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Atmosphere
Earth’s atmosphere is a thin layer of gas held around the surface by gravity.
90% of the atmosphere’s mass is within 15 km of the earth’s surface – Earth's radius is about 6400 km – The atmosphere is like a layer of paint on a basketball Atmosphere
The atmosphere protects life on Earth by:
Absorbing ultraviolet solar radiation
Warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variations).
The Mass of the atmosphere: It is about 5.15×1018 kg, three-quarters of which is within about 11 km of the surface. Atmosphere Ø The Earth's atmosphere is characterized by variations of temperature and pressure with height. Ø In fact, the variation of the average temperature profile with altitude is the basis for distinguishing the layers of the atmosphere.
Origins of the Atmosphere
When the Earth has formed 4.6 billion years ago, Earth’s atmosphere was probably mostly hydrogen (H) and helium (He) plus hydrogen compounds, such as methane (CH 4) and ammonia (NH 3). Those gases eventually escaped to space.
The release of gases from rock through volcanic eruption (so-called outgassing) was the principal source of atmospheric gases. Î The primeval atmosphere produced by the outgassing was mostly carbon dioxide (CO 2) with some Nitrogen ( N 2) and water vapor ( H 2 O), and trace amounts of other gases.
Most of the atmospheric mass is confined to the lowest 100 km above sea level.
The thickness of the atmosphere is only about 2% of Earth’s thickness (Earth’s radius = 6500km). Because of the shallowness of the atmosphere, its motions over large areas are primarily horizontal. Typically, horizontal wind speeds are a thousand times greater than vertical wind speeds. (But the small vertical displacements of air have an important impact on the state of the atmosphere.)
Troposphere.
The lowest layer of the atmosphere, extending from the Earth's surface up to the tropopause, which is at 10-15 km altitude depending on latitude and time of year (Higher near the equator and lower towards poles); characterized by decreasing temperature with height; rapid vertical mixing (baring BL). Stratosphere. Extends from the tropopause to the stratopause (From ~ 45 to 55 km altitude); temperature increases with altitude. Mesosphere. Extends from the stratopause to the mesopause (From 80 to 90 km altitude); temperature decreases with altitude to the mesopause, which is the coldest point in the atmosphere.
The very cold temperature of the tropopause layer at the top of the troposphere serves as a barrier that causes water vapor to condense to ice so that it cannot reach altitudes at which it would photo dissociate through the action of intense high energy ultraviolet radiation. If this happened, the hydrogen produced would escape the earth’s atmosphere and be lost.
Troposphere (“overturning” sphere) contains 80% of the mass surface heated by solar radiation strong vertical motion where most weather events occur Stratosphere (“layer” sphere) weak vertical motions dominated by radiative processes heated by ozone absorption of solar ultraviolet (UV) radiation warmest (coldest) temperatures at summer (winter) pole Mesosphere (“in-between” sphere) heated by solar radiation at the base heat dispersed upward by vertical motion Thermosphere (“heated” sphere) very little mass
The atmospheric layer directly above the troposphere is the stratosphere, in which the temperature rises to a maximum of about -2˚C with increasing altitude.
The heating effect is caused by the absorption of ultraviolet radiation energy by ozone.
Ozone serves as a natural atmospheric filter to prevent this light from reaching the surface, thereby protecting Earth's life from damages.
The upper regions of the mesosphere and higher define a region, called the exosphere, from which molecules and ions can completely escape the atmosphere.
Extending to the far outer reaches of the atmosphere is the thermosphere, in which the highly rarified gas reaches temperatures as high as 1200˚C by the absorption of very energetic radiation of wavelengths less than approximately 200 nm by gas species in this region. Atmosphere In Thermosphere temperatures increases again with altitude due to absorption of strong UV solar radiation by N2 and O2. The troposphere and stratosphere account together for 99.9% of the total atmospheric mass and are the domains of main interest from an environmental perspective. The fraction of total atmospheric weight located above altitude z is P (z)/P (0). At 80 km altitude, the atmospheric pressure is down to 0.01 hPa, meaning that 99.999% of the atmosphere is below that altitude.
Stratosphere
Stratosphere (from Understanding Weather & Climate) Standard Atmosphere lapse rate = 6.5 C/km.
The reason for the inversion in the stratosphere is due to the ozone absorption of ultraviolet solar energy. Although maximum ozone concentration occurs at 25km, the lower air density at 50km allows solar energy to heat up temperature there at a much greater degree. Also, much solar energy is absorbed in the upper stratosphere and cannot reach the level of ozone maximum
Mesosphere
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.
Thermosphere
There is little ozone to absorb solar energy in the mesosphere, and therefore, the air temperature in the mesosphere decreases with height. Also, air molecules are able to lose more energy than they absorb. This cooling effect is particularly large near the top of the mesosphere.
In the thermosphere, oxygen molecules absorb solar rays and warm the air. Because this layer has a low air density, the absorption of a small amount of solar energy can cause a large temperature increase.
The air temperature in the thermosphere is affected greatly by solar activity
Exosphere
Although some experts consider the thermosphere to be the uppermost layer of our atmosphere, others consider the exosphere to be the actual "final frontier" of Earth's gaseous envelope. As you might imagine, the "air" in the exosphere is very, very, very thin, making this layer even more space-like than the thermosphere. In fact, the air in the exosphere is constantly - though very gradually - "leaking" out of Earth's atmosphere into outer space. There is no clear-cut upper boundary where the exosphere finally fades away into space. Different definitions place the top of the exosphere somewhere between 100,000 km (62,000 miles) and 190,000 km (120,000 miles) above the surface of Earth. The latter value is about halfway to the Moon!
Ionosphere
The ionosphere is an electrified region within the upper atmosphere where a large concentration of ions and free electrons exist.
The ionosphere starts from about 60km above Earth’s surface and extends upward to the top of the atmosphere. Most of the ionosphere is in the thermosphere.
The ionosphere plays an important role in radio communication.
Water Vapor (H2O)
The most abundant variable gas.
Water vapor is supplied to the atmosphere by evaporation from the surface and is removed from the atmosphere by condensation (clouds and rains).
The concentration of water vapor is maximum near the surface and the tropics (~ 0.25% of the atmosphere by volume) and decreases rapidly toward higher altitudes and latitudes (~ 0% of the atmosphere).
Water vapor is important to climate because it is a greenhouse gas that can absorb thermal energy emitted by Earth and can release “latent heat” to fuel weather phenomena.
Carbon dioxide
Carbon dioxide is supplied into the atmosphere by plant and animal respiration, the decay of organic material, volcanic eruptions, and natural and anthropogenic combustion.
Carbon dioxide is removed from the atmosphere by photosynthesis.
CO2 is an important greenhouse gas
Nitrogen (N2):
Is inert chemically,
Has molecular speeds too slowly to escape to space,
Is not very soluble in water.
The amount of nitrogen being cycled out of the atmosphere was limited.
Nitrogen became the most abundant gas in the atmosphere.
