Figure 5. Sverdrup balance: close up of Benguela region in JJA. a,c) Term i) of (1). b, d) Term ii) of (1). Top panels: CCSM4-1º, bottom panels: CCSM4-0.5º. (c) Nm -3 Vert. int.  0 V WSC (a) Nm -3 (b) Vert. int.  0 V WSC (d) Nm -3

W (45m) E. P. Figure 6. a, d), vertical velocity at 45m in JJA. Positive values indicate upwelling. b, e) corresponding Ekman pumping. c, f) Meridional component of surface stress in JJA. Top Panels: CCSM4-1º, bottom panels: CCSM4-0.5º. W (45m) E. P. mday -1 (a)(b) (d) (e) mday -1 Nm -2 (c) (f) TAUY

Figure 7. Difference of SST due to changing the atmospheric resolution in CCSM4. CCSM4-0.5º minus CCSM4-1º, in JJA.

Figure 8. SST differences of nRCM from equivalent CCSM4 baseline run, for JJA. a) nRCM-1º minus CCSM4-1º. b) nRCM-0.5º minus CCSM4-0.5º. c) nRCM- MOD minus CCSM4-0.5º. (a) I (c) (b)

ROMS, ORIGINAL QuiKSCAT ROMS, MODIFIED(a) (b) (c) Figure 9. Meridional component of wind stress in JJA, a) in ROMS part of nRCM-0.5º, b) corresponding field from nRCM- MOD, c) from QuikSCAT. Nm -2

QuiKSCAT (a) (b) (c) Wind stress Nm -2 Latitude Figure 10. a, b, c) Wind stress at coastal points as a function of latitude. The stress is the magnitude of time-averaged vector components, at the closest data point to the west Africa coastline. a) in ROMS part of nRCM-0.5º. b) corresponding field from nRCM- MOD, and c) from QuikSCAT. ROMS, ORIGINAL ROMS, MODIFIED

Figure 11. a), b) Sverdrup balance in nRCM-0.5º in JJA. a) Term i) of (1). b, Term ii) of (1). c), vertical velocity at 45m in ROMS part of nRCM-0.5º, d) corresponding Ekman pumping. (a) (b) Ekman Pumping W mday -1 (c)(d) Nm -3 Vert. int.  0 V WSC

Figure 12. Sverdrup balance terms in nRCM-MOD in JJA. a) Term i) of (1). b, Term ii) of (1) Nm -3 (a)(b) Vert. int.  0 V WSC

V ms -1 SURF CURR SURF CURR nRCM- 0.5 nRCM- MOD (a) (b) (d) (e) Figure 13. a,b) Time-mean surface current (arrows) and meridional velocity (color). Only vectors with magnitude > 0.1ms -1 shown. (d,e), vertical velocity at 45m. a, b) From ROMS part of nRCM-0.5 º and b, e) from ROMS part of nRCM-MOD experiment. c, f) are close-ups of the southern part of b,e). SURF CURR MOD ms -1 (c) mday -1 W (45M) nRCM- 0.5 mday -1 W (45M) mday -1 (f) nRCM- MOD ms -1

(a) (b) (c) (d) Figure 14. Meridional velocity sections vs longitude and depth. a), b) are along the line shown in c). d,e) are along the line shown in f). Left panels: from nRCM-0.5º. Middle panels: from nRCM-MOD. Shading in right panels shows the surface velocity from c) nRCM-0.5º and f) nRCM-MOD. (e) (f) V ms -1 nRCM- 0.5 nRCM- MOD nRCM- 0.5 nRCM- MOD nRCM- 0.5 nRCM- MOD

(a) (c) (b) (d) Figure 15. Potential temperature sections (ºC) vs longitude and depth. a), b) are along the northern line shown in Fig. 14c). b,d) are along the southern line shown in Fig. 14f). Left panels: from nRCM-0.5º. Middle panels: from nRCM-MOD. Note change of temperature color range from upper row to lower row. nRCM- 0.5 nRCM- MOD nRCM- 0.5 nRCM- MOD TºC

NRCM (a) (b) Figure 16. Top-level temperature (taken as SST) from a) ROMS part of nRCM-0.5º b) from ROMS part of nRCM-MOD experiment, c) from the NOAA analysis of observed SST (Reynolds et al 2007), d) from Levitus gridded onto POP grid. ºC LEVITUS (c) (d) nRCM- 0.5 nRCM- MOD- on ROMS grid NOAA OISST

MOD (a) (c) Figure 17. SST difference for JJA. a) for the nRCM-MOD experiment, relative to nRCM-0.5º, data on ROMS grid, b) as a), but on POP grid and showing a larger area, c) between nRCM-MOD and Levitus observations. (b)