Response of the North Atlantic Circulation to the realistic and anomalous wind stress

1. Response of the North Atlantic Circulation to the realistic and anomalous wind stress Yongqi Gao , Helge Drange, Mats Bentsen and Jan Even Nilsen Nansen-Zhu International Research Centre, IAP/CAS, China Nansen Environmental and Remote Sensing Center, Norway Bjerknes Centre for Climate Research, Norway

2. Micom • Miami Isopycnic Coordinate Ocean Model (Bleck et al., 1992) • Mixed layer+Isopycnic layers below • Global domain with sea ice module

3. Experimental Design • Spin-up time 180 yrs; • W0, 1948-2004, three cycles; • W1/2, 1948-2004, three cycles; • W1, 1948-2004, three cycles; • W2, 1948-2004, three cycles; Gao et al., updating, 2009

4. AMOC and Normalized AMOC W2 W1 W1/2 W0

5. Simulated and Data-estimated Meridional Heat Transport W2 W1 W1/2 W0 Obs (red line):Trenberth and Caron (2001)

6. Simulated Maximum Mixed Layer Depth W0 W1/2 W2 W1

7. Simulated Isopycnal Volume Transport at 24oN W0 W1/2 W2 W1

9. Simulated Isopycnal Volume Transport at Section ABD W0 W1/2 W2 W1

10. Mean Volume Transport at Northern Atlantic W0 W1/2 W2 W1

11. Mean Dense Water Volume Transport at Northern Atlantic W0 W1/2 W2 W1

12. Dense Water Formation Rate in the Irminger Sea basin And Normalized AMOC in W1 (red) and W0 (blue)

14. Simulated Dense Water Volume Transport through Sections 24oN W0 W1/2 AB W2 W1

15. Subpolar Gyre Index W2 W0 W1/2 Obs (blue line): Hatun et al. 2005

16. Summing up • AMOC is sensitive to the strength of the wind stress • Wind stress is responsible for the short-term variabilities in the simulated AMOC • Long-term increasing trend in the simulated AMOC is mainly governed by the thermohaline forcing • Realistic wind stress can lift the AMOC in the subtropical North Atlantic by 7.3 Sv • Subpolar Gyre Index can be used as an potential indicator of the AMOC