Annual cycle of equatorial zonal currents in the Pacific

Noel Keenlyside, Richard Kleeman

Research output: Contribution to journalArticle

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 languageEnglish (US)
Pages (from-to)8-1
Number of pages8
JournalJournal of Geophysical Research: Space Physics
Volume107
Issue number8
StatePublished - Aug 15 2002

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annual cycle
equators
cycles
undercurrent
oceans
wind variations
baroclinic mode
Ocean currents
ocean models
trade wind
Advection
ocean
upper ocean
Rossby wave
annual variations
advection
planetary waves
nonlinearity
annual variation
atmospheres

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

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

In: Journal of Geophysical Research: Space Physics, Vol. 107, No. 8, 15.08.2002, p. 8-1.

Research output: Contribution to journalArticle

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