40

The mean of 10% strongest 6hourly 10m wind speed

QSCAT/NCEP NCEP

CRCM

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

0

5

10

15

20

25

30

35

40

945 955 965 975 985 995 1005

ERA40

NCEP

CFSR

CGCM3

CRCM

0

510

1520

2530

3540

45

7 11 15 19 23 27 31 35 39

ERA40

NCEP

CFSR

CRCM

CFSRNCEPERA-40

CGCM3 CRCM

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)

0

1000

2000

3000

4000

5000

6000

945 955 965 975 985 995 1005

Future

Current

Minimum MSLP

0

1000

2000

3000

4000

5000

6000

7000

8000

7 11 15 19 23 27 31 35 39

Future

Current

0

1000

2000

3000

4000

5000

6000

945 955 965 975 985 995 1005

Future

Current

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

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

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

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

Northwest Atlantic

Northeast Atlantic

Future climate of the 1000-hPa wind speeds (shaded) and mean sea level pressure (contour)

FUTURECURRENT

Future climate

Northwest Atlantic Northeast Atlantic

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

Future climate

FUTURE

CURRENT

SummarySummary

• CRCM can capture the general CRCM can capture the general characteristics of the characteristics of the storm tracksstorm tracks and and wind wind fieldsfields suggested by the reanalysis data for suggested by the reanalysis data for the current climate over the North Atlantic the current climate over the North Atlantic (NA) area.(NA) area.

• In terms of In terms of storm structurestorm structure, composite , composite analyses of the most intense cyclones show analyses of the most intense cyclones show that they tend to become that they tend to become largerlarger and and more more intenseintense in the A1B climate change scenario. in the A1B climate change scenario.