On the Generation of Rossby Solitons During EL Nino

The excitation of equatorial Rossby solitons during El Nino is studied numerically using a one-layer reduced-gravity formulation. The model basin - an idealization of the tropical Pacific - extends 15,000 km zonally and 3,000 km meridionally. Forcing is applied as a patch of zonal wind stress representing the relaxation of the equatorial easterlies preceding El Nino. It is shown that a relaxation of the equatorial winds generates internal Rossby solitons subsequent to the reflection of an equatorial Kelvin wave front from the eastern boundary. The meridional structure of the soliton is that of a first latitudinal mode Rossby wave. The simple El Nino simulations result in the excitation of two or three solitons separated by approximately 3,000 km. The results of this study suggest that internal Rossby solitons are most likely to be observed in the central and western Pacific during a major El Nino year.