Abnormal features of the Pacific wind system during the 1997-1998 El Nino

The 1997-1998 El Nino, the strongest in recorded history, manifested itself with a number of unusual features associated with the Pacific wind system. These features include: (1) an annual cycle of an east-west migration of a weakened wind speed zone between 2 degrees N-9 degrees N; (2) an asymmetri c see-saw process of trade wind variations between the two hemispheres in t erms of relative intensity and central position; and (3) an 18-month cycle of meridional oscillations of the Pacific doldrums and trade wind belts. In addition, the commonly-used argument of trade wind relaxation in associati on with El Ninos appears to be partly introduced, at least for the present case, by the 'tilt effect' of the Pacific zonal winds. These novel findings , revealed by the newly available multi-year TOPEX altimeter data, may help to improve existing theories on El Nino formation, and may also contribute to its future prediction.