These two disasters originate from a special geographical condition, that is, there is a vast cold water ocean in the eastern equatorial Pacific Ocean. This cold water sea surface is an extremely special natural phenomenon. Because, according to the distribution principle that the solar radiation decreases with the increase of latitude, the equator should be the place with the highest temperature, but here, in reverse, a cold ocean surface appears, becoming the largest cold source (heat sink) in low latitude areas, so it has a very special impact on the atmospheric circulation.

Cold water surface temperature changes in the eastern equatorial Pacific Ocean: formation of El Nino and La Nina

The cold water surface in the eastern equatorial Pacific Ocean is formed by the Peru Cold Current. As long as you look at the map, you will notice that the ocean surface of the southern hemisphere is much larger than the land surface. The three oceans around Antarctica, the Atlantic Ocean, the Pacific Ocean and the Indian Ocean, have converged into a vast water area called the Southern Ocean. The Southern Ocean is the zone where westerlies prevail. The current here is the circumpolar current from west to east. This circumpolar current flows eastward in the vast Southern Ocean. However, the South American continent extends southward to about 55 degrees south latitude, and the Antarctic Peninsula on the opposite bank extends northward to 64 degrees south latitude. Thus, a narrow channel with a width of no more than 10 latitudes is formed here. The ocean current is blocked by this land threshold, making part of the current turn north along the concave coastline on the west coast of South America, which is the Peru Current. 　

Affected by the rotation of the earth, the Peruvian current gradually deflects westward during its northward flow, and becomes the south equatorial current from east to west near the equator due to the influence of the easterly belt. As the ocean current leaves the coast, it is conducive to the upwelling of cold and nutrient rich deep sea water, creating good conditions for the development of plankton, and forming excellent fish farms and breeding grounds for birds here.

However, every few years, the cold water sea surface here heats up. This is El Nino, which is the cause of many local disasters. First of all, it affects that the deep sea water will no longer rise, making plankton unable to survive due to lack of nutrients, and fish and birds will also die due to lack of food, becoming the main cause of fish industry disasters; In addition, this was originally a dry area with little rain. At this time, due to the rising sea temperature, the air convection was strengthened, resulting in heavy rain. Because this phenomenon is often the most prominent around Christmas, people call it El Nino, that is, the meaning of the baby. 　

In contrast to El Ni ñ o, when the water surface temperature in the eastern equatorial ocean is lower than normal, and the water temperature in the western region is higher than normal, disasters can also be caused, which is called La Ni ñ a. In the winter of 2007-2008, there was a tornado in the United States, while in China, there was a snow disaster that was not seen for many years, which was related to the rising water temperature in the western equatorial ocean. 　

El Ni ñ o and La Ni ñ a: Climate anomalies that cannot completely dominate China

El Nino and La Nina have occurred frequently in recent decades, the most recent being the La Nina event formed in the equatorial Middle East Pacific since the second half of 2007. Under the influence of La Nina, since January 2008, the south of China has experienced a large area of low temperature, snow and freezing disaster weather once in a century, which has caused huge losses. 1997-1998 and 1982-1983 were two years of great influence, especially in 1997-1998, after El Nino, there was a strong La Nina. Since June 1997, torrential rains have caused disasters in Ecuador, Peru, Brazil, Chile and the north of Argentina in South America, making the arid desert here ecologically prosperous; However, Indonesia and Australia in the western equatorial Pacific Ocean experienced drought disasters that were not seen for many years, with frequent heat disasters. The record breaking high temperature was found in many places, and the high temperature of 46 ℃ was also found in Port Hedland and Mandora Town in Australia. 　

The global weather is composed of the interaction of three major oscillations, which constitute the overall picture of the global atmospheric circulation. These three oscillations are the North Pacific Oscillation composed of the North Pacific Subtropical High and the Aleutian Low, the North Atlantic Oscillation composed of the North Atlantic Subtropical High and the Iceland Low, and the South Oscillation composed of the Eastern Equatorial Pacific High and the Western Equatorial Pacific Low. These three oscillations not only affect each other, but also each oscillation has a seesaw pressure change, that is, one member's pressure rise is accompanied by the other member's pressure drop, on the contrary, one member's pressure drop is accompanied by the other.

El Nino occurs in the East Pacific high region of the Southern Oscillation, so it is connected with the atmospheric circulation through the Southern Oscillation. When El Nino occurs, the seesaw relationship of the Southern Oscillation is reversed: the low pressure area in the western part of the equatorial Pacific between Indonesia and Australia has weakened, or even become high pressure, which makes the climate where there was a lot of rainfall become dry and rainy; On the contrary, the high pressure in the East Pacific Ocean has become low pressure, making the originally dry climate here moist and rainy. So El Nino connects the equatorial Pacific Ocean as a whole, and it is also closely related to the changes of atmospheric circulation. They are collectively called ENSO, the English abbreviation for El Nino and Southern Oscillation.

China is not located in the center of ENSO, but in its edge area. China's annual climate is related to the alternation and interaction of winter monsoon and summer monsoon. El Nino mainly affects China through the summer monsoon, and the winter monsoon is not directly affected by El Nino, so it is impossible for El Nino to completely dominate the climate anomaly in China. Under the influence of strong El Nino, the subtropical high in winter and spring in China may be extremely developed, which directly affects the rainy phenomenon in winter in China.
　　
Now the global warming is very obvious. The center of the warming is in the north and south polar regions, where the warming amplitude is twice the global average. In 2007, the minimum ice and snow area of the Arctic Ocean was only 3 million square kilometers, about 1/7 of the total area of the Arctic Ocean. The ice and snow in Antarctica are also melting. As a result, the temperature difference between the polar region and the equator will be significantly reduced, which will affect the intensity of the westerly wind, thus reducing the intensity of the circumpolar current and moving its position northward, thus affecting the Peruvian current; The increase in temperature will strengthen the subtropical high, and the evaporation of seawater in the high pressure area will accelerate, which is conducive to the strengthening of the thermohaline current. These many phenomena play different roles, which is the reason for the increase of El Ni ñ o phenomenon. However, some of the effects are opposite, so it needs special research on the impact of El Nino.