Atmosphere PDF

THE ATMOSPHERE The components of the atmosphere can be divided into three categories: The atmosphere is the gaseous envelope that surrounds the earth. 1) Non-variable gases Although relative...

THE ATMOSPHERE The components of the atmosphere can be divided into three categories: The atmosphere is the gaseous envelope that surrounds the earth. 1) Non-variable gases Although relatively transparent and seemingly insubstantial, it nonetheless The non-variable gases comprise over 98 percent of the total atmosphere by profoundly affects nearly every aspect of our physical environment. Life on volume. These gases are sufficiently stable, both physically and chemically. earth could not exist without it. The most abundant gas by far, is nitrogen, which by volume comprises 78 The atmosphere is the outermost of the four environmental spheres percent of the atmospheric total of non-variable gases. that interface at the surface of the Earth. It essentially forms a canopy over the Most of the remainder of the atmosphere consists of oxygen (almost 21 others: the hydrosphere, lithosphere, and biosphere. percent), which is essential to the respiratory processes of plants and animals. Earth’s atmosphere is believed to have been derived primarily from volcanic gases released from our planet’s interior. It performs a number of 2) Variable gases vital functions that profoundly affect the nature of the Earth’s surface and its Several gases exist in variable quantities in the atmosphere. Although they ability to support life, such as the supplying of oxygen to animals and carbon collectively comprise only a very small proportion of the atmosphere’s total dioxide to plants, and protecting our planet from the impact of small meteors. mass, and volume, three of these variable gases – carbon dioxide, water The atmosphere has the capacity to absorb large quantities of the vapor, and ozone – are crucial to the existence of life. radiation that reaches the Earth both from the Sun and from elsewhere in space. 3) Particulates Finally, the atmosphere makes possible the cycle of evaporation and Atmospheric particulates consist of liquids and solids derived primarily from precipitation that provides water to the land areas of the earth. Without this the earth’s surface. They vary considerably in size, and the smallest are cycle, there would be no clouds, no rain or snow, no rivers or lakes, little or no capable of remaining aloft almost indefinitely. Most particulates are solids, vegetation or soil, and little animal life either on land or in the sea. rather than liquids, and are collectively referred to as dust. COMPOSITION OF THE ATMOSPHERE The atmosphere is a physical mixture of VERTICAL CHARACTERISTICS OF THE gaseous elements and compounds. Most of ATMOSPHERE these gases exist in constant proportions in all but the atmosphere’s outermost layers. The atmosphere is layered with respect to temperature. There are five principal layers:  The upper edge of the stratosphere is marked by the stratopause, another thermal boundary. The lowest and most The third thermal layer, the mesosphere, is located between 50 and important of thermal layers is the 80 km above the earth’s surface. The temperature stops rising and begins troposphere, which contains nearly falling at this layer. 80 percent of the atmosphere’s total Above the mesosphere, a final reversal in temperature occurs in the mass. This is the zone in which most thermosphere. In this zone, located at altitudes above 80 km cca up to observable weather phenomena occur 600km, the temperature rises gradually to reach the highest readings occuring and in which we live. The troposphere anywhere in the atmosphere. In the upper thermosphere, temperatures may contains the great majority of the exceed 1100 ◦C because of the absorption of ultraviolet radiation from the atmosphere’s water vapor. sun. Consequently, it contains nearly all The fifth thermal layer, the exosphere, extends to an altitude of cca clouds and is the origin of all 800 km and it has an elliptic shape as it merges with the space. precipitation reaching the surface. The dominant vertical characteristic of the WIND SYSTEMS troposphere is a rather rapid decrease in temperature with increasing altitude. Air pressure is created due to uneven heating of the Earth’s surface since warm air is light and thus rises creating area of low pressure unlike cold The rather sharply defined air which is heavy and descends creating area of high pressure. This vertical upper boundary of the troposphere, the movement of the air is called convection. tropopause, is the level at which the These differences in pressure are equalized by a horizontal movement temperature stops falling with of air which is called wind and is characterized by its speed and direction. increasing altitude. The second thermal layer, the stratosphere, extends from the tropopause to an altitude of 50 km. The lower stratosphere, up to 32 km, remains fairly constant in temperature, but above this level a gradual temperature rise occurs. This is caused by the absorption of solar ultraviolet radiation by ozone, which converts this energy into heat. The stratosphere is characterized by cloudless, dry air and is often subject to strong horizontal winds. Notes on Earth’s Atmosphere ◦ Earth’s atmosphere: A body of air/gases surrounding Earth. ◦ Functions: Protects the planet and supports life. ◦ Major constituents: Nitrogen, Oxygen, and Argon. ◦ Five distinct layers: Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere. Layers of the Atmosphere (Closest to farthest) 1. Troposphere (0–12 km) ⁃ Closest layer to Earth, part of the lower atmosphere. ⁃ Contains the air humans breathe. ⁃ Weather occurs here. ⁃ Temperature decreases with height. 2. Stratosphere (Above the Troposphere) ⁃ Contains the ozone layer, which absorbs most UV radiation. ⁃ Jets fly in the lower stratosphere to avoid turbulence. ⁃ Temperature increases with height but remains below freezing. 3. Mesosphere ⁃ Air is thin; molecules are far apart. ⁃ Coldest layer, with temperatures reaching -90°C. ⁃ Meteors burn up here. ⁃ Along with the stratosphere, it forms the middle atmosphere. 4. Thermosphere ⁃ Extends several hundred kilometers above Earth’s surface. ⁃ Temperature increases with height due to solar activity, reaching up to 2000°C. ⁃ Air feels cold as molecules are sparse. 5. Exosphere ⁃ Outermost layer with very few molecules. ⁃ Some molecules escape into space. ⁃ Some scientists consider it part of outer space. ⁃ No clear upper boundary. ◦ Kármán Line: Marks the altitude (~100 km) where traditional aircraft can no longer fly effectively. ◦ Exobase: ⁃ Lower boundary of the exosphere. ⁃ Known as the “critical altitude.” ⁃ Barometric conditions no longer apply, and atmospheric temperature stabilizes. Atmospheric pressure Atmospheric or air pressure is the force per unit of area exerted on the Earth’s surface by the weight of the air above the surface. Air pressure is greater at the sea level and decreases with increasing altitude. Standard atmosphere is defined as 1013.27 hPa. Meteorological reports typically state atmospheric pressure in millibars. Pressure measurement device is called barometer.  Low pressure system - Cyclone A cyclone is a low pressure system of the atmosphere in which air pressure has dropped below the standard atmospheric pressure winds rotate inward in a counterclockwise direction in the northern hemisphere and clockwise direction in the southern hemisphere Tropical cyclones, which develop over tropical oceans, are commonly characterized by intense low-pressure system, high wind speeds, and storm surges.  Tropical cyclones are known by many names depending on their geographical location: Atlantic coasts of North America and Europe: Hurricane Pacific coasts of East Asia and Pacific Islands: Typhoon Indian Ocean coasts of South Asia and Australia: Cyclone  High pressure system - Anticyclone An anticyclone is an area of high pressure which brings long periods of settled weather, dry and bright conditions. Warm air falls, clouds do not form because as the air sinks it warms, meaning it can hold more water.  In summer, high pressure usually results in clear skies, gentle breezes and fine weather. In cold conditions, anticyclones may also bring fog and mist. This is because the cold forces moisture in the air to condense at low altitudes. In winter, high pressure leads to clear skies and colder conditions. The absence of fronts means winds may be very light. https://www.worldatlas.com/articles/what-is-an-anticyclone.html Atmospheric pressure in the world  WIND The atmosphere is composed of air molecules The air is free to move in every way unless something is blocking it wind is the movement of air molecules in the atmosphere Wind is the flow of a huge amount of air, usually from a high-pressure area to a low-pressure area. As a result of uneven heating, there are Earth´s surfaces that vary a lot in temperature. Air on surfaces with higher temperature begins to rise. As it rises, it creates low atmospheric pressure. Air on surfaces with cooler temperatures sinks. The sinking creates higher atmospheric pressure.  Wind systems Vertical movement of the air is called convection Horizontal movement of air which is called wind and is characterized by its speed and direction Divison of winds ◦ Constant winds = General circulation of air in the troposphere ◦ Regular winds = they change direction seasonally ◦ Local winds = equalize pressure and heat differences in small areas Regular Winds = Monsoon ◦ created by the temperature contrasts that exist between the surfaces of land and ocean ◦ occurs over distances of thousands of kilometres ◦ typically occurs in South & South-east Asia ◦ two types: summer & winter monsoon REGULAR WINDS CONSTANT WINDS Monsoons General Circulation of Air in the Troposphere/Global Circulation created by the temperature contrasts that exist between the surfaces of land and ocean occur over distances of thousands of kilometers typically in South & South-east Asia two types: summer & winter monsoon During the summer, monsoon winds blow from the cooler ocean surfaces onto the warmer continents. In the summer, the continents become much warmer than the oceans. Coriolis Effect/Force Over the major parts of the Earth's surface there are large-scale wind circulations present. The global circulation can be described as the world-wide system of winds by which the necessary transport of heat from tropical to polar latitudes is accomplished. Precipitation is normally associated with the summer monsoons. Onshore Instead of one large circulation in each hemisphere, there are three winds blowing inland from the warm ocean are very high in humidity, and circulations in each (three cells = Hadley cell, Ferrel cell and Polar cell): slight cooling of these air masses causes condensation and rain. Hadley cell (1) –Named after English physicist and meteorologist George In the winter, the wind patterns reverse as the ocean surfaces are now Hadley, who proposed the single circulation for each hemisphere in 1735. warmer. With little solar energy available, the continents begin cooling rapidly. At low latitudes, air moves toward the equator, where it is heated and rises The ocean surface retains its heat energy longer. The winter monsoons bring vertically. In the upper atmosphere, air moves poleward. This forms a clear dry weather and winds that flow from land to sea. convection cell that covers tropical and sub-tropical climates. In the northern hemisphere, the winds flow to the right and are called northeast trade winds. In the southern hemisphere the winds flow to the left and are called the southeast trade winds. This is down to the Coriolis force and friction. Ferrel cell (2) – Proposed by William Ferrell in 1856, it was the first to account Between each of these circulation cells are surface-level bands of high and low for westerly winds between 35° and 60° N/S. pressure. The high pressure band is located at about 30° N/S latitude and at each pole. Low pressure bands are found at the equator and 50°-60° N/S. In this mid-latitude atmospheric circulation cell, air near the surface flows poleward and eastward, while air higher in the atmosphere moves equatorward and westward. Polar cell (3) – At higher latitudes, air rises and travels toward the poles. Once over the poles, the air sinks, forming areas of high atmospheric pressure called the polar highs. At the surface, air moves outward from the polar highs, creating east-blowing surface winds called polar easterlies. It is the smallest and weakest of the cells. These cells describe circulations in both the Northern and Southern Hemispheres, although the difference in landmasses result in varying degrees of uniformity.