Components of each layer:
Components of each layer:
The Troposphere
https://web.physics.ucsb.edu/~lgrace/chem123/troposphere.htm
The troposphere is the lowest layer of Earth's atmosphere and site of all weather on Earth. The troposphere is bonded on the top by a layer of air called the tropopause, which separates the troposphere from the stratosphere, and on bottom by the surface of the Earth. The troposphere is wider at the equator (10mi) than at the poles (5mi).
The troposphere contains 75 percent of atmosphere's mass- on an average day the weight of the molecules in the air is 14.7 lb..(sq. in.)- and most of the atmosphere's water vapor. Water vapor concentration varies from trace amounts in Polar Regions to nearly 4 percent in the tropics. Most prevalent gases are nitrogen (78 percent) and oxygen (21 percent), with the remaining 1- percent consisting of argon, (.9 percent) and traces of hydrogen ozone ( a form of oxygen), and other constituents. Temperature and water vapor content in the troposphere decrease rapidly with altitude. Water vapor plays a major role in regulating air temperature because it absorbs solar energy and thermal radiation from the planet's surface.
The troposphere contains 99% of the water vapor in the atmosphere. Water vapor concentrations vary with latitudinal position(north to south). They are greatest above the tropics, where they might be as high as 3% and decrease toward the polar regions.
Carbon dioxide is present in small amounts, but its concentration has nearly doubled since 1900.Like water vapor, carbon dioxide is a greenhouse gas which traps some of the Earth's heat close to the surface and prevents its release into space. Scientists fear that the increasing amounts of carbon dioxide could raise the Earth's surface temperature during the next century, bringing significant changes to worldwide weather patterns. Such changes may include a shift in climatic zones and the melting of the polar ice caps, which could raise the level of the world's oceans.
The uneven heating of the regions of the troposphere by the sun ( the sun warms the air at the equator more than the air at the poles )causes convection currents, large-scale patterns of winds that move heat and moisture around the globe. In the Northern and Southern hemispheres, air rises along the equator and subpolar ( latitude about 50 to about 70 north and south ) climatic regions and sinks in the polar and subtropical regions. Air is deflected by the Earth's rotation as it moves between the poles and equator, creating belts of surface winds moving from east to west ( easterly winds ) in tropical and polar regions, the winds moving from west to east ( westerly winds ) in the middle latitudes. This global circulation is disrupted by the circular wind patterns of migrating high and low air pressure areas, plus locally abrupt changes in wind speed and direction known as turbulence.
A common feature of the troposphere of densely populated areas is smog, which restricts visibility and is irritating to the eyes and throat. Smog is produced when pollutants accumulate close to the surface beneath an inversion layer ( a layer of air in which the usual rule that temperature of air decreases with altitude doesn't apply ), and undergo a series of chemical reactions in the presence pollutants from escaping into the upper atmosphere. Convection is the mechanism responsible for the vertical transport of heat in the troposphere while horizontal heat transfer is accomplished through advection.
The exchange and movement of water between the earth and atmosphere is called the water cycle. The cycle, which occurs in the troposphere, begins as the sun evaporates large amounts of water from the earth's surface and the moisture is transported to other regions by the wind. As air rises, expands, and cools, water vapor condenses and clouds develop. Clouds cover large portions of the earth at any given time and vary from fair weather cirrus to towering cumulus clouds. When liquid or solid water particles grow large enough in size, they fall toward the earth as precipitation. The type of precipitation that reaches the ground, be it rain, snow, sleet, or freezing rain, depends upon the temperature of the air through which it falls.
As sunlight enters the atmosphere, a portion is immediately reflected back to space, but the rest penetrates the atmosphere and is absorbed by the earth's surface. This energy is then remitted by the earth back into atmosphere as long-wave radiation. Carbon dioxide and water molecules absorb this energy and emit much of it back towards the earth again. This delicate exchange of energy between the earth's surface and atmosphere keeps the average global temperature from changing drastically from year to year.
The Troposphere
https://web.physics.ucsb.edu/~lgrace/chem123/troposphere.htm
The troposphere is the lowest layer of Earth's atmosphere and site of all weather on Earth. The troposphere is bonded on the top by a layer of air called the tropopause, which separates the troposphere from the stratosphere, and on bottom by the surface of the Earth. The troposphere is wider at the equator (10mi) than at the poles (5mi).
The troposphere contains 75 percent of atmosphere's mass- on an average day the weight of the molecules in the air is 14.7 lb..(sq. in.)- and most of the atmosphere's water vapor. Water vapor concentration varies from trace amounts in Polar Regions to nearly 4 percent in the tropics. Most prevalent gases are nitrogen (78 percent) and oxygen (21 percent), with the remaining 1- percent consisting of argon, (.9 percent) and traces of hydrogen ozone ( a form of oxygen), and other constituents. Temperature and water vapor content in the troposphere decrease rapidly with altitude. Water vapor plays a major role in regulating air temperature because it absorbs solar energy and thermal radiation from the planet's surface.
The troposphere contains 99% of the water vapor in the atmosphere. Water vapor concentrations vary with latitudinal position(north to south). They are greatest above the tropics, where they might be as high as 3% and decrease toward the polar regions.
Carbon dioxide is present in small amounts, but its concentration has nearly doubled since 1900.Like water vapor, carbon dioxide is a greenhouse gas which traps some of the Earth's heat close to the surface and prevents its release into space. Scientists fear that the increasing amounts of carbon dioxide could raise the Earth's surface temperature during the next century, bringing significant changes to worldwide weather patterns. Such changes may include a shift in climatic zones and the melting of the polar ice caps, which could raise the level of the world's oceans.
The uneven heating of the regions of the troposphere by the sun ( the sun warms the air at the equator more than the air at the poles )causes convection currents, large-scale patterns of winds that move heat and moisture around the globe. In the Northern and Southern hemispheres, air rises along the equator and subpolar ( latitude about 50 to about 70 north and south ) climatic regions and sinks in the polar and subtropical regions. Air is deflected by the Earth's rotation as it moves between the poles and equator, creating belts of surface winds moving from east to west ( easterly winds ) in tropical and polar regions, the winds moving from west to east ( westerly winds ) in the middle latitudes. This global circulation is disrupted by the circular wind patterns of migrating high and low air pressure areas, plus locally abrupt changes in wind speed and direction known as turbulence.
A common feature of the troposphere of densely populated areas is smog, which restricts visibility and is irritating to the eyes and throat. Smog is produced when pollutants accumulate close to the surface beneath an inversion layer ( a layer of air in which the usual rule that temperature of air decreases with altitude doesn't apply ), and undergo a series of chemical reactions in the presence pollutants from escaping into the upper atmosphere. Convection is the mechanism responsible for the vertical transport of heat in the troposphere while horizontal heat transfer is accomplished through advection.
The exchange and movement of water between the earth and atmosphere is called the water cycle. The cycle, which occurs in the troposphere, begins as the sun evaporates large amounts of water from the earth's surface and the moisture is transported to other regions by the wind. As air rises, expands, and cools, water vapor condenses and clouds develop. Clouds cover large portions of the earth at any given time and vary from fair weather cirrus to towering cumulus clouds. When liquid or solid water particles grow large enough in size, they fall toward the earth as precipitation. The type of precipitation that reaches the ground, be it rain, snow, sleet, or freezing rain, depends upon the temperature of the air through which it falls.
As sunlight enters the atmosphere, a portion is immediately reflected back to space, but the rest penetrates the atmosphere and is absorbed by the earth's surface. This energy is then remitted by the earth back into atmosphere as long-wave radiation. Carbon dioxide and water molecules absorb this energy and emit much of it back towards the earth again. This delicate exchange of energy between the earth's surface and atmosphere keeps the average global temperature from changing drastically from year to year.
The stratosphere is a layer of Earth's atmosphere. The stratosphere is the second layer, as one moves upward from Earth's surface, of the atmosphere. The stratosphere is above the troposphere and below the mesosphere.
The top of the stratosphere occurs at 50 km (31 miles) altitude. The boundary between the stratosphere and the mesosphere above is called the stratopause. The altitude of the bottom of the stratosphere varies with latitude and with the seasons, occurring between about 8 and 16 km (5 and 10 miles, or 26,000 to 53,000 feet). The bottom of the stratosphere is around 16 km (10 miles or 53,000 feet) above Earth's surface near the equator, around 10 km (6 miles) at mid-latitudes, and around 8 km (5 miles) near the poles. It is slightly lower in winter at mid- and high-latitudes, and slightly higher in the summer. The boundary between the stratosphere and the troposphere below is called the tropopause.
The stratosphere is very dry; air there contains little water vapor. Because of this, few clouds are found in this layer; almost all clouds occur in the lower, more humid troposphere. Polar stratospheric clouds (PSCs) are the exception. PSCs appear in the lower stratosphere near the poles in winter. They are found at altitudes of 15 to 25 km (9.3 to 15.5 miles) and form only when temperatures at those heights dip below -78° C. They appear to help cause the formation of the infamous holes in the ozone layer by "encouraging" certain chemical reactions that destroy ozone. PSCs are also called nacreous clouds.
Air is roughly a thousand times thinner at the top of the stratosphere than it is at sea level. Because of this, jet aircraft and weather balloons reach their maximum operational altitudes within the stratosphere.
The mesosphere https://scied.ucar.edu/shortcontent/mesosphere-overview
The mesosphere is a layer of Earth's atmosphere. The mesosphere is directly above the stratosphere and below the thermosphere. It extends from about 50 to 85 km (31 to 53 miles) above our planet.
Temperature decreases with height throughout the mesosphere. The coldest temperatures in Earth's atmosphere, about -90° C (-130° F), are found near the top of this layer.
The boundary between the mesosphere and the thermosphere above it is called the mesopause. At the bottom of the mesosphere is the stratopause, the boundary between the mesosphere and the stratosphere below.
The mesosphere is difficult to study, so less is known about this layer of the atmosphere than other layers. Weather balloons and other aircraft cannot fly high enough to reach the mesosphere. Satellites orbit above the mesosphere and cannot directly measure traits of this layer. Scientists use instruments on sounding rockets to sample the mesosphere directly, but such flights are brief and infrequent. Since it is difficult to take measurements of the mesosphere directly using instruments, much about the mesosphere is still mysterious.
Most meteors vaporize in the mesosphere. Some material from meteors lingers in the mesosphere, causing this layer to have a relatively high concentration of iron and other metal atoms. Very strange, high altitude clouds called "noctilucent clouds" or "polar mesospheric clouds" sometime form in the mesosphere near the poles. These peculiar clouds form much, much higher up than other types of clouds. Odd electrical discharges akin to lightning, called "sprites" and "ELVES", occasionally appear in the mesosphere dozens of kilometers (miles) above thunderclouds in the troposphere below.
The stratosphere and mesosphere together are sometimes referred to as the middle atmosphere. At the mesopause (the top of the mesosphere) and below, gases made of different types of atoms and molecules are thoroughly mixed together by turbulence in the atmosphere. Above the mesosphere, in the thermosphere and beyond, gas particles collide so infrequently that the gases become somewhat separated based on the types of chemical elements they contain.
Various types of waves and tides in the atmosphere influence the mesosphere. These waves and tides carry energy from the troposphere and the stratosphere upward into the mesosphere, driving most of its global circulation.
Randy Russell - 03/30/2017 - 3:49pm
The thermospher https://scied.ucar.edu/shortcontent/thermosphere-overview
The thermosphere is a layer of Earth's atmosphere. The thermosphere is directly above the mesosphere and below the exosphere. It extends from about 90 km (56 miles) to between 500 and 1,000 km (311 to 621 miles) above our planet.
Temperatures climb sharply in the lower thermosphere (below 200 to 300 km altitude), then level off and hold fairly steady with increasing altitude above that height. Solar activity strongly influences temperature in the thermosphere. The thermosphere is typically about 200° C (360° F) hotter in the daytime than at night, and roughly 500° C (900° F) hotter when the Sun is very active than at other times. Temperatures in the upper thermosphere can range from about 500° C (932° F) to 2,000° C (3,632° F) or higher.
The boundary between the thermosphere and the exosphere above it is called the thermopause. At the bottom of the thermosphere is the mesopause, the boundary between the thermosphere and the mesosphere below.
Although the thermosphere is considered part of Earth's atmosphere, the air density is so low in this layer that most of the thermosphere is what we normally think of as outer space. In fact, the most common definition says that space begins at an altitude of 100 km (62 miles), slightly above the mesopause at the bottom of the thermosphere. The space shuttle and the International Space Station both orbit Earth within the thermosphere!
Below the thermosphere, gases made of different types of atoms and molecules are thoroughly mixed together by turbulence in the atmosphere. Air in the lower atmosphere is mainly composed of the familiar blend of about 80% nitrogen molecules (N2) and about 20% oxygen molecules (O2). In the thermosphere and above, gas particles collide so infrequently that the gases become somewhat separated based on the types of chemical elements they contain. Energetic ultraviolet and X-ray photons from the Sun also break apart molecules in the thermosphere. In the upper thermosphere, atomic oxygen (O), atomic nitrogen (N), and helium (He) are the main components of air.
Much of the X-ray and UV radiation from the Sun is absorbed in the thermosphere. When the Sun is very active and emitting more high energy radiation, the thermosphere gets hotter and expands or "puffs up". Because of this, the height of the top of the thermosphere (the thermopause) varies. The thermopause is found at an altitude between 500 km and 1,000 km or higher. Since many satellites orbit within the thermosphere, changes in the density of (the very, very thin) air at orbital altitudes brought on by heating and expansion of the thermosphere generates a drag force on satellites. Engineers must take this varying drag into account when calculating orbits, and satellites occasionally need to be boosted higher to offset the effects of the drag force.
High-energy solar photons also tear electrons away from gas particles in the thermosphere, creating electrically-charged ions of atoms and molecules. Earth's ionosphere, composed of several regions of such ionized particles in the atmosphere, overlaps with and shares the same space with the electrically neutral thermosphere.
Like the oceans, Earth's atmosphere has waves and tides within it. These waves and tides help move energy around within the atmosphere, including the thermosphere. Winds and the overall circulation in the thermosphere are largely driven by these tides and waves. Moving ions, dragged along by collisions with the electrically neutral gases, produce powerful electrical currents in some parts of the thermosphere.
Finally, the aurora (the Southern and Northern Lights) primarily occur in the thermosphere. Charged particles (electrons, protons, and other ions) from space collide with atoms and molecules in the thermosphere at high latitudes, exciting them into higher energy states. Those atoms and molecules shed this excess energy by emitting photons of light, which we see as colorful auroral displays.
Randy Russell - 03/30/2017 - 4:36pm
The exosphere https://scied.ucar.edu/shortcontent/exosphere-overview
The exosphere is the uppermost region of Earth's atmosphere as it gradually fades into the vacuum of space. Air in the exosphere is extremely thin - in many ways it is almost the same as the airless void of outer space.
The layer directly below the exosphere is the thermosphere; the boundary between the two is called the thermopause. The bottom of the exosphere is sometimes also referred to as the exobase. The altitude of the lower boundary of the exosphere varies. When the Sun is active around the peak of the sunspot cycle, X-rays and ultraviolet radiation from the Sun heat and "puff up" the thermosphere - raising the altitude of the thermopause to heights around 1,000 km (620 miles) above Earth's surface. When the Sun is less active during the low point of the sunspot cycle, solar radiation is less intense and the thermopause recedes to within about 500 km (310 miles) of Earth's surface.
Not all scientists agree that the exosphere is really a part of the atmosphere. Some scientists consider the thermosphere the uppermost part of Earth's atmosphere, and think that the exosphere is really just part of space. However, other scientists do consider the exosphere part of our planet's atmosphere.
Since the exosphere gradually fades into outer space, there is no clear upper boundary of this layer. One definition of the outermost limit of the exosphere places the uppermost edge of Earth's atmosphere around 190,000 km (120,000 miles), about halfway to the Moon. At this distance, radiation pressure from sunlight exerts more force on hydrogen atoms than does the pull of Earth's gravity. A faint glow of ultraviolet radiation scattered by hydrogen atoms in the uppermost atmosphere has been detected at heights of 100,000 km (62,000 miles) by satellites. This region of UV glow is called the geocorona.
Below the exosphere, molecules and atoms of atmospheric gases constantly collide with each other. However, air in the exosphere is so thin that such collisions are very rare. Gas atoms and molecules in the exosphere move along "ballistic trajectories", reminiscent of the arcing flight of a thrown ball (or shot cannonball!) as it gradually curves back towards Earth under the pull of gravity. Most gas particles in the exosphere zoom along curved paths without ever hitting another atom or molecule, eventually arcing back down into the lower atmosphere due to the pull of gravity. However, some of the faster-moving particles don't return to Earth - they fly off into space instead! A small portion of our atmosphere "leaks" away into space each year in this way.
Although the exosphere is technically part of Earth's atmosphere, in many ways it is part of outer space. Many satellites, including the International Space Station (ISS), orbit within the exosphere or below. For example, the average altitude of the ISS is about 330 km (205 miles), placing it in the thermosphere below the exosphere! Although the atmosphere is very, very thin in the thermosphere and exosphere, there is still enough air to cause a slight amount of drag force on satellites that orbit within these layers. This drag force gradually slows the spacecraft in their orbits, so that they eventually would fall out of orbit and burn up as they re-entered the atmosphere unless something is done to boost them back upwards. The ISS loses about 2 km (1.2 miles) in altitude each month to such "orbital decay", and must periodically be given an upward boost by rocket engines to keep it in orbit.
Randy Russell - 03/30/2017 - 4:41pm
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