Loca1 and Remote Forcing of ENSO Ocean Waveguide Response

View More View Less
  • 1 NOAA/PMEL, Seattle, Washington
© Get Permissions
Full access

Abstract

Several experiments using an ocean general circulation model have been carried out in order to explore the degree to which the oceanic waveguide response during the 1982–83 ENSO event was 1ocally and remotely forced. Experiments in which the chosen monthly mean surface stress field was imposed only within three degrees of the equator (3°N/S) and within seven degrees of the equator (7°N/S) reveal that the 7°N/S winds reproduce the equatorial results of the full winds case to within differences small compared to the variability of interest The 3°N/S winds case reproduce equatorial dynamic height acceptably, but introduces errors in SST and upper-ocean currents that approach the ENSO signal. A 7°N–S experiment in which the meridional stress is set to zero (NOYST) snows that meridional stress plays a nontrivial, but not dominant role, in the 1982–83 model behavior; errors generally are comparable to those of the 3°N/S case. A final experiment, in which the 1982–83 winds were imposed west of the dateline and climatological winds were imposed east of 170°W (WPAC), illustrates the extent to which the central and eastern Pacific were forced by winds in the western Pacific. While there is nontrivial remote forcing, the locally forced variability is roughly twice as great.

Implications for coupled ocean-atmosphere modeling and for design of future surface wind stress monitoring arrays for ENSO prediction are considered.

Abstract

Several experiments using an ocean general circulation model have been carried out in order to explore the degree to which the oceanic waveguide response during the 1982–83 ENSO event was 1ocally and remotely forced. Experiments in which the chosen monthly mean surface stress field was imposed only within three degrees of the equator (3°N/S) and within seven degrees of the equator (7°N/S) reveal that the 7°N/S winds reproduce the equatorial results of the full winds case to within differences small compared to the variability of interest The 3°N/S winds case reproduce equatorial dynamic height acceptably, but introduces errors in SST and upper-ocean currents that approach the ENSO signal. A 7°N–S experiment in which the meridional stress is set to zero (NOYST) snows that meridional stress plays a nontrivial, but not dominant role, in the 1982–83 model behavior; errors generally are comparable to those of the 3°N/S case. A final experiment, in which the 1982–83 winds were imposed west of the dateline and climatological winds were imposed east of 170°W (WPAC), illustrates the extent to which the central and eastern Pacific were forced by winds in the western Pacific. While there is nontrivial remote forcing, the locally forced variability is roughly twice as great.

Implications for coupled ocean-atmosphere modeling and for design of future surface wind stress monitoring arrays for ENSO prediction are considered.

Save