Local and equatorial forcing of seasonal variations of the North Equatorial Countercurrent in the Atlantic Ocean
MetadataShow full item record
The seasonal variation of the North Equatorial Countercurrent (NECC) in the tropical Atlantic Ocean is investigated by using a linear, one-layer reduced-gravity ocean model and by analyzing sea surface height (SSH) data from Ocean Topography Experiment (TOPEX)/Poseidon (T/P) altimeters. The T/P data indicate that the seasonal variability of the NECC geostrophic transport, between 3° and 10°N, is dominated by SSH changes in the southern flank of the current. Since the southern boundary of the NECC is located partially within the equatorial waveguide, the SSH variation there can be influenced considerably by the equatorial dynamics. Therefore, it is hypothesized that the wind stress forcing along the equator is the leading driver for the seasonal cycle of the NECC transport. The wind stress curl in the NECC region is an important but smaller contributor. This hypothesis is tested by several sensitivity experiments that are designed to separate the two forcing mechanisms. In the first sensitivity run, a wind stress field that has a zero curl is used to force the ocean model. The result shows that the NECC geostrophic transport retains most of its seasonal variability. The same happens in another experiment in which the seasonal wind stress is applied only within a narrow band along the equator outside the NECC range. To further demonstrate the role of equatorial waves, another experiment was run in which the wind stress in the Southern Hemisphere is altered so that the model excludes hemispherically symmetrical waves (Kelvin waves and odd-numbered meridional modes of equatorial Rossby waves) and instead excites only the antisymmetrical equatorial Rossby modes. The circulation in the northern tropical ocean, including the NECC, is affected considerably even though the local wind stress there remains unchanged. All these appear to support the hypothesis presented in this paper.
Author Posting. © American Meteorological Society, 2006. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 36 (2006): 238-254, doi:10.1175/JPO2848.1.
Showing items related by title, author, creator and subject.
Observations of the dispersion characteristics and meridional sea level structure of equatorial waves in the Pacific Ocean Farrar, J. Thomas (American Meteorological Society, 2008-08)Spectral techniques applied to altimetry data are used to examine the dispersion relation and meridional sea level structure of wavelike variability with periods of about 20 to 200 days in the equatorial Pacific Ocean. ...
Thompson, Geoffrey (Woods Hole Oceanographic Institution, 1981-11)This report gives details on the sampling locations, rock types recovered and bathymetry and morphology of the Islets of St. Paul's Rocks (equatorial Atlantic) and the surrounding sea floor. This work was done during ...
SOFAR float trajectories from an experiment to measure the Atlantic cross equatorial flow (1989-1990) Richardson, Philip L.; Zemanovic, Marguerite E.; Wooding, Christine M.; Schmitz, William J.; Price, James F. (Woods Hole Oceanographic Institution, 1992-08)Neutrally buoyant SOFAR floats at nominal depths of 800, 1800, and 3300 m were tracked for 21 months in the vicinity of western boundary currents near 6N and at several sites in the Atlantic near 11N and along the equator. ...