thunderstorm

The title of this article is ambiguous. Further meanings are listed under Thunderstorm (disambiguation) .

A thunderstorm is a complex meteorological phenomenon associated with air-electric discharges ( lightning and thunder ) . On average, occur on the earth in 1600 thunderstorms around the same time, which take place at about 0.3 percent of the Earth's surface.

Left: "Thunderstorm" , symbol for weather forecast maps right: "Light or moderate thunderstorm with sleet or hail at the time of observation" , symbol for analytical weather maps

Thunderstorms are usually accompanied by heavy torrential rain or hail showers. In front of a storm front, gusty winds blow up to storm strength . Less common side effects are tornadoes and downbursts . Strong thunderstorms can also be referred to as thunderstorms . Summer thunderstorms occur much more frequently than winter thunderstorms, which can also be associated with heavy snow showers .

A large thundercloud (also called cumulonimbus ) builds up into the higher, colder troposphere as a result of rising, moist, warm air masses . Such ascending air currents form when a higher temperature is reached in a limited area than in the immediate vicinity (e.g. as a result of solar radiation or different heat dissipation from the subsoil, as in the case of bodies of water, fields and forest areas or heat release through condensation ).

Thunderstorm over the sea, Garajau, Madeira

Thunder and rain (audio recording)

Thunderstorm in South Hesse

Thunderstorm in the Kalahari near Stampriet , Namibia

Emergence

Extreme light conditions before a thunderstorm

Right under storm clouds; a few minutes before the thunderstorm

Three factors are required for thunderstorms to occur:

• Unstable stratification of the troposphere (sufficient temperature decrease with altitude)
• Air humidity in the air layer close to the ground
• Trigger mechanism to uplift of air parcels and condensation leads

Storm cloud in the Heilbronn district

Approaching thunderstorm over Tiefenbach, Heilbronn

Conditions of origin

Supercell thunderstorm

Thunderstorms can occur when there is a sufficiently large vertical decrease in temperature in the atmosphere ; H. when the temperature decreases so much with increasing altitude that an air parcel becomes unstable due to condensation and rises (conditionally unstable stratification). For this, the temperature has to decrease by more than 0.65 K for every 100 meters of altitude. An ascending condensed air parcel cools down by approx. 0.65 K / 100 m ( humid adiabatic ascent ). Due to the released heat of condensation , however, it cools less quickly than the surrounding air. This makes it warmer and therefore lighter than the ambient air due to the decrease in density; a lift is generated. For this reason, a moist air layer close to the ground is necessary for the formation of a thunderstorm , which represents the energy supplier for the moisture convection via the latent heat and thus makes the thunderstorm possible in the first place. The latent heat is the energy hidden in water vapor that is released in the form of heat during condensation. The convective index , as a meteorological quantity, is one of many indicators for the thunderstorm tendency.

Even if the basic conditions (suitable temperature stratification and humidity close to the ground) for a thunderstorm are met, one does not necessarily have to arise. Only the uplift of warm, humid air at the floor triggers a thunderstorm. For this, factors such as wind and air pressure conditions , the topography and the air stratification are relevant. Since some of these factors are difficult to predict using predictive models and vary widely from place to place, thunderstorm forecasting is extremely difficult.

As researchers at the University of Karlsruhe found out, the severity of thunderstorms has increased on average over the long term, but not their frequency. This is particularly evident from the increase in hail storms .

Warning times

Thunderstorms usually form over a longer period of time on the Central European sea coasts. This corresponds to z. B. the language regulation of the British Maritime Weather Service for storm warnings: imminent ( imminent ) means within the next six hours, soon ( soon ) means within twelve hours and later ( later ) in the following time. The German sea weather report issues storm warnings for the next twelve hours.

A thunderstorm that is actually approaching or building can usually be recognized early on by the dark and threatening clouds on the coast and inland. In contrast, in the Alps and in the foothills a thunderstorm within 10 to 15 minutes may occur literally "out of the blue", announcing at best in changes in air pressure, temperature and humidity, which usually without encoders only by locals senses are can.

Formation process of a thunderstorm cell

By raising a moist cool air packet initially trockenadiabatisch (1.0 K / 100 m), until its temperature, the dew point reached. From this temperature, the water vapor contained in the air package begins to condense and a swelling cloud forms , which, under suitable conditions, can eventually grow into a thundercloud, a so-called cumulonimbus (Cb for short). During the condensation process, energy stored in the water vapor ( latent heat ) is released in the form of heat, which increases the temperature. This reduces the density of the air parcel relative to the surroundings and it receives additional buoyancy. If there is a so-called conditionally unstable stratification of the atmosphere, the air parcel rises to a height where the temperature difference per height unit ( temperature gradient ) decreases again. This reduces the temperature and density difference compared to the ambient air. If the density of the air parcel finally equals the density of the surrounding air, the buoyancy force disappears and the rising air is slowed down. This level is called the equilibrium level and at this air mass boundary the cloud can spread horizontally. This creates its characteristic diapir-like anvil shape , which is why it is also called anvil cloud . Most of the time, this level of equilibrium is near the tropopause . In Central Europe this is between 8 km in winter and 12 km in summer. In the tropics , the tropopause is about 16 km above sea level. That is why the thunderstorms in the tropics are much higher than in our latitudes.

The kinetic energy that an air parcel receives during its ascent is also known as instability energy . The greater the instability energy, the higher the maximum updraft speed in the thundercloud. The intensity of thunderstorms is closely related to the instability energy present. Due to their inertia, the air parcels can shoot out of the equilibrium level (convective overshooting) similar to a fountain, and the higher the greater the instability energy and thus the speed of the updraft. Such overshooting tops can reach heights of over 20 km.

Schematic section through a thundercloud.

Precipitation formation

There are strong updrafts in the thundercloud , which may prevent smaller raindrops from falling down from the cloud. The raindrops and ice grains are then carried up again and again, where they freeze and new ice is deposited. This process is repeated until the grains of ice have become so heavy that they can no longer be held by the updrafts. Then either very thick, cold raindrops, sleet or even hailstones fall from the storm cloud onto the earth. The stronger the updrafts in the thundercloud, the bigger the hailstones can get. In the case of very large droplets of convective precipitation ( heavy rain ), in the warm season or in the tropics it is mostly a matter of melted hailstones.

Flash formation

lightning

→ Main article : Lightning

The lightning occurs due to the high vertical wind speeds that can only occur within thunderclouds. Another condition for the formation of lightning are ice crystals within the thundercloud. Due to their size, ice crystals transport different charges and lead to further charge separation at the interfaces between up and down currents. The lightning discharge ultimately ensures that the electrical voltage that has built up is reduced .

Dry storm

If there is no precipitation on the ground during a thunderstorm, one speaks of a dry thunderstorm. This happens when all the rain evaporates in a very dry air mass between the cloud base and the ground. The risk of fire is particularly high because the rain does not have a fire-retardant effect. Major fires in the Portuguese mountain forests in the summer of 2017 have been linked to dry thunderstorms. Dry thunderstorms are rare in Germany.

Types of thunderstorm cells

Mushroom- or anvil-shaped thunderstorm cell

A thunderstorm cell is the smallest self-contained unit from which a thunderstorm can be built. It always goes through three stages, a growth stage , a maturity stage and a decay stage . A thunderstorm cell is made up of a cumulonimbus cloud in which updrafts and downdrafts occur. Often several thunderstorm cells join together and form larger, coherent units of thunderstorms.

Single cell thunderstorm

The single cell is a single thunderstorm cell. It is the smallest possible self-contained form in which a thunderstorm can occur. Their lifespan is between 30 minutes and an hour. It occurs with weak wind shear , that is, when the wind increases only insignificantly with height. Mostly single cells cause relatively weak thunderstorms.

Life cycle of a thunderstorm cell

The single cell goes through three stages:

• Growth stage: In this phase there is only an updraft. This is generated by the release of instability energy. First a cumulus congestus forms. When the cloud freezes in the upper parts, a cumulonimbus, the actual thundercloud, is created. There are still no downdrafts and no precipitation falls from the cloud. In rare cases, however, weak tornadoes can occur.
• Maturity stage: in this stage there are both updrafts and downdrafts. The downdraft is formed by falling precipitation, which transports cold air down from higher layers. Because of the weak wind shear, the updraft and downdraft cannot separate. Precipitation also falls back into the updraft, weakening it. Precipitation sets in on the ground in the form of rain, sleet or small hail . At first, weak tornadoes can occur. Most of the time, the intensity of precipitation is highest at the beginning of the ripening phase. Occasional gusts occur on the ground. Almost all lightning occurs during this phase.
• Decay or dissolution stage: In this phase there is only a downturn. The cell rains out. The cumulonimbus cloud dissolves. The icy cloud cover ( cirrus or cirrostratus cumulonimbogenitus) can persist for a long time.

Impulse thunderstorm

A special form of the single cell is an impulse thunderstorm that occurs when there is a lot of instability energy with little wind shear. An impulse thunderstorm is more powerful than a normal single cell and can cause weak tornadoes, powerful downbursts and hail.

Isolated single cells are rare. Usually several thunderstorm cells occur next to each other, so-called multi-cell thunderstorms.

Supercell thunderstorm

• Formation of a mesocyclone
• 

  Stage 1: Wind shear from different directions (red arrows) lead to a horizontal rotation of the air masses (green spiral)

• 

  Stage 2: As the air masses rotate (green spiral), the rotating column of air begins to straighten up (blue arrow)

• 

  Stage 3: The upright rotating column of air (green spiral) in turn sucks new air into the column of air, which is then reinforced (blue spiral)

Schematic representation of a super cell with a tornado

Super cell

Super cell with tornado formation from space

In supercell is a special form of single cells, which are excellent in organized structure by its high degree. They can also be embedded in a cell cluster or a gust line.

An essential feature of a super cell is a deep, persistent rotation of the updraft area, the so-called mesocyclone . High means that at least a third of the updrafts rotate; Persistent means that the rotation lasts at least as long as a convection cycle. This is usually around 10 to 20 minutes, but by definition there must be at least 30 minutes of rotation in order to be considered a supercell. The cyclonic rotation predominates : counterclockwise in the northern hemisphere and the other way round in the southern hemisphere.

The cause is vertical wind shear , i.e. a change in wind speed and direction with altitude. Most of the time, the wind increases with altitude while turning right. The Coriolis force has no direct influence on this, as mesocyclones are too small. However, it plays an indirect role insofar as the large-scale wind field in which the mesocyclone is embedded is determined by the Coriolis force - in addition to pressure gradient , centrifugal force and ground friction. The mentioned clockwise rotation of the wind with height is such an effect.

In addition to the presence of a mesocyclone, other characteristics of a super cell are the spatial separation of the upwelling and downwash areas. The updraft is inclined due to the vertical increase in speed, mostly in the direction of the wind at a medium-high level (approx. 5 km). The precipitation falling in the downwash area does not disturb the supply of warm, moist air into the updraft area due to its evaporative cooling .

A distinction is made between three types of supercells based on the intensity of precipitation:

• LP supercell ( English low precipitation supercell ) - here the precipitation field is mostly small and limited to the cell nucleus. However, there can be very large hail, while tornadoes rarely occur. This type occurs frequently in the western Great Plains of the USA on the border of warm, humid air from the Gulf of Mexico and hot, dry desert air from the southwest of the USA. It is quite rare in Central Europe.
• Classic supercell ( English classic supercell ) - the most common and typical form of supercells. The precipitate field is more extensive than in the previous case and the nucleus with the strongest rainfall (heavy rain and hail) wound generally hook-shaped at the mesocyclone ( hook echo or engl. Hook echo ). Tornadoes occur much more frequently with this type than with the LP supercell.
• HP supercell ( English high precipitation supercell ) - the precipitation intensive form of supercells. The precipitation field is very extensive and there is heavy rain or hail over a fairly large area. The nucleus with the most intense precipitation often has a kidney-shaped structure. The precipitation area largely encloses the mesocyclones and thus sometimes obscures the view of a possible tornado ( bear's cage ). This wrapped rain ( rain-wrapped ) tornadoes are especially dangerous and responsible for most deaths in the United States.

In addition, there is the special form of flat supercells ( low-topped supercell, mini supercell ) with a lower elevation, but with persistent mesocyclones. These usually occur in cold air masses. It is also important that a super cell does not have to show any electrical activity ( lightning ), even if most of the super cells not only appear as showers but also as thunderstorms.

The differences between a super cell and a normal cell:

• A super cell is generally much more durable, sometimes lasting several hours. Their spatial expansion can be considerable, but is not necessarily larger than that of a single or multi-cell.
• The pulling direction of supercells mostly shows a pulling out to the right (in the southern hemisphere to the left) compared to the controlling wind in the middle level of the troposphere, which determines the pulling direction of normal thunderstorm cells.
• Significantly more intense weather phenomena and cloud forms and also special cloud shapes occur. This includes above all the so-called wall cloud, which appears as a lowering of the rain-free cloud base under the rotating updraft.
• The intense side effects make super cells the most dangerous type of thunderstorm cells. They are often accompanied by downpours , large hail over 4 cm in diameter and heavy gusts ( downbursts ). Mesocyclonal tornadoes form in around 10–20% of all supercells .

For a long time, with a few exceptions, supercells were limited to the USA (according to the latest findings there are several thousand per year here), but it has now been shown that they can occur in many areas of the world (including the tropics) under suitable conditions.

The number of rotating storms is probably around 5% of the total number of thunderstorms (studies from the USA and Central Europe), but the attempt to include all annual supercells in a statistical analysis is currently only known from Austria (a little more on average from 2003 to 2005 registered as 50 rotating thunderstorms annually).

Almost all very strong or devastating tornadoes (F3 and above on the Fujita scale ) arise from supercells or the associated mesocyclones. Weaker tornadoes (F0 to F2) can be of both mesocyclonic and non-mesocyclonic origins. Depending on the region, the latter type predominates here.

Supercells can only be clearly identified by means of the rotation (TVS, Tornado Vortex Signature ) , which is also visible during the Doppler velocity scan in the weather radar .

• Details of super cells
• 

  Thundercloud (super cell) of a strong hailstorm on Lake Constance , at least the middle cloud top with pileus formation

• 

  Underside of a super cell

• 

  The gust roller of a super cell

• 

  Storm cloud over Enschede , the Netherlands with a pronounced shelf cloud

Multi-cell thunderstorm

Multi-cell over the Black Forest with two trained anvils

A multicell consists of several individual thunderstorm cells that are relatively close together and interact with each other. The cells can be in different stages of development. With the multicell, the downdraft of a thunderstorm cell creates a new cell. Although the life of a cell within the complex is no longer than that of an isolated single cell, the whole system can exist for significantly longer than an hour. The thunderstorm cells either occur in groups ( multicell clusters ) or are arranged along a multicell line .

Multi-cell line

The thunderstorm cells can be arranged in lines. These thunderstorm lines can be several 100 km long. They are also known as squall lines , as strong storm winds often occur on the front of them. This gust front ensures that new thunderstorm cells are constantly created, replacing the old ones. This happens because the cooler and heavier air that forms under the thunderstorms pushes itself in front of the thunderstorm line. There, the warm and humid and thus high-energy air mass is raised, creating a new cell. This process continues as long as the air at the front is unstably stratified and sufficiently moist.

Derecho

In a Derecho ( [[IPA | [ d ə r eɪ tʃ oʊ ]]] from Spanish derecho ) is an elongated, durable squall line that spreads strong storm winds ( downbursts caused). In order to do justice to the definition of a derecho, it must be effective over a length of at least 450 km and repeatedly produce heavy gusts of wind over 93 km / h.

In August 2020, a derecho wiped out over 40% of Iowa's crops .

Multicell cluster

Thunderstorm cells can group themselves into so-called clusters, which as a whole have a longer lifespan. Clusters appear in the satellite image as collections of round or oval point clouds, with the points representing the individual cells.

• Mesoscale Convective System (MCS): An MCS is a complex of several thunderstorm cells that are organized on a larger scale than a single thunderstorm cell. An MCS has a lifespan of several hours. The MCS can be round or oval when viewed from above. It can also occur within tropical cyclones , thunderstorm lines, and MCCs.
• Mesoscale Convective Complex (MCC): An MCC is a large MCS that is usually round or slightly oval in shape. It usually reaches its greatest intensity during the night. An MCC is defined by its size, service life and eccentricity (also roundness ), based on the cloud screen that can be observed on the satellite image :
  • Size: The temperature of the top of the cloud must be −32 ° C or less over an area of ​​at least 100,000 km². The temperature of the top of the cloud must be −52 ° C or less over an area of ​​at least 50,000 km².
  • Lifespan: The size criterion must be met for at least 6 hours.
  • Eccentricity: The ratio between the shortest and longest axis must not be less than 0.7.
• Mesoscale Convective Vortex (MCV): An MCV is a large mesocyclone of an MCS. After an MCS has resolved, "his" MCV can survive for up to 2 days and is not infrequently the source of the next thunderstorm outbreak. When an MCV moves into tropical waters, it can become the core of a tropical storm or hurricane.

Classification of thunderstorms

Thunderstorm frequency: global lightning distribution (lightning per year per km²; impacts & cloud-cloud; without secondary lightning)

The formation of deep convective clouds and thunderstorms requires, in addition to a conditionally unstable stratification to trigger the moisture convection, an uplift drive. With regard to the trigger mechanisms, different types of thunderstorms can be distinguished.

Air mass thunderstorms

Air mass thunderstorms occur in a uniform air mass , i. H. the temperature hardly changes in the horizontal direction. However, the temperature must decrease sufficiently with height and there must be a heating mechanism close to the ground (one speaks of thermal triggering of the thunderstorm). A distinction is made between two main types of air mass thunderstorms: heat thunderstorms and winter thunderstorms.

Heat thunderstorms

Heat thunderstorms (also called summer thunderstorms or convection thunderstorms ) occur in Central Europe almost exclusively in the summer months. The strong solar radiation heats the air above all near the ground and also allows a lot of water to evaporate through evapotranspiration . This increases the vertical temperature gradient over the course of the day. The temperature rises sharply, especially on the ground, while it remains almost constant at altitude. From a certain temperature ( trigger temperature ), warm air bubbles begin to rise, as they are warmer and therefore lighter than the air around them. They cool down and finally reach the condensation level. If the atmosphere is stratified above it with unstable moisture, thermal thunderstorms are triggered in this way. Heat thunderstorms mostly occur in the afternoon and evening hours.

Winter storm

Winter thunderstorms occur in the winter half-year. They are much rarer than heat thunderstorms in summer. In principle, their formation is the same as that of thermal thunderstorms. However, there is often insufficient sunlight in winter. Therefore, a high temperature gradient can only come about through strong cooling at altitude. This is done by supplying cold air at high altitude , which is mostly of polar origin. At sea, the moisture convection is triggered spontaneously and thermally independent of the time of day by the strong temperature gradient between the relatively warm sea surface and the relatively cold air above it. These air masses can be clearly recognized on satellite images by the cellular convective clouds. Over land, on the other hand, this mechanism recedes and a diurnal convection curve can be observed under the influence of the - albeit weak - irradiation. Winter thunderstorms are most common around noon and early afternoon. However, the air that is warmed up in the lower layers above the sea is often sufficiently unstable far into the interior to trigger convection. The most severe weather phenomena are in the coastal regions ( lake effect snow ) . Winter thunderstorms are often associated with strong sleet showers and snow showers . Since colder air contains less water vapor and is therefore less energetic, these thunderstorms are usually less intense than heat thunderstorms in summer. However, thunderstorms in the winter months can often lead to unexpectedly strong storms.

Front thunderstorm

Frontal thunderstorms are caused by dynamic uplift caused by the fronts. However, the basic conditions for thunderstorms must already be met before the front penetration. The front is only the trigger. Frontal thunderstorms occur primarily on the front of cold fronts . Only in rare cases can they occur on warm fronts . In this case, the atmosphere is labilized by the introduction of warm and humid air masses in the lower areas of the troposphere, and so-called warm air thunderstorms occur .

When a cold front draws in, the cold air is pushed like a wedge under the warm, moist air, which lifts it up. At a certain altitude, the water vapor condenses and cumulus clouds form , which, under suitable conditions, can eventually grow into thunderclouds. Such frontal thunderstorms can occur all year round, but are more frequent in summer than in winter and are usually more violent.

Prefrontal convergence

A special feature that occurs especially in the warm season are linearly arranged thunderstorms along convergences , which are often in front of a cold front and in this case are referred to as prefrontal convergences . In the area of ​​convergence, where wind currents from different directions flow together, there is not yet a change in air mass. The convergence is noticeable on the ground through a wind jump , which is caused by the convergent wind field. The trigger or lifting mechanism here is the air flowing together, which is forced to rise along the convergence. In winter, such convergences are usually not very active in terms of weather, while in summer the main thunderstorm activity is often found at the convergence and not at the subsequent cold front. Within cold air mass behind a cold front occurs along trough lines to raising events that Feuchtekonvektion and can also trigger thunderstorms. This mechanism can be observed at all times of the year, especially in winter, as this is when the dynamics of low pressure areas are most pronounced.

Orographic thunderstorms

Orographic thunderstorms are caused by uplift in mountains. If an air mass flows over a mountain range, it is inevitably lifted. It cools down and can condense out. A thundercloud can form under suitable conditions. Orographic thunderstorms can cause enormous amounts of rain in congested areas , as they may form over and over again in the same place.

Electrical phenomena

Lightning bolt in the night sky

A lightning bolt within the clouds

The electrostatic charge in the atmosphere in the vicinity of thunderstorms can lead to two different phenomena: earth lightning and Elmsfeuer . The latter can be observed especially on tall ship masts, church spiers or the cockpit window of aircraft and indicates an imminent lightning strike.

Biological phenomena

A particularly high number of people have asthma symptoms during thunderstorms . According to an Australian study from 2001, this is due to the fact that during a thunderstorm, pollen is first swirled upwards from the fields and then the gusts are pushed back down with the pollen. The rain can also break up the pollen grains, creating small particles that can penetrate the lungs. In Melbourne on November 27, 2016, six people died in such an "asthma thunderstorm". The storm had burst ryegrass pollen. 8500 people had to receive medical treatment.

The faster deterioration of food in thunderstorms, which is often observed, is due to the fact that heat and moisture before and during a thunderstorm provide ideal conditions for microorganisms to multiply.

hazards

→ Main article : Lightning

In some cases, strong thunderstorms harbor dangers such as B. Storm damage from downbursts or tornadoes , floods from heavy rain and damage from hail . Damage from lightning , such as short circuits , fires or even injuries, rarely occurs . Since the invention of the lightning rod , many buildings have been protected from lightning. However, there are still lightning strikes on farms (especially in the countryside), which then lead to major fires. Staying in the woods during a thunderstorm can be life-threatening. If the lightning strikes a tree, the water contained in it can suddenly evaporate due to the lightning energy and the tree burst.

The danger of a lightning strike still exists at some distance from the actual thunderstorm cell ; occasionally lightning strikes from drizzle without previously audible and visible thunderstorms are reported. Cloud-ground lightning can even cover very large distances of 32 kilometers and more. That is why you should not stay near metal objects when thunderstorms are reported, including wire rope protection on via ferratas in the mountains.

Rules of conduct when staying outdoors during a thunderstorm

To minimize the likelihood of being injured by lightning, the following must be observed:

• Seek protection in buildings or vehicles. Vehicles with a closed metal body and many buildings with a lightning protection system work in good approximation like a Faraday cage and thus offer protection from high electrical field strengths inside.
• If protection cannot be found in buildings or vehicles:
  • In order not to be struck directly by lightning:
    • Avoid staying in open terrain as well as on hills and ridges.
    • Avoid standing in water and swimming pools.
    • To keep the step tension low in the event of a lightning strike nearby : put your feet together, crouch, hold your arms against your body and draw your head. Do not lay flat on the floor, rubber soles and insulating materials are advantageous as standing surfaces.
  • In order not to be affected by secondary effects:
    • Avoid the immediate vicinity of trees, masts and towers. Lightning strikes particularly often in tall objects, especially when they are free. If the base area of ​​the object is small, the potential difference of the ground in its immediate vicinity is particularly large and the possible step voltage is therefore particularly high. If the conductivity of the object is limited, as is the case with trees, for example, there is a risk of parts being thrown off and the lightning escaping close to the ground.
    • Avoid cave entrances and narrow hollows (furrows, gullies or ditches). It is better to crouch on level terrain with your feet together or go deeper into the cave (but be careful: Inside the cave there is a risk of sudden and strong water rise due to heavy precipitation). After an impact, the lightning initially spreads near the surface of the ground, which it may not be able to follow at cave entrances and narrow hollows. Then a secondary lightning bolt jumps over, which can hit those seeking protection.

Safety depends on foresighted behavior: A thunderstorm never comes “out of the blue”, except in the Alps and in the Alpine foothills; If you regularly take a look at the sky, you can recognize an approaching thunderstorm early on by the dark and threatening clouds. If the thunderstorm is noticed, the safest accessible refuge should be sought, depending on its distance and speed. Using the time difference between lightning ( speed of light ) and thunder ( speed of sound , approx. 340 m / s), the distance of the lightning can be calculated: ${\displaystyle t}$ ${\displaystyle c_{\text{S}}}$ ${\displaystyle d}$

${\displaystyle d=c_{\text{S}}\cdot t}$

By repeating the calculation, the direction and speed of movement of the thunderstorm can be estimated: every second that the distance between lightning and thunder becomes shorter, it comes 340 m closer. Less than 6 seconds between lightning and thunder, i.e. less than approx. 2 km away, there is always the possibility of an impact in the vicinity.

The distance of the lightning can be estimated using the following rule of thumb:

${\displaystyle {\text{Entfernung [in Kilometern]}}\approx {\frac {\text{Zeit [in Sekunden] zwischen Blitz und Donner}}{3}}}$

An old German proverb is life- threatening :

You shall give way to the oaks .

And you should avoid the pastures .

Do not flee to the pine trees ,

You shall find linden trees

But you have to look for the beeches !

One reading assumes that earlier low growths (bushes) were called "Bucken" in German. So you should rather hit the bushes than stand next to a tree. Another reading is based on the observation that beech trees are less likely to be blown up by lightning. This is not because they would not be hit, but because of their smooth bark, which becomes wet over a large area during a thunderstorm and then forms a natural lightning rod that prevents lightning from going through the inside of the tree.

Behavior in buildings during a thunderstorm

Inside a building, there may be hazards from cables coming in from outside (including power lines or water pipes). However , these can be avoided by proper earthing in the form of a main equipotential bonding . It is only in buildings without this prescribed lightning protection that you should therefore avoid showering, bathing or handling electrical devices during thunderstorms, as this can be life-threatening. Telephones can pose a further danger here, especially if the telephone line is routed to the house above ground. If possible, phone calls should not be made with corded landline telephones. If lightning strikes the line, the telephone receiver in hand provides a good connection to earth. Cordless telephones are not dangerous due to their construction.

The general rule is that you should not use elevators during a thunderstorm so as not to get stuck in the event of a power failure.

Operation of vehicles during a thunderstorm

The interior of all vehicles with a closed metal body (land vehicles, aircraft, ships) is a Faraday cage in which there is no direct risk of lightning strikes. Open windows do not impair the protection of the vehicle itself. In tests in high-voltage laboratories, traces of fire were found on the paintwork and across the tire sidewalls. According to unproven suspicions, secondary damage from a lightning strike could also affect the occupants.

• Fire of combustible parts on the outside such as B. tires, grille, bumpers
• Defect in the on-board electronics and all electronic devices in the car (air ionization)
• Defect of important devices for controlling the vehicle (brakes, steering)

If there is a risk of a lightning strike, the driving speed should be reduced in order to be able to stop immediately if the on-board electronics fail or if your driving ability is restricted. However, since thunderstorms are often accompanied by hail and heavy downpours, a reduced driving speed is recommended anyway. On motorways, even during a thunderstorm, you may only park on the hard shoulder with the hazard warning lights switched on.

Ships made of metal (all-metal structures) offer the best protection inside; staying on deck during a thunderstorm should be avoided. As with land vehicles, windows and doors should be kept closed and contact with metallic objects should be avoided. Boats made of plastic or wood, on the other hand, offer little or no protection, unless there is an integrated and continuous wire mesh in the cabin and hull, or the boat has its own lightning rod.

Aircraft and helicopters made of metal offer good protection if they are closed all round and have tested lightning protection devices. Due to the use of modern composite materials in aircraft, there are always complications because they are not or only weakly conductive. As a result, a lightning strike can leave so-called burn marks on the outer skin of the aircraft. For this reason, more lightning protection systems for aircraft are constantly being developed. With a few exceptional cases in the past, lightning strikes have no lasting effects on the serviceability of today's commercial aircraft. Nevertheless, thunderstorms are flown around in almost all cases, because the aircraft structure and the passengers want to be protected from turbulence and damage to the outer shell by hailstones is to be avoided. Smaller aircraft generally avoid thunderstorms, especially since, apart from the risk of lightning strikes, they are not designed for the strong winds that occur in and around thunderstorm cells.

See also

• ALDIS : Austrian Lightning Detection & Information System
• BLIDS : Lightning information service from Siemens (lightning detection for D, CH, BeNeLux, GB and PL)
• The frequency of thunderstorms in an area is in meteorology as keraunic level indicated
• William Rankin is the only known person who survived a fall from a cumulonimbus storm cloud

literature

• Rainer Grießbach: Forces of nature - the thunderstorm . epubli, Berlin 2012, ISBN 978-3-8442-2145-9

media

• 100 million volts - inferno in the sky

Web links

Wiktionary: Thunderstorm  - explanations of meanings, word origins, synonyms, translations

Wikiquote: Thunderstorm  Quotes

Commons : Thunderstorm  - Album with pictures, videos and audio files

• skywarn.de: Forecasting Severe Thunderstorms - A Guide ( Memento from September 3, 2011 in the Internet Archive )
• Characteristics and formation of thunderstorms - knowledge platform Earth and Environment ESKP
• Thunderstorm Radar - Current thunderstorm cells and earth lightning, shown on a map

Individual evidence

1. ↑ The Brockhaus. Weather and climate . Page 117, Brockhaus, Leipzig / Mannheim 2009, ISBN 978-3-7653-3381-1
2. ↑ Weather chaos: Europe in a storm. In: Frankfurter Rundschau. Retrieved June 4, 2017 . 
3. ↑ Marine forecasts glossary of the UK Met Office
4. ↑ Sea weather report for the North and Baltic Seas. German Weather Service
5. ^ Ildiko Holderer, How thunderstorms arise without rain , WDR, June 19, 2017.
6. ^ Deutscher Wetterdienst Wetterlexikon: Blitz , accessed on July 7, 2017.
7. ↑ Dry thunderstorms could have triggered a devastating fire , Die Welt, June 19, 2017
8. ^ Deutscher Wetterdienst Wetterlexikon: Gewitter , accessed on July 7, 2017.
9. ↑ https://www.washingtonpost.com/weather/2020/08/12/iowa-derecho-corn-damage/
10. ↑ Houze, RA, Jr. (2004): Mesoscale convective systems. In: Rev. Geophys. 42: RG4003
11. ↑ http://cimss.ssec.wisc.edu/goes/misc/970708.html
12. ↑ Alexander Stahr, air mass thunderstorms , Wissen.de, accessed on 25 July 2017th
13. ↑ Heat thunderstorm - Wetterlexikon , Wetter Online, accessed on July 25, 2017.
14. ↑ Thomas Sävert, Why are there thunderstorms in winter too? Kachelmann Weather, November 18, 2016.
15. ↑ Why thunderstorms take your breath away. In: Spiegel Online , May 23, 2001.
16. ↑ Six people die after an asthma thunderstorm. ( Memento from November 27, 2016 in the Internet Archive ) In: Deutschlandfunk , November 27, 2016.
17. ^ US National Weather Service Caribou, Lightning Obliterates Tree in Saratoga Springs, NY , June 7, 2014, accessed July 7, 2017.
18. ↑ Meteorologists measure longest lightning. In: Spiegel online . 19th September 2016.
19. ↑ Merle Sievers, Wrath of the Gods - Behavior in thunderstorms . Süddeutsche Zeitung, July 29, 2013, accessed on July 7, 2017.
20. ↑ Andreas Kohler, Behavior in thunderstorms . Planet Wissen, April 5, 2017, accessed July 7, 2017.
21. ↑ VDE lightning protection and lightning research: Are caves a safe place during thunderstorms? June 13, 2014, accessed July 7, 2017.
22. ↑ Gerhard Lux, caution high voltage  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.   , German Weather Service 2016, accessed on July 7, 2017.
23. ↑ Calculate distance from thunderstorm + formula + behavior. Retrieved on May 27, 2018 (German). 
24. ↑ Christoph Drösser, right ? - Don't look for a book! , The TIME No. 17 1998.
25. ↑ VDI, Lightning Protection in Buildings , July 18, 2013.
26. ↑ BVS - Fire Prevention Center for Upper Austria, fire control for passenger elevators  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.   , Leaflet, March 15, 2006.
27. ^ ADAC, Safety even in the event of a lightning strike , July 3, 2015.
28. ↑ Sportbootfuehrerschein.de Thunderstorm at Sea , March 6, 2008.
29. ↑ Nikolaus Braun Is a thunderstorm dangerous for an airplane? , airliners.de, December 1, 2015.

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