1. Didier Swingedouw, Masa Kageyama, Juliette Mignot,
Impact of freshwater release in the North Atlantic under different climate conditions in an OAGCM
Didier Swingedouw, Masa Kageyama, Juliette Mignot,
Pascale Braconnot, Eloi Mosquet, Charline Marzin, Ramdane Alkama, Olivier Marti
LSCE-IPSL, France

2. Abrupt climate changes during glacial period
Cooling and iceberg surge
Monsoon changes (Wang et al. 2001)
Origin?
Mechanisms for the teleconnections ?
ITCZ migration(Peterson et al. 2000)
Courstesy of M. Kageyama

3. What about warm climates?
Reduction of the Greenland ice sheet during the Eemian
Potential collapse in the future
With
Greenl.
CTRL No
Swingedouw et al. Clim. Dyn. 2007
AMOC
What are the freshwater inputs under different climate conditions?
Are the climatic responses and mechanisms similar under different climate conditions?

4. Insolation at the top of the atmosphere
Experimental design
Insolation at the top of the atmosphere
10 simulations using the IPSL- CM4 AOGCM of 250 years, with and without (computed) freshwater input
Last Interglacial (126 kyr BP, LIG)
Last Glacial Maximum (21 kyr BP LGM)
Holocene (6 kyr BP, HOL)
Preindustriel (PRE) : 0.1 Sv hosing following Stouffer et al. 2006)
Future (2xCO2, FUT)
PRE, FUT
HOL-PRE
LGM-PRE
LIG-PRE
-126 kyr
-21 kyr
-6 kyr
1860
2250
LIG
LGM
HOL
PRE
FUT

5. Freshwater input and AMOC response
LIGc
LGMc
LGMh
LIGh
HOLc
PREc
FUTc
HOLh
PREh
FUTh
Atlantic Meridional Overturning Circulation (year )
Freshwater input and AMOC response
Freshwater is computed according to the heat flux budget over land-ice area in the model (except for PRE and LGM)
Greenland melting after 250 years

6. Climatic impact of « hosing »
Temperature (year , hosing-CTRL)
Precipitation
LIG
LGM
HOL
PRE
FUT
LIG
LGM
HOL
PRE
Refroidissement hémisphere nord ds ts les climats
Léger réchauffement local le long des cotes est groenlandaise du fait d’une interaction vent glace de mer (ds ce modèle), pour tous les climats chauds mais pas en glaciaire
Migration vers le nord de l’ITCZ dans tous les climats
Migration plus forte si refroidissement plus fort + propagation au Pacifique
FUT

7. Sea level pressure response
SLP (year , hosing-CTRL)
Sea level pressure response
LIG
LGM
HOL
PRE
Change in the mean state
Resembling the Aleutian Low-Icelandic Low seesaw (Honda et al )
Adjustment of the storm track to different temperature gradients
FUT
En TW

8. Explanation for the « slight warming » pattern
Sea-ice cover and wind stress changes (year , hosing-CTRL)
Explanation for the « slight warming » pattern
LIG
LGM
HOL
PRE
Changes in surface winds associated with large-scale SLP changes
Interaction with sea ice cover
Albedo feedback leads to the observed « slight warming »
FUT
En TW

9. A complex energetic adjustment
Net SW LW
TOA
AHT
Atmosphere
Atmosphere
Land
Sea ice
Explication du schéma
OHT
Ocean
25° N
90° N

10. A complex energetic adjustment
Net=+ 13
SW= -172
LW=+ 185
Common mechanisms:
Oceanic heat transport decreases due to AMOC weakening
Partial compensation by the atmosphere
Differences:
AMOC changes
Radiative adjustment and changes in reservoirs (sea ice)
TOA
AHT= +99
Atmosphere
Atm=-2
Glace=-91
Exemple d’une paire de simulation :
Similarités avec les autres paires
Différences quantitatives subtiles
OHT= -232
Oce=-17
25° N
90° N
Hosing preind. (en TW)

11. ITCZ migration amplitude
Zonal precipitation changes over the Atlantic (year , hosing-CTRL)
The amplitude of the ITCZ shift depends on the experiment
What drives these changes?
LIG
LGM
FUT
HOL
PRE

12. ITCZ migration mechanism
SST and wind stress changes (year , hosing-CTRL)
ITCZ migration mechanism
LIG
LGM
Fast signal
C-shape wind change in the tropics
Atmospheric bridge and oceanic tunnel
Wind-Evaporation-SST feedback (Chiang et al )
HOL
PRE
FUT

13. Linearity
Phase diagram of the response of different climate indicators (after 250 years)
Temperature changes in the NH linear with clear sky radiative changes (sea ice)
ITCZ changes linear with cooling (atmospheric bridge)

14. Conclusions
The Greenland freshwater input amount computed during the Eemian is larger than a 2xCO2 (using a simple heat flux budget) after 250 years
In the IPSL-CM4, the climatic impact of a freshwater input shares similarities∀ the climate
Cooling of the Northern Hemisphere
Southward ITCZ migration, mainly in the Atlantic
Slight warming on the west coast of Greenland
Complex energetic adjustment: important role of the sea ice

15. Thank you Swingedouw et al
Thank you Swingedouw et al. Impact of freshwater release in the North Atlantic under different climate conditions in an OAGCM. Journal of Climate 22, , 2009