Abstract
Abstract. An analysis of archived data from the NEMO 1∕12th degree global ocean model shows the importance of the North Equatorial Counter Current (NECC) in the development of the strong 1982–1983 and 1997–1998 El Niños. The model results indicate that in a normal year the core of warm water in the NECC is diluted by the surface Ekman transport, by geostrophic inflow and by tropical instability waves. During the development of the 1982–1983 and 1997–1998 El Niños, these processes had reduced effect at the longitudes of warmest equatorial temperatures and to the west. During the autumns of 1982 and 1997, the speed of the NECC was also increased by a stronger-than-normal annual Rossby wave. The increased transport of warm water by the NECC due to these changes resulted in warm water reaching the far eastern Pacific and appears to have been a major factor in moving the centre of deep atmospheric convection eastwards across the Pacific.
Highlights
Studies of the tropical Pacific often focus on the equatorial waveguide and the propagation of equatorial Kelvin waves generated by westerly wind events (i.e. Levine and McPhaden, 2016; Chen et al, 2016; Hu and Fedorov, 2017)
Whereas most discussions of the El Niño focus on the role of the equatorial waveguide, these results show that, in the model, strong eastern Pacific El Niño events, like the 1982– 1983 El Niño, occur primarily as a result of heat transported by the North Equatorial Counter Current
This paper is the result of a preliminary analysis of archived data from an early run of a high-resolution global ocean model
Summary
Studies of the tropical Pacific often focus on the equatorial waveguide and the propagation of equatorial Kelvin waves generated by westerly wind events (i.e. Levine and McPhaden, 2016; Chen et al, 2016; Hu and Fedorov, 2017). 3 uses the results to plot the time series of average sea surface temperatures in the equatorial band during the period 1980 to 2000 Such a time series clearly shows the strong El Niño events of 1982– 1983 and 1997–1998 as well as the weaker warm pool events in intermediate years. The El Niño is often described as resulting from increased eastward heat advection in the equatorial waveguide, the contribution of the NECC is seen to be roughly 4 times larger than the contribution from currents close to the Equator This is true for water warmer than 28 ◦C at 180◦ E. The argument made here has to be based on a mixture of theory and analysis of the model results
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