Journal of Oceanography

, Volume 70, Issue 2, pp 165–174 | Cite as

Oceanic Rossby waves induced by the meridional shift of the ITCZ in association with ENSO events

  • Hiroto Abe
  • Youichi Tanimoto
  • Takuya Hasegawa
  • Naoto Ebuchi
  • Kimio Hanawa
Original Article

Abstract

This study investigated the eastern Pacific Intertropical Convergence Zone (ITCZ) as an atmospheric forcing to the ocean by using various observed and reanalysis data sets over 29 years. Climatologically, a zonal band of positive wind stress curl (WSC) with a 10° meridional width was exhibited along the ITCZ. A southward shift of the positive WSC band during the El Niño phase induced a negative (positive) WSC anomaly along the northern (southern) portion of the ITCZ, and vice versa during the La Niña phase. This meridional dipole accounted for more than 25 % of interannual variances of the WSC anomalies (WSCAs), based on analysis of the period 1993–2008. The negative (positive) WSCA in the northern portion of the ITCZ during the El Niño (La Niña) phase was collocated with a positive (negative) sea surface height anomaly (SSHA) that propagated westward as a Rossby wave all the way to the western North Pacific. This finding indicates that this off-equatorial Rossby wave is induced by the WSCA around the ITCZ. Our analysis of a 1.5-layer reduced gravity model revealed that the Rossby waves are mostly explained by wind stress forcing, rather than by reflection of an equatorial Kelvin wave on the eastern coastal boundary. The off-equatorial Rossby wave had the same SSHA polarity as the equatorial Kelvin wave, and generation of a phase-preserving Rossby wave without the Kelvin wave reflection was explained by meridional movement of the ITCZ. Thus, the ITCZ acts as an atmospheric bridge that connects the equatorial and off-equatorial oceanic waves.

Keywords

ITCZ Meridional migration Wind stress curl Rossby wave ENSO 

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Copyright information

© The Oceanographic Society of Japan and Springer Japan 2014

Authors and Affiliations

  • Hiroto Abe
    • 1
  • Youichi Tanimoto
    • 2
    • 3
  • Takuya Hasegawa
    • 3
    • 4
  • Naoto Ebuchi
    • 1
  • Kimio Hanawa
    • 5
  1. 1.Institute of Low Temperature ScienceHokkaido UniversitySapporoJapan
  2. 2.Faculty of Environmental Earth ScienceHokkaido UniversitySapporoJapan
  3. 3.Research Institute for Global ChangeJapan Agency for Marine-Earth Science and TechnologyYokosukaJapan
  4. 4.Earth Simulator CenterJapan Agency for Marne-Earth Science and TechnologyYokohamaJapan
  5. 5.Department of Geophysics, Graduate School of ScienceTohoku UniversitySendaiJapan

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