Geography of College Entrance Examination: What is Strong Convective Weather?

Strong convective weather refers to short-term heavy precipitation, thunderstorm and strong wind, tornado, hail, squall line and other disastrous weather, which lasts for a short time, is strong and extremely destructive. Strong convective weather occurs in small and medium-scale weather systems, and the spatial scale is small. Generally, the horizontal range is about ten kilometers to two or three hundred kilometers, and some horizontal ranges are only tens of meters to ten kilometers. Often occurs in convective clouds or single convective clouds. Its life history is short, with obvious suddenness, about one hour to more than ten hours, and the shorter one is only a few minutes to an hour. When strong convective weather comes, it is often accompanied by severe weather such as thunder and lightning, wind and rain, which causes houses to be destroyed, crops and trees to be destroyed, telecommunications traffic to be damaged, and even casualties. This is a disastrous weather with great destructive power. Disaster characteristics Strong convective weather is based on large-scale weather system, which affects or determines the generation, development and movement process of small-scale weather system, and small-scale weather system has feedback effect on large-scale weather system. As far as Guangdong Province is concerned, the characteristics of severe convective weather are mainly manifested in the following aspects: Severe convective weather-hail (1) appears early and ends late. The severe convective weather in Guangdong generally begins in February and gradually decreases after September. Some years can appear in 65438+ 10 in advance and end in10 ~ 65438+February. (2) High strength and strong destructiveness. The severe convective weather in Guangdong, like severe convective weather in other areas, has the characteristics of high vertical speed, strong suddenness and great destructive power. For example, when severe convective weather occurs, the instantaneous wind speed of some processes reaches 12 or even exceeds 100 m/s (3). The horizontal scale is small, and the life history is short and strong. Strong convective weather is one of the most common natural disasters in Guangdong, with strong winds, squall lines, hail and tornadoes appearing frequently. For example, in some years, it hails four times a day, and the longest hail can last for half an hour. In some months, there may be hail for several days in the whole province. The horizontal scale of strong convective weather is small, generally less than 200 kilometers, and some are only a few kilometers. Life history is very short, usually only a few hours to dozens of hours. In addition, it also has the basic characteristics of large gradient of meteorological elements, non-geostrophic balance and non-static balance. Convective weather is easy to form and develop in some specific areas, such as on both sides of mountains, at the border between land and sea, around lakes and swamps. Therefore, the physical process of the formation of various severe convective weather is not exactly the same, which is closely related to the influence of dynamic and thermal effects of the underlying surface. Circulation caused strong convective weather in some areas. The main reason is that the cold air in the south is extremely active, and the cold air in the south frequently collides with the wet airflow, which is very unstable. This humid and warm atmosphere will produce strong vertical movement in the hot afternoon in summer, which will lead to strong convective weather. In addition, the upper air in the northern region is controlled by the strong northwest airflow, and the weather is fine during the day, the solar radiation is strong, and the near-surface temperature rises rapidly, while the vortex in North China is relatively stable, which often leads to cold advection southward, forming an unstable atmosphere with cold upper and warm lower in some areas, making these areas prone to strong convective weather. Another culprit of severe convective weather is global warming. The occurrence time of strong convective weather varies from place to place. The south comes earlier than the north, and strong convective weather in Guangdong may occur all year round. Thunderstorms and strong winds mostly occur in spring, summer and autumn, and are rare in winter. Short-term heavy precipitation can be seen all year round, mostly in spring, summer and autumn. Tornadoes usually occur at the turn of spring and summer or at the turn of summer and autumn (April ~ 10), and the former is mostly. Squall lines often occur in the warm area before the cold front in the spring and summer transition season, and they often appear in the typhoon front, mostly in March-September. Hail mostly occurs in February-May when cold and warm air meet fiercely, and it can also land in the intense and persistent thunderstorm in midsummer. Disaster classification Strong convective weather can be divided into the following categories: (1) squall line meteorology The so-called squall line refers to the sudden gale phenomenon in which the wind direction suddenly changes and the wind force suddenly increases. Squall line refers to the weather change zone where the wind direction and wind force change dramatically. Severe weather phenomena such as thunderstorm, rainstorm, gale, hail and tornado may occur along the squall line, which is a thunderstorm or cumulonimbus cloud belt. Squall line is a comprehensive result of dynamic and thermal effects caused by undulating terrain and uneven thermal distribution. The formation and development of strong convective weather-gale is not only closely related to the weather situation, but also plays an extremely important role in local conditions. It often occurs before the arrival of thunderstorm clouds or cold front, and it is most likely to occur in cumulonimbus clouds in spring and summer. The wet and unstable gas layer can promote the strong development of squall line. When it is about to appear, the weather is sultry, the wind direction is chaotic or southerly. When strong cold air invades, there is unstable stratification in the warm air mass before the ground cold front or near the trough of low pressure, and squall line weather is most likely to form at this time. Squall lines mostly occur in the evening to night. The squall line can be divided into three stages from formation to extinction: (1) the primary stage, which usually lasts for 3-5 hours, with 6-level gale and thunderstorm. (2) In its heyday, it lasts for 1 ~ 2 hours, the wind direction changes suddenly, and the wind speed increases suddenly, often from level 8 to above 12, the air pressure rises sharply, and the temperature drops sharply, which will drop to above 10℃ in a short time. The storm at this stage is extremely destructive. (3) Dissipation stage, lasting about 2 hours, the wind decreases, the intensity of thunderstorm weakens, the air pressure gradually decreases, the temperature gradually increases, and the weather gradually improves. (2) Tornado Tornado is a strong, small-scale air vortex, which is a strong whirlwind produced by funnel-shaped clouds (tornadoes) extending from the bottom of thunderstorm clouds to the ground. Its wind power can reach more than 12, and the maximum can reach more than 100 m/s, usually accompanied by thunderstorms and sometimes hail. It is the strongest vortex phenomenon in the atmosphere. Although its impact is small, it is extremely destructive. It often destroys crops and tens of thousands of fruit trees in an instant, interrupts traffic, collapses houses and loses human and animal lives. Tornadoes are divided into land tornadoes and sea tornadoes. Tornadoes that appear on land are called land tornadoes, and tornadoes that appear at sea are called sea tornadoes. It has a strong rotating force, and often carries water, dust and sediment on the earth's surface upwards, and gathers them into a tube from all directions, just like a "dragon falling from the sky", hence the name. Most land tornadoes are surrounded by sediments; The periphery of the sea tornado is mostly seawater. This kind of sea tornado is also called "dragon sucking water". Tornadoes are caused by strong air convection in extremely unstable weather, and their formation and development are not essentially different from squall line systems, but tornadoes are more serious. Its formation and development must have a large amount of energy supply, so it needs the existence of strong convective unstable energy. It is similar to tropical cyclone in nature, but the scale is much smaller than tropical cyclone. In the process of formation and development, due to air convection, the air pressure in the center of tornado becomes very low. Under the action of pressure gradient force, the air with higher pressure around flows to the center of the tornado, and when it does not flow to the center, it rotates around the center, thus forming a vortex of air. The horizontal range of tornadoes is very small, ranging from several meters to several hundred meters in diameter, with an average of about 250 meters and a maximum of about 1 km. The diameter can reach several kilometers in the air, and the maximum is 10 km. The maximum wind speed can reach 150 km to 450 km per hour, and the duration of tornado is usually only a few minutes, and the longest is no more than a few minutes, but the disaster caused is very serious. Guangdong is one of the tornado-prone areas in China, which occurs all year round. From the time point of view, it is mostly in late spring and early summer. From the regional point of view, there are many coastal areas and few inland areas. (3) Hail Hail is hard spherical, conical or irregular solid precipitation falling from thunderstorm clouds. Common hailstones are as big as beans, about 2 cm in diameter, as big as eggs (about 10 cm in diameter), and as big as 30 cm or more. Hail is a kind of solid precipitation, which falls because ice crystals or raindrops roll and condense several times in convective cumulonimbus clouds. It is usually produced in the process of systematic frontal activity or tropical cyclone landing, but it is also local. Hail usually occurs at the turn of spring and summer; To produce hail of 10 cm, there must be upward airflow movement of more than 50 m/s (generally, the cumulonimbus clouds that produce thunderstorms only move about 10 m/s). Such a strong upward movement is entirely obtained by the release of unstable energy in the atmosphere. Therefore, a necessary condition for hail suppression is the existence of extremely unstable atmosphere in the air. The thicker the unstable layer, the better the hail suppression. In cumulonimbus clouds, clouds below 0℃ are composed of water droplets, clouds above 0℃ are composed of supercooled water droplets, and clouds above 0℃ are composed of supercooled water droplets mixed with snowflakes and ice crystals. If the updraft in cumulonimbus clouds is sometimes strong and sometimes weak, when the rising cooling water droplets collide with the ice crystals or snowflakes above, the supercooled water droplets freeze into the core of hail. After the hail is formed, it is either weakened by the updraft or reduced by its heavy weight. When it drops below 0℃, some water drops will stick to it. At this time, if the updraft increases, it will be taken to the low temperature area above 0℃, and the water on the surface of the hail core will freeze into ice again. When the updraft can no longer hold it, it falls to the ground and becomes hail. (4) Thunderstorm gale Thunderstorm gale refers to the weather phenomenon that the wind reaches or exceeds Grade 8 (≥ 17.2m/s) on a thunderstorm day. Sometimes thunderstorms and strong winds are called storms. During a thunderstorm and gale, dark clouds roll, thunder and lightning, accompanied by heavy precipitation and sometimes hail, and the wind speed is extremely high. Generally, it only covers a few kilometers to dozens of kilometers. Thunderstorm gale often appears in the thunderstorm high pressure before the strong cold front. Thunderstorm high is a small local high existing in the ground pressure field near the thunderstorm area. The temperature of the thunderstorm high pressure center is lower than that of the surrounding area, and the downward flow is very obvious. The front of thunderstorm high pressure is a warm area with updraft. Just between the downdraft and the updraft, there is a narrow wind shear zone, which is where thunderstorms and strong winds occur, and it will bring extremely strong storms when it passes. If a thunderstorm gale occurs in a single air mass, it is often caused by uneven local heating. Thunderstorms and strong winds have a short life history. (5) Short-term heavy precipitation Short-term heavy precipitation refers to a weather phenomenon in which the precipitation intensity is large in a short period of time and the rainfall reaches or exceeds a certain value. The regulation of this value varies from place to place. (6) Thunderstorms and strong convective weather often bring thunderstorms. When the stratification in the atmosphere is unstable, strong convection is easy to occur. When the potential difference between clouds and between clouds and the ground reaches a certain level, discharge will occur. Sometimes thunder rumbles and dazzling lightning flashes across the sky, often accompanied by strong winds, showers or hail. Therefore, thunderstorm weather is always associated with strong cumulonimbus clouds. Because the occurrence and development of thunderstorms are linked with cumulonimbus clouds, from the appearance to the disappearance of thunderstorm clouds, it is very local and sudden, with a horizontal range of only a few kilometers and a time scale of only 2-3 hours. Therefore, this small and medium-sized weather system has certain difficulty in forecasting. Strong thunderstorm is a kind of disastrous weather. Lightning will cause lightning fire danger, strong winds will blow down houses, uproot trees, and fruits, vegetables and other crops will suffer serious losses or even no harvest after being attacked by hail. Sometimes local heavy rain will also cause geological disasters such as mountain torrents and mudslides. Severe convective weather disasters can generally be divided into wind disasters, waterlogging disasters and hail disasters. When severe convective weather occurs, several disasters often occur at the same time, which has a great impact on the national economy and people's livelihood and agricultural production. Strong wind is one of the most significant meteorological elements of squall line, tornado and thunderstorm. Although the horizontal scale of the squall line is small, strong wind and rain disasters will occur within its influence range, which can cause trees to fall, houses to overturn, debris to fly, people and animals to be injured, and crops to fall. Because all kinds of strong convective weather have their own seasons and characteristics, agricultural production is outdoor work, arranged according to seasons, so the harm of strong convective weather to various crops in agricultural production is different. The above floods, strong winds and hail are the main hazards that affect agricultural production in severe convective weather disasters. The direct harm of strong convective weather to agricultural production is the destruction of crops by external forces, and the indirect harm is that waterlogging induces and spreads pests and diseases, resulting in crop yield reduction or even crop failure. With the improvement of people's living standards and the development of economic construction, the losses caused by strong convective weather are more serious. Severe convective weather disasters are closely related to the type, influence range and duration of severe convective weather. The strong convective weather in this section of the disaster prevention editing catalogue is sudden, with many kinds of disasters and great destructive power, which often causes serious disasters. At present, there is no effective method of artificial weakening and prevention, and the strategy of combining prevention with rescue should be adopted. 1. Establish the structure and measures for agriculture, forestry and animal husbandry to resist disasters and achieve stable production (I) Establish the structure for agriculture, forestry and animal husbandry to resist disasters and achieve stable production. In places where severe convective weather disasters occur, especially in mountainous areas, we should vigorously plant grass and trees, close hillsides to facilitate afforestation, green barren hills, increase forest coverage, do a good job in soil and water conservation, reduce soil erosion, and minimize air convection to reduce the occurrence of severe convective weather disasters. Agricultural areas should increase the proportion of forest and animal husbandry, and increase the proportion of crops that are resistant to severe convective weather disasters and have strong disaster resistance; In areas with frequent severe convective weather disasters, a variety of root crops. The frequent periods of severe convective weather disasters in the key growth period are staggered. Mature crops should be harvested in time. (2) windproof. Planting trees, greening the environment, strengthening buildings, preventing wind damage such as thunderstorms and tornadoes, changing the ecological environment, preventing soil desertification, protecting water sources and dredging swamps. (three) the crops need to take timely remedial measures after the disaster. After the severe convective weather disaster, crops not only suffered mechanical damage, but also suffered many indirect hazards. Therefore, it is necessary to take timely remedial measures according to the resilience of different disasters, different crops and different growth periods. (4) Cultivate excellent crop varieties resistant to severe convective weather disasters and improve crop resilience. 2. Improve the forecast level of severe convective weather, strengthen the theoretical research of severe convective weather system (1) to improve the forecast level of severe convective weather. First of all, we should do a good job in forecasting the occurrence and movement of strong convective weather. Meteorological radar monitoring can be used to strengthen the joint defense of meteorological stations and forecast the occurrence and activities of severe convective weather. It is also possible to explore and track the occurrence, development, movement and disappearance of severe convective weather by using the cloud images taken continuously by geosynchronous satellites, and help to judge and predict the area where severe convective weather occurs with the analysis of weather situation maps, thus improving the forecasting level of severe convective weather. Before the occurrence of severe convective weather, timely release forecast information and take necessary defensive measures. (2) Strengthen the theoretical research of severe convective weather system. For example, strengthen the research on the mechanism of strong convective weather, encrypt the monitoring sites of strong convective weather and update the monitoring methods; Establish a computer command system for disaster prevention and mitigation, apply it to disaster relief as soon as possible, improve adaptability, systematically sort out the severe convective weather disasters affecting the region, and establish a database of severe convective weather and disasters to provide accurate disaster information for leaders to make decisions and take timely measures. 3. Establish and improve the disaster prevention system (1) and report to the police in time when severe convective weather is found. Quickly transmit the possible severe convective weather forecast to all relevant regions and units; Timely delivery through radio, television, high-frequency telephone, etc. (2) Build water conservancy projects, clean ditches, dredge waterways, rectify dirty, chaotic and poor conditions, and prevent waterlogging caused by heavy precipitation. (3) Artificial hail suppression. The main measure of hail suppression is to eliminate hail, so that the clouds forming hail blocks can be thinned or dissipated, and to prevent hail from brewing in the clouds and small hail from growing into large hail. There are two methods: one is to put silver iodide or lead iodide into the cumulonimbus cloud that forms hail by burning on the ground or sowing by plane, so as to make the hail embryo in the cumulonimbus cloud increase and make it form small hail, which is not easy to grow into large hail. The second is the explosion. Anti-aircraft guns, rockets and explosives are used to bombard the cumulonimbus clouds of hail, which causes strong air vibration and disturbs the updraft, thus inhibiting the development of hail clouds and enhancing the chance of collision between cloud droplets, so that some cloud droplets quickly grow into raindrops and land. When strong convective weather occurs, the instantaneous strong wind is likely to cause trees to break and houses to collapse, thus causing casualties. When strong winds such as squall line system or tornado appear, the public should stay away from fragile trees, billboards and dangerous houses. In addition, we should strengthen the prevention of lightning, don't stay in the open air, and avoid buildings with lightning protection facilities; If you are outdoors, if you have a car, try to avoid it.