Influence of a Southern Shift of the ITCZ from Quick Scatterometer Data on the Pacific North Equatorial Countercurrent

By analyzing the climatologically averaged wind stress during 2000--2007, itis found that the easterly wind stress in the northern tropical PacificOcean from Quick Scatterometer (QSCAT) data was stronger than those fromTropical Atmosphere Ocean (TAO) data and from National Centers forEnvironmental Prediction/National Center for Atmospheric Research(NCEP/NCAR) reanalysis I. As a result, the Intertropical Convergence Zone(ITCZ) in the Pacific Ocean is more southward in the QSCAT data than in theNCEP/NCAR data. Relative to the NCEP wind, the southern shift of the ITCZ inthe QSCAT data led to negative anomaly of wind stress curl north of alatitude of 6^oN. The negative anomaly results in downward Ekman pumpingin the central Pacific. The excessive local strong easterly wind alsocontributes to the downward Ekman pumping. This downward Ekman pumpingsuppresses the thermocline ridge, reduces the meridional thermocline slopeand weakens the North Equatorial Countercurrent (NECC). These effects wereconfirmed by numerical experiments using two independent ocean generalcirculation models (OGCMs). Furthermore, the excessive equatorial easterlywind stress was also found to contribute to the weaker NECC in the OGCMs. Acomparison between the simulations and observation data indicates that thestronger zonal wind stress and its southern shift of QSCAT data in the ITCZregion yield the maximum strength of the simulated NECC only 33% of themagnitude derived from observation data and even led to a ``missing" NECCin the western Pacific.