Extreme weather events such as persistent high temperatures, heavy rains or sudden cold waves in Shanxi Province in China have brought great losses and disasters to people’s production and life. It is of great practical significance to study the temporal and spatial distribution characteristics of extreme weather events and the circulation background field. We selected daily high temperature data (≥35°C), daily minimum temperature data and daily precipitation data (≥50 mm) from 109 meteorological stations in Shanxi Province, China from 1981 to 2010, then set the period in which the temperature is ≥35°C for more than 3 days as a high temperature extreme weather event, define the station in which 24 hour cumulative precipitation is ≥50 mm precipitation on a certain day (20 - 20 hours, Beijing time) as a rainstorm weather, and determine the cold air activity with daily minimum temperature dropped by more than 8°C for 24 hours, or decreased by 10°C for 48 h, and a daily minimum temperature of ≤4°C as a cold weather process. We statistically analyze the temporal and spatial characteristics and trends of high temperature, heavy rain and cold weather and the circulation background field. We count the number of extreme weather events such as persistent high temperatures, heavy rains and cold weather frosts in Shanxi, and analyze the temporal and spatial distribution characteristics, trends and general circulation background of extreme weather events. We analyze and find out the common features of the large-scale circulation background field in various extreme weather events. Through the study of the temporal and spatial distribution characteristics of extreme weather events in Shanxi, including persistent high temperature, heavy rain or sudden cold wave frost weather, we summarize the large-scale circulation characteristics of such extreme weather events. It will provide some reference for future related weather forecasting.
Extreme weather and climate events mean that the state of the weather and climate deviates significantly from its average state and is statistically a small probability event (i.e., an event that is unlikely to occur). Although the frequency of extreme events is low, it often has a great impact on the natural environment and human society. In recent years, the extreme weather and climate events have become more and more harmful to society and nature. For example, the catastrophic floods in the Yangtze River Basin in 1998 caused more than 3000 deaths and economic losses of up to 36 billion US dollars. In the summer of 2003, heat waves hit Europe, and high temperatures caused more than 22,000 people died; in August 2005, Katrina attacked the southern coastal areas of the United States, killing more than 1300 people, leaving more than 1 million people homeless and economic losses as high as $81.2 billion. Due to the vast territory of China and the influence of the Southeast Asian monsoon year-round, various types of extreme weather and climate events often occur. For example, cold air in winter often affects most of the northern part of China; in summer, high temperature and drought weather often occur in southern China. Drought occurs in northwestern China, and floods often invade the middle and lower reaches of the Yangtze River.
In recent years, extreme weather and climate events have occurred frequently throughout the world. Meteorologists at home and abroad have made research from different angles. Karl et al. (1991; 1993) , Horton (1995) , and Cooter & Leduk (1993) have the highest and lowest temperature research results in the world, showing their performance in the global warming process in recent years. The asymmetry of the temperature change between day and night is obvious, and the daily difference is small. According to Gruaz et al. (1999) , the extremely high temperature days in Russia showed a significant increase, and the rate of extremely low temperature days decreased more than the rate of extremely high temperature days (Frich et al., 2002) . The work of Ren & Yan (1998) and Zhai et al. (1999) pointed out the seasonal characteristics and regional differences of extreme events in China. Ma et al. (2003) studied the extreme temperature trends in northern China, showing that the frequency of the lowest temperature in the arid and semi-arid regions of northern China has decreased significantly in the past 50 years, and the highest temperature occurred in most regions before the 1990s. There is no significant change in frequency, but there has been a clear increase in the past 10 years. Lin & Wu (1998) analyzed the climatic characteristics of the cold wave activity in Guangdong Province in the past 44 years. The research shows that since 1960, the total number of cold waves in Guangdong and the number of cold waves above medium intensity have been decreasing. Shan et al. (2005) analyzed the climatic characteristics of cold wave weather in Weifang area. The results show that the cold wave weather in the past 40 years is decreasing year by year, the cold wave process in the 1960s and 1990s is strong, and the cold wave in the 1970s and 1980s. The process is weak. In recent years, China’s temperature has risen markedly, especially in the winter. Some studies have found that in the context of this warming, the frequency and intensity of the cold wave in China have also changed significantly; Wei (2008) pointed out that after the climate warming, the frequency of cold wave in North China decreased and the intensity weakened. In addition, some meteorologists have also done some research on the causes of the cold wave in China, and have reached meaningful conclusions. For example, Wang & Ding (2006) analyzed the climate characteristics and changes of the cold wave in China, and discussed the reasons for the frequent reduction of the cold wave in China, and pointed out that the intensity of Siberian high and winter winds weakened. The low temperature of low-rise cold reactors over Siberia and the significant increase in surface temperature in China are the reasons for the cold wave in China and the accompanying reduction in the frequency of winds. Shanxi meteorological workers (Zhou et al., 1989) summarized the climatic characteristics and forecasting techniques of the torrential rains in Shanxi, China before 1974. In recent years, a number of meteorological work colleagues have done a lot of diagnostic analysis of the study of heavy rain in Shanxi (Zhao & Cheng, 2006; Zhao, 2005; Zhao et al., 2007; Zhao & Li, 2003) .
Since the 1970s, severe droughts and rains have increased significantly from a worldwide perspective. In the last 20 to 30 years, the probability of global extreme weather and climate events has clearly exceeded the sum of extreme weather and climate events in the past few decades, even centuries, for global warming, this global Climate events, many experts and scholars at home and abroad have been studying this aspect for decades. Therefore, research on extreme weather and climate events has received increasing attention from people at home and abroad. Shanxi Province, China is located in the eastern part of the Loess Plateau. It is located in the edge of the East Asian summer monsoon. It is affected by the summer monsoon and the blocking high pressure in the mid-high latitudes of winter. The interannual variation of climate, especially precipitation, is very large, and it is easy to appear in some areas, extremely hot or cold weather frosty weather. In the process of climate change in recent decades, the temperature in Shanxi has shown a clear upward trend, and the incidence of drought has increased with the increase of climate temperature. The relevant literature points out that in the past 50 years, the climate of Shanxi In general, it has experienced three stages: drought, flood, and drought. At present, Shanxi Province is in a relatively dry climate. Under this climatic background, the probability of persistent high temperature, heavy rain or sudden cold wave frost weather increases a lot. This extreme weather event has brought great losses and disasters to people’s production and life. Therefore, it is of great practical significance to study the temporal and spatial distribution characteristics of extreme weather events and the circulation background field under arid climate conditions.
The weather station data used in this paper is taken from Shanxi Provincial Meteorological Information Center, China, and includes daily maximum temperature (≥35˚C) data, daily minimum temperature data and daily precipitation (≥50 mm) data from 1961 to 2010 in the province. Through the investigation of the data, it is found that the altitude and climate of Wutaishan Station are quite different from those of other stations. The number of stations with complete historical data for 50 years is only about 60%, and most stations have complete historical data for 30 years above. The World Meteorological Organization used the average of 30 samples in the past 30 years in history as the reference point for the perennial value of the corresponding climatic factors, and was updated 10 years. The average climate value that was launched in 2012 is the statistic data of 1981-2010 (Zhang et al., 2015; Zheng et al., 2013) . Considering the different ages of station construction, the inconsistent length of time series and the continuity of data integrity, we selected 108 stations (excluding Wutaishan Station) to analyze the temporal and spatial characteristics and trends of high temperature and heavy rain, also selected 109 stations to analyze the temporal and spatial characteristics and trends of the cold wave, and determined the data analysis time as 1981-2010.
The use of trend coefficients (Nishiya et al., 2010) and rate of change can be used to represent the nature and magnitude of trends in climate elements. The trend coefficient is calculated, as in
r k t = ∑ i = 1 n ( x i − x ¯ ) ∑ i = 1 n ( i − t ¯ ) ∑ i = 1 n ( x i − x ¯ ) 2 ∑ i = 1 n ( i − t ¯ ) 2 . (1)
where, rkt is the trend coefficient; n is the time series length (years); xi is the magnitude of the climatic element of the i-year; x ¯ is the sample mean; t ¯ = (n + 1)/2.
The China Meteorological Administration stipulates that the maximum daily temperature is ≥35˚C for high temperature days, and the high temperature for more than 3 days is called high temperature heat wave. In this paper, the daily maximum temperature ≥35˚C, ≥37˚C, ≥40˚C is used as the quantitative characterization index. As long as there is one station with high temperature of 35˚C, 37˚C and 40˚C, it is recorded as a ≥35˚C, ≥37˚C, ≥40˚C high temperature day; a station with more than 3 days (including 3 days) with high temperature above 35˚C, which is marked as a continuous high temperature weather process.
Figures 1(a)-(c) are the spatial distributions of cumulative high temperature days of ≥35˚C, ≥37˚C, and ≥40˚C for 30 years from 1981 to 2010, respectively.
Linfen are more than 7 days, and the maximum of 30 days in Lushan. The probability of high temperature above 40˚C in other counties and cities in the province is very small, and the high temperature area of ≥40˚C is mainly concentrated in Yuncheng and Linfen areas
temperature daily stations above 37˚C and above 40˚C is very large. In 2005, the high temperature stations above 37˚C were as many as 523 stations, and the high temperature stations above 40˚C. The number of times was 77 stations; in 1983 and 1984, there were only 4 stations (1 day) for high temperature days above 37˚C; there were no high temperature days above 40˚C for 11 years in 30 years. Between 1981 and 2010, the high temperature days of 37˚C and 40˚C increased.
A high temperature weather above 35˚C occurs for more than 3 consecutive days (including 3 days) at a station, which is marked as a continuous high temperature weather process. Through statistical analysis, from 1981 to 2010, there were 1859 high-temperature processes in the province that lasted for more than 3 days, and 206 high-temperature processes lasted for more than 7 days.
days, the number of processes reaches 14 times, the highest temperature process lasts for 3 days, up to 863 times, and the high temperature process lasts for more than 3 - 5 days. The persistent high temperature is mainly found in Linfen and Yuncheng.
Based on the statistical analysis and census analysis of the 500 hPa high-altitude circulation situation occurring in the extreme maximum temperature from June to September, the two circulation situations of the western Pacific subtropical high when extreme extreme temperatures occur are summarized:
Sub-high latitude type: when the western Pacific subtropical high is lifted northward and reaches the eastern part of the northwestern region, the 5880 gpm line covers a large area, and the northwestern region is controlled by the east to the northeast of the northeast. The northern part of China will have hot and cold weather. The characteristics of this situation are: the latitudinal circulation in the middle and high latitudes of Europe and Asia, the cold air in the north is not easy to go south, and the front area is generally located at 44˚N - 51˚N.
Sub-high meridional type: when the western Pacific subtropical high is extended to the northwest of the northwestern region, the East Asian trough strongly deepens the formation of a relatively stable two-slot-ridge type in the middle and high latitudes of Asia, making it difficult for the western Pacific subtropical high to retreat. Under its control, there will be hot and cold weather in the east of the northwestern region to the west of the Bohai Bay. For the
Qinghai-Tibet high pressure, which belongs to the subtropical high, its formation and eastward movement on the eastern side of the Qinghai-Tibet Plateau is another influence system that causes the high temperature weather in Shanxi in the summer.
In summary, the 500 hPa circulation situation affecting high temperature in Shanxi mainly includes subtropical high latitude, subtropical high meridional and continental high pressure control type, sweltering weather when subtropical high control, and dry (clear) heat when continental high pressure control the weather.
The rainstorm specified in the meteorology refers to the precipitation with a cumulative precipitation of ≥50.0 mm at 24 h on a certain station (20 - 20 pm, Beijing time). According to its precipitation intensity, it is divided into three grades, that is, 24 h cumulative precipitation is 50.0 mm - 99.9 mm for heavy rain; 100.0 mm - 249.9 mm for heavy rain; 250 mm or more is extraordinarily heavy rain.
From the spatial distribution of the average number of occurrences of heavy rains in the province (
and the eastern part of Yuncheng is more than 2.5 days, and the Jinzhong area is generally on the 1st, while the Datong area in the north is the area with the least number of heavy rains, accumulating ≥100 mm. The number of heavy rain days is below 0.5 days. The spatial distribution of the occurrence of the above-mentioned rainstorms in Shanxi is closely related to the terrain of Shanxi, that is, the rainstorm-prone areas are mainly distributed in the windward slope area of the mountain range, and the southeastern part of the Taihang Mountains is a high-incidence area.
Through the statistical analysis and census analysis of the 500 hPa high-altitude circulation situation during the May-September rainstorm process, it is concluded that the 500 hPa geopotential height field is distributed in the
middle and high latitudes of the entire Eurasia region. Among them, two troughs are located in the east of the Ural Mountains and east of Baikal Lake. The two weak ridges are located in the west of Baikal and in the northeast of China to the Sea of Okhotsk. From Shanxi to the Jianghuai River Basin is an obvious high-altitude trough, the western Pacific subtropical high is a zonal band, 584 dagpm line extends to 80˚E, and the subtropical high ridge is located near 28˚N, with the westerly wind over Shanxi. The trough formed an obvious “east-high-west-low” situation. In the low latitudes, the Bay of Bengal is an obvious trough of low pressure. Under this circulation situation, it caused the occurrence of heavy rain in Shanxi.
According to the “Cold Air Rating” in the “National Standards of the People’s Republic of China” implemented on November 1, 2006, the daily minimum temperature drops by more than 8˚C for 24 h, or decreases by 10˚C for 48 h, and the daily minimum temperature is ≤4˚C, then cold air activity was identified as a “cold wave”. The cold wave intensity is expressed by 24 h and 48 h cooling. It is prescribed that more than 2/3 of the stations have a cold wave, which is the province's cold wave process. More than 1/4 of the stations have a cold wave, which is the regional cold wave process. The station data used in this section selects the daily minimum temperature data of 109 stations from September of the year from 1981 to 2010 to the analysis of the temporal and spatial characteristics and trends of the cold wave.
During the 30 years from 1981 to 2010, there were a total of 1542 cold waves in Shanxi Province. Among them, the province’s cold wave (prescribed more than 2/3 sites, which is the province’s cold wave process) 5 times, as shown in
north, and in some parts of the north, there will be occasional cold waves in September. Due to the high altitude, Wutai Mountain has cold wave events in addition to the cold wave season (October to April), and sometimes in May and
Year | Month | Days | Number of stations |
---|---|---|---|
1988 | 1 | 21 | 88 |
1992 | 1 | 29 | 74 |
1994 | 1 | 16 | 97 |
1999 | 2 | 17 | 78 |
2000 | 1 | 11 | 75 |
September. This is due to the high altitude, low temperature and low temperature, which is easy to reach the cold wave standard. From the monthly distribution of cold wave frequency, the frequent cold wave months are from November to March, all of which are more than 230 times. The most frequent occurrence of cold wave is January, with a cumulative frequency of 299; the rest of the month is below 120, and the cold wave is the lowest in September. , only accumulated 4 times. From the distribution of the cold wave station for several months, the months with more cold wave stations are December, January and February, and the cumulative number of stations is above 2400 stations. The rest of the months are below 1900 stations, and the least in September. There are only 4 stops at the station. In November and March, there were more frequent cold waves and fewer cold wave stations, indicating that from December to February, it is prone to provincial and regional large-scale cold weather processes, and in November and March, it is prone to a single-station small-scale cold wave weather process.
Through the study of the frequency sequence of the Shanxi cold wave from 1981 to 2010 and the monthly calculation of the 500 hPa sea level pressure field and the sea temperature field in the same period, it was found that the cold air from the Arctic Ocean, especially from Eastern Siberia, cooperated with Lake
Baikal and Its negative anomaly in the southeast will cause frequent cold surges in the later period, that is, the cold air from Eastern Siberia is one of the main sources of the cold wave in Shanxi. It can be seen that the characteristics of the 500 hPa correlation field are mostly characterized by high positive latitude anomalies and high negative anomalies at low latitudes, which often lead to more frequent occurrences of cold waves in the next year. Such circulation conditions are favorable for cold air from high latitudes. It brings cold weather to the south.
By analyzing the daily maximum temperature of ≥35˚C, ≥37˚C and ≥40˚C in Shanxi 108 station from 1981 to 2010, it is concluded that the number of high temperature days decreases with the elevation of latitude, and the west is more than the east and the south is more than the north. The spatial distribution of the basin is more than that of the mountainous area; June-August is a frequent occurrence of high-temperature weather, and in July, high-temperature weather above 35˚C is more likely to occur. After entering the 1990s, the number of high temperature days has gradually increased, and the duration, intensity and range of high temperature have increased. The 500 hPa circulation situation affecting the high temperature in Shanxi mainly includes subtropical high latitude, subtropical high meridional and continental high pressure control type. The subtropical high control is sweltering weather, while the continental high pressure control is dry (clear) hot weather.
By analyzing the daily precipitation of ≥50 mm and ≥100 mm in Shanxi 108 station from 1981 to 2010, it is concluded that the spatial distribution of the number of rainstorm days in Shanxi is spatially distributed in the south and more than the west, and the east is more than the west, and the mountainous area is more than the basin; The flood season (July-August) is the most concentrated period of heavy rain in Shanxi Province. In the past 10 years, the number of rainstorm days has gradually increased, the range of heavy rains has increased and the intensity has increased. The circulation situation affecting the heavy rain in Shanxi is the 500 hPa geopotential height field. The middle and high latitudes of the Eurasian continent are distributed as “two troughs and two ridges”, and the western Pacific subtropical high is distributed in a zonal band, forming a westerly trough over Shanxi, obviously the situation of “high-east-low-west”. In the low latitudes, the Bay of Bengal is an obvious trough of low pressure. Under this circulation situation, it caused the occurrence of heavy rain in Shanxi.
Based on the analysis of the daily minimum temperature from September to May of Shanxi Province from 1981 to 2010, it is concluded that the frequency distribution of cold wave in Shanxi is decreasing from north to south, and it is greatly affected by the altitude of the terrain. The cold wave frequent month is from November to March, and from December to February, it is prone to provincial and regional large-scale cold weather processes. In November and March, it is prone to single-site Small range cold wave weather process. Under the background of global warming, the frequency of cold wave is decreasing year by year, but the range and intensity of the cold wave process are increasing. The characteristics of the 500 hPa correlation field in Shanxi cold wave weather are characterized by high altitude latitude and high altitude negative anomalies at low latitudes, which often lead to more frequent cold wave occurrences in the next year. Such circulation conditions are favorable for cold air from high latitudes. It brings cold weather to the south. The cold air from Eastern Siberia is one of the main sources of the cold wave in Shanxi.
The authors declare no conflicts of interest regarding the publication of this paper.
Li, Y. M., Zhi, H., & Zhang, D. F. (2019). Analysis of Temporal and Spatial Distribution and Large-Scale Circulation Features of Extreme Weather Events in Shanxi Province, China in Recent 30 Years. Journal of Geoscience and Environment Protection, 7, 160-176. https://doi.org/10.4236/gep.2019.73009