El Niño is a phenomenon characterized by the occasional appearance of warm water off the coast of Peru, leading to catastrophic consequences for the fishing industry. A new theory is presented, suggesting that El Niño is not caused by weakened southeast trade winds but by excessively strong southeast trade winds in the central Pacific before the event. These strong winds intensify the South Pacific subtropical gyre, strengthen the South Equatorial Current, and increase the east-west slope of sea level by accumulating water in the western equatorial Pacific. When the wind stress in the central Pacific relaxes, the accumulated water flows eastward, likely in the form of an internal equatorial Kelvin wave, leading to warm water accumulation off Ecuador and Peru and a depression of the thermocline. El Niño is thus the result of the equatorial Pacific Ocean's response to atmospheric forcing by the trade winds. The paper discusses the seasonal cycle of El Niño, showing that it is not a normal annual event but occurs in certain years with excessive warm water accumulation, leading to the cessation of upwelling and the disappearance of fish stocks. Sea surface temperature is the primary indicator of El Niño, with temperature curves showing that El Niño lasts about 16 months. Observational evidence challenges the idea that El Niño is caused by weakened trade winds, showing that trade winds are not abnormally weak during El Niño but are instead strong in the central Pacific. The paper also examines the relationship between wind and temperature along the equator, showing that strong zonal winds are associated with increased upwelling and lower surface temperatures. The southeast trade winds are shown to be stronger in the central Pacific before El Niño, leading to a buildup of water in the western Pacific. When the wind stress relaxes, the accumulated water flows eastward, triggering El Niño. The paper also discusses the slope of sea level under the southeast trades, showing that it responds well to wind stress, leading to the buildup of a strong east-west slope of sea level. The theory proposed explains El Niño as the result of the response of the equatorial Pacific Ocean to the relaxation of the southeast trades after a prolonged period of strong winds and the accumulation of water. The paper concludes that El Niño is a complex phenomenon with global implications, and that no two El Niño events are quite alike.El Niño is a phenomenon characterized by the occasional appearance of warm water off the coast of Peru, leading to catastrophic consequences for the fishing industry. A new theory is presented, suggesting that El Niño is not caused by weakened southeast trade winds but by excessively strong southeast trade winds in the central Pacific before the event. These strong winds intensify the South Pacific subtropical gyre, strengthen the South Equatorial Current, and increase the east-west slope of sea level by accumulating water in the western equatorial Pacific. When the wind stress in the central Pacific relaxes, the accumulated water flows eastward, likely in the form of an internal equatorial Kelvin wave, leading to warm water accumulation off Ecuador and Peru and a depression of the thermocline. El Niño is thus the result of the equatorial Pacific Ocean's response to atmospheric forcing by the trade winds. The paper discusses the seasonal cycle of El Niño, showing that it is not a normal annual event but occurs in certain years with excessive warm water accumulation, leading to the cessation of upwelling and the disappearance of fish stocks. Sea surface temperature is the primary indicator of El Niño, with temperature curves showing that El Niño lasts about 16 months. Observational evidence challenges the idea that El Niño is caused by weakened trade winds, showing that trade winds are not abnormally weak during El Niño but are instead strong in the central Pacific. The paper also examines the relationship between wind and temperature along the equator, showing that strong zonal winds are associated with increased upwelling and lower surface temperatures. The southeast trade winds are shown to be stronger in the central Pacific before El Niño, leading to a buildup of water in the western Pacific. When the wind stress relaxes, the accumulated water flows eastward, triggering El Niño. The paper also discusses the slope of sea level under the southeast trades, showing that it responds well to wind stress, leading to the buildup of a strong east-west slope of sea level. The theory proposed explains El Niño as the result of the response of the equatorial Pacific Ocean to the relaxation of the southeast trades after a prolonged period of strong winds and the accumulation of water. The paper concludes that El Niño is a complex phenomenon with global implications, and that no two El Niño events are quite alike.