How to judge whether this year is El Ni?o or La Ni?a based on temperature and precipitation?

1. What are El Ni?o and La Ni?a?

Why are there different names for "phenomenon", "state" or "event"?

El Ni?o refers to a large-scale sustained abnormally high sea surface temperature (referred to as SST) that occurs in the central and eastern equatorial Pacific Ocean, that is, the sea water is abnormally warm. The word "El Ni?o" comes from Spanish and means "Holy Child". One theory is that early on, fishermen from Peru, Ecuador and other countries on the equatorial eastern Pacific coast went fishing and found a large number of dead fish stuck on fishing boats. The peak period occurred around Christmas, which was known as the "Holy Child". This is a natural phenomenon, and the term may be used again in a few years. On the contrary to this phenomenon, the sea temperature in this sea area is abnormally low, that is, it is abnormally cold, which is called La Ni?a phenomenon, which means little girl or "saint".

Later, people gradually realized that El Ni?o and La Ni?a are not simple ocean phenomena, but the result of the interaction between the atmosphere and the ocean. They echo the weakening or strengthening of the trade winds and are often accompanied by the seesaw effect of atmospheric pressure in the east and west Pacific. —The so-called "Southern Oscillation". Before its formation, the subsurface sea temperature below the ocean surface usually fluctuates first.

Once El Ni?o or La Ni?a forms, it will have an important and far-reaching impact on the climate. In short, El Ni?o and La Ni?a are strong signals of interannual variability in the global climate system. For convenience of expression, El Ni?o/La Ni?a is used to describe this phenomenon in general below.

Each El Ni?o may seem similar, but there are differences. As the saying goes, "flowers are similar every year, but people are different every year." In order to accurately describe, analyze and predict El Ni?o or La Ni?a, it is necessary to establish The monitoring indicator system and specific quantitative indicators have led to the El Ni?o/La Ni?a “state” and the El Ni?o or La Ni?a “event”. In the early days when the sea temperature anomaly reached the quantitative standard, it was not clear whether it would be a short-lived flash in the pan or whether it could maintain the data. For months, in this early stage, it can be called entering a "state"; when this phenomenon continues and reaches the specified duration, it is called an "event".

2. What indicators are used to determine El Ni?o/La Ni?a?

What does a large-scale sustained abnormally warm or abnormally cold mean? Generally speaking, the specific heat capacity of the ocean is very large, and the sea temperature does not change as drastically as the air temperature. It is not easy to be a few degrees higher or lower. However, large-scale sustained anomalies are warmer or colder. According to the indicators, the sea temperature is higher. It may be more than 0.5 degrees Celsius lower, the time scale will last for more than several months, and the spatial range will be more than thousands of kilometers in the east-west direction and more than 1,000 kilometers in the north-south direction.

Business and scientific research institutions in various countries have not yet reached a consensus on the specific detection indicators for this incident. At present, China is based on the monitoring information released by the National Climate Center of the China Meteorological Administration, which is the so-called Nino 3.4 area (Nino3.4) monitoring key area in the range of 5 degrees north and south latitude on both sides of the equator and 120 degrees to 170 degrees west longitude. Area, use the monthly average sea temperature anomaly value to calculate the regional average, as the index, that is, one value per month, and then look at the monthly changes in the index.

When the absolute value (rounded to one decimal place) of the 3-month moving average of the Nino3.4 index reaches or exceeds 0.5 degrees Celsius and lasts for at least 5 months, it is determined to be an El Ni?o/La Ni?a event. If the Nino3.4 index is greater than or equal to 0.5 degrees Celsius, it is an El Ni?o event, and if the Nino3.4 index is less than or equal to -0.5 degrees Celsius, it is a La Ni?a event.

The trajectory is usually divided into Ni?o zones 1, 2, 3 and 4. The 3.4 zone mentioned above is divided into two zones: 3 and 4. For the mixed zone, calculate the regional average of these zones to obtain the corresponding zone index. These four districts are combined to form the so-called comprehensive district, and the comprehensive district index is obtained. Before mid-spring 2016, my country mainly used the comprehensive zone index. After late spring, after discussions with the World Meteorological Organization, it now switched to the 3.4 zone index.

What indicators are used to judge El Ni?o/La Ni?a events, as well as intensity, duration, and regional type? Roughly speaking, intensity is divided into peak intensity and cumulative intensity. The monthly peak value of the index (the maximum monthly anomaly value of sea temperature) is used as the peak intensity, and the cumulative anomaly value with a monthly anomaly of more than 0.5 degrees Celsius is the cumulative intensity. The intensity of the event is mainly Look at the peak intensity. The duration is from the beginning month when the monthly anomaly standard of 0.5 degrees Celsius is reached to the last month when the standard is reached as the duration period. Regional type refers to which area of ??the Pacific Ocean it mainly occurs in, divided into central type and eastern type (in the central or eastern Pacific Ocean).

3. What are the rules for the occurrence of El Ni?o/La Ni?a?

Due to different selection of indicator areas, slight differences in definitions, and even differences in detection methods, the number and start and end times of El Ni?o/La Ni?a events determined by each country are somewhat different.

According to the monitoring indicator system of the National Climate Center of the China Meteorological Administration based on the Ni?o 3.4 zone index, since 1950, 19 El Ni?o events and 14 La Ni?a events have occurred in history.

Among the 19 El Ni?o events, there were three super strong events, which occurred in 1982-1983, 1997-1998 and 2014-2016 respectively; there were one strong, moderate and weak event respectively. 7 times and 8 times. Among the 14 La Ni?a events, there were no super strong events, only 1 strong event, 8 moderate and 5 weak events respectively. In terms of regional types, regardless of El Ni?o or La Ni?a, about 70% is the eastern type and 30% is the central type.

El Ni?o and La Ni?a may look like brothers and sisters, but their personalities are quite different. One has a "violent temper" and comes and goes in a hurry, while the other is "docile and comfortable" and looks like a good girl.

In terms of the number of events, El Ni?o events*** occurred 19 times, which is 36amp more than the 14 times of La Ni?a events; in terms of event intensity, El Ni?o was strong, with 3 super strong events and strong The event lasted 4 times, which was significantly stronger than La Ni?a. In terms of duration, El Ni?o was shorter than La Ni?a. Each El Ni?o event lasted an average of 11.1 months, which was 1.5 months shorter than each La Ni?a event.

4. When did my country start paying attention to El Ni?o/La Ni?a?

In its external climate business exchanges, my country’s meteorological department has experimented with national and provincial climate impact assessments, and noted the impact of El Ni?o on climate from relevant world and North American climate impact assessments in the United States and Canada. Some pilot provinces in my country (such as Hebei Province) directly attribute climate anomalies in their provinces to El Ni?o.

It took about another 10 years before my country gradually began to explore El Ni?o/La Ni?a and its impact on my country’s climate, and applied it in long-term forecasts—now called short-term climate forecasts. Later, the hydrological department We have also gradually begun to pay attention to this ocean-atmosphere abnormal event. After the establishment of the National Climate Center, my country's meteorological department has significantly strengthened research in this field and gradually expanded international research and business exchanges in this field.

Based on the historical statistical relationship between El Ni?o and my country’s later flood season precipitation and droughts and floods, as well as the study of some mechanisms, at the national climate trend prediction conference jointly organized by the Ministry of Water Resources and the China Meteorological Administration, based on the previous occurrence The analysis of extreme factors such as the super El Ni?o event, the abnormally strong Northwestern Pacific Subtropical High, and the abnormally high snow cover on the Tibetan Plateau in winter and spring has successfully predicted in advance that precipitation in the middle and lower reaches of the Yangtze River will be abnormally high during the flood season, and timely reports have been provided to the National Defense Headquarters. A report was made and received great attention, making the report preparation work more targeted that year.

The Water Conservancy Information Center of the Ministry of Water Resources also successfully predicted that the rainfall in the Songhua River Basin during the flood season will be significantly higher. During the flood season, based on the study and judgment of abnormal factors such as El Ni?o, a relatively accurate prediction was made on the trend of more rain and less safe typhoons in the middle and lower reaches of the Yangtze River during the flood season that year.

5. How does El Ni?o/La Ni?a affect droughts and floods in my country?

El Ni?o/La Ni?a occurs in the central and eastern equatorial Pacific. Its peak period is mostly in winter. Even counting from the west of Ni?o 3.4 area, the spatial distance from my country is more than 7,000 kilometers, and the time difference is about half a year. , how can it affect droughts and floods during flood seasons in our country? After the occurrence of El Ni?o/La Ni?a in historical statistics, is it just a coincidence that the reason why my country's climate is related to them?

To explain this, let’s first talk about the climate system, which includes the atmosphere, hydrosphere, cryosphere, lithosphere and biosphere. In addition to the atmosphere and biosphere, the hydrosphere is mainly the ocean, accounting for about 70% of the earth's surface; the cryosphere mainly includes polar ice caps, as well as permanent or semi-permanent glaciers and snow on plateaus and mountains; the lithosphere is the underlying surface of land. The sun is the fundamental source of energy for the movement of the Earth's climate system, but energy may be stored in various circles of the climate system for inter-circle exchange and space transfer, especially in the atmosphere and oceans, through common sensible heat exchange and through evaporation and condensation precipitation. A huge latent heat exchange occurs, and both are fluids, which can realize spatial transfer of energy in a large spatial range.

El Ni?o/La Ni?a is a large-scale sustained sea surface temperature anomaly event. In addition to directly affecting the local sea area and surrounding climate, it also has a major impact on the global climate through ocean currents and other ocean movements and atmospheric circulation movements. . Generally, the stronger the El Ni?o is and the longer it lasts, the more severe the impact of floods and droughts will be and the longer the impact will last.

A large number of studies have shown that El Ni?o/La Ni?a most mainly and directly affects areas near the equatorial Pacific. Usually, when El Ni?o occurs, climate anomalies are more obvious in the equatorial and low-latitude areas on both sides of the Pacific Ocean. Heavy rains and floods occur frequently along the coast of South America, and Australia, Indonesia, and India are prone to drought.

my country’s mainland is mainly located in the subtropical and temperate zones. El Ni?o usually indirectly affects my country’s precipitation, droughts and floods by strengthening the subtropical high. El Ni?o is conducive to the rising motion of the equatorial central and eastern Pacific, which leads to the strengthening of the Hadley cell of atmospheric circulation, and is conducive to the intensity and area increase of the northwest Pacific subtropical high. Generally, the stronger and longer El Ni?o lasts, the more significant its impact on the strengthening of the subtropical high.

Statistics show that in most El Ni?o-affected years, my country is prone to two rainy belts in the north and south. The southern rainy belt is mainly located in the Yangtze River Basin, and sometimes is larger and can cover the Huaihe River Basin; the northern rainy belt is mostly located in North China to Northeast, but the north-south position and intensity of the northern rainy belt are not as stable as the southern rainy belt. In other words, in some years affected by El Ni?o, the northern rain belt is not very obvious. Some rain belts are from northern North China to northern Northeast China, and some are located in southern Northeast China. In this way, during El Ni?o years, the Yangtze River Basin—especially the middle and lower reaches of the Yangtze River—is prone to flooding. The corresponding relationship between La Ni?a and my country’s precipitation, droughts and floods is far less obvious than in El Ni?o-affected years, and it is not an inverse display of the impact of El Ni?o events. This point will be explained later in conjunction with this La Ni?a event.

The climate system is extremely complex. Although El Ni?o/La Ni?a events have an important impact on my country’s climate and droughts and floods, their effects are currently being significantly exaggerated and demonized. It seems that all abnormal phenomena are attributed to For El Ni?o and La Ni?a, this is incorrect, incomplete and unscientific.

It is worth noting that the subtropical high itself has periodic changes in strength and weakness, and El Ni?o is only one of the important reasons for its strengthening, not the only factor. In addition, although a stronger subtropical high will help my country receive more rainfall, it also requires the cooperation of cold air from the north.

Looking at the atmosphere-ocean system, even if we only observe these two circles, energy is transferred and converted between the ocean and the atmosphere, including the obvious sensible heat exchange and the more important latent heat exchange. The atmosphere and oceans are both fluids and can transfer energy to very distant places. For example, due to the influence of the North Atlantic Warm Current, the Netherlands in Western Europe and my country's northernmost Heilongjiang Mohe are roughly the same latitude. In January, the temperature difference between the two places is more than 20 degrees Celsius.

The ocean also has the function of storing energy, so that the energy from the abnormal sea temperature in the equatorial central and eastern Pacific in winter is transferred and delayed to the atmosphere through the horizontal ocean currents and vertical movement and energy exchange, which may cause abnormal summer climate in the northern hemisphere and Droughts and floods occur frequently.

Existing studies have shown that the impact of the atmosphere on the ocean lags at least 3-6 months or even longer. Even if the El Ni?o event ends, its impact will continue for at least 1-2 quarters.

my country’s summer precipitation is affected by the northwest Pacific subtropical high, the cold air brought by the westerly circulation in mid- and high-latitudes, the southwest monsoon related to the Indian Ocean and Bay of Bengal, the thermal effects of the Tibetan Plateau, and typhoon activity in the northwest Pacific, etc. , it also has an important impact on droughts and floods in our country. In particular, the North Atlantic Ocean and the Arctic Ocean play an important role in the high-altitude atmospheric circulation in the westerly belt and the activities of cold air that affect our country. In addition, although the typhoon activity in the northwest Pacific is closely related to El Ni?o, the air flow across the equator in the Southern Hemisphere also contributes a lot and cannot be ignored.

In short, El Ni?o/La Ni?a is not the only factor affecting droughts and floods in our country, and sometimes it is not even the most important factor - every El Ni?o year has its own uniqueness and differences. It is obvious that the distribution of droughts and floods in my country is not exactly the same.