Where and when storms occur in France?
In most areas, thunderstorms occur most often during the months of June, July and August. The south-east of France is an exception: storms are often more numerous in September or in October and November for Corsica.
On the whole year, thunderstorms are more frequent in Corsica and southern Aquitaine. There are on average more than thirty days per year with thunderstorms. On the north of Aquitaine, Midi-Pyrenees, the relief of the Provence-Alpes-Cote d’Azur, Limousin, Auvergne, Rhone-Alpes, the south of Burgundy, Franche-Comte, l ‘Alsace and Lorraine, thunderstorms each year are also relatively high. On the rest of the country, they are less frequent, even on rare Brittany.
For the sole summer period (June-July-August), the distribution is a little different. In summer, thunderstorms are frequent and much more in Corsica than in the Parisian region. Especially on an axis Sud-ouest/Nord-est and the Alpine regions that are most frequent summer thunderstorms. There are generally each of these regions were fifteen to twenty days with thunderstorms. As for the whole year, it is in Britain they are increasingly rare in summer, with an average of less than five days with storms.
The dangers associated with thunderstorms
A storm may be hazardous to a given point, because of the power it produces phenomena and their randomness.
Lightning is the name given to a flashpoint when it affects the soil (or aircraft). This intense electric shock can kill a man or an animal, a tree or calcine cause fires.
The heavy rains accompanying the storms can cause devastating flash floods. An audience of 1 km wide and 10 km in height contains 1 million liters of water. A storm dumped more frequently from 50 to 100 liters of water per square meter in a few hours. In September 1992, 400 to 500 liters of water had fallen on Vaison-la-Romaine.
Hail is a type of precipitation composed of small pieces of ice, which can devastate example in a few minutes a vineyard or an orchard.
The wind blows in a cumulonimbus by violent gusts up to about 140 km / h and frequently change direction. More rarely are created under the cloud base a whirl wind very devastating tornado.
Pilots, even large aircraft, avoid cross cumulonimbus they could be raised several hundred meters, then suddenly folded in what is commonly called the “air holes.”
Lighting explained
Since the dawn of humanity, man is fascinated by lightning. He attributed the phenomenon then stormy mythical dimension which reflected the anger of the gods.
Since the twentieth century that the study of lightning has become a science. It was then discovered that thunderstorms are essential to life, they maintain the electric fields of our planet.
Since the mid-twentieth century to today, the development of transport and distribution of energy, information technology and electronics motivates serious research on protection against lightning and thus the phenomenon it own.
Lightning Facts and figures:
- An average of 1 000 000 lightning strikes per year (source METEORAGE)
- – The annual cost of damage caused by lightning are estimated in billions of francs
- Between 8 and 15 deaths per year (source Association. Protection. Lightning)
- 20 000 animals foudroyés
- 20 000 claims due to lightning fires, including 15 000
- 50 000 electricity meters destroyed
- 250 bells destroyed
Physical phenomenon
Although one could observe lightning in storms of sand, snow or in the pyroclastic flows of volcanic eruptions, the main generator is the cumulonimbus storm clouds.
This cloud is growing in altitude to over 10 km and its base, which is about 2 to 3 kilometers above the ground, occupies several tens of square kilometers. It is home to very strong winds ascending and descending, causing the collision of ice particles, water surfondue involved. This is the friction between the particles resulting in electrifying the cloud and the separation of charges. The heavier particles (water drops) are negatively charged at the bottom of the cloud, while the lighter particles (ice crystals) are positively charged at the top of the cloud. Sometimes an island of positive charges is contained in the negative ground.
Under the influence of negative charges is located at the bottom of the cloud, the atmospheric electric field on the ground usually around 100 volts / meter reverses and reaches values of about -15 to -20 kV / m: The potential difference between the cloud and the ground is such that the discharge is imminent.
There are two types of lightning, the intra (or inter-cloud) that the discharge occurs within the cloud (or between two clouds) and cloud-ground, or thunderbolt, which the discharge occurs between the cloud and the ground. The latter are responsible for numerous losses and damage caused to the environment, buildings and men.
In most cases, fall in love (or cloud-to-ground) is a descendant.The phenomenon of the discharge is initiated by a succession of pre-discharge from the cloud to the ground and progressing by leaps (precursor for bonds).
Once one of the peaks of the precursor approaches the ground, pre-discharge bottom (tracers) form and join the forerunner down. It was then a driver bridge between the cloud and the ground (ion channel) that will allow the passage of a current of high intensity. This current is the expense of surface soil back channel ion neutralizes charges from the cloud: the arched back. The warming of the air caused by the current will lead to its expansion and an explosion will follow: the thunder.
The first discharge leaves a conductor connecting the cloud to the ground.
Moments later (10 to 70 ms) of new precursors and descendants arches will take back that track moving much faster. On average, 4 to go back on the same track. The human eye, because of the persistence of vision, usually does not receive a single flash.
There is a minority of cases of lightning strikes ancestors, in this case the tracer develops from a large prominence on the ground. On observe le phénomène en montagne ou sur des grands immeubles. There is the phenomenon in the mountains or tall buildings.
In addition to the thunderbolt descending and ascending, a classification based on the polarity of the impact of lightning. There are lightning strikes that is negative from a negative charge from the cloud and lightning strikes positive from a positive charge.
How to protect themselves from lightning?
Avoid the edges and vertices.
If one is surprised on a summit, down below and as soon as possible.
Away from any metal (ice axes, crampons, carabiners, pitons, telescopic poles, towers, etc.)..
Do not park under a single tree, or under an overhang.
Avoid handling any conductor of electricity (water running off …).
Sit on the floor, because lightning is attracted to anything that goes beyond (a tree, a peak or a man standing). Do not lie down or rest against a wall.
Isolated maximum soil through any insulating material: roll rope, sleeping bag or backpack in which the frame is placed on the ground.
The storm is coming from various phenomena:
- The sky darkens rapidly Over the sky is dark, the cloud is more dense.
- The wind is increasing and turns to the gust. These bursts often precede heavy rains .
- Your radio sizzles and reveals a strong electrical activity, due to lightning nearby.
- In the mountains, you can see light fragrance at the end of objects (St. Elme lights) or hear buzzing diffuse. These signs indicate an impending coup de foudre.
How to detect there the impact of lightning?
What is lightning, lightning and thunder?
Lightning is an electric shock. The lightning is the visible result of the warm air, while the thunder is the noise produced by the vibration of air along the electric shock during propagation. In a few thousandths of a second, air temperature reaching 30 ° C and 000 suffered heavy cuts dilatations followed by equally violent. These sudden movements and successive produce sound waves that produce clicks, rumbles of thunder and bearings.
The company METEORAGE (www.meteorage.fr), a subsidiary of Meteo-France, since 1987 detects the impact of lightning on French soil by a network of 18 sensors that detect and localize. Agreements with the networks of neighboring countries (Italy, Spain and Benelux) for exploiting the boundary of 12 sensors. With maps of points of impact, the thunderstorm activity can be monitored in real time on the Internet or Minitel. METEORAGE also provides alerts lightning or assess the risk of lightning strike to a given site.
Fauna and Flora in NZ
At the time of the installation of Maoris in the country, two species of lizards, the gecko and will tuatara it existed, some species of frogs and bats. Stags, rabbits, sheep, goat, pig were imported in Zealand News. There exist a great number of indigenous birds such as the kea or the takahe. They are species in the process of disappearance and very protected. And the kiwi, which is the animal emblematic of the New Zealanders of which they kept the nickname of Kiwis! The kiwi, practically deprived of wings, is a rare night bird and shy person who hides in the moved back places of the country. He is unfortunately threatened of disappearance.
Contrary, the New Zealand flora is exceptionally developed. The insulation of the island and its late colonization contributed to the development of single plant species. One would count 1500 species which exist only in Zealand News, such as kowhai gilded or the pohutukawa. The kaponga which is a symbol of the country.
The greatest richness is however underwater: the peninsula of Kaikoura advances above a large canyon rich in plankton, which attracts many species of dolphins and Cetacea. In the abyssals zone, the large cachalots drive out most imperceptible of the preys: the giant squid. Passed Christchurch, capital of the island of the South, the southern influence is more felt. In the middle same of the port of Oamaru, one attends the very mediatized return of the blue penguins, smallest of the world (40 cm). All is held at the fallen night, under the eye of the projectors… Some more isolated sites are attended by the extremely rare penguin in yellow eye, of which would remain only approximately 400 reproductive couples. To see emerging from the floods, after an interminable day spent to fish to 30 kms with broad, is one moment full with emotion.
On the peninsula of Otago and beyond, one crosses also albatross and sea elephants. The insulation of Fiordland was worth, as for him, one crowned surprised with the scientists: in 1948, on the embrumés tops of the Murchison mounts, with more than 1.000 m of altitude, they have redécouvert a bird which one believed disappeared for a long time, the takahe, which nourishes tussock (thick grass) pushing on the slopes.
cumulonimbus
How does a cumulonimbus Occur?
The air heated by radiation from the Sun on the Earth’s surface expands and becomes lighter than air on top of him. It rises, like a balloon. If the air is humid enough, water vapor in it condenses into water droplets: a type of cumulus cloud appears. In an unstable atmosphere, the vertical motion of air are intense and will encourage this by condensing the magnification of the cloud, which is growing and gaining altitude. The highest droplets turn into ice crystals: the cumulus becomes a cumulonimbus.
What will happen in a cumulonimbus?
The audience is a plant thermodynamics, which is nurtured by warm, moist air to provide energy for upward movement. His energy is considerable: each second, a large cumulonimbus can aspire 700 000 tons of air and absorb and 8 800 tonnes of water vapor. The same cloud can return to the earth’s surface 4 000 tons of water in the form of liquid water, snow or hail.
The storms generally act as electric generators, creating a common ground led to the cloud. Indeed, the vertical motion of air in the audience are very violent: brewed by winds exceeding 130 km / h, the particles of water and ice cloud collide. These collisions cause many electrifying the cloud, where particles of opposite sign regroup at various stages since the surface (negatively charged) to the summit (positively charged). . Microdécharges the spread and then eventually establish electric connection between the cloud and the ground.
Storm explained
A storm is an atmospheric phenomenon characterized by a series of lightning and thunder shots. A flash can be activated within the cloud, between two clouds or between the cloud and the ground (the lightning strike).
The storm is always linked to the presence of a cumulonimbus cloud type, also called storm cloud. It is often accompanied by a set of phenomena violent gusts of wind, precipitation – sometimes small – and sometimes winds folding, or waterspout or tornado.
The storm is usually a short-term phenomenon: from a few tens of minutes to several hours. It can be isolated (storm due to the presence of reliefs or caused by the warming of the soil in summer) or organized online (the “squall line″ by meteorologists).
For certain conditions, thunderstorms can regenerate continuously in the same place or replace them at their peak of maturity. They cause and during several hours of heavy rainfall leading to floods.
The storm cloud: the mighty cumulonimbus
The cumulonimbus cloud is the characteristic phenomena thunderstorms. It is also responsible for all hailstorms. This giant cloud threatening, off 5 to 10 km, can reach up to 15 km altitude in our latitudes. At its peak, the audience faces the stratosphere and spread widely, which gives it its shape Anvil (or, sometimes, panache or hair ébouriffée).