The work fits into research on climate variability, where neighboring articles address El Niño prediction, ocean energetics, and atmospheric dynamics. Nearby work has already shown that the signal can be predicted up to a year and a half in advance and that Enceladus's ocean acts as a heat pump. This article continues the line of studying mechanisms but shifts the focus from vertical processes to horizontal currents. The author challenges three classical theories: Bjerknes's positive feedback, the delayed oscillator model, and the recharge model. All of them, in one way or another, rely on equatorial dynamics and the thermocline. Here, instead, a test is proposed for the hypothesis that the cycle depends on horizontal heat advection by specific currents.
The analysis uses sea surface temperature data from 1950 to 2017 (2×2 degree grid) and geostrophic current velocities from 1993 to 2016 (1×1 degree grid, five-day averaging). A new signal decomposition method, ESMD, is applied, which breaks time series into modes with different periods and extracts an optimal global mean. Unlike standard EOF, the method preserves the spatiotemporal evolution of anomalies. Based on the obtained modes, the author constructs indices for four sensitive regions: Niño-A, Niño-B, Niña-A, and Niña-B. These regions correspond to the pathways of warm water transport from the north and cold water from the south. Comparing the time series of these indices with temperature anomalies reveals cause-and-effect relationships.
It was found that the appearance of the central equatorial countercurrent (CECC) leads positive temperature anomalies in the central Pacific by 2–3 months. Intensification of the northern equatorial countercurrent (NECC) precedes anomalies in the eastern part with a lead of several months to two years. For the eastern type of El Niño, the Niño-B index, reflecting warm water transport from the coast of Central America southward, proved decisive. For the central type, the Niño-A index, associated with the eastern low-velocity gap of the NECC, plays the main role. For La Niña, it was found that intensification of the southern branch of the South Equatorial Current (SSEC) carries cold water from the southeastern part of the ocean directly into the central equatorial zone, explaining strong La Niña events. The asymmetry between the cycle phases is explained by the different geography of warm and cold water sources.
The article proposes a new mechanism for generating El Niño and La Niña based on horizontal currents. This distinguishes it from neighboring works that either focus on prediction or on vertical dynamics. If the results are confirmed, classical models relying on the thermocline and waves will require revision. The practical value lies in the fact that current indices can serve as early indicators of events. For example, NECC intensification precedes El Niño by several months, providing time for preparation. For La Niña, the lead time is 5–7 months. This could improve seasonal climate forecasts.
The topic may develop toward incorporating current indices into operational forecasting systems. Verification on independent data and comparison with existing models will be needed. It may be possible to refine the role of the 'tropical Pacific triangle' vortex, which the author describes as a carrier of warm water. The question of how atmospheric pressure and wind control the rearrangement of currents remains open. Further research could link the proposed indices to pressure and wind fields to close the dynamical loop.
The work could influence physical oceanography, climatology, and seasonal weather forecasting. The new current indices may be useful for monitoring the state of the tropical Pacific.
Verify the reproducibility of the results on longer data records and in other ocean basins. Integrate current indices into existing ENSO forecast models.
The article directly addresses the unresolved problem of El Niño and La Niña asymmetry, as well as the debate over the mechanisms behind different event types. The proposed horizontal advection mechanism may resolve long-standing contradictions in ENSO theories.
The name 'El Niño' originally referred to a warm current that appeared annually off the coasts of Peru and Ecuador during the weakening of the southeast trade winds, not to a temperature anomaly as such.