Model analysis of deep water transport variabilities in the subpolar Atlantic!

Transcription

1 ASOF ISSG Meeting and Workshop! Model analysis of deep water transport variabilities in the subpolar Atlantic! Patricia Handmann, Jürgen Fischer, Martin Visbeck, Lavinia Patara, Eric Behrens!!

2 Outline! Outline! 1. Transport variability DWBC Observations! 2. North Atlantic Oscillation and Transport Variabiliy! 3. Transport variability DWBC - Viking20 Model! Model Observation Comparison Model Analysis for Process Understanding! 4. Summary and Further Work

3 Transport variability DWBC Transport variability DWBC Observation network installed for ~two decades 53 N Section Mean Extreme Velocities 80 Latitude [ ] 70 AR7W 60 Ovide 53 N Oleander Longitude [ ] [2] J.Fischer et al. (in prep)!

4 Transport variability DWBC 53 N 53 N Section 5 LNADW > 1850m full array K9 regr 90d lp 1y avg 400 m 10 Sv LSW 1850 m mean : 16.4 Sv stdev : 2.7 Sv min : 9.2 Sv max : 22.0 Sv NEADW DSOW m m > LSW < 1850m Sv 10 Transport integrated over depth layers! Quasi-decadal period in LNADW transport! Mode not found in LSW Transport! mean : 15.5 Sv stdev : 2.8 Sv min : 1.9 Sv max : 23.4 Sv ! Jun ! [2] J.Fischer et al. (in prep)!

5 North Atlantic Oscillation and Transport Variabiliy! NAO + NAO-M1=~30y NAO-M2+3=~ 8-9 y LNADW-M1=~8-9y [3]! NAO - Quasi-decadal period in LNADW transport! 2+3 Mode in NAO equally quasi-decadal period! NAO pacemaker?! J. Fischer!

6 Model! Viking 20! Current speed snapshot σ=27.85 ORCA25 with 1/20 nest! 30 year spin-up with ORCA25! Main run (Viking20 ORCA25)! CORE2 Forcing (rain reduction 10% N. 62 N)! NEMO model configurations [4] Fischer et al [12] Erik Behrens 2013

7 Model-Observation Comparison Model velocity field close to observations Observations Mean Velocity Model Mean Velocity ( ) [m/s] depth [m] [1] Fischer et al Longitude [ W]

8 Model Analysis for Process Understanding! LNADW Transport 53 N LSW Transport 53 N

9 Model Analysis for Process Understanding! LNADW Transport 53 N LSW Transport 53 N

10 Summary and Further Work Summary Model western boundary current is largely consistent with observations Model decadal variability is roughly in phase with observations Latitude [ ] Further Work Compare Model more completely with observations 80 Extent to Ovide and Oleander Investigate mechanisms of 70 quasi- decadal variability 60 Depth levels for model transports AR7W 53 N Ovide Oleander Longitude [ ]

11 Literature [1] Fischer, J.; Visbeck, M.; Zantopp, R. & Nunes, N. Interannual to decadal variability of outflow from the Labrador Sea Geophysical Research Letters, Wiley Online Library, 2010, 37 [2] J.Fischer et al. Coherent Decadal Variations of the Atlantic Meridional Overturning Circulation [3] [4] Fischer, J.; Karstensen, J.; Zantopp, R.; Visbeck, M.; Biastoch, A.; Behrens, E.; Böning, C. W.; Quadfasel, D.; Jochumsen, K.; Valdimarsson, H. & others,intra-seasonal variability of the DWBC in the western subpolar North Atlantic, Progress in Oceanography, Elsevier, 2014 [6] Dengler, M.; Fischer, J.; Schott, F. A. & Zantopp, R., Deep Labrador Current and its variability in Geophysical Research Letters, Wiley Online Library, 2006, 33 [12] - Erik Behrens. The oceanic response to Greenland melting: the effect of increasing model resolution. PhD thesis, Kiel, Christian-Albrechts-Universit at, Diss., 2013, 2013.

12 AMOC fluctuations in the North Atlantic