### Abstract

Observational (Tropical Atmosphere-Ocean array) data on the annual cycle of upper ocean zonal currents on the equator are analyzed using a simple dynamical ocean model in order to investigate underlying dynamics. The model, by treating linear and nonlinear terms semi-independently, allows a separation of various linear and nonlinear effects. The model focuses on linear dynamics of low-order baroclinic modes. By realistically simulating the vertical structure of annual cycle, the model shows that linear dynamics determines the vertical and meridional structure of the annual cycle. Nonlinearity is weak and only important in the undercurrent, where it provides a simple mechanism for the annual cycle: mean meridional advection of the annual cycle north of the equator onto the equator, with the boreal springtime surge in the undercurrent being a direct result of a surge centered at 2°N. Model results show that annual variations in zonal currents are out of phase across the equator, surging in the corresponding spring. This behavior is a response to trade wind variations, which are also equatorially antisymmetric, and is generated by the second meridional mode Rossby wave.

Original language | English (US) |
---|---|

Pages (from-to) | 8-1 |

Number of pages | 8 |

Journal | Journal of Geophysical Research: Space Physics |

Volume | 107 |

Issue number | 8 |

State | Published - Aug 15 2002 |

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### Keywords

- Baroclinic mode model
- Equatorial ocean currents
- Equatorial undercurrent
- Equatorial waves
- Tropical Pacific
- Zonal momentum balance

### ASJC Scopus subject areas

- Earth and Planetary Sciences (miscellaneous)
- Atmospheric Science
- Geochemistry and Petrology
- Geophysics
- Oceanography
- Space and Planetary Science
- Astronomy and Astrophysics

### Cite this

*Journal of Geophysical Research: Space Physics*,

*107*(8), 8-1.

**Annual cycle of equatorial zonal currents in the Pacific.** / Keenlyside, Noel; Kleeman, Richard.

Research output: Contribution to journal › Article

*Journal of Geophysical Research: Space Physics*, vol. 107, no. 8, pp. 8-1.

}

TY - JOUR

T1 - Annual cycle of equatorial zonal currents in the Pacific

AU - Keenlyside, Noel

AU - Kleeman, Richard

PY - 2002/8/15

Y1 - 2002/8/15

N2 - Observational (Tropical Atmosphere-Ocean array) data on the annual cycle of upper ocean zonal currents on the equator are analyzed using a simple dynamical ocean model in order to investigate underlying dynamics. The model, by treating linear and nonlinear terms semi-independently, allows a separation of various linear and nonlinear effects. The model focuses on linear dynamics of low-order baroclinic modes. By realistically simulating the vertical structure of annual cycle, the model shows that linear dynamics determines the vertical and meridional structure of the annual cycle. Nonlinearity is weak and only important in the undercurrent, where it provides a simple mechanism for the annual cycle: mean meridional advection of the annual cycle north of the equator onto the equator, with the boreal springtime surge in the undercurrent being a direct result of a surge centered at 2°N. Model results show that annual variations in zonal currents are out of phase across the equator, surging in the corresponding spring. This behavior is a response to trade wind variations, which are also equatorially antisymmetric, and is generated by the second meridional mode Rossby wave.

AB - Observational (Tropical Atmosphere-Ocean array) data on the annual cycle of upper ocean zonal currents on the equator are analyzed using a simple dynamical ocean model in order to investigate underlying dynamics. The model, by treating linear and nonlinear terms semi-independently, allows a separation of various linear and nonlinear effects. The model focuses on linear dynamics of low-order baroclinic modes. By realistically simulating the vertical structure of annual cycle, the model shows that linear dynamics determines the vertical and meridional structure of the annual cycle. Nonlinearity is weak and only important in the undercurrent, where it provides a simple mechanism for the annual cycle: mean meridional advection of the annual cycle north of the equator onto the equator, with the boreal springtime surge in the undercurrent being a direct result of a surge centered at 2°N. Model results show that annual variations in zonal currents are out of phase across the equator, surging in the corresponding spring. This behavior is a response to trade wind variations, which are also equatorially antisymmetric, and is generated by the second meridional mode Rossby wave.

KW - Baroclinic mode model

KW - Equatorial ocean currents

KW - Equatorial undercurrent

KW - Equatorial waves

KW - Tropical Pacific

KW - Zonal momentum balance

UR - http://www.scopus.com/inward/record.url?scp=0037104895&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0037104895&partnerID=8YFLogxK

M3 - Article

VL - 107

SP - 8

EP - 1

JO - Journal of Geophysical Research: Space Physics

JF - Journal of Geophysical Research: Space Physics

SN - 0148-0227

IS - 8

ER -