Climatic characteristics of El Nino

The name El Nino (meaning "El Nino" in Spanish) originated from fishermen along the coast of Peru at the end of 19, which refers to the seasonal invasion of warm ocean currents flowing southward, replacing the cold ocean currents flowing northward when they used to fish. This phenomenon usually happens around Christmas. Nowadays, El Nino no longer refers to the seasonal variation of local ocean currents, but refers to a part of ENSO phenomenon. El Nino/Southern Oscillation (ENSO) refers to the persistent but irregular atmospheric and ocean circulation phenomenon that affects the whole world. El Nino refers to the abnormal warming of the ocean surface in the Middle East and the Pacific Ocean and its interaction with the lower atmosphere, which can have a significant weather impact. Accordingly, since 1985, the phenomenon of abnormal sea surface cooling in the Middle East and Pacific Ocean is called "La Nina" (little girl). It takes about four years for El Nino and La Nina to transform into each other.

In recent years, various media have paid more and more attention to such a climatological term: El Nino. Many climatic phenomena and disasters are attributed to the ravages of El Niñ o, such as forest fires in Indonesia, heavy rains in Brazil, floods and snowstorms in North America, droughts in Africa and so on. Almost became synonymous with disaster!

But what is the El Nino phenomenon? In a word: El Nino is the product of the interaction between tropical atmosphere and ocean. It originally refers to an abnormal warming of equatorial sea surface, and now it is defined as a global climate anomaly caused by air-sea interaction.

El Nino phenomenon is an example of a strong coupling event between atmospheric circulation and ocean circulation. The stress exerted by atmospheric circulation (wind) on the ocean is the main driving force of ocean circulation. At the same time, as we can see, the heat from the ocean, especially evaporation, has a great influence on the atmospheric circulation.

The simplified model of El Nino shows the role of different fluctuations in the process of ocean energy transfer. In this simplified model, the waves in the ocean are called Rossby waves, which propagate westward from the unusually warm sea near the equator. When it reaches the western boundary of the ocean, it will be reflected into a different wave called kelvin wave. This fluctuation spread eastward, offsetting or changing the original signs of abnormal temperature in the warm sea, and causing cooling events. The time required for this half cycle in the whole El Niñ o event is determined by the propagation speed of these waves, which takes about 2 years.

This phenomenon is essentially driven by ocean dynamics, and the corresponding atmospheric change is determined by sea surface temperature (in turn, atmospheric change will strengthen the distribution pattern of ocean temperature), and the distribution of sea surface temperature is determined by ocean dynamics, so the El Niñ o phenomenon represented by the above simplified model is predictable in nature.