possible north atlantic extratropical cyclone activity in a warmer climate lanli guo william perrie...
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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.