Invited paper on the South Atlantic J. Lutjeharms

Transcription

1 AGU Chapman Conference on the Agulhas System Stellenbosch South Africa October 8 12, 2012

2 With regard to the thermohaline circulation, we identify some key locations where very important processes occur, and need to be monitored. the Brazil Malvinas Confluence, the Agulhas Retroflection, the Benguela Current and the bifurcation of the South Equatorial Current Invited paper on the South Atlantic: E. Campos, A. Busalacchi, S. Garzoli, J. Lutjeharms, R. Matano, P. Nobre, D. Olson, A. Piola, C. Tanajura, e I. Wainer, 2001: Important Aspects of the South Atlantic to the Understanding of the Global Climate. In: Observing the Ocean in the 21st Century, C. Koblinsky & N. Smtith, Eds. GODAE Project Office and Bureau of Meteorology, Melbourne, Australia, 2001

3 The initial efforts towards a climate observing system for the South Atlantic

4 Shifting Westerlies J. R. Toggweiler, 2009 Is the Agulhas leakage increasing due to the changing winds? If so, does it matter? To whom? AGU Chapman Conference on the Agulhas System Stellenbosch South Africa October 8 12, 2012 Beal et al., 2011

5 Subsurface salinity and Temperature anomalies from the Agulhas region can reach the Tropical Atlantic in a coupled ocean atmosphere simulation. Anomalies from the Agulhas Retroflection region propagate in the thermocline and reach the Equatorial Undercurrent in about 10 years. Some of the signal upwells in the Guinea Dome. Haarsma, R.J, Campos, E.J.D et al., 2011: Impacts of Interruption of the Agulhas Leakage on the Tropical Atlantic. Clim. Dynamics, V. 36, DOI: /s OI: / s

6 Temperature Effects on the Tropical Atmosphere Anomalous precipitation (mm day -1 ) and wind stress (Nm -2 ) averaged over the last 10 years. Salinity Vertical profiles of T and S anomalies along the equator. The thermocline gets cooler and fresher while the mixed layer gets warmer. Increased temperature gradient due to the cooler South Atlantic displaces the ITCZ northward, resulting in decreased precipitation in the Tropical South Atlantic. Haarsma, Campos et al., 2011

7 Trends in the NCEP/ Reanalysis winds Mean zonal wind (ms -1 ) Linear trend of zonal wind (ms -1 /year) AGU Chapman Conference on the Agulhas System Stellenbosch South Africa October 8 12, 2012

8 Wind Stress Curl Colors: Strength of the wind stress curl averaged from 1960 to 2010 Vectors: mean wind velocity NCEP 1 Colors: Linear trend of the wind stress curl. The black and yellow lines indicate zero curl line, before and after the trend. Vectors: Linear trend of the wind velocity AGU Chapman Conference on the Agulhas System Stellenbosch South Africa October 8 12, 2012

9 Numerical simulation forced with NCEP/Reanalysis o S SST - HYCOM 22 layers 0.25-deg horiz. Resolution 65 o S 98 o W 114 o E AGU Chapman Conference on the Agulhas System Stellenbosch South Africa October 8 12, 2012

10 Checking the Results (Linear trend in heat content from 0 to 700 m ) IPCC AR4 HYCOM HYCOM AGU Chapman Conference on the Agulhas System Stellenbosch South Africa October 8 12, 2012

11 Checking the Results (Temperature trend ) Biastoch et al., 2009 Hycom Simulation HYCO M AGU Chapman Conference on the Agulhas System Stellenbosch South Africa October 8 12, 2012

12 Biastoch et al., 2009 HYCOM Simulation

13 Checking the Results (Compare with Backeberg et al., 2012 ) AGU Chapman Conference on the Agulhas System Stellenbosch South Africa October 8 12, 2012

14 Checking the results A B D C AC profiles across sections A,B,C,D compares well with literature (De Ruijter et al. 1999; Lutjeharms, 2006; Paldor and Lutjeharms, 2009)

15 Comparing with observations Mean SSH AVISO Standard deviation Model

16 Comparing with observations Mean SST Pathfinder Model Standard Deviation

17 KE and SSH Trends in the Agulhas region Linear trend of KE from 1960 to 2010, in m 2 s -1 yr -1. The contours represent the mean field. Linear Trend of SSH from 1960 to 2010, in m yr -1. Contours represent the mean field. The thick lines indicate values before (black) and after the trend (yellow). AGU Chapman Conference on the Agulhas System Stellenbosch South Africa October 8 12, 2012

18 If the leakage is increasing, what would be impact in the South Atlantic? Would the signal reach the Tropical Atlantic?.. The North Atlantic?

19 Isopycnal layers along 30 o W Colors: Zonal mean velocity K=6 K=8 K=10 K=12

20 K=1 K=5 K=6 K=8 K=10 K=8 K=9 K=12 K=10 K=12 Some of the drifters released in the thermocline (k=6 thru k=11) reach the Tropical Atlantic after 10 years Drifter distribution after 10 years of constant release in the region indicated by the red stars AGU Chapman Conference on the Agulhas System Stellenbosch South Africa October 8 12, 2012

21 Propagation of Temperature and Salinity anomalies in the thermocline, from 1960 to Apr-2005 Jan-1997 Oct-1988 ~ 112 months Aug-1980 Apr-1972 Jan

22 Mean temperature and salinity differences in layer k=10 ( minus ) σ=25.77 σ=25.77 Mean Salinity difference Mean temperature difference

23 Atlantic Meridional Overturning Cell

24 (Campos et al., 2012, in prep.) AGU Chapman Conference on the Agulhas System Stellenbosch South Africa October 8 12, 2012

25 2004 Other Catarinas? C SST 0.1 SSS Catarina, the 1 st Hurricane in the South Atlantic Mar 2004 SSH

26 P, Brandt/Kiel Current meter moorings across BC (Atlas-B) and NBC (P. Brandt/Kiel), to monitor south and northward fluxes

27 Summary Results seem to compare well with other simulations and observations; Model present a increase in the westward barotropic transport of the AC, south of the Cape, and a poleward displacement of the Subtropical Front. Predominance of positive trends of SST and SSS in the South Atlantic, particularly in the Agulhas leakage and in the Brazil Malvinas Confluence T and S anomalies from the Agulhas region reach the Equatorial Atlantic within the thermocline Model show trends in the Atlantic MOC AGU Chapman Conference on the Agulhas System Stellenbosch South Africa October 8 12, 2012