It is very important to accurately predict the weather of two months-瞭新社

It is very important to accurately predict the weather of two months

2022-01-20

ISO can not only directly affect the long-term weather changes and cause short-term climate anomalies in its region, but also indirectly affect the global weather and climate by changing atmospheric convection and circulation, stimulating atmospheric fluctuations, interacting with climate modes of El Nino and other time scales. Go out in the morning and watch the weather forecast. When you travel on business, you have to look at the weather forecast. Weather forecast is closely related to our life, but we often find that the weather forecast within one day is more accurate. The later the time is, the more inaccurate the forecast results are, and the current forecast time limit can only be within 14 days. The time limit of weather forecast involves the study of Intraseasonal Oscillation (ISO) of the atmosphere. Recently, Du Yan, a researcher of the State Key Laboratory of tropical marine environment (LTO) of the South China Sea Institute of Oceanography, Chinese Academy of Sciences, made new progress in the research on the ISO of the tropical Indian Ocean dynamic process affecting the atmosphere. The relevant research results were published in climate dynamics. In the future, once the ISO is thoroughly studied, the time limit of weather forecast can be extended to one or two months, so that we can take response measures in advance to the upcoming extreme weather and realize "seamless" climate prediction. ISO is closely related to long-term and short-term climate "ISO is not limited to a specific phenomenon, but describes the change of a kind of time scale." Dr. Liang Yun, a member of Du Yan's team, said: "for a thing, the observation data we actually get is the result of the superposition of multiple spatio-temporal scale changes. The formation mechanism of different scale changes is different. Therefore, in the research process, in order to simplify the problem, we usually separate the changes of different scales." What is the time scale? Liang Yun takes the daily change as an example: "the temperature change law of each day is basically cold in the morning and evening, and the hottest at noon. This is the daily change caused by the law of sunrise and sunset caused by the earth's rotation, which is our most common 'Day' time scale." "ISO is a change with a time scale greater than one month but less than one quarter." Liang Yun said. ISO can not only directly affect the long-term weather change and cause short-term climate anomalies in its region, but also indirectly affect the global weather and climate by changing atmospheric convection and circulation, stimulating atmospheric fluctuations, interacting with climate modes of El Ni ñ O and other time scales, which has become one of the important frontier topics in climate change research in recent years. ISO is particularly active in tropical areas, which can be roughly divided into two types: North transmission and east transmission. Among them, the eastward transmission type was first discovered by Madden and Julian scientists, so it is often called the Madden Julian oscillation (MJO). "The eastward ISO is a planetary scale deep convection system. With the changes of pressure, wind field, precipitation, sea surface temperature and other factors, it was initially generated in the tropical West Indian Ocean and propagated eastward at the speed of 5-10 meters per second. It was significantly strengthened in the tropical southeast Indian Ocean. After passing through the West Pacific Ocean, the intensity gradually weakened, and the deep convection finally disappeared near the diurnal line." Liang Yun pointed out that the ISO has significant seasonal characteristics, and is the strongest in winter in the northern hemisphere, that is, from December to February of the next year. The continuous activity of eastward ISO in some areas often leads to some extreme weather, such as the rain, snow and freezing disaster in southern China in early 2008, the floods in the Yangtze River Basin in the summer of 1998 and 2020, and the Centennial drought in Yunnan in the winter of 2009 and 2010. The anomalies of eastward ISO convection and circulation near the equator can even affect the development and evolution of some phenomena in the ocean and even the growth of marine microorganisms by affecting ocean evaporation, flow and fluctuation. "ISO can affect the weather and climate in many regions, such as the Asian monsoon region, the African continent, the Pacific Islands, and even the west coast of North America." Liang Yun pointed out that ISO is a bridge connecting weather and climate. Understanding the occurrence and development of ISO is not only an important link in studying weather and climate change, but also the key to realizing "seamless" climate prediction. Find the reason for the strongest transmission in winter Du Yan's team focused on the eastward ISO. Past scientific studies generally believed that ISO was an atmospheric internal mode, and some studies analyzed the generation of ISO in the tropical Southwest Indian Ocean from the perspective of ocean. "We mainly analyze the strengthening effect of marine dynamic processes on ISO in the tropical southeast Indian Ocean from the perspective of ocean." Liang Yun said, "because the change of the ocean is slower than that of the atmosphere, we usually say that the ocean has a memory function. In some cases, we can trace the impact of previous atmospheric changes on the ocean through ocean fluctuations, which provides a certain signal for our prediction research." Before that, the research on eastward ISO generally started from the disturbance in the atmosphere and paid attention to the changes of atmospheric elements such as water vapor and wind field. However, Du Yan's team focused on the ocean dynamic process and advanced the research time to autumn. In this process, sea surface temperature (SST) is used as an important medium, and ocean fluctuations affect the atmosphere by affecting SST. Based on the analysis of observation data and reanalysis data, Du Yan's team found that the ISO signals of the tropical southeast Indian Ocean and atmosphere have strong correlation in 50-80 days. Both of them are the most active in winter in the northern hemisphere and have the characteristics of Eastward Transmission. Liang Yun said: "the monsoon transformation in autumn can lead to the fluctuation of the equator. We found that in the northern hemisphere, the southwest monsoon over the Indian Ocean changes to the northeast monsoon in autumn. The wind field near the equator has a large variability, and the influence of the wind field accumulates along the coast of Sumatra, which promotes the generation of sinking Rossby wave." The sinking Rossby wave has the characteristics of westward propagation, and corresponds to the deepening thermocline and warm SST anomaly. After the sinking Rossby wave was generated along the coast of Sumatra, it spread to the west near 90 ° east longitude, warming the SST there, and strengthening the deep convection related to ISO. In addition, because the generation of this wave is mainly related to the monsoon transition in autumn, it takes 5-6 weeks to spread to 90 ° east longitude, so the strengthening of atmospheric ISO mainly occurs in winter. This process also explains the reason why the eastward ISO is the strongest in winter to a certain extent. "On the one hand, we explained how the ocean strengthens the deep convection phenomenon in the atmosphere, that is, ocean fluctuations first affect the sea surface temperature, and then affect the atmosphere; on the other hand, we explained why the eastward ISO is the strongest in winter, thus explaining its seasonal characteristics." Liang Yun said. The key to realizing "seamless" climate prediction "At present, the accurate prediction time of weather forecast is limited to 14 days, and it is difficult to accurately predict climate change modes such as El Nino Southern Oscillation, which is precisely because the research on ISO is not perfect." Liang Yun pointed out, "once we can study it thoroughly, the time limit of weather forecast can be extended to one or two months, so we can take countermeasures in advance for possible extreme weather." The changes of different scales do not exist independently, but interact and transfer energy. Liang Yun added that the weather we usually talk about is usually a small-scale change with a time scale of less than two weeks, while the climate is a large-scale change longer than a quarter, and the time scale of ISO is between the two. It is worth mentioning that a thorough study of ISO can improve the accuracy of El Ni ñ o prediction. El Nino refers to the phenomenon that the sea water temperature in the tropical ocean areas in the middle and east of the Pacific Ocean is abnormally and continuously warming, which affects the climate of the whole world. El Ni ñ o phenomenon can have a devastating impact on the global climate, causing floods, droughts and crop failures. Through the teleconnection of air sea interaction, it can have a certain impact on the circulation changes in quite far areas and even in the middle and high latitudes of the northern hemisphere. For example, the precipitation in most parts of China tends to be less. "The prediction of El Ni ñ o has the phenomenon of spring prediction obstacles. The spring prediction obstacles are closely related to the westerly outbreak in the tropical western Pacific, and the westerly outbreak has a great relationship with ISO. The eastward ISO is the strongest in winter. After it reaches the Western Pacific, it can affect the westerly outbreak in the next spring. At present, it is impossible to accurately predict the westerly outbreak, which is the cause of El Ni ñ o spring One of the important reasons for prediction obstacles. We hope to predict El Nino earlier, so as to minimize the losses caused by weather disasters related to it. " Liang Yun explained. When can the weather forecast for one or two months and the accurate forecast of El Ni ñ o be realized? In this regard, Liang Yun said, "our research is mainly discussed from physical phenomena and explained from the mechanism. We still need to continue to improve the principle of the mechanism and theorize it. At the same time, weather prediction is also inseparable from the strong support of computer technology. (Xinhua News Agency)

Edit：Li Ling Responsible editor：Chen Jie

Source：Science and Technology Daily

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