The European Commission is an institution of the European Union, responsible for proposing legislation, implementing decisions, upholding the EU treaties and managing the day-to-day business of the EU. Commissioners swear an oath at the European Court of Justice in Luxembourg City, pledging to respect the treaties and to be independent in carrying out their duties during their mandate. Unlike in the Council of the European Union, where members are directly and indirectly elected, the European Parliament, where members are directly elected, the Commissioners are proposed by the Council of the European Union, on the basis of suggestions made by the national governments, appointed by the European Council after the approval of the European Parliament; the Commission operates with 28 members of the Commission. There is one member per member state, but members are bound by their oath of office to represent the general interest of the EU as a whole rather than their home state. One of the 28 is the Commission President proposed by the European Council and elected by the European Parliament.
The Council of the European Union nominates the other 27 members of the Commission in agreement with the nominated President, the 28 members as a single body are subject to a vote of approval by the European Parliament. The current Commission is the Juncker Commission, which took office in late 2014, following the European Parliament elections in May of the same year; the term Commission is variously used, either in the narrow sense of the 28-member College of Commissioners or to include the administrative body of about 32,000 European civil servants who are split into departments called directorates-general and services. The procedural languages of the Commission are English and German; the Members of the Commission and their "cabinets" are based in the Berlaymont building in Brussels. The European Commission derives from one of the five key institutions created in the supranational European Community system, following the proposal of Robert Schuman, French Foreign Minister, on 9 May 1950.
Originating in 1951 as the High Authority in the European Coal and Steel Community, the Commission has undergone numerous changes in power and composition under various presidents, involving three Communities. The first Commission originated in 1951 as the nine-member "High Authority" under President Jean Monnet; the High Authority was the supranational administrative executive of the new European Coal and Steel Community. It took office first on 10 August 1952 in Luxembourg City. In 1958, the Treaties of Rome had established two new communities alongside the ECSC: the European Economic Community and the European Atomic Energy Community; however their executives were called "Commissions" rather than "High Authorities". The reason for the change in name was the new relationship between the Council; some states, such as France, expressed reservations over the power of the High Authority, wished to limit it by giving more power to the Council rather than the new executives. Louis Armand led the first Commission of Euratom.
Walter Hallstein led the first Commission of the EEC, holding the first formal meeting on 16 January 1958 at the Château of Val-Duchesse. It achieved agreement on a contentious cereal price accord, as well as making a positive impression upon third countries when it made its international debut at the Kennedy Round of General Agreement on Tariffs and Trade negotiations. Hallstein notably began the consolidation of European law and started to have a notable impact on national legislation. Little heed was taken of his administration at first but, with help from the European Court of Justice, his Commission stamped its authority solidly enough to allow future Commissions to be taken more seriously. In 1965, accumulating differences between the French government of Charles de Gaulle and the other member states on various subjects triggered the "empty chair" crisis, ostensibly over proposals for the Common Agricultural Policy. Although the institutional crisis was solved the following year, it cost Etienne Hirsch his presidency of Euratom and Walter Hallstein the EEC presidency, despite his otherwise being viewed as the most'dynamic' leader until Jacques Delors.
The three bodies, collectively named the European Executives, co-existed until 1 July 1967 when, under the Merger Treaty, they were combined into a single administration under President Jean Rey. Owing to the merger, the Rey Commission saw a temporary increase to 14 members—although subsequent Commissions were reduced back to nine, following the formula of one member for small states and two for larger states; the Rey Commission completed the Community's customs union in 1968, campaigned for a more powerful, European Parliament. Despite Rey being the first President of the combined communities, Hallstein is seen as the first President of the modern Commission; the Malfatti and Mansholt Commissions followed with work on monetary co-operation and the first enlargement to the north in 1973. With that enlargement, the Commission's membership increased to thirteen under the Ortoli Commission, which dealt with the enlarged community during economic and international instability at that time; the external representation of the Community took a step forward when President Roy Jenkins, recruited to the presidency in January 1977 from his role as Home Secretary of the United Kingdom's Labour government, became the first President to att
I. M. Pei
Ieoh Ming Pei, FAIA, RIBA known as I. M. Pei, is a Chinese American architect. Born in Guangzhou and raised in Hong Kong and Shanghai, Pei drew inspiration at an early age from the gardens at Soochow. In 1935, he moved to the United States and enrolled in the University of Pennsylvania's architecture school, but transferred to the Massachusetts Institute of Technology, he was unhappy with the focus at both schools on Beaux-Arts architecture, spent his free time researching emerging architects Le Corbusier. After graduating, he joined the Harvard Graduate School of Design and became a friend of the Bauhaus architects Walter Gropius and Marcel Breuer. In 1948, Pei was recruited by New York City real estate magnate William Zeckendorf, for whom he worked for seven years before establishing his own independent design firm I. M. Pei & Associates in 1955, which became I. M. Pei & Partners in 1966 and in 1989 became Pei Cobb Freed & Partners. Pei retired from full-time practice in 1990. Since he has taken on work as an architectural consultant from his sons' architectural firm Pei Partnership Architects.
Pei's first major recognition came with the National Center for Atmospheric Research in Colorado. His new stature led to his selection as chief architect for the John F. Kennedy Library in Massachusetts, he went on to design the East Building of the National Gallery of Art. He returned to China for the first time in 1975 to design a hotel at Fragrant Hills, designed Bank of China Tower, Hong Kong, a skyscraper in Hong Kong for the Bank of China fifteen years later. In the early 1980s, Pei was the focus of controversy when he designed a glass-and-steel pyramid for the Musée du Louvre in Paris, he returned to the world of the arts by designing the Morton H. Meyerson Symphony Center in Dallas, the Miho Museum in Japan, the Suzhou Museum in Suzhou, Museum of Islamic Art in Qatar, the Grand Duke Jean Museum of Modern Art, abbreviated to Mudam, in Luxembourg. Pei has won a wide variety of prizes and awards in the field of architecture, including the AIA Gold Medal in 1979, the first Praemium Imperiale for Architecture in 1989, the Lifetime Achievement Award from the Cooper-Hewitt, National Design Museum in 2003.
In 1983, he won. Pei's ancestry traces back to the Ming Dynasty. Finding wealth in the sale of medicinal herbs, the family stressed the importance of helping the less fortunate. Ieoh Ming Pei was born on 26 April 1917 to Tsuyee and Lien Kwun, the family moved to Hong Kong one year later; the family included five children. As a boy, Pei was close to his mother, a devout Buddhist, recognized for her skills as a flautist, she invited him to join her on meditation retreats. His relationship with his father was less intimate, their interactions were respectful but distant. Pei's ancestors' success meant that the family lived in the upper echelons of society, but Pei said his father was "not cultivated in the ways of the arts"; the younger Pei, drawn more to music and other cultural forms than to his father's domain of banking, explored art on his own. "I have cultivated myself," he said later. At the age of ten, Pei moved with his family to Shanghai. Pei attended Saint Johns Middle School, run by Protestant missionaries.
Academic discipline was rigorous. Pei enjoyed playing billiards and watching Hollywood movies those of Buster Keaton and Charlie Chaplin, he learned rudimentary English skills by reading the Bible and novels by Charles Dickens. Shanghai's many international elements gave it the name "Paris of the East"; the city's global architectural flavors had a profound influence on Pei, from the Bund waterfront area to the Park Hotel, built in 1934. He was impressed by the many gardens of Suzhou, where he spent the summers with extended family and visited a nearby ancestral shrine; the Shizilin Garden, built in the 14th century by a Buddhist monk, was influential. Its unusual rock formations, stone bridges, waterfalls remained etched in Pei's memory for decades, he spoke of his fondness for the garden's blending of natural and human-built structures. Soon after the move to Shanghai, Pei's mother developed cancer; as a pain reliever, she was prescribed opium, assigned the task of preparing her pipe to Pei. She died shortly after his thirteenth birthday, he was profoundly upset.
The children were sent to live with extended family. Pei said: "My father began living his own separate life pretty soon after that." His father married a woman named Aileen, who moved to New York in her life. As Pei, neared the end of his secondary education, he decided to study at a university, he decided to enroll at the University of Pennsylvania. Pei's choice had two roots. While studying in Shanghai, he had examined the catalogs for various institutions of higher learning around the world; the architectural program at the University of Pennsylvania stood out to him. The other major factor was Hollywood. Pei was fascinated by the representations of college life in the films of Bing Crosby, which differed tremendously from the academic atmosphere in China. "College life in the U. S. seemed to me to be fun and games", he said in 2000. "Since I was too young to be serious, I wanted to be part of it... You could get a feeling for it in Bing Crosby's movies. College life in America seemed
Luxembourg railway station
Luxembourg railway station is the main railway station serving Luxembourg City, in southern Luxembourg. It is operated by the state-owned railway company. 80,000 passengers use this station every day. It is the hub of Luxembourg's domestic railway network, serving as a point of call on all but one of Luxembourg's railway lines, it functions as the country's international railway hub, with services to all the surrounding countries: Belgium and Germany. Since June 2007, the LGV Est has connected the station to the French TGV network; the station is located 2 kilometres south to the south of the River Pétrusse. The station gives its name to Gare, one of the Quarters of Luxembourg City; the original railway station was built from timber, was opened in 1859. The position of the new station on the south bank of the Pétrusse, away from the original built-up area of the city, was on account of Luxembourg's role as a German Confederation fortress; the first connection to the city proper came in 1861, with the construction of the Passerelle viaduct.
After the 1867 Treaty of London, the fortifications were demolished, leading to the expansion of the city around the station. The old wooden station was replaced by the modern building between 1907 and 1913, at the height of an economic boom, fuelled by iron from the Red Lands; the new station was designed by a trio of German architects in the Moselle Baroque Revival style that dominates Luxembourg's major public buildings. The station lies at the end of the Avenue de la Liberté, one of the city's major thoroughfares, its imposing clock tower can be seen from a considerable distance. In 2006, the Ministry of Transport began a six-year renovation project on Luxembourg station that totaled €95 million; the improvements included new ticketing and sales facilities inside the main hall, expanding platforms, new lifts, a new passenger subway, upgraded overhead electrical wiring, installation of two platform escalators, a new entrance porch, a redesigned forecourt, a glass passenger hall, a four-storey car park.
As of December 2017 the station is served by the following services: High speed services Paris - Metz - Thionville - Luxembourg Intercity services Luxembourg - Arlon - Namur - Brussels Intercity services Luxembourg - Ettelbruck - Kautenbach - Troisvierges - Gouvy - Liege - Liers Intercity services Luxembourg - Wasserbillig - Trier - Koblenz - Köln - Düsseldorf Regional services Luxembourg - Wasserbillig - Trier - Koblenz Regional services Luxembourg - Ettelbruck - Diekirch Regional services Luxembourg - Bettembourg - Esch - Petange - Rodange Regional services Luxembourg - Bettembourg - Dudelange - Volmerange-les-Mines Regional services Luxembourg - Thionville - Metz - Nancy Local services Luxembourg - Ettelbruck - Kautenbach - Wiltz Local services Luxembourg - Ettelbruck Local services Luxembourg - Wasserbillig Local services Luxembourg - Kleinbettingen Local services Luxembourg - Bettembourg - Esch - Belval - Petange - Rotange Local services Luxembourg - Petange - Rotange - Athus - LongwyLuxembourg station has some voltage-switchable tracks for Line 50 to Arlon, electrified with the Belgian voltage of 3 kV DC.
These are due to disappear in 2018 History of rail transport in Luxembourg Luxembourg railway network CFL Gare de Luxembourg official webpage Luxembourg Central Station at Structurae Rail.lu page on Luxembourg station
In geology and physical geography, a plateau called a high plain or a tableland, is an area of a highland consisting of flat terrain, raised above the surrounding area with one or more sides with steep slopes. Plateaus can be formed by a number of processes, including upwelling of volcanic magma, extrusion of lava, erosion by water and glaciers. Plateaus are classified according to their surrounding environment as intermontane, piedmont, or continental. Plateaus can be formed by a number of processes, including upwelling of volcanic magma, extrusion of lava, erosion by water and glaciers. Volcanic plateaus are produced by volcanic activity; the Columbia Plateau in the northwestern United States is an example. They may be formed by upwelling of volcanic extrusion of lava; the underlining mechanism in forming plateaus from upwelling starts when magma rises from the mantle, causing the ground to swell upward. In this way, flat areas of rock are uplifted to form a plateau. For plateaus formed by extrusion, the rock is built up from lava spreading outward from cracks and weak areas in the crust.
Plateaus can be formed by the erosional processes of glaciers on mountain ranges, leaving them sitting between the mountain ranges. Water can erode mountains and other landforms down into plateaus. Dissected plateaus are eroded plateaus cut by rivers and broken by deep narrow valleys. Computer modeling studies suggest that high plateaus may be a result from the feedback between tectonic deformation and dry climatic conditions created at the lee side of growing orogens. Plateaus are classified according to their surrounding environment. Intermontane plateaus are the highest in the world, bordered by mountains; the Tibetan Plateau is one such plateau. Lava or volcanic plateaus are the plateau; the magma that comes out through narrow cracks or fissures in the crust spread over large area and solidifies. These layers of lava sheets form volcanic plateaus; the Antrim plateau in Northern Ireland, The Deccan Plateau in India and the Columbia Plateau in the United States are examples of lava plateaus. Piedmont plateaus are bordered on one side by mountains and on the other by a sea.
The Piedmont Plateau of the Eastern United States between the Appalachian Mountains and the Atlantic Coastal Plain is an example. Continental plateaus are bordered on all sides by oceans, forming away from the mountains. An example of a continental plateau is the Antarctic Polar Plateau in East Antarctica; the largest and highest plateau in the world is the Tibetan Plateau, sometimes metaphorically described as the "Roof of the World", still being formed by the collisions of the Indo-Australian and Eurasian tectonic plates. The Tibetan plateau covers 2,500,000 km2, at about 5,000 m above sea level; the plateau is sufficiently high to reverse the Hadley cell convection cycles and to drive the monsoons of India towards the south. The second-highest plateau is the Deosai Plateau of the Deosai National Park at an average elevation of 4,114 m, it is located in northern Pakistan. Deosai means'the land of giants'; the park protects an area of 3,000 km2. It is known for its rich flora and fauna of the Karakoram-West Tibetan Plateau alpine steppe ecoregion.
In spring it is covered by a wide variety of butterflies. The highest point in Deosai is Deosai Lake, or Sheosar Lake from the Shina language meaning "Blind lake" near the Chilim Valley; the lake lies at an elevation of 4,142 m, one of the highest lakes in the world, is 2.3 km long, 1.8 km wide, 40 m deep on average. Some other major plateaus in Asia are: Najd in the Arabian Peninsula elevation 762 to 1,525 m, Armenian Highlands, Iranian plateau, Anatolian Plateau, Mongolian Plateau, the Deccan Plateau. Another large plateau is the icy Antarctic Plateau, sometimes referred to as the Polar Plateau, home to the geographic South Pole and the Amundsen-Scott South Pole Station, which covers most of East Antarctica where there are no known mountains but rather 3,000 m high of superficial ice and which spreads slowly toward the surrounding coastline through enormous glaciers; this polar ice cap is so massive that the echolocation sound measurements of ice thickness have shown that large parts of the Antarctic "dry land" surface have been pressed below sea level.
Thus, if that same ice cap were removed, the large areas of the frozen white continent would be flooded by the surrounding Antarctic Ocean or Southern Ocean. On the other hand, were the ice cap melts away too the surface of the land beneath it would rebound away through isostasy from the center of the Earth and that same land would rise above sea level. A large plateau in North America is the Colorado Plateau, which covers about 337,000 km2 in Colorado, Utah and New Mexico. In northern Arizona and southern Utah the Colorado Plateau is bisected by the Colorado River and the Grand Canyon. How this came to be is that over 10 million years ago, a river was there, though not on the same cours
Mass is a term used to describe the main eucharistic liturgical service in many forms of Western Christianity. The term Mass is used in the Catholic Church and Anglican churches, as well as some Lutheran churches, Western Rite Orthodox and Old Catholic churches; some Protestants employ terms such as worship service, rather than the word Mass.. For the celebration of the Eucharist in Eastern Christianity, including Eastern Catholic Churches, other terms such as Divine Liturgy, Holy Qurbana, Badarak are used instead; the English noun mass is derived from Middle Latin missa. The Latin word was adopted in Old English as mæsse, was sometimes glossed as sendnes; the Latin term missa itself was in use by the 6th century. It is most derived from the concluding formula Ite, missa est. However, there have been other explanations of the noun missa, i.e. as not derived from the formula ite, missa est. Fortescue cites older, "fanciful" etymological explanations, notably a latinization of Hebrew matzâh "unleavened bread.
The French historian Du Cange in 1678 reported "various opinions on the origin" of the noun missa "mass", including the derivation from Hebrew matzah, here attributed to Caesar Baronius. The Hebrew derivation is learned speculation from 16th-century philology. Thus, De divinis officiis explains the word as a mittendo, quod nos mittat ad Deo, while Rupert of Deutz derives it from a "dismissal" of the "enmities, between God and men"; the Catholic Church sees the Mass or Eucharist as "the source and summit of the Christian life", to which the other sacraments are oriented. The Catholic Church believes that the Mass is the same sacrifice that Jesus Christ offered on the Cross at Calvary; the ordered celebrant is understood to act in persona Christi, as he imitates the words and gestures of Jesus Christ at the Last Supper. By virtue of the mediation of the Holy Spirit, said to be present in the apostolic church, through the words proffered by the celebrant, similar to the Word of God the Son, there takes place a transubstantiation of: the wine into the Precious Blood, the sacramental bread into the Holy Body of Jesus Christ.
Hence, Roman Catholic and Orthodox believe that the Holy Trinity is in the host, celebrated during the Holy Mass and in the previous context of the Christian consecrations. The Holy Mass renews, makes alive at any time the innocent sacrifice of Jesus Christ, as He is "the Holy One of God", thus the unique door of salvation for the human sins; the term "Mass" is used only in the Roman Rite, while the Byzantine Rite Eastern Catholic Churches use the analogous term "Divine Liturgy" and other Eastern Catholic Churches have terms such as Holy Qurbana. Although similar in outward appearance to the Anglican Mass or Lutheran Mass, the Catholic Church distinguishes between its own Mass and theirs on the basis of what it views as the validity of the orders of their clergy, as a result, does not ordinarily permit intercommunion between members of these Churches. In a 1993 letter to Bishop Johannes Hanselmann of the Evangelical Lutheran Church in Bavaria, Cardinal Ratzinger affirmed that "a theology oriented to the concept of succession, such as that which holds in the Catholic and in the Orthodox church, need not in any way deny the salvation-granting presence of the Lord in a Lutheran Lord's Supper."
The Decree on Ecumenism, produced by Vatican II in 1964, records that the Catholic Church notes its understanding that when other faith groups "commemorate His death and resurrection in the Lord's Supper, they profess that it signifies life in communion with Christ and look forward to His coming in glory."Within the fixed structure outlined below, specific to the Ordinary Form of the Roman Rite, the Scripture readings, the antiphons sung or recited during the entrance procession or communion, certain other prayers vary each day according to the liturgical calendar. The priest enters, with a deacon, if there is one, altar servers. After making the sign of the cross and greeting the people liturgically, he begins the Act of Penitence; this concludes with the priest's prayer of absolution, however, lacks the efficacy of the Sacrament of Penance. The Kyrie, eleison, is sung or said, followed by the Gloria in excelsis Deo, an ancient praise, if appropriate for the liturgical season; the Introductory Rites are brought to a close by the Collect Prayer.
On Sundays and solemnities, three Scripture readings are given. On other days there are only two. If there are three readings, the first is from the Old Testament, or the Acts of the Apostles during Eastertide; the first reading is sung responsorially or recited. The second reading is from the New Testament from one of the Pauline e
Société Nationale des Chemins de Fer Luxembourgeois
The Société Nationale des Chemins de Fer Luxembourgeois is the national railway company of Luxembourg. In 2013, it carried 20.7 million passengers and 804 million tonnes kilometers of goods. The company employs 3,090 people; the Luxembourg rail system comprises 275 route-kilometres, of which 140 kilometres is double track and 135 kilometres single track. Of the total track length of 617 kilometres, 574 kilometres are electrified; the majority of the electrified track is operated at 25 kV, 50 Hz, though some 48 kilometres are run at 3 kV DC. Luxembourg borders Belgium and Germany. Correspondingly, there are cross-border services into these countries; some are wholly run by CFL, whereas others are run by SNCF, NMBS/SNCB and DB. CFL passenger trains cover the majority of the network. CFL operates the majority of its passenger trains using EMUs and electric locomotives with push-pull stock; the company has a fleet of diesel locomotives for hauling freight trains and for general shunting purposes. Luxembourg is a member of the International Union of Railways.
The UIC Country Code for Luxembourg is 82. CFL is the result of a nationalisation of private railway companies in 1946. History of rail transport in Luxembourg CFL advertises its passenger network as made up of seven lines: Line 10 Luxembourg – Troisvierges-Frontière – Liège, Kautenbach – Wiltz and Ettelbrück – Diekirch Line 30 Luxembourg – Wasserbillig-Frontière – Trier Line 50 Luxembourg – Kleinbettingen-Frontière – Brussels Line 60 Luxembourg – Esch-sur-Alzette – Rodange, Bettembourg – Dudelange – Volmerange-les-Mines, Bettembourg – Noetzange – Rumelange and Bettembourg – Esch-sur-Alzette – Audun-le-Tiche Line 70 Luxembourg – Rodange – Athus with extensions to Arlon and Virton, Rodange – Longwy with extension to Longuyon Line 80 Thionville – Esch-sur-Alzette – Longwy Line 90 Luxembourg – Thionville – Metz – Nancy Internally it uses a different system with more sub divisions: Ligne 1 Luxembourg – Troisvierges-Frontière Ligne 1a Ettelbruck – Diekirch Ligne 1b Kautenbach – Wiltz Ligne 2a Kleinbettingen – Steinfort Ligne 2b Ettelbruck – Bissen Ligne 3 Luxembourg – Wasserbillig-Frontière via Sandweiler-Contern Ligne 4 Luxembourg – Berchem – Oetrange Ligne 5 Luxembourg – Kleinbettingen-Frontière Ligne 6 Luxembourg – Bettembourg-Frontière Ligne 6a Bettembourg – Esch/Alzette Ligne 6b Bettembourg – Dudelange-Usines Ligne 6c Noertzange – Rumelange Ligne 6d Tétange – Langengrund Ligne 6e Esch-sur-Alzette – Audun-le-Tiche Ligne 6f Esch-sur-Alzette – Pétange Ligne 6g Pétange – Rodange-Frontière Ligne 6h Pétange – Rodange-Frontière Ligne 6j Pétange – Rodange-Frontière Ligne 6k Brucherberg – Scheuerbusch Ligne 7 Luxembourg – Pétange All neighbouring railways use the same gauge but differing electrification types, listed below: Belgium – 3 kV DC France – 25 kV AC Germany – 15 kV AC Passenger ridership carried on CFL-trains for each fiscal year ).
Passenger kilometers on CFL-trains for each fiscal year ). CFL owns a modern fleet of passenger trains, with a majority of double-decker trains. Nearly all routes are operated with electric trains. CFL locomotives and rolling stock CFL Cargo Denmark Trams in Luxembourg Transport in Luxembourg CFL official website 2006 Annual Report Collection of Google Earth locations of CFL stations from the Google Earth Community forum
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation include drizzle, sleet, snow and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and "precipitates", thus and mist are not precipitation but suspensions, because the water vapor does not condense sufficiently to precipitate. Two processes acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called "showers."Moisture, lifted or otherwise forced to rise over a layer of sub-freezing air at the surface may be condensed into clouds and rain. This process is active when freezing rain occurs. A stationary front is present near the area of freezing rain and serves as the foci for forcing and rising air.
Provided necessary and sufficient atmospheric moisture content, the moisture within the rising air will condense into clouds, namely stratus and cumulonimbus. The cloud droplets will grow large enough to form raindrops and descend toward the Earth where they will freeze on contact with exposed objects. Where warm water bodies are present, for example due to water evaporation from lakes, lake-effect snowfall becomes a concern downwind of the warm lakes within the cold cyclonic flow around the backside of extratropical cyclones. Lake-effect snowfall can be locally heavy. Thundersnow is possible within lake effect precipitation bands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation. On the leeward side of mountains, desert climates can exist due to the dry air caused by compressional heating. Most precipitation is caused by convection; the movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah climes.
Precipitation is a major component of the water cycle, is responsible for depositing the fresh water on the planet. 505,000 cubic kilometres of water falls as precipitation each year. Given the Earth's surface area, that means the globally averaged annual precipitation is 990 millimetres, but over land it is only 715 millimetres. Climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes. Precipitation may occur on other celestial bodies, e.g. when it gets cold, Mars has precipitation which most takes the form of frost, rather than rain or snow. Precipitation is a major component of the water cycle, is responsible for depositing most of the fresh water on the planet. 505,000 km3 of water falls as precipitation each year, 398,000 km3 of it over the oceans. Given the Earth's surface area, that means the globally averaged annual precipitation is 990 millimetres. Mechanisms of producing precipitation include convective and orographic rainfall.
Convective processes involve strong vertical motions that can cause the overturning of the atmosphere in that location within an hour and cause heavy precipitation, while stratiform processes involve weaker upward motions and less intense precipitation. Precipitation can be divided into three categories, based on whether it falls as liquid water, liquid water that freezes on contact with the surface, or ice. Mixtures of different types of precipitation, including types in different categories, can fall simultaneously. Liquid forms of precipitation include drizzle. Rain or drizzle that freezes on contact within a subfreezing air mass is called "freezing rain" or "freezing drizzle". Frozen forms of precipitation include snow, ice needles, ice pellets and graupel; the dew point is the temperature to which a parcel must be cooled in order to become saturated, condenses to water. Water vapor begins to condense on condensation nuclei such as dust and salt in order to form clouds. An elevated portion of a frontal zone forces broad areas of lift, which form clouds decks such as altostratus or cirrostratus.
Stratus is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass. It can form due to the lifting of advection fog during breezy conditions. There are four main mechanisms for cooling the air to its dew point: adiabatic cooling, conductive cooling, radiational cooling, evaporative cooling. Adiabatic cooling occurs when air expands; the air can rise due to convection, large-scale atmospheric motions, or a physical barrier such as a mountain. Conductive cooling occurs when the air comes into contact with a colder surface by being blown from one surface to another, for example from a liquid water surface to colder land. Radiational cooling occurs due to the emission of infrared radiation, either by the air or by the surface underneath. Evaporative cooling occurs when moisture is added to the air through evaporation, which forces the air temperature to cool to its wet-bulb temperature, or until it reaches saturation; the main ways water vapor is added to the air are: wind convergence into areas of upward motion, precipitation or virga falling from above, daytime heating evaporating water from the surface of oceans, water bodies or wet lan