Intraseasonal variability of the tropical Pacific subsurface temperature in the two flavours of El Niño

Abstract

ABSTRACTThe spatial structure and temporal evolution of the intraseasonal variability (ISV) of the subsurface ocean temperature (STA) in the equatorial Pacific associated with the two flavours of El Niño [i.e. the canonical or eastern Pacific (EP) El Niño and the central Pacific (CP) El Niño] 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 Niño, although both oscillate along the thermocline in the form of the intraseasonal equatorial Kelvin wave (IEKW), 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 Niño broadly distributes in 50–80 days with the spectra peaking in 60–65 days. By contrast, the spectrum of STA ISV during EP El Niño shows a peak in 75–80‐day period. This indicates that the wave speed is faster in the CP El Niño than in EP El Niño. Second, the ISV activity peaks in previous spring during the developing phase of EP El Niño, whereas during CP El Niño it becomes the most active during the mature phase. Third, the strongest IEKW occurs in the CP around the dateline during CP El Niño and attenuates quickly east of 130°W due to strong eddy viscosity dissipation, while the IEKW during the EP El Niño propagates efficiently from the western to the eastern Pacific with a relative weak diffusion.