What does El Niño refer to?

El Niño refers to a short-term periodic change in ocean temperatures, typically occurring in the central and eastern tropical Pacific Ocean. This phenomenon is characterized by a rise in sea surface temperatures, which can significantly affect global weather patterns. The fluctuations associated with El Niño typically occur every two to seven years and can last anywhere from a few months to over a year.

These temperature changes in the ocean can lead to various climatic effects, such as increased rainfall in some regions and droughts in others, emphasizing the interconnectedness of oceanic and atmospheric systems. The impacts are felt globally, making understanding El Niño crucial for predicting and preparing for weather variations that might affect agriculture, weather patterns, and ecosystems.

The other options, while related to oceanic and climatic phenomena, do not accurately capture the specific nature of El Niño. A periodic increase in ocean temperature does occur during El Niño, but it is the short-term and cyclical nature of these temperature fluctuations that defines the phenomenon. Long-term climate changes might refer to the broader concept of climate change which is not specific to El Niño, and a permanent change in ocean currents does not accurately describe the oscillatory characteristics of El Niño, which is a temporary deviation rather than a lasting change.