Sverdrup and nonlinear dynamics of the Pacific SEC
# Sverdrup and nonlinear dynamics of the Pacific South Equatorial Current

### Slides shown during talks:

(This talk has evolved greatly since I started giving talks on it!)
I think the latest version (KMNI) exists in pdf!

The gif files below are are mixture of old and new, false and true ....

- PMEL informal seminar, 17 Oct 2001
- UW PO seminar, 24 Oct 2001
- OSU PO seminar, 30 Oct 2001
- Lamont PO seminar, 6 Dec 2001
- NCAR ocean seminar, 7 Dec 2001
- Scripps PO seminar, 9 Jan 2002
- Flinders Univ. seminar, 5 Feb 2002
- CSIRO (Hobart) Frohlich lecture, 22 Feb 2002
- WHOI PO seminar, 9 Jul 2002
- Pedro Ripa Memorial Colloquium (CICESE), 3 Oct 2002
- KNMI seminar, 14 Apr 2003

Download the manuscript accepted at JPO

- Introduction
- Why is the Sverdrup circulation so weak near the equator?

Talk will use ADCP observations and an OGCM
- ADCP data ....(Johnson et al. 2001 data distribution)
- (y,z) sections of zonal current at 110°W, 155°W, 165°E
- Maps of surface zonal current and zonal transport.

Here work with mean, vertically-integrated quantities.

Define "currents" based on the vertically-integrated zonal transports.
- ERS curl and Sverdrup zonal transport
- Part of the answer is that the ship winds
*were* wrong: Compare wind products Tau-x at 130°W-100°W

Why is the scatterometer curl better?

Wallace et al 89: Cold tongue slows wind speed.

Chelton et al 01: Since winds cross front at an angle, there is a curl:

TMI SST and QuikSCAT Stress (Chelton et al. Fig. 1)
- New Sverdrup transport is better, but there are still problems:

Compare Sverdrup and observed zonal transports

Transports of the zonal "currents"

1. Sverdrup SEC(N) extends all the way west.

2. Sverdrup SEC(S) weak near the equator.

3. Sverdrup equatorial eastward transport grows all the way west.

4. Sverdrup transports too weak by a factor of 2.
- Turn to the model (model intro)
- Zonal transports: ADCP, Sverdrup, Model. Model agrees with obs much better than Sverdrup does.
- Maps of model momentum terms (Advection, Coriolis, PG, Tau). Model is nearly linear but not Sverdrupian.
- Diagnosing the nonlinear terms
- Dynamics
- Convergence of zonal momentum flux (Overlay friction) Meridional circulation
- Curl and Sverdrup U for wind stress, advective and friction terms
- Effect of advection terms along equator: total term and high-frequency part

- Conclusions

A few other slides in reserve to respond to questions:
- SST, Stress, Div and Curl during 2-4 Sep 1999 (Chelton et al. Fig. 4)
- ADCP and model surface zonal current
- The Sverdrup eastern boundary condition
- Flux-form advective terms in the Gent/Cane model
- Mean model momentum balance along the equator
- Maps of mean advective terms. All similar magnitude.
- uux from model and ADCP obs
- Advective terms from time-smoothed velocities. uux is similar from smooth (even mean) velocities.
- Advective terms difference. Difference due to high-frequencies (mostly TIW).