Pacific (Sub) tropical circulation in ORCA025 and ORCA05

Pacific (Sub) tropical circulation in ORCA025 and

ORCA05

DRAKKAR Meeting 2007Joke Lübbecke

Introduction SST STCs Zonal Currents NGCU Conclusions

Schott et al., 2004

NEC

EUC

nSECsSEC

NECC

o In ORCA05 some problems in the tropical pacific:• no Tsuchiya Jets• EUC too deep• transport too high

better representationwith higher resolution?

Introduction SST STCs Zonal Currents NGCU Conclusions

o Differences between the ORCA025 experiments:• KAB001 (CORE forcing, weak 3-dim restoring in high lat.)• KAB002 (CORE forcing, strong surface restoring)• G70 (ERA-40, strong surface restoring)

Nino3 SST

COADS obs.ORCA05ORCA025

Introduction SST STCs Zonal Currents NGCU Conclusions

Meridional Overturning Stream Function

ORCA025:KAB001G70

20/15 Sv30/2035/35 45/40

Eq.10°S 10°N20°S 20°N30°S 30°N

Introduction SST STCs Zonal Currents NGCU Conclusions

STC Strength

ORCA05KAB001G70

Introduction SST STCs Zonal Currents NGCU Conclusions

explaination for different trends ???

ORCA05 ORCA025

EUC: mean equatorial zonal velocity

0.9 0.9

Introduction SST STCs Zonal Currents NGCU Conclusions

ORCA05 ORCA025

Mean zonal velocity at 155°W

EUC

nSECcSEC

NECNECC

EIC

EUC

nSECcSEC

NECCNEC

EIC

NSCC

SSCC

Tsuchiya Jets (NSCC, SSCC) in ORCA025

Introduction SST STCs Zonal Currents NGCU Conclusions

Introduction SST STCs Zonal Currents NGCU Conclusions

Tsuchiya Jets

eastward velocities averaged over 26.0< <27.0

NSCC

EUC

SSCC

Eq.

5°N

5°S

10°S

10°N

155°W165°E 110°W

Mean zonal velocity at 155°W

KAB001

G70

Introduction SST STCs Zonal Currents NGCU Conclusions

0.80 m/s0.85 m/s

1991-2000

mean EUC Transport

Introduction SST STCs Zonal Currents NGCU Conclusions

Experiment 165°E 155°W 110°W

ORCA05

KAB042

34 Sv 46 Sv 28 Sv

ORCA025

KAB001

32 Sv 38 Sv 23 Sv

ORCA025

G70

22 Sv 27 Sv 18 Sv

Johnson et al., 2002

17 Sv 35 Sv 26 Sv

in density range 22.5<<26.0

EUC Transport variability

Introduction SST STCs Zonal Currents NGCU Conclusions

at 155°W,in density range22.5<<26.0KAB001

G70

annual cycle

KAB001KAB002G70

Introduction SST STCs Zonal Currents NGCU Conclusions

Mean velocity in 150m depth

7°S section

ORCA2 ORCA05 ORCA025

0.35

0.4

0.1

Introduction SST STCs Zonal Currents NGCU Conclusions

Transport

transport variability mean transport

(24.0 << 26.7)5°S to 10°S average:

• ORCA2: ~ 13 Sv• ORCA05: ~ 20 Sv• ORCA025: ~20 Sv

ORCA2ORCA05ORCA025

Introduction SST STCs Zonal Currents NGCU Conclusions

Introduction SST STCs Zonal Currents NGCU Conclusions

• improvements with ORCA025: Tsuchiya Jets present EUC extension not that deep more realistic EUC transport representation of western boundary current

• KAB001 compared to G70: structure of zonal currents and OT similar all wind driven features weaker in G70 EUC transport variability in phase with offset

• open question: different STC trends: ORCA05 > G70 > KAB001

KAB001KAB002

ORCA05 (KAB042)ORCA025 (KAB001)ORCA025 (KAB002)ORCA025 (G70)