Using Satellite Altimeter and SST Observations of the 1997-1998 El Nino to check the key ocean processes involved in a strong El Nino

A recent high-resolution ocean model study of the strong El Ninos of 1982-1983 and 1997-1998 highlighted a previously neglected ocean mechanism which was active during their growth. The mechanism involved a weakening of both the Equatorial Current and the tropical instability eddies in mid-ocean. It also involved an increase in the strength of the North Equatorial Counter Current due to the passage of the annual Rossby wave. This presentation reports how satellite altimeter and satellite SST data was used to validate the model results the key areas, confirming the changes in the current and eddy fields and the resulting eastward extension of the region of highest SST values. The SST changes were sufficient to trigger new regions deep-atmospheric convection and so had the potential to have a significant impact on the development of the El Nino and the resulting changes in the large scale atmospheric circulation.