climate variability and basin scale forcing over the north atlantic jim hurrell climate and global...
DESCRIPTION
The Mean State and Stationary Waves (DJF) L H L H H Sea Level Pressure Mid Tropospheric Height LOW HIGHTRANSCRIPT
![Page 1: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/1.jpg)
Climate Variability and Basin Scale Forcingover the North Atlantic
Jim Hurrell
Climate and Global Dynamics Division
National Center for Atmospheric Research (NCAR)
BASIN Science Meeting12-14 March 2005
Reykjavik, Iceland
![Page 2: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/2.jpg)
Climate Phenomena in the Atlantic
North Atlantic Oscillation (NAO)North Atlantic Oscillation (NAO)
Tropical Atlantic Variability (TAV)Tropical Atlantic Variability (TAV)
Meridional Overturning Circulation (MOC)Meridional Overturning Circulation (MOC)
• MOC, TAV and NAO interact, but in ways that are not well understoodMOC, TAV and NAO interact, but in ways that are not well understood• Understanding Atlantic climate variability/change requires a global viewUnderstanding Atlantic climate variability/change requires a global view
![Page 3: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/3.jpg)
The Mean State and Stationary Waves (DJF)
L
H
LH
H
Sea Level Pressure
Mid Tropospheric Height
LOW
HIG
H
![Page 4: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/4.jpg)
Change in Winter Surface Temperature since 1980
Human activities are superimposed on the background “noise” of natural variability
Cold
Warm
![Page 5: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/5.jpg)
Change in Winter Sea Level Pressure since 1980(hPa)Dec-Mar
Pressure Falls
Pressure Rises
(related to)El Niño/Southern Oscillation (ENSO)
North Atlantic Oscillation (NAO)
![Page 6: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/6.jpg)
The North Atlantic Oscillation
Spatial Structure and Seasonal Variability
DJF
SON
MAM
JJA
![Page 7: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/7.jpg)
Alternative Definition: Cluster Analysis (Winter Only)NAO- 29%NAO- 29% NAO+ 20%NAO+ 20%
Scand 21%Scand 21%Ridge 30%Ridge 30%
![Page 8: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/8.jpg)
NAO+ NAO+
NAO- NAO-
Scand Scand
RidgeRidge
Time History of Occurrence
![Page 9: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/9.jpg)
The North Atlantic Oscillation: Winter
Spatial StructureDec-Mar 39% SLP (hPa)
••
Temporal EvolutionDec-Mar
r = 0.92
StrongerWesterlies
hPa
![Page 10: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/10.jpg)
Winter Surface Temperature
Change since 1980
°C
Cold Warm
NAO influence (1 )
°C
Cold Warm
![Page 11: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/11.jpg)
NAO Influence on Winter Precipitation
DRYWET
(Positive Index Phase)
Energy Supply and Demand (Example: Norwegian Energy Trade)
Export
Import
Positive NAO
Negative NAO
Visbeck et al. 2002
![Page 12: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/12.jpg)
Ocean Response to NAO Variability
![Page 13: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/13.jpg)
Leading patterns of North Atlantic climate variabilitySea Surface Temperature 500 hPa Geopotential Height
Ocean Response to NAO Variability
r = 0.72r = 0.72
![Page 14: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/14.jpg)
Ocean Response to NAO VariabilityWinter Index (1864-2002)
WeakerWesterlies
StrongerWesterlies
SST
SST SST
![Page 15: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/15.jpg)
Ocean Response to NAO Variability
Visbeck et al. (2003)Courtesy of Igor Yashayaev
Changes in Water Masses
![Page 16: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/16.jpg)
Ocean Response to NAO Variability
Curry and McCartney (2001)
Circulation Changes
Oceanic NAO analogue: Eastward Transport Index
![Page 17: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/17.jpg)
Deser et al. (2000)
+
-
Sea Ice Response to NAO Variability
![Page 18: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/18.jpg)
What Climate Processes Govern NAO Variability?
Random and Unpredictable Variations
Simulated (Dec-Mar)
• 200 years of CCM3 without variations in “external” forcings• Basic structure & time scale arises from internal nonlinear atmospheric dynamics
EOF1 SLP(Dec-Mar)
![Page 19: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/19.jpg)
What Climate Processes Govern NAO Variability?
Random and Unpredictable Variations
Consistent with Observations(Climate Noise Paradigm)
Observed
Simulated NAO Index
A role for external forcing?
• Basic structure & time scale arises from internal nonlinear atmospheric dynamics
• 200 years of CCM3 without variations in “external” forcings EOF1 SLP
(Dec-Mar)
r (1yr) = -0.07
r (1yr) = -0.06 Except for the latter half of the 20th Century
Observed
r (1yr) = 0.4
![Page 20: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/20.jpg)
Rises
JFM 500 hPa Height Trend (1950-1999) m
Global SST Tropical SST
Observed
Falls
The Role of Ocean Forcing
![Page 21: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/21.jpg)
JFM Trend in Tropical SST (1950-1999)
Cold Warm
Warm Pool (60°-170°E; 15°S-15°N)
0.62 ± 0.13°C
Tropics (15°S-15°N)
0.46 ± 0.25°C
![Page 22: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/22.jpg)
Precipitation (mm day-1)
WETDRY
JFM Response to Indo-W. Pacific SST Trend
500 hPa Height (m)
FALLS RISES
r = 0.80
![Page 23: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/23.jpg)
Change in Tropical SST (1950-1999)
0.62 ± 0.13°C
ObservedObserved Indian Ocean Temperature Indian Ocean Temperature
0.59 ± 0.14°C
Climate ModelForced with ObservedChanges in GreenhouseGas Concentrations
SimulatedSimulated Indian Ocean Temperature Indian Ocean Temperature
![Page 24: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/24.jpg)
NAO is most prominent and recurrent pattern of atmospheric variability, driving upper-ocean and sea ice variations
Basic structure and time evolution results from internal, nonlinear atmospheric dynamics
Climate noise paradigm does not explain behavior in recent decades
Concerning observed winter North Atlantic climate change
Model experiments suggest North Atlantic climate change has been driven, at least in part, by warming tropical SSTs, with the Indo-Pacific region key
Nonlinear approaches reveal spatial asymmetries between the two NAO phases
![Page 25: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/25.jpg)
Future Change?
Numerous modeling studies indicate two Atlantic phenomena that might change
NAO and MOC
![Page 26: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/26.jpg)
Future Change
Most climate models simulate an increasing trend, with pressure decreases over the far North Atlantic and pressure increases in middle latitudes Details vary considerably from model-to-model, and the simulated trends are smaller than observed
NAO
![Page 27: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/27.jpg)
Future Change
NAO
Observed (low pass filtered)Observed (low pass filtered)Simulated (7 models)Simulated (7 models)
Inability to capture mechanisms of by which stratospheric flow anomalies affect the tropospheric evolution Details of the simulated SST field are important
Concerning the discrepancy with observations Gillett et al. 2003
![Page 28: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/28.jpg)
Future Change
Most, but not all, climate models project some weakening due to warming and freshening
MOC
Courtesy Jonathan Gregory
![Page 29: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/29.jpg)
Future Change
Most, but not all, climate models project some weakening due to warming and freshening
Nature of changes and mechanisms vary considerably from model-to-model
MOC
Ongoing CMIP subproject to investigate model differences
Effect of weakening is to moderate regional warming
![Page 30: Climate Variability and Basin Scale Forcing over the North Atlantic Jim Hurrell Climate and Global Dynamics Division National Center for Atmospheric Research](https://reader035.vdocuments.site/reader035/viewer/2022070605/5a4d1adc7f8b9ab059975292/html5/thumbnails/30.jpg)