clivar/godae synthesis evaluation

CLIVAR/GODAE Synthesis Evaluation

Item#5: volume transport, temperature & salinity fluxes through key straits:

• Indonesian throughflow (ITF)

• ACC at Drake Passage

• Florida Current at Florida Strait

Tony Lee, JPL

Some details about legends

3D-VARRTS smoother

ITF

ITF volume transport (Sv)

Anomaly relative to 1993-2001 mean

Total

Spinup problem

Remarkable consistency

Island Rule doesn’t work? Or effect of geometry/topography?

ITF volume transport from 1992 (Sv)

Total

Anomaly relative to 1993-2001 mean

ITF temperature flux (PW)

Total

Anomaly relative to 1993-2001 mean

ITF temperature flux from 1992

Total

Anomaly relative to 1993-2001 mean

ITF salinity flux

Total

Anomaly relative to 1993-2002 mean

ITF salinity flux from 1992

Total

Anomaly relative to 1993-2001 mean

1993-2001 averaged seasonal anomaly of ITF

ITF property flux (volume, heat, and salt) estimated by various products are overall consistent (for mean as well as for seasonal, interannual, and decadal variability: e.g., large magnitude of seasonal cycle relative to mean value, low ITF during El Nino, lack of decadal variability.

ACC

ACC volume transport

Total

Anomaly relative to 1993-2001 mean

ACC volume transport from 1992

Total

Anomaly relative to 1993-2001 mean

ACC temperature flux

Total

Anomaly relative to 1993-2001 mean

Relatively consistent decadal variability

No such large adjustment in volume transport

ACC temperature flux from 1992

Total

Anomaly relative to 1993-2001 mean

ACC salinity flux

Total

Anomaly relative to 1993-2001 mean

ACC salinity flux from 1992

Total

Anomaly relative to 1993-2001 mean

1993-2001 averaged seasonal anomaly of ACC

Relatively large difference in mean and seasonal variability, but relatively consistent on decadal time scale.

Florida Current at Florida Strait

Two different ways of computing Florida Current (FC) transport by various groups:

(1) meridional transport near 26.5N between Florida (~80W) to 75W (more consistent with cable measurements),

(2) zonal transport between Florida and Cuba (better defined in models).

The time mean of (2) is significantly smaller than that of (1) because a portion of (1) comes through a “short circuit” north of the Caribbean instead of from the loop Current (esp. in models)

FC volume transport

Anomaly relative to 1993-2001 mean

Total

Grey curve – cable data

FC volume transport from 1992

Total

Anomaly relative to 1993-2001 mean

Grey curve – cable data

Zonal (upper) and meridional (lower) Florida Current transports

Zonal: between Florida & Cuba (well-defined)

Meridional: 26.5N, 80-75W (near cables)

Grey curve – cable data

FC temperature flux

Total

Anomaly relative to 1993-2001 mean

FC temperature flux from 1992

Total

Anomaly relative to 1993-2001 mean

FC salinity flux

Total

Anomaly relative to 1993-2001 mean

FC salinity flux from 1992

Total

Anomaly relative to 1993-2001 mean

1993-2001 averaged seasonal anomaly of Florida Current

Relatively large spread, partly because of definition problem.

In most models, the flow going into the Gulf of Mexico is weak; some flow take a short cut north of Cuba to joint the Florida Current.

Summary Statistics

ITF FC ACC ITFt ITFs FCt FCs ACCt ACCs

Sv Sv Sv PW PW PW Kg/s Kg/s Kg/s

K7 -12.4 157

CRFS-A -12.9 16.6 147

CRFS-2 -13.2 24.2 147

ECCO-50yr -11.0 29.3 129 -1.0 -0.4 2.1 1.1 1.4 4.5

ECCO-SIO -10.7 30.6 154 -0.9 -0.4 2.2 1.1 1.6 5.3

ECMWF -10.6 14.8 148

GFDL -15.7 24.3 171 -1.0 -0.6 1.6 0.8 1.7 6.1

INGV -11.9 24.6 127 2.8 0.9

MOVE-G -23.4 179

ECCO-JPLKF -13.2 27.6 132 -1.2 -0.5 2.3 1.0 1.4 4.6

MCTR 3DVAR -18.7 15.0 142

MCTR KF -12.8 21.8 149

ECCO-GODAE -11.1 26.6 148 -0.9 -0.4 1.9 1.0 1.5 5.1

SODA -14.5 27.5 158 -1.2 -0.5 2.1 1.0 1.7 5.6

Obs. Analysis -10 ~ -15

31.9 120~160

1993-2001 mean transports/fluxes: For Florida Current: black - meridional transport near 26.5N, 80-75W; red – zonal transport between Florida & Cuba.

The largest mean ITF (> 23Sv): consistent with Island rule (integration of South Pacific curl)? Or effect of geometry/topography?

High mean ACC transports (170-180 Sv): too strong zonal wind? lack of form drag due to smooth topography? Small viscosity?

(all in Sv) ITF FC ACC rms dev. of FC from cable data

K7 3.5 7.0

CRFS-A 5.0 4.7 6.4 4.9

CRFS-2 5.2 4.7 6.2 5.3

ECCO-50yr 2.4 1.6 4.1 2.9

ECCO-SIO.it69 2.5 2.2 4.6 3.1

ECMWF 3.0 2.2 4.0 3.0

GFDL 2.5 2.8 5.0 3.6

INGV 3.1 5.6 3.5 5.5

MOVE-G 4.0 6.3

ECCO-JPL RTS smoother 3.0 3.0 4.1 3.4

MCTR 3DVAR 5.5 5.1 6.6 5.3

MCTR KF 3.2 1.4 4.6 2.8

ECCO-GODAE.v2.199 2.6 2.2 4.4 3.3

SODA 4.3 2.6 4.5 5.0

rms diff. among models 2.3 3.0 3.5

Measurement 2.5

1993-2001 rms variability of volume transport, rms difference among models, and rms difference from cable measurements