Atmosphere

All Music Guide:

Atmosphere are a hip-hop group from Minneapolis centering around rapper Slug (aka Sean Daley). The son of a black father and a white mother who divorced when he was a teenager, Slug became entranced with hip-hop, graffiti, and breakdancing, and formed the Rhymesayers collective with two high-school friends -- Siddiq Ali (Stress) and Derek Turner (Spawn). After some early gigs as Urban Atmosphere, where Slug DJed behind Spawn's rhyming, the pair hooked up with producer Ant (Anthony Davis), as well as like-minded locals such as MC Musab, Mr. Gene Poole, and the Abstract Pack, forming an underground hip-hop clique dedicated to freestyling, clever and complex lyrics, and anti-gangsta positivity. In 1998, Atmosphere released their debut album, Overcast!, which quickly became regarded as an underground hip-hop classic thanks to Slug's deeply personal, poetic musings, as well as Ant's bare-bones -- but inventive -- production.

The next Atmosphere album was titled Sad Clown Bad Dub II, a 2000 set originally sold while the group was on tour. (Now out of print, it's a highly sought-after collector's item.) A year later, the group released Lucy Ford: The Atmosphere EP's, a collection of three EPs built around the theme of Slug's complicated relationship with his ex-girlfriend, the lost love of his life. The group has toured consistently, both at home and overseas; while Ant usually doesn't accompany the group on the road, Mr. Dibbs of the group 1200 Hobos often joins in behind the turntables and Slug is usually assisted on the mike by young rappers like the teenaged Eyedea. In June 2002, the group -- down to the duo of Slug and Ant -- unleashed God Loves Ugly, an 18-track effort that returned to previous themes ("F*@k You Lucy"), but also contained the group's most pop-friendly single to date, "Modern Man's Hustle."

By this time indie rap superstars, Atmosphere returned with their fourth album, Seven's Travels, in 2003, followed two years later by You Can't Imagine How Much Fun We're Having. The group continued to put music out during the next couple of years, including the free download Strictly Leakage in late 2007, a near-party album that they followed up with When Life Gives You Lemons, You Paint That Shit Gold in April 2008, a record that featured plenty of live instrumentation and guest background vocal spots from Tom Waits and TV on the Radio's Tunde Adebimpe. The “double-EP” To All My Friends: Blood Makes the Blade Holy appeared in 2010, with the full-length album The Family Sign following in 2011.

Wikipedia:

An atmosphere (New Latin atmosphaera, created in the 17th century from Greek ἀτμός [atmos] "vapor" and σφαῖρα [sphaira] "sphere") is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low. Some planets consist mainly of various gases, but only their outer layer is their atmosphere.

The term stellar atmosphere describes the outer region of a star, and typically includes the portion starting from the opaque photosphere outwards. Relatively low-temperature stars may form compound molecules in their outer atmosphere. Earth's atmosphere, which contains oxygen used by most organisms for respiration and carbon dioxide used by plants, algae and cyanobacteria for photosynthesis, also protects living organisms from genetic damage by solar ultraviolet radiation. Its current composition is the product of billions of years of biochemical modification of the paleoatmosphere by living organisms.

Pressure [edit]

Atmospheric pressure is the force per unit area that is always applied perpendicularly to a surface by the surrounding gas. It is determined by a planet's gravitational force in combination with the total mass of a column of gas above a location. Units of air pressure are based on the internationally recognized standard atmosphere (atm), which is defined as 101,325 Pa (or 1,013,250 dynes per cm). One (atm) equals 14.696 pounds per square inch (psi).

The pressure of an atmospheric gas decreases with altitude due to the diminishing mass of gas above each location. The height at which the pressure from an atmosphere declines by a factor of (an irrational number with a value of 2.71828..) is called the scale height and is denoted by . For an atmosphere with a uniform temperature, the scale height is proportional to the temperature and inversely proportional to the mean molecular mass of dry air times the planet's gravitational force per unit area of on the surface of the earth. For such a model atmosphere, the pressure declines exponentially with increasing altitude. However, atmospheres are not uniform in temperature, so the exact determination of the atmospheric pressure at any particular altitude is more complex.

Escape [edit]

Surface gravity, the force that holds down an atmosphere, differs significantly among the planets. For example, the large gravitational force of the giant planet Jupiter is able to retain light gases such as hydrogen and helium that escape from lower gravity objects. Second, the distance from the sun determines the energy available to heat atmospheric gas to the point where its molecules' thermal motion exceed the planet's escape velocity, the speed at which gas molecules overcome a planet's gravitational grasp. Thus, the distant and cold Titan, Triton, and Pluto are able to retain their atmospheres despite relatively low gravities. Interstellar planets, theoretically, may also retain thick atmospheres.

Since a gas at any particular temperature will have molecules moving at a wide range of velocities, there will almost always be some slow leakage of gas into space. Lighter molecules move faster than heavier ones with the same thermal kinetic energy, and so gases of low molecular weight are lost more rapidly than those of high molecular weight. It is thought that Venus and Mars may have both lost much of their water when, after being photo dissociated into hydrogen and oxygen by solar ultraviolet, the hydrogen escaped. Earth's magnetic field helps to prevent this, as, normally, the solar wind would greatly enhance the escape of hydrogen. However, over the past 3 billion years the Earth may have lost gases through the magnetic polar regions due to auroral activity, including a net 2% of its atmospheric oxygen.

Other mechanisms that can cause atmosphere depletion are solar wind-induced sputtering, impact erosion, weathering, and sequestration — sometimes referred to as "freezing out" — into the regolith and polar caps.

Composition [edit]

Initial atmospheric makeup is generally related to the chemistry and temperature of the local solar nebula during planetary formation and the subsequent escape of interior gases. The original atmospheres started with the radially local rotating gases that collapsed to the spaced rings that formed the planets. They were then modified over time by various complex factors, resulting in quite different outcomes.

The atmospheres of the planets Venus and Mars are primarily composed of carbon dioxide, with small quantities of nitrogen, argon, oxygen and traces of other gases.

The atmospheric composition on Earth is largely governed by the by-products of the very life that it sustains. Earth's atmosphere contains roughly (by molar content/volume) 78.08% nitrogen, 20.95% oxygen, a variable amount (average around 1.247%) water vapor, 0.93% argon, 0.038% carbon dioxide, and traces of hydrogen, helium, and other "noble" gases.

The low temperatures and higher gravity of the gas giants — Jupiter, Saturn, Uranus and Neptune — allows them to more readily retain gases with low molecular masses. These planets have hydrogen-helium atmospheres, with trace amounts of more complex compounds.

Two satellites of the outer planets possess non-negligible atmospheres: Titan, a moon of Saturn, and Triton, a moon of Neptune, which are mainly nitrogen. Pluto, in the nearer part of its orbit, has an atmosphere of nitrogen and methane similar to Triton's, but these gases are frozen when farther from the Sun.

Other bodies within the Solar System have extremely thin atmospheres not in equilibrium. These include the Moon (sodium gas), Mercury (sodium gas), Europa (oxygen), Io (sulfur), and Enceladus (water vapor).

The atmospheric composition of an extra-solar planet was first determined using the Hubble Space Telescope. Planet HD 209458b is a gas giant with a close orbit around a star in the constellation Pegasus. The atmosphere is heated to temperatures over 1,000 K, and is steadily escaping into space. Hydrogen, oxygen, carbon and sulfur have been detected in the planet's inflated atmosphere.

Structure [edit]

Earth [edit]

The Earth's atmosphere consists, from the ground up, of the troposphere (which includes the planetary boundary layer or peplosphere as lowest layer), stratosphere (which includes the ozone layer), mesosphere, thermosphere (which contains the ionosphere), exosphere and also the magnetosphere. Each of the layers has a different lapse rate, defining the rate of change in temperature with height.

Three quarters of the atmospheric mass resides within the troposphere, and the depth of this layer varies between 17 km at the equator and 7 km at the poles. The ozone layer, which absorbs ultraviolet energy from the Sun, is located primarily in the stratosphere, at altitudes of 15 to 35 km. The Kármán line, located within the thermosphere at an altitude of 100 km, is commonly used to define the boundary between the Earth's atmosphere and outer space. However, the exosphere can extend from 500 up to 1,000 km above the surface, where it interacts with the planet's magnetosphere.

Others [edit]

Other astronomical bodies such as these listed have known atmospheres.

In the Solar System [edit]

Outside the Solar System [edit]

Circulation [edit]

The circulation of the atmosphere occurs due to thermal differences when convection becomes a more efficient transporter of heat than thermal radiation. On planets where the primary heat source is solar radiation, excess heat in the tropics is transported to higher latitudes. When a planet generates a significant amount of heat internally, such as is the case for Jupiter, convection in the atmosphere can transport thermal energy from the higher temperature interior up to the surface.

Importance [edit]

From the perspective of the planetary geologist, the atmosphere is an evolutionary agent essential to the morphology of a planet. The wind transports dust and other particles which erodes the relief and leaves deposits (eolian processes). Frost and precipitations, which depend on the composition, also influence the relief. Climate changes can influence a planet's geological history. Conversely, studying surface of earth leads to an understanding of the atmosphere and climate of a planet — both its present state and its past.

For a meteorologist, the composition of the atmosphere determines the climate and its variations.

For a biologist, the composition is closely dependent on the appearance of the life and its evolution.