1. The Role of Inter-ocean Exchanges on Long-term Variability of the Northward Heat Transport in the South Atlantic
Shenfu Dong
CIMAS/UM and NOAA/AOML
S. L. Garzoli, M.Baringer
NOAA/AOML, Miami, Florida USA
June 9, 2010
R. Lumpkin, NOAA/AOML

2. Objective:
To investigate the role of the inter-ocean exchanges in the variability of the northward heat transport in the South Atlantic.
Specific Question:
Where does the variability in the northward heat transport come from?
Inter-ocean exchanges with the Pacific Ocean.
Inter-ocean exchanges with the Indian Ocean.
Air-sea heat exchanges.
heat storage in the basin.

3. OGCM for the Earth Simulator (OFES)
The model code is based on MOM3.
OFES covers 75S to 75N.
0.1 horizontal resolution.
54 vertical levels.
Spun up for 50 years
followed by a 57-yr hindcast run (1950–2006).
Forcing from the NCEP–NCAR reanalysis.

4. Time-Mean Volume and Temperature Transport
Results based on XBT measurements at nominal 35S:
Total volume transport: 0.5 Sv
Total heat transport: PW
AMOC strength: 17.9 Sv
AMOC from OFES: 15 Sv

5. Relationship between AMOC and Northward Heat Transport at 35S
XBT observations
OFES Model
HT(PW)  0.05 * AMOC (Sv)

6. The Strength of the AMOC at 35S
Linear increasing trend in AMOC: 0.9 Sv per decade

7. Northward Temperature Transport across 35S - I
0.03 PW per decade

8. Northward Temperature Transport across 35S - III
Baroclinic: , Horizontal:

9. Volume Transports across Drake Passage and South of Africa

10. Temperature Transports across Drake Passage and South of Africa
0.03 PW/decade
-0.04 PW/decade

11. Linear Trend (PW/decade)
Linear Trend (PW/decade)
0.07 PW per decade

12. Anomalous Air-Sea Heat Flux
Decreasing trend: PW/decade

13. Linear Trend (PW/decade)

14. Temperature Transports--- South of Africa
ACC-dominant eastward transport
0.03 PW per decade
Total
-0.04 PW per decade
Agulhas leakage
-0.07 PW per decade

15. Trend PW/decade

16. Conclusions
Both XBT measurements and the OFES model suggest that 1 sverdrup increase in the AMOC strength would cause an increase in the northward heat transport of 0.05 PW at approximately 35S.
The OFES model suggests an increase in the northward heat transport across 35S from 1980 to 2006.
The increasing trend in the northward heat transport is likely due to the increase in Agulhas leakage into the South Atlantic.
About half of the increase in Agulhas leakage is lost to the atmosphere through air-sea heat exchange.

17. Temperature Transports across Drake Passage and South of Africa

18. Northward Temperature Transport across 35S - II