Intraseasonal Kelvin wave along the equatorial Pacific in the two flavors of El Nino

The spatial structure and temporal evolution of the intraseasonal variability (ISV) of the subsurface ocean temperature (STA) in the equatorial Pacific associated with the two flavors of El Nino (i.e., the canonical or eastern Pacific (EP) El Nino and the central Pacific (CP) El Nino) are investigated using observations and 1.5-layer linear reduced gravity model. Results suggest that the ISV characteristics show some differences in the two types of El Nino, though both oscillate along the thermocline in the form of the intraseasonal equatorial Kelvin wave, which is excited in the western tropical Pacific by the zonal wind stress associated with the Madden-Julian oscillation (MJO). First, the period of dominant mode of the STA ISV during CP El Nino broadly distributes in 50-80 days with the spectra peaking in 60-65-day. By contrast, the spectrum of STA ISV during EP El Nino shows a peak in 75-80-day period. This indicates the wave speed is faster in the CP El Nino than in EP El Nino. Second, the ISV activity peaks in previous spring during the developing phase of EP El Nino, whereas during CP El Nino it becomes the most active during the mature phase. Third, the strongest IEKW occurs in the central Pacific around the dateline during CP El Nino and attenuates quickly east of 130°W due to strong eddy viscosity dissipation, while the IEKW during the EP El Nino propagates efficiently from the western to the eastern Pacific with a relative weak diffusion.