The northeast cold vortex is a large high-altitude cold vortex active in or near northeast China.It is a deep system that can last 3-4 days or more.[4]The Northeast Cold Vortex causes low temperature and cold damage, continuous rain and floodhailThe important weather systems of sudden severe convection weather, such as thunderstorms and gales, have a significant impact on the weather and climate in Northeast China.
The "hometown" of the Northeast Cold Vortex is in the range of 35~60 degrees north latitude and 115~145 degrees east longitude;After generation, it also concentrated in the Northeast and its vicinity.[5]The northeast cold vortex is a cold air column, and at least one closed isobar line can be analyzed on the 500 hPa weather map, with cold center or obvious cold trough matching;This cold air column rotates counterclockwise and continuously. During its rotation, a stream of cold air will be thrown out, producing precipitation.As the northeast cold vortex is a deep weather system, it moves slowly for a long time, and its impact is generally 3-5 days, or even longer.
The northeast cold vortex may appear all year round, but the probability of its appearance in summer is obviously greater than that in winter.The largest concentration zone of northeast cold vortex activity gradually moved southward from April.The early spring of the cold vortex concentrated area is mainly in the north of the Northeast Plain, about 52 degrees north latitude, and it is distributed in the latitudinal direction.Another major concentration area is located in the middle of the Northeast Plain and along the northwest coast of the Sea of Japan.In general, the northeast cold vortex in the 40-45 degrees north latitude area often brings continuous intermittent precipitation for several days and continuous temperature drop weather for many days to Liaoning. The frequency of the northeast cold vortex in the 40-45 degrees north latitude area is low in early spring.
Weather Impact and Hazards
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The northeast cold vortex is a cold air column from the ground to 6000 meters above. At least one closed contour line can be analyzed on the 500 hPa weather map, and there is a cold center or obvious cold trough.The air column in the cold vortex is in an unstable state of upper cold and lower warm, which often produces unstable weather such as showers, thunderstorms, even thunderstorms, gales or hail. Sometimes, the strong development of the cold vortex will also cause large-scale rainstorm weather.As the Northeast Cold Vortex is a deep weather system, it moves slowly for a long time, generally 3-5 days, up to more than 10 days, bringing cold and rainy weather for several consecutive days, or intermittent rain weather for several consecutive days.
The northeast cold vortex is an important weather system that causes sudden severe convective weather in northeast China, such as low temperature and cold damage, continuous rainfall and flood, hail, thunderstorm and gale, and has a significant impact on the weather and climate in northeast China.
The northeast cold vortex weather in spring and summer is very harmful to agriculture and animal husbandry.The low temperature affects the spring sowing of rice, sorghum, corn, soybean and other crops or the development and growth of seedlings, resulting in a reduction in autumn grain production.In the pastoral area, the grass cannot turn green in time, and cattle and sheep lose weight due to insufficient feed.The impact on crops varies according to the time when low temperature occurs.The low temperature in June prevented the normal growth of crops and delayed the growth period;In August, the crops are in the stage of dry matter accumulation of milk ripening, and need the weather with high temperature and sufficient sunshine. Low temperature is easy to cause the grain to be not full or empty and reduce the yield.
Recent developments
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On March 24-28, 2008, the Northeast Cold Vortex caused continuous light rain or sleet weather for five days in Liaoning. The average precipitation of the province on March 24-28 was 4.5 mm, ranking the sixth in the same period in history. The average temperature of the province during the impact of the cold vortex was 4 ℃, 2.4 ℃ lower than the previous period.From the statistical analysis data, it is rare for the northeast cold vortex to appear so southward and maintain for a long time in early spring. It only appeared on March 29-31, 1975, March 24-25, 1994, and March 29-30, 1997 in history, which is a 10-year return period.
On April 2, 2022, the 6th northeast cold vortex in 2022 has been formed. Affected by it, rain, snow, strong wind and cooling weather will occur in northern China.[3]
Related research
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To the Northeast Cold Vortex and theWeather phenomenonIt has always been a concern and research issue for meteorological science and technology workers. The research on the northeast cold vortex rainstorm in China can be traced back to 1950. Many meteorologists have studied the northeast cold vortexrainstorm、thunderstorm、hailAnd so on.However, because of the "uncertainty" of the Northeast Cold Vortex, it is difficult for forecasters to grasp the intensity, falling area and time of the convective precipitation of the Northeast Cold Vortex, so that the prediction of the strong convection of the Northeast Cold Vortex has always been a difficult problem for forecasters.
In recent years, on the basis of the previous research results, the meteorological workers in the northeast region have carried out research on the mechanism and evolution law of the mesoscale system induced by the northeast cold vortex, aiming at the prediction of the severe convection weather of the northeast cold vortex, hoping to reveal the internal structural characteristics of the northeast cold vortex and the physical mechanism of the occurrence and development of the mesoscale system, the northeast cold vortexMesoscale convective systemTo improve the overall forecast level of the northeast cold vortex severe convection weather.It is believed that with the efforts of meteorologists, the day of unveiling the Northeast Cold Vortex will soon come.
Northeast Cold Vortex and Its Climate Impact
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Plum Rain(Known as Changma in South Korea and Baiu in Japan) is the product of the East Asian summer monsoon, which occurs in the northern hemisphere in summer from June to July. The Meiyu area extends eastward from the middle and lower reaches of the Yangtze River in China to the Korean Peninsula and Japan.Meiyu has long been an important part of short-term climate prediction in China and even the world.Scientists in many countries and regions have done a lot of research on it.Taking a comprehensive view of these studies, more attention has been paid to the influencing factors in tropical low latitudes, while more attention has been paid to the circulation system originating in the mid high latitudes of the Northern Hemisphere, and less detailed research has been done.In fact, the atmospheric circulation in the middle and high latitudes also has an important impact on the East Asian summer monsoon precipitation, including the Meiyu.
As we all know, the northeast cold vortex is an important part of the Asian mid high latitude atmospheric circulation system. The life cycle of an activity of the northeast cold vortex is generally 5-7 days, so it is a synoptic scale system.However, from the perspective of space, the northeast cold vortex not only has a great impact on the weather and climate in northeast China, but also can guide the cold air in high latitudes southward to affect the middle and low latitudes;From the perspective of time, the "climate effect" produced by the frequent northeast cold vortex activities not only affects the medium and short term weather, but also has a significant impact on the long-term weather.All these are also the starting point of this study.These studies can not only understand the role of Asian mid high latitude circulation system in Meiyu, but also provide reference results for short-term climate prediction in Meiyu region.
Data and methods
Table 1
The reanalysis data used in the research are taken from the ERA-40 data set of the European Medium Range Weather Forecast Center (ECMWF) (horizontal resolution 2.5 °× 2.5 °), and the SST data are taken from the extended and reconstructed SST (ERSST) of the National Oceanic and Atmospheric Administration (NOAA) (horizontal resolution 2.0 °× 2.0 °).
Figure 1
The statistical analysis shows that the most significant feature of the northeast cold vortex on summer weather is the continuous low temperature and continuous rain in the affected area, especially the continuous low temperature.The more frequent and stronger the northeast cold vortex activity is, the more frequent the cold events are, and the longer the accumulated low temperature time is, which leads to the lower seasonal average temperature in the northeast cold vortex affected area. On the contrary, when the northeast cold vortex activity is less and the intensity is weaker, the seasonal average temperature in the northeast cold vortex affected area is higher.Based on this, we call the seasonal average temperature and precipitation anomalies caused by the northeast cold vortex activity anomaly as the "climate effect" of the northeast cold vortex activity.In order to quantitatively describe the impact of the "climate effect" of the northeast cold vortex activity on the Meiyu in East Asia, this paper defines a Meiyu period (June to July) northeast cold vortex intensity index NECVI (NortheastColdVortex Index). The specific method is as follows: the average temperature of East Asia (100 ° E~145 ° E, 20 ° N~160 ° N) in the 1000hPa Meiyu period is decomposed by rotating EOF,The first six principal components of the EOF decomposition are taken as the principal components of the initial rotation, and the variance contribution of the first mode after rotation accounts for 22.9% of the total variance (as shown in Figure 1). It can be seen that the area (127 ° E-145 ° E, 37 ° N-145 ° N) is covered by the negative value center (the shaded area in Figure 1), which is one of the areas where the northeast cold vortex is active [161].We define the opposite number of 1000 hPa average temperature from June to July within the shaded area in Figure 1 as the northeast cold vortex intensity index NECVI (Table 1) during the Meiyu period.The purpose of taking the opposite number here is to make the index more consistent with the usual usage, that is, the higher the index, the stronger the northeast cold vortex, the lower the index, and the weaker the northeast cold vortex.The standardized NECVI values greater than 1 and less than - 1 are defined as high and low NECVI index years in the Meiyu period.
Relationship between Northeast Cold Vortex and Precipitation in Meiyu Period
Figure 2
Figure 2 shows the correlation coefficient between NECVI and precipitation during the Meiyu period.From the middle and lower reaches of the Yangtze River to the Korean Peninsula and Japan via the East China Sea, there is a large significant positive correlation zone, indicating that when the NECVI value is higher (i.e., the northeast cold vortex is stronger), the precipitation in the above areas is likely to be more; when the NECVI value is lower (i.e., the northeast cold vortex is weaker), the precipitation in the above areas is likely to be less.The significant positive correlation area in Figure 2 basically coincides with the Meiyu area in East Asia, so the Meiyu amount is likely to be more in the year when the northeast cold vortex is stronger during the Meiyu period, while it is likely to be less in the year when the northeast cold vortex is weaker.Because the distribution of Meiyu precipitation is skewed rather than normal, z index is used to describe the change of precipitation in many precipitation analysis.
In order to further verify the correlation between the northeast cold vortex and the plum rain, the research cited literature[1]The Meiyu z index is defined according to the literature[1]For the Meiyu area defined, first calculate the distribution probability of Meiyu y, then calculate the inverse cumulative distribution function of its normal distribution, and standardize it to get the z index value.The larger the z-index is, the more the Meiyu precipitation is. The smaller the z-index is, the less the Meiyu precipitation is.Figure 3 shows the NECVI index time series and Meiyu z index time series of the Northeast cold vortex from 1958 to 2002. It can be seen that the z index time series and the NECVI time series have similar change trends. The correlation coefficient of the two is calculated to reach 0.44, which exceeds the 99% confidence test. It shows that the larger the NECVI value, the larger the z index value is likely to be,The smaller the NECVI value, the smaller the z-index value is likely to be.
To sum up, there is a significant correlation between the northeast cold vortex and the Meiyu during the Meiyu period. The stronger the northeast cold vortex, the more likely the Meiyu amount is. The weaker the northeast cold vortex, the less likely the Meiyu amount is.
Analysis of the Possible Mechanism of the Northeast Cold Vortex Affecting Meiyu
Figure 3
Previous studies have shown that the northeast cold vortex appears as a cold low-pressure center on the 500hPa weather map.In order to verify whether the Northeast Cold Vortex Intensity Index (NECVI) defined by the research can quantitatively describe the physical image of the Northeast Cold Vortex and describe its structural characteristics, we calculated the 500hPa composite potential height and temperature difference field (as shown in Figure 3) in the years with strong (high NECVI) and weak (low NECVI) anomalies of the Northeast Cold Vortex in the pre flood season.From the perspective of height field ((a) in Figure 4), from North China and Northeast China through the Korean Peninsula to Japan, there is a large range of significant difference low pressure center, which indicates that in the high NECVl year, the above areas have low pressure center development, while in the low index year, the above areas are low pressure filling or high pressure development;From the perspective of temperature field ((b) in Figure 4), the above areas are covered by the low temperature center of significant difference, which is slightly smaller than the height field, indicating that there is a cold center development in this area in the high NECVl year, while the opposite is true in the low NECVl year.From the above analysis, we can see that the Northeast Cold Vortex Intensity Index (NECVI) value defined in this paper basically reflects the main characteristics of the Northeast Vortex, so it can be used to quantitatively describe the strength of the Northeast Cold Vortex.
Figure 4
Figure 5
Figure 5 shows the distribution of the correlation coefficients of the relative vorticity fields of NECVl and 850100hPa during the Meiyu period.From the configuration of the high and low level relative vorticity fields in the northeast cold vortex active region, the ocean surface from the east of Inner Mongolia to the east of Japan is basically covered by a significant positive correlation area ((a) in Figure 5), and the upper level area is also controlled by a significant band positive correlation area ((b) in Figure 5), indicating that the high and low level relative vorticity fields in the northeast cold vortex active region have basically the same change trend,It can be seen that the Northeast Cold Vortex is a deep system with quite barotropic structural characteristics.In high NECVl years, positive vorticity develops in the above areas, while in low NECVl years, negative vorticity develops.We also note that there is a significant positive correlation area in the middle and lower reaches of the Yangtze River in the lower layer, and a significant negative correlation area in the south of the middle and lower reaches of the Yellow River ((a) in Figure 5). The situation in the upper layer is just the opposite ((b) in Figure 5), which shows that the relative vorticity field in the upper and lower levels of these areas has opposite trends, and the baroclinicity is increasing. It is not difficult to find that these areas are located at the bottom of the area affected by the northeast cold vortex,It is also an active area of the Meiyu belt.In addition, we know that positive (negative) vorticity is often accompanied by upward (downward) movement.Therefore, in the strong years of the northeast cold vortex, the middle and lower reaches of the Yangtze River tend to correspond to the development of positive vorticity and upward movement, while the areas south of the middle and lower reaches of the Yellow River correspond to the development of negative vorticity and downward movement.In the weak years of the Northeast cold vortex, the situation is opposite.
Figure 6
The intensity of water vapor transport has an important impact on the amount of Meiyu rainfall.Next, we will analyze the water vapor transport in the lower troposphere during the Meiyu period of the northeast cold vortex anomaly year.Figure 6 shows the 850hPa synthetic water vapor transport difference field in the northeast cold vortex abnormal year during the Meiyu period. The convergence line of water vapor transport difference is from the middle and lower reaches of the Yangtze River to the Korean Peninsula to the east of Japan (the black thick line in Figure 6). The south of the convergence line is covered by the significant west southwest water vapor transport difference area, and the north is controlled by the significant north water vapor transport difference area.In the year when the northeast cold vortex is stronger, the difference of water vapor transport between the west and southwest to the south of the convergence line and the difference of water vapor transport between the north and the west to the north of the convergence line increase, which makes the water vapor transport and convergence in the lower level of the region increase, providing favorable water vapor conditions for the increase of Meiyu rainfall;In the weak years of the Northeast cold vortex, the situation is just the opposite.The reason is that in the year when the northeast cold vortex is strong, most areas from the north of the Yangtze River in the lower troposphere to the northeast have positive vorticity development ((a) in Figure 5), which is conducive to the development of the cyclonic circulation in this area. The area north of the Yangtze River is just at the bottom of the cyclonic circulation anomaly, thus forming an abnormal west northwest wind water vapor transport (Figure 6), while in the subtropical western Pacific ((a) in Figure 5)）The strong year of the northeast cold vortex is often accompanied by the development of abnormal negative vorticity, which is conducive to the enhancement of the anticyclonic circulation in the region, thus leading to the enhancement of the western Pacific subtropical high. The Meiyu region is located at the northwest edge of the western Pacific subtropical high, so an abnormal west southwest wind water vapor transport is formed on the south side of the region (Figure 6).From the above analysis, it is not difficult to find that the combined effect of the Northeast Cold Vortex and the Western Pacific Subtropical High may be the reason for the enhanced water vapor convergence in the East Asia Meiyu region.
Figure 7
Stratification is another important influencing factor of Meiyu precipitation.We calculated the correlation coefficient distribution of NECVl and 1000100hPa relative humidity field during the Meiyu period (Figure 7).In the year when the northeast cold vortex is stronger, the low-level Meiyu area (the middle and lower reaches of the Yangtze River - the Korean Peninsula - the ocean surface to the east of Japan) is basically covered by positive correlation ((a) in Figure 7), and the significant positive correlation centers are located in the middle and lower reaches of the Yangtze River and the regions to the south, northeast to the Korean Peninsula, and the ocean surface to the southeast of Japan, indicating that the relative humidity in the lower levels of these regions increases, and in the upper levels ((b) in Figure 7,30 ° N~150 ° N is a significant band negative correlation area, indicating that the relative humidity in this area decreases, which forms a high and low altitude configuration of "dry at the top and wet at the bottom", aggravates the unstable stratification in the Meiyu area, and is conducive to the increase of the amount of Meiyu.In the weak years of the Northeast cold vortex, the situation is opposite.
Figure 8
In addition, the ascending motion is also a major factor affecting the precipitation of Meiyu.The vertical profile difference flow field of the northeast cold vortex anomaly year in longitude (along 120 ° E) and latitude (along 27 ° 50N) is shown here (Fig. 8).From the meridional profile ((a) in Figure 8), the troposphere in East Asia at 25 ° N-30 ° N is mainly controlled by the significant differential updraft, while the troposphere between 30 ° N-35 ° N is basically controlled by the significant differential downdraft.From the latitudinal profile ((b) in Figure 8), the lower layer of 105 ° E-135 ° E (below 850hPa) is controlled by a significant differential updraft, and the upper layer (near 100hPa) is controlled by a significant differential downdraft.All these indicate that in the strong year of the northeast cold vortex, the upward movement of the troposphere develops in the region (25 ° N~30 ° N, 105 ° E~135 ° E), and the downward movement develops in the region (30 ° N~35 ° N, 105 ° E~135 ° E).In the weak year of the Northeast cold vortex, the situation is just the opposite.
Figure 9
Through the above analysis, we can get the possible mechanism of the influence of the Northeast Cold Vortex on the Meiyu: in the strong year of the Northeast Cold Vortex, the Northeast Cold Vortex led the northern "dry and cold" air to invade southward, and intersected with the low-level strong southwest warm and wet air flow at the northern edge of the Meiyu area, forming an unstable stratification of "dry at the top and wet at the bottom", which ultimately led to more Meiyu under the trigger of upward movement;The weak years of the Northeast cold vortex are just the opposite.
Relationship between the North Pacific SST and the Northeast Cold Vortex Anomaly Given the close relationship between the atmospheric circulation anomaly and the SST anomaly, we calculated the correlation between the NECVI in the Meiyu period and the global SST in the previous six months (from December of the previous year to May of the current year) and the same period (from June to July of the current year), and found that the correlation with the SST in the North Pacific was most significant (as shown in Figure 9).In December of the previous year ((a) in Figure 9), a small negative correlation area appeared in the central part of the North Pacific, and then the area expanded month by month and expanded to the northwest ((b) - (g) in Figure 9). By July of that year ((h) in Figure 9), the entire northwest Pacific was covered by a large negative correlation area, with the center roughly between 40 ° N-45 ° N, indicating that when the northeast cold vortex was stronger in the early or the same period of the Meiyu period,The sea surface temperature in the above sea areas is often significantly low, which is conducive to the development of abnormal subsidence movement in the above sea areas.At the same time, as the thermal properties of the East Asian continent change from winter to summer (the East Asian continent is a cold source in winter, the wind blows from the mainland to the ocean, the East Asian continent turns into a heat source in summer, and the wind blows from the ocean to the continent), the SST of the Northwest Pacific tends to be low in summer due to the strong northeast cold vortex, and the thermal differences between the Northwest Pacific and the East Asian continent are mainly east-west sea land,Therefore, the easterly anomaly will occur between the lower East Asian continent and the Northwest Pacific Ocean.At the same time, the low sea surface temperature in the northwest Pacific increases the thermal difference between the region and the middle and low latitude regions in East Asia, resulting in the enhancement of the upper westerly jet.When the northeast cold vortex appeared, there was an ascending movement in the middle and high latitudes of East Asia, so a closed circulation of abnormal air flow was formed between the middle and high latitudes of East Asia and the northwest Pacific, which was conducive to the further activity and strengthening of the northeast cold vortex.On the contrary, the northeast cold vortex is weak.Therefore, the early North Pacific SST anomaly may be one of the factors leading to the northeast cold vortex anomaly during the Meiyu period.
It is easy to see that the sea land thermal contrast in summer promotes the northeast cold vortex, while in winter it inhibits the northeast cold vortex.This is because the northwest Pacific is the heat source in winter, while the East Asian continent is the cold source. Therefore, the low-level wind blows from the East Asian continent to the northwest Pacific, that is, the westerly wind. Its direction is consistent with the upper level, which is not conducive to the development of the ascending movement in the middle and high latitudes of East Asia. This may also be the reason why the frequency of the northeast cold vortex in summer is much higher than that in other seasons.
research conclusion
The northeast cold vortex occurs occasionally in the middle and high latitudes of East Asia in summer. For a long time, some research has been carried out on it from the perspective of synoptic science, but there is little research on the "climate effect" caused by frequent northeast cold vortex activities.This paper focuses on the analysis of the "climate effect" of the northeast cold vortex on the Meiyu, proposes a possible physical mechanism, and analyzes the reasons for the anomaly of the northeast cold vortex during the Meiyu period from the perspective of air sea interaction.Based on the above analysis, we can draw the following conclusions:
(1) During the Meiyu period, there is a significant correlation between the northeast cold vortex and the precipitation. The stronger the northeast cold vortex, the more likely the Meiyu is. The weaker the northeast cold vortex, the less likely the Meiyu is.
(2) In the strong year of the Northeast Cold Vortex, the Northeast Cold Vortex led the northern "dry and cold" air to invade southward, and intersected with the low level strong southwest warm and wet air flow at the northern edge of the Meiyu District, forming an unstable stratification of "upper dry and lower wet". Triggered by the rising movement, the amount of Meiyu was finally excessive;In the weak years of the Northeast Cold Vortex, the situation is just the opposite.
(3) The early North Pacific SST anomaly may be one of the factors leading to the northeast cold vortex anomaly during the Meiyu period.The sea land thermal contrast in summer promotes the northeast cold vortex, while in winter it inhibits the northeast cold vortex.[2]
