Weather systems play a role of the air conditioner thanks to what our planet remains lived.
Weather systems are circular areas of vortical streams of air in width from 150 4000 km. Their thickness strongly fluctuates, reaching 12-15 km and settling down actually on all height of troposphere (the atmospheric layer closest to the Earth). The thickness of other, smaller and quickly moving systems, does not exceed 1-3 km. Weather systems are characterised by changes of pressure of air, and also various winds blowing in them.
The Basic weather (baricheskimi) systems are cyclones and anticyclones. The anticyclone is an area of the raised atmospheric pressure with descending air streams. The cyclone represents area of the lowered atmospheric pressure with ascending streams of air. Therefore for cyclones cloudy, rainy weather is characteristic.
Anticyclones, or areas of the raised atmospheric pressure, are usually characterised by steady weather which essentially does not vary more often within several days. Winds blow clockwise round the center in Northern hemisphere and counter-clockwise - in Southern. On weather maps anticyclones are represented in the form of concentric isobars (the lines connecting areas with identical pressure) round the center with the greatest pressure. For anticyclones breezes and an unflawed sky are usually characteristic. Absence of overcast means that warmly, radiated by a surface of the Earth, disappears in a space. As a result soil and pripoverhnostnyj air layer are quickly cooled at night. In the winter such cooling is at the bottom of frosts or, at damp air, hoarfrost or a fog.
Some anticyclones arise in cold regions. Air here dense that creates a high pressure at a surface. Similar anticyclones develop in the winter over the Central Canada and Siberia. As a rule, their depth does not exceed 3 km.
Other powerful anticyclones are formed in area "ъюэёъш§ °шЁю=" (during former times with zashtilevshih in this strip of courts threw out for a board of dead horses), between 20 and 30 ° northern and a southern latitude. These systems deeper and steady. Pressure of air in these widths high as there air which has risen in an upper atmosphere in tropical areas because of intensive heating of soil, falls back to a terrestrial surface. On a land the hottest deserts of the world get to a strip of horse widths, including Sahara.
From systems of a high pressure around horse widths trade winds blow back along a surface in an equator direction, while warm western winds - towards a pole. Finally, vesty meet with cold ostami, blowing of ice polar areas. The border between warm and cold air is called as polar front. The polar front does not settle down as the crow flies - it is bent in those places where cold air makes the way in an equator direction, and warm aspires to a pole. These movings create a whirlwind strengthened by fast winds (jet currents), blowing in the top part of troposphere. In cyclones winds blow in a direction opposite to anticyclones, namely - counter-clockwise in Northern hemisphere and clockwise - in Southern. On weather maps cyclones are represented in the form of concentric isobars round the center with the least pressure of air.
the Birth of cyclones
The Warm air, flowing waves in polar front, flows through a stream of cold air, instead of mixes up with it. Cold air follows for warm, and the cyclone thus is formed. Usually in a cyclone there are two fronts. The warm front separates coming nearer stream of warm air from the cold. Thus warm air rises over a layer being ahead of cold dense air. In ascending cooled air water steams are condensed and form clouds. The warm front is followed by cold front. Along this front cold air makes the way under a layer of warm air, forcing it to rise upwards. Therefore the cold front also bears cloudy, rainy weather. The cold front moves faster warm owing to what they eventually face also warm air is superseded upward. This phenomenon is called okkljuziej. Soon after formation okkljuzii the cyclone weakens.
Meteorologists have carefully studied sequence of the weather conditions connected with a cyclone. This knowledge is extremely important for weather forecast. For example, thin plumose clouds of the top circle often are cyclone harbingers. Soon there are more dense vysokosloistye clouds of an average circle which follow grey sloisto-rain the bottom circle. These clouds usually bear the rains pouring within several hours before will take place warm front.
Behind warm front there is an area of warm air with overcast inherent in it and humidity. Then the cold front where owing to ascending currents of air there are thunder-storms follows. Often along border of cold front the strong rain which duration usually is less, than in the conditions of warm front drops out. After passage of cold front there comes clear, cool weather.
Thunder-storms happen everywhere, except subpolar areas. According to scientists, every minute all over the world storm about 2000 thunder-storms. Many of them arise along cold fronts where dark kuchevo-rain (storm) clouds in quickly rising streams of the warm damp air which is over a wedge of cold air are formed. The strongest thunder-storms burst in tropics owing to intensive heating of soil and pripoverhnostnogo air layer. As a result of such thunder-storms for days drops out to 600 mm of deposits. The similar thunder-storms caused by intensive heating of the earth, are observed also in hot sunny days (usually along toward evening) in moderate belts. When from the first companions pictures of the Earth have been received, scientists have paid attention on krugoverti of clouds around equator. These weather systems are formed as a result of lifting of heat and a moisture from an earth surface in the top layers of air. Sometimes some of them merge and dvizhutsja aside from equator, forming the powerful systems of low pressure named tropical cyclones, and also hurricanes in the North America, tropical storm to Australia and typhoons in East Asia.
Hurricanes much more masshtabnee, than thunder-storms. As a matter of fact, thunder-storms quite often are a part of hurricanes, whose extent from edge to edge makes from 200 to 500 km. In the center there is a hurricane eye where air falls downwards. The calm here reigns. And round the center upwards powerful streams of air promptly rush, sucking in a moisture from a surface and creating rotating system of clouds and very strong winds. Speed of gale-force winds above 119 km/hour, sometimes it reaches 300 km/hour.
On islands or continent coast the strong wind and a torrential rain accompanying hurricane, cause serious destructions, zataplivaja the big areas, rooting out trees, overturning houses. On the average, the North America annually visit 11 hurricanes which have arisen over northern Atlantic. Passing over a land, hurricanes gradually "т№ф№§р¦=ё " as all of them any more do not have a moisture which there is no place to take.
The Tornado, or a tornado, is a small storm in the size of all some honeycombs of metres in a diameter. However they are most destructive of all storm. Especially well-known to the USA, a tornado represent a funnel from promptly rotating air. Speed of a wind at a tornado quite often exceeds 320 km/hour.
Traces of destructions
Tornadoes usually live not for long - as a rule, only one hour. However in process of the advancement with huge speed they leave a strip of serious destructions on the way. Such storms are usual both in the USA, and in Australia. The most well described tornadoes are that occur in the central states of the USA (approximately 500-600 annually). The reason of occurrence of a tornado is not found out. Frequently they are connected with thunder-storms, as columns of rotating air usually "Ёрё=ѕ=" downwards from the basis of thunderclouds while warm air rises upwards and rotates about the axis. Pressure of air in a funnel extremely low. Cases when the difference of pressure of air in a tornado and in buildings led "тчЁ№трь" are known; buildings. Moving air on a spiral can lift also upwards people and even to uproot the big trees. Are similar to them and water tornadoes which are formed over the seas and lakes. However these rotating water funnels usually are weaker, than tornadoes. Water tornadoes usually have about 30 m in a diameter and, as a rule, "цштѕ=" less than one hour.
Whirlwinds and simooms
Smaller on phenomenon scales - whirlwinds, or dust tornadoes. These narrow columns of air differ from a tornado that often arise in clear, sunny days when air rises upwards and starts to rotate. The similar phenomenon - a simoom - is observed in all hot deserts.
The Most known winds in the world, bearing rains, are called as monsoons (that means "ёхчюэ"). They meet in coastal regions in India and other regions strongly pronounced pressure differences of air between winter and in the summer.
- In 1970 the tropical cyclone (hurricane) has fallen upon islands in delta of the river Ganges in a southern part Bangladesh therefore were lost about one million person.
- In September, 1985 hurricane "+ыюЁш " it was carried by from the State of North Carolina at east coast USA through the State of New York to the State of Connecticut, having put a damage in 3,5 billion pounds sterling
- the Tornado has carried away lives of 1300 persons to Bangladesh in 1989.
- the highest known speed of a wind in a tornado equals 450 km/hour. It has been registered in Uichita-Fols, Texas, in 1958.
- In April, 1986 of a hailstone in weight to 1 kg have killed to Bangladesh 96 persons.