Thunderstorm

Thunderstorm
Thunderstorm over Corfu.jpg
A thunderstorm over Corfu.
Area of occurrencePrimarily tropical and also temperate regions.
SeasonMost common in spring and summer.
EffectDepends on the storm, may involve rain, hail, and/or high winds. May cause flooding or fires.
A typical thunderstorm over a field

A thunderstorm, also known as an electrical storm, lightning storm, or thundershower, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder.[1] Thunderstorms occur in a type of cloud known as a cumulonimbus. They are usually accompanied by strong winds, heavy rain, and sometimes snow, sleet, hail, or, in contrast, no precipitation at all. Thunderstorms may line up in a series or become a rainband, known as a squall line. Strong or severe thunderstorms include some of the most dangerous weather phenomena, including large hail, strong winds, and tornadoes. Some of the most persistent severe thunderstorms, known as supercells, rotate as do cyclones. While most thunderstorms move with the mean wind flow through the layer of the troposphere that they occupy, vertical wind shear sometimes causes a deviation in their course at a right angle to the wind shear direction.

Thunderstorms result from the rapid upward movement of warm, moist air, sometimes along a front. As the warm, moist air moves upward, it cools, condenses, and forms a cumulonimbus cloud that can reach heights of over 20 kilometres (12 mi). As the rising air reaches its dew point temperature, water vapor condenses into water droplets or ice, reducing pressure locally within the thunderstorm cell. Any precipitation falls the long distance through the clouds towards the Earth's surface. As the droplets fall, they collide with other droplets and become larger. The falling droplets create a downdraft as it pulls cold air with it, and this cold air spreads out at the Earth's surface, occasionally causing strong winds that are commonly associated with thunderstorms.

Thunderstorms can form and develop in any geographic location but most frequently within the mid-latitude, where warm, moist air from tropical latitudes collides with cooler air from polar latitudes.[2] Thunderstorms are responsible for the development and formation of many severe weather phenomena. Thunderstorms, and the phenomena that occur along with them, pose great hazards. Damage that results from thunderstorms is mainly inflicted by downburst winds, large hailstones, and flash flooding caused by heavy precipitation. Stronger thunderstorm cells are capable of producing tornadoes and waterspouts.

There are four types of thunderstorms: single-cell, multi-cell cluster, multi-cell lines, and supercells. Supercell thunderstorms are the strongest and most severe. Mesoscale convective systems formed by favorable vertical wind shear within the tropics and subtropics can be responsible for the development of hurricanes. Dry thunderstorms, with no precipitation, can cause the outbreak of wildfires from the heat generated from the cloud-to-ground lightning that accompanies them. Several means are used to study thunderstorms: weather radar, weather stations, and video photography. Past civilizations held various myths concerning thunderstorms and their development as late as the 18th century. Beyond the Earth's atmosphere, thunderstorms have also been observed on the planets of Jupiter, Saturn, Neptune, and, probably, Venus.

Life cycle

Stages of a thunderstorm's life.

Warm air has a lower density than cool air, so warmer air rises upwards and cooler air will settle at the bottom[3] (this effect can be seen with a hot air balloon).[4] Clouds form as relatively warmer air, carrying moisture, rises within cooler air. The moist air rises, and, as it does so, it cools and some of the water vapor in that rising air condenses.[5] When the moisture condenses, it releases energy known as latent heat of condensation, which allows the rising packet of air to cool less than the cooler surrounding air[6] continuing the cloud's ascension. If enough instability is present in the atmosphere, this process will continue long enough for cumulonimbus clouds to form and produce lightning and thunder. Meteorological indices such as convective available potential energy (CAPE) and the lifted index can be used to assist in determining potential upward vertical development of clouds.[7] Generally, thunderstorms require three conditions to form:

  1. Moisture
  2. An unstable airmass
  3. A lifting force (heat)

All thunderstorms, regardless of type, go through three stages: the developing stage, the mature stage, and the dissipation stage.[8] The average thunderstorm has a 24 km (15 mi) diameter. Depending on the conditions present in the atmosphere, each of these three stages take an average of 30 minutes.[9]

Developing stage

The first stage of a thunderstorm is the cumulus stage or developing stage. During this stage, masses of moisture are lifted upwards into the atmosphere. The trigger for this lift can be solar illumination, where the heating of the ground produces thermals, or where two winds converge forcing air upwards, or where winds blow over terrain of increasing elevation. The moisture carried upward cools into liquid drops of water due to lower temperatures at high altitude, which appear as cumulus clouds. As the water vapor condenses into liquid, latent heat is released, which warms the air, causing it to become less dense than the surrounding, drier air. The air tends to rise in an updraft through the process of convection (hence the term convective precipitation). This process creates a low-pressure zone within and beneath the forming thunderstorm. In a typical thunderstorm, approximately 500 million kilograms of water vapor are lifted into the Earth's atmosphere.[10]

Mature stage

Anvil-shaped thundercloud in the mature stage

In the mature stage of a thunderstorm, the warmed air continues to rise until it reaches an area of warmer air and can rise no farther. Often this 'cap' is the tropopause. The air is instead forced to spread out, giving the storm a characteristic anvil shape. The resulting cloud is called cumulonimbus incus. The water droplets coalesce into larger and heavier droplets and freeze to become ice particles. As these fall, they melt to become rain. If the updraft is strong enough, the droplets are held aloft long enough to become so large that they do not melt completely but fall as hail. While updrafts are still present, the falling rain drags the surrounding air with it, creating downdrafts as well. The simultaneous presence of both an updraft and a downdraft marks the mature stage of the storm and produces cumulonimbus clouds. During this stage, considerable internal turbulence can occur within, which manifests as strong winds, severe lightning, and even tornadoes.[11]

Typically, if there is little wind shear, the storm will rapidly enter the dissipating stage and 'rain itself out',[8] but, if there is sufficient change in wind speed or direction, the downdraft will be separated from the updraft, and the storm may become a supercell, where the mature stage can sustain itself for several hours.[12]

Dissipating stage

A thunderstorm in an environment with no winds to shear the storm or blow the anvil in any one direction

In the dissipation stage, the thunderstorm is dominated by the downdraft. If atmospheric conditions do not support super cellular development, this stage occurs rather quickly, approximately 20–30 minutes into the life of the thunderstorm. The downdraft will push down out of the thunderstorm, hit the ground and spread out. This phenomenon is known as a downburst. The cool air carried to the ground by the downdraft cuts off the inflow of the thunderstorm, the updraft disappears and the thunderstorm will dissipate. Thunderstorms in an atmosphere with virtually no vertical wind shear weaken as soon as they send out an outflow boundary in all directions, which then quickly cuts off its inflow of relatively warm, moist air, and kills the thunderstorm's further growth.[13] The downdraft hitting the ground creates an outflow boundary. This can cause downbursts, a potential hazardous condition for aircraft to fly through, as a substantial change in wind speed and direction occurs, resulting in a decrease of airspeed and the subsequent reduction in lift for the aircraft. The stronger the outflow boundary is, the stronger the resultant vertical wind shear becomes.[14]

Other Languages
Afrikaans: Donderstorm
العربية: عاصفة رعدية
aragonés: Tronada
asturianu: Nube eléctrica
বাংলা: বজ্রঝড়
башҡортса: Күк күкрәү
беларуская: Навальніца
беларуская (тарашкевіца)‎: Навальніца
čeština: Bouřka
Deutsch: Gewitter
eesti: Äike
Ελληνικά: Καταιγίδα
Esperanto: Fulmotondro
euskara: Trumoi-ekaitz
français: Orage
Frysk: Swierwaar
galego: Treboada
한국어: 뇌우
հայերեն: Ամպրոպ
हिन्दी: तड़ितझंझा
Bahasa Indonesia: Badai petir
íslenska: Þrumuveður
italiano: Temporale
ქართული: ჭექა-ქუხილი
қазақша: Найзағай
latviešu: Negaiss
Lëtzebuergesch: Donnerwieder
lietuvių: Perkūnija
lumbaart: Temporal
magyar: Zivatar
Bahasa Melayu: Ribut petir
မြန်မာဘာသာ: လေမုန်တိုင်း
Nederlands: Onweer
日本語: 雷雨
norsk: Tordenvær
norsk nynorsk: Torevêr
occitan: Auratge
Picard: Hernu
polski: Burza
português: Trovoada
Runa Simi: Tuyur
русский: Гроза
Simple English: Thunderstorm
slovenčina: Búrka
slovenščina: Nevihta
srpskohrvatski / српскохрватски: Grmljavinska oluja
suomi: Ukkonen
svenska: Åska
Türkçe: Oraj
українська: Гроза
Tiếng Việt: Dông
walon: Oraedje
吴语: 雷暴
žemaitėška: Perkūnėjė
中文: 雷暴