Topographic thunderstorm, due toTopographical actionCaused bythunderstorm。Thunderstorms are particularly likely to occur in mountainous areas.WhenWarm airafterhillsideWhen forced to rise, the air on the windward side of the mountain rises along the hillside, and becomes cold at a certain height to form thunderclouds;But on the leeward side of the mountain, the air sinks along the hillside, the temperature rises, and the thunderstorm dissipates or weakens.[1]
Topographic thunderstorm: It is a thunderstorm caused by the forced lifting of warm, humid and unstable air on the windward slope of the mountain.There are many mountains in China, and the terrain is complex, and the terrain thunderstorm is a kind of thunderstorm encountered by mountain pilots in summer.Because warm and humid air often exists in summer, and the gas layer is unstable, if the wind speed component perpendicular to the mountain trend is large, the hillside is steep, and the terrain uplift is obvious, thunderstorms will be formed.[2]
In the first stage of thunderstorm, the downhill intensified, and terrain forcing played a major role in three aspects: (1) The terrain slope made the thunderstorm cold pool flow accelerate downhill and form a strong convergence zone of southerly airflow with stable maintenance;(2) Topographic uplift makes the southward warm and wet inflow rise strongly, which intensifies the development of convection;(3) The terrain raises the outflow height of the cold pool, which makes the derived flow and the southerly flow near the ground form a vertical wind shear at the lower level that rotates with height. There is a cold advection superimposed on the warm air at the lower level, which increases the dynamic and thermal instability in front of the thunderstorm.The main reasons for the second stage of thunderstorm strengthening again in the plain area are: after the well-organized thunderstorm reached the plain area, its cold pool and the low-level warm tongue faced each other in the urban area (Chaoyang area), resulting in a strong disturbance temperature gradient;The strong cold pool outflow interacts with the southerly warm and humid airflow with the same force to produce a strong convergent updraft, which coexists with the downdraft for a long time;The negative vorticity generated by the outflow of the cold pool is approximately in balance with the positive vorticity generated by the low-level shear.Using the RKW theory, the three factors lead to the strongest convergence and uplift of the lower level in front of the thunderstorm, which is most conducive to the maintenance and development of thunderstorms.[3]
Topographic thunderstorms occur in mountainous areas
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In the summer of September 3, 2006, there was a strong thunderstorm weather caused by the terrain in the Qilian Mountains. On the 700hPa altitude map, the area from the Qilian Mountains to Haixi Prefecture in Qinghai Province is the Xinjiang High andSubtropical highThe eastern section of the shear line is almost along the trend of the mountains. The south-west wind is on the south side of the Qilian Mountains, and the northerly wind is on the north side of the Qilian Mountains. Both the north and south sides of the shear line rise and converge over the mountains. This is the reason why the eastern section of the shear line is almost consistent with the trend of the mountains, highlighting the contribution of the topographic factors of the Qilian Mountains to the formation of the shear line.From the satellite cloud map, it can be seen that there are strong convective cloud clusters in the north and south of the Qilian Mountains. From the development process of these two cloud systems, it can be clearly seen that the role of the Qilian Mountains is that the convective cloud clusters moving from north to south have climbed from the north side of the mountains to the south since 16:00, the vertical speed has been strengthened, the cloud clusters have grown and expanded, and they jumped onto the mountains as a whole at 20:00,The convective cloud cluster on the southern slope developed to the strongest after dissolving and converging with the southern slope, and began to decline southward at 21:00. The cloud system dissipated and weakened, and the cloud top collapsed significantly.[4]
On August 14, 2008, a local rainstorm in the form of thunderstorm clusters occurred in Beijing. The location of thunderstorm regeneration is complex and changeable, forming multiple γ mesoscale heavy rainfall centers. Thunderstorms in the surrounding areas of Beijing flow along the valley terrain or towards the plain area through the outflow of thunderstorm cold pools, forming a convergence lifting mechanism with the warm and humid air in the boundary layer of Beijing valleys or urban areas, triggering thunderstorm regeneration[5]
The release of unstable energy in the atmosphere is finally achieved through the role of the convection trigger mechanism, so the source of thunderstorms often appears in the occasions with the best conditions for the trigger mechanism.That is, in the weather system favorable for uplift and convergence, such as front, low pressure and convergence line, and in the geographical environment favorable for thermal and topographic uplift.Here, the source of thunderstorms is analyzed based on different geographical conditions.
Under the same conditions of water vapor and atmospheric stability, the thermal effect of mountains is more significant than that of plains, and they also have the effect of terrain uplift. The trigger force conditions are good, and they are most likely to become the source of thunderstorms.In particular, the mountains surrounded by plains, even if they are small in scope, can become the source of thunderstorms as long as they reach the isolated mountains with the same scale as the single thunderstorm.
Peak and knot
The valley wind circulation caused by thermal action converges from the foot of the mountain to the peak area in the daytime, which makes the peak area have a strong convection trigger mechanism.Especially in the mountain knot area, that is, a mountain area where several mountains like knots stretch out all around, the valley wind between the ridges is stronger, and the upward movement towards the mountain knot area is stronger, which is more conducive to the formation and development of thunderstorms.
Sunny slope
The sun facing slope has a large direct solar radiation angle, strong solar radiation and fast heating in the daytime, which is conducive to the development of convection and the formation of thunderstorms.In summer, the sunny slope of the high mountain above the snow line consumes heat and cools the air due to snow melting, while the lower part of the sunny slope rapidly heats up in the daytime. In this case, the cold air at the upper part slides and meets the warm air at the lower part, resulting in extremely unstable air on the slope surface and developing thunderstorms, even becoming a source of hail.
Windward slope
The warm and humid air flow climbs along the hillside. If the air mass is convective and unstable, thunderstorms will occur.summer,Nanling MountainsThat's why there are many thunderstorms on the windward slope of.In addition, when the cold front moves over the windward slope, the warm, wet and unstable air in front of the front is lifted by both the front and the terrain, and thunderstorms are most likely to develop or strengthen.
Leeward slope
The leeward slope area generally sinks, which is unfavorable to the development of thunderstorms, but under certain conditions, it can also become the source of thunderstorms.For example, when there is strong air flow across the mountains, gravity waves are often generated in the leeward slope area. The stronger the air flow, the longer the wavelength, the more unstable the gas layer, and the greater the amplitude.If the wavelength develops to the same scale as the thunderstorm monomer, and the gas layer is very unstable, thunderstorms can be developed in the ascending movement area of gravity waves, which are often parallel to mountains in a belt.On the other hand, when cold air flows from higher mountains into the leeward slope area, and the lower air in the leeward slope area is warm and wet, it will also aggravate the instability of the air column and form thunderstorms.[6]
Formation process of thunderstorm
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Thunderstorms are local storms accompanied by lightning, thunder and strong showers caused by strong cumulonimbus clouds.Lightning and thunder without precipitation are called dry thunderstorms.When thunderstorms pass through the country, meteorological elements and weather phenomena will change dramatically, such as sudden increase of pressure, sharp turn of wind direction, sharp increase of wind speed, sudden drop of temperature, and then heavy rain.Severe thunderstorms even bring hail, tornado and other serious disasters.Generally, thunderstorms accompanied only by showers are called ordinary thunderstorms, and thunderstorms accompanied by rainstorm, gale, hail, tornado and other severe disastrous weather phenomena are called strong thunderstorms.Both are formed by strongly developed cumulonimbus clouds, which are called thunderstorm clouds.A thunderstorm process is not just a thunderstorm cloud, but often consists of several or more thunderstorm cells at different stages of development.Although these thunderstorm cells are located in the same thunderstorm cloud, each cell has an independent intra cloud circulation, which has gone through the development stage (through the updraft in the cloud), the maturity stage (precipitation appears in the cloud and precipitation dragged downdraft) and the dissipation stage (downdraft in the cloud), and is in the process of metabolism of continuous regeneration and disappearance.Thunderstorm activity has certain regional and seasonal characteristics.According to statistics, thunderstorms occur more frequently at low latitudes than at mid latitudes, and more frequently at mid latitudes than at high latitudes.This is due to the high temperature and rainy weather at low latitudes all the year round. The air is warm and humid and unstable, which is easy to form thunderstorms.In the mid latitude summer half year, the temperature and humidity of the near surface atmosphere increase, and the atmospheric stratification instability increases. At the same time, there are frequent weather system activities, and the number of thunderstorms is also high.In high latitudes, the temperature is low, the humidity is low, the atmosphere is relatively stable, and thunderstorms rarely occur.In terms of the same latitude, the number of thunderstorms is generally more in mountainous areas than in plains, and more in inland areas than in coastal areas.Thunderstorms occur most frequently in summer, followed by spring and autumn, and rarely in winter except warm wetland areas.Thunderstorm movement is greatly affected by geographical conditions.In mountainous areas, thunderstorms often move along the mountains because they are blocked by mountains. If the mountains are not high, powerful thunderstorms can cross the mountains.In coastal, river and lake areas, due to the low water surface temperature in the daytime, local downdraft often occurs, which weakens or even disappears the intensity of thunderstorms. Some weaker thunderstorms often cannot cross the water surface and move along the coast, but at night, thunderstorms may increase.[7]
characteristic
There are three kinds of thunderstorms, namely single thunderstorm, multi single thunderstorm and super single thunderstorm.
Thunderstorm weather
The method to distinguish them is based on the instability of the atmosphere and the relative wind speed at different levels (seewind shear）。
Single cellstorms
It occurs when the atmosphere is unstable, but there is little or no wind shear.These thunderstorms are usually relatively short and will not last for more than 1 hour.There are also many opportunities to see such thunderstorms on weekdays, so they are also called array thunderstorms.
Multicellstorms
It is composed of several single thunderstorms and is the further development of single thunderstorms.At this time, a gust belt will be formed due to the flow of air flow. This gust belt can last for several miles. If the wind speed increases, the atmospheric pressure increases and the temperature drops, the gust belt will become larger and larger, and will hit a larger area.
Supercellstorms
It occurs when the wind shear is extremely great and is composed of thunderstorms of various degrees.This kind of thunderstorm is the most destructive, and it is 30% possible to producetornado。
According to different atmospheric and topographic conditions when thunderstorms are formed, thunderstorms are generally divided intoThermal thunderstorm、Frontal thunderstormandTopographic thunderstormThree categories.In addition, some people also classify thunderstorms that occur in winter into one category, called winter thunderstorms.In the south of China, there are also frequent occurrences of so-called drought thunderstorms, also known asDry thunderstorm。
energy
ThunderstormenergyIt is very big. It is emitted by lightning of a few thousandths to ten tenths of a secondelectric energyIt can reach billions to hundreds of billions of watts, and the temperature is 10000~20000 degrees Celsius.Of course, thunderstorms can also benefit mankind. They can bring a lot of rain to the earth;Lightning struck air can produce hundreds of millions of tons of nitrogen fertilizer every year, which can seep into the land with rain.Of course, we must not forget that thunderstorms are extremely destructive.Strength standard is used habitually“Thunderstorm day”That is to say, the intensity of lightning activity in the region is indicated by the number of days in the year when thunder can be heard.
Hazards of terrain thunderstorms
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Although thunderstorm is a kind of strong weather, its duration is generally short, and the life history of a single thunderstorm generally does not exceed 2 hours.Thunderstorms usually occur in the afternoon. At night, the temperature stratification in the cloud layer becomes unstable due to the radiation cooling of the cloud top, which can also cause thunderstorms, called night thunderstorms.Thunderstorm is a discharge phenomenon in the atmosphere, usually accompanied by showers, sometimes there will be local strong wind, hail and other strong convection weather.Severe thunderstorm weather sometimes brings disasters, so it is a dangerous weather phenomenon. It will not only affect the flight safety of aircraft and interfere with radio communication, but also destroy buildings, power transmission and communication lines, electric locomotives, kill people and animals, and cause fires.
Thunderstorms can produce lightning strikes and hail attacks that do great harm to aircraft. The interference of its powerful electric field often causes the failure or even burning of airborne electronic equipment;Due to the strong vertical movement in the thunderstorm cloud, the aircraft is severely bumped;Thunderstorm clouds contain a large number of supercooled water droplets, so strong icing often occurs when flying above them. Thunderstorm not only seriously harms aircraft flying in the clouds, but also brings with it weather phenomena such as downburst, torrential rain, low cloud fragmentation, and low visibility, which also pose a serious threat to under cloud flight and flight takeoff and landing.The strong shower reduces the flight visibility and changes the aerodynamic performance of the aircraft, evenairplane engineFlameout;Strong gusts make it difficult to control the aircraft;Downburst, on the other hand, often causes catastrophic flight accidents during the takeoff and landing of aircraft.
matters needing attention
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1. Stay indoors.People working outdoors should hide in the building.
2. Do not swim or engage in other water sports.Get out of the water and find a place to hide.
3. Avoid using telephones or other appliances with plugs, including computers.
4. Do not touch the antenna, faucet, water pipe, wire mesh or other similar metal devices.
5. Avoid showering with a shower.
6. Do not handle flammable materials contained in open containers.Do not stand on the top of a mountain or near objects with high conductivity.Trees or masts are easy to be struck by lightning and should be kept as far away as possible.After lightning strikes an object, the current will spread through the ground, so don't lie on the ground, especially on wet ground.You should squat down and minimize the area of contact with the ground.
7. Hikers and other outdoor activities should take their radios with them and keep an eye on the latest weather information sent by the meteorological observatory.
8. Pay attention to the possibility of rainstorm at any time. Do not stay in rivers, streams or low-lying areas.
9. Motorists should be aware of strong gusts when driving on expressways or overpasses.
10. Small craft at sea should be careful against strong wind orWaterspouta surprise attack.
11. In case of tornado, hide in a solid building immediately.Keep away from windows, crouch on the ground and protect your head with hands or thick pads.If you are outdoors, keep away from trees, cars or other objects that can be blown up by tornadoes.
