Atmosfer adalah lapisan udara yang melingkupi sebuah planet, termasuk Bumi, dari permukaan planet tersebut sampai jauh di luar angkasa. Udara merupakan kumpulan berbagai macam gas.

Komponen Gas Penyusun

Atmosfer bumi terdiri dari berbagai komponen gas, komponen gas penyusun atmosfer bumi dapat dilihat pada tabel berikut:

Gas Simbol Volume

Nitrogen N2 78.08

Oksigen O2 20.95

Argon Ar 0.93

Karbondioksida CO2 0.035

Neon Ne 0.0018

Methan CH4 0.00017

Helium He 0.0005

Hidrogen H2 0.000009

Xenon Xe 0.000004Atmosfer Bumi terdiri kumpulan berbagai macam gas. Gas penyusun atmosfer Bumi memiliki banyak manfaat untuk kehidupan manusia

NitrogenMerupakan unsur gas yang paling besar prosentasenya di atmosfer. Gas nitrogen sangat dibutuhkan dalam pertumbuhan tanaman. Gas nitrogen sering juga digunakan sebagai bahan dasar industri pupuk

OksigenOksigen merupakan unsur gas yang sangat diperlukan untuk pernafasan manusia dan mahluk hidup lainnya seperti hewan dan tumbuhan. Komposisi oksigen dalam atmosfer mencapai 21%, oksigen terdapat di perairan terutama perairan laut dangkal dan di daratan sampai batas ketinggian tertentu di atas permukaan air laut, semakin tinggi tempat suatu wilayah dari permukaan air laut, lapisan oksigennya semakin tipis. Karena ada oksigen kita dapat bernafas, menyalakan lilin dan lainnya.

ArgonArgon simbolnya Ar, merupakan elemen gas terbesar ke tiga di atmosfer Bumi setelah unsur gas nitrogen dan oksigen. Nama elemen Argon, diambil dari bahasa Yunani Argos yang artinya tidak aktif, karena Argon tidak mudah ber-reaksi dengan elemen lain. Argon digunakan bersama dengan gas Neon dalam industri listrik untuk mengisi lampu neon. Gas Argon berwarna biru. Lampu neon yang diisi dengan Gas Argon lebih hemat listrik dibandingkan lampu listrik biasa.

Gas Neon

Karbondioksida (CO2)Karbondioksida merupakan gas tidak berwarna, tidak berbau dan gas asam yang ringan. Karbondioksida disebut juga gas asam karbon, molekulnya terdiri dari 1 atom karbon dan 2 atom oksigen, disimbolkan CO2. Karbondioksida sering disebut udara campuran.

Beberapa manfaat Gas Karbondioksida :

Karbondioksida digunakan untuk memproduksi Sodium Carbonat Na2CO3, sodium bikarbonat NaHC03 dan bahan kimia lainnya yang dapat dimanfaatkan untuk kepentingan manusia.

Gas Karbondioksida bersifat tidak mudah terbakar dan dapat melokalisir panas, itu sebabnya digunakan sebagai pengisi tabung pemadam kebakaran.

Gas Karbondioksida dibutuhkan dalam pernafasan dan fotosintesis tumbuhan.

Kandungan Karbondioksida dalam jumlah yang banyak di atmosfer dapat menyebabkan polusi udara sehingga menimbulkan gangguan pada pernafasan mahluk hidup, misalnya sesak nafas pada manusia.

NeonNeon adalah gas yang tidak berwarna, tidak berbau dan non reaktif. Neon termasuk gas mulia seperti halnya Gas Helium, Argon, Kripton, Xenon dan Radon.

Kegunaan Gas Neon adalah sebagai berikut:

Dimanfaatkan untuk lampu neon Kota di malam hari Keperluan iklan Dapat dimanfaatkan untuk indikator tegangan tinggi Dimanfaatkan dalam dunia kedokteran, misalnya untuk membantu melihat hasil

rontgen

Methan (CH4)Gas Methan terdiri dari Carbon dan Hidrogen. Methan adalah gas yang tidak berwarna berbau, mudah terbakar dan lebih ringan dari udara. Di beberapa planet seperti Jupiter, Saturnus, Uranus dan Neptunus, methan merupakan komponen besar di dalam atmosfernya.

Methan digunakan sebagai bahan bakar karena Gas Alam yang digunakan sebagai bahan bakar mengandung 85% Gas Methan (CH4), 10% Etane (C2H6) dan selebihnya adalah Propane (C3H8), Butane (C4H10), Pantene (C5H2) dan Alkane

HeliumHelium berasal dari bahasa Yunani Helios, yang artinya Matahari. Helium termasuk gas

mulia, lebih ringan dari udara, sehingga dimanfaatkan untuk pengisi balon gas dan balon udara. Helium juga digunakan untuk bahan bakar yang dapat menggerakan mesin roket.

Hidrogen digunakan pada industri kimia, untuk membuat amonia (NH3), kegunaan amonia antara lain untuk membuat pupuk.

Para ahli metalurgi menggunakan hidrogen untuk memisahkan logam murni dengan oksida, contohnya digunakan untuk menghasilkan lembaran tembaga.

Bijih tembaga dan Peleburan tembaga(sumber : www.hardesource.com)

XenonXenon berasal dari bahasa Yunani, Xenon yang artinya asing. Xenon merupakan gas mulia, tidak berwarna dan tidak berbau, Gas Xenon tidak ber-reaksi dengan elemen lain, sehingga banyak digunakan untuk pekerjaan yang berhubungan dengan lingkungan pada industri kimia dan indusri elektronik.

03. Lapisan Atmosfer

Atmosfer bumi terdiri dari beberapa lapisan,yaitu :

Troposfer Stratosfer Mesosfer Termosfer

Eksosfer

1. Troposfer

Merupakan lapisan atmosfer yang letaknya paling dekat dengan permukaan bumi yaitu 0-12 Km. Di lapisan ini terjadi berbagai gejala cuaca dan iklim seperti hujan, badai, arah angin, dan sebagainya.

Badai di pantai

Arah angin dilihat dari atmosfer

2. Stratosfer

Merupakan lapisan atmosfer yang berada pada ketinggian 12 - 50 Km dari permukaan bumi. Pada lapisan ini terdapat lapisan ozon yang berfungsi sebagai pelindung lapisan troposfer dan lapisan permukaan Bumi dari radiasi sinar ultra violet Matahari

3. Mesosfer

Merupakan lapisan atmosfer yang berada di atas lapisan stratosfer, pada ketinggian 50 - 80 Km dari permukaan bumi. Pada lapisan ini, energi Matahari yang diserap hanya sedikit sehingga temperatur turun dengan sangat drastis, yaitu pada ketinggian 80 km suhunya mencapai - 90º C. Lapisan mesosfer melindungi bumi dari meteor dan benda-benda luar angkasa yang menuju ke Bumi.

4. Termosfer

Merupakan lapisan atmosfer yang berada pada ketinggian 80 – 500 Km dari permukaan bumi. Pada lapisan terjadi penguraian gas menjadi atom-atom sebagai akibat dari radiasi ultra violet dan sinar X, serta berkurangnya daya campur antar gas.

Di lapisan ini suhu udara mulai naik secara bertahap hingga mencapai 1000º C. Pada lapisan ini terdapat proses ionisasi. Ionisasi adalah proses dimana atom yang netral kehilangan sebuah elektron dan dari sebuah elekton akan menjadi elektron negatif, oleh sebab itu lapisan ini bermuatan listrik, sehingga lapisan ini dapat dimanfaatkan untuk bidang pantul gelombang radio.

5. Eksosfer

Merupakan lapisan atmosfer yang berada pada ketinggian di atas 500 Km dari permukaan bumi, merupakan lapisan paling luar dari atmosfer bumi yang menyatu dengan ruang hampa udara di angkasa luar. Batas atas lapisan ini adalah ruang antar planet. Pada

lapisan ini molekul udara sudah sangat langka. Hal ini memungkinkan terlepasnya partikel-partikel netral terhadap pengaruh gravitasi bumi.

04. Manfaat Lapisan Atmosfer

Tanpa atmosfer tidak akan ada kehidupan di permukaan bumi. Mengapa? Karena atmosfer merupakan salah satu pendukung utama kehidupan. Ada beberapa manfaat lapisan atmosfer bagi kehidupan di permukaan bumi, antara lain :

* Unsur seperti nitrogen, oksigen dan karbondioksida sangat dibutuhkan oleh mahluk hidup.* Merupakan pelindung bumi dari benda-benda ruang angkasa* Media untuk terjadinya peristiwa cuaca seperti angin, awan dan hujan* Merupakan pelindung bumi dari radiasi ultraviolet Matahari.

II. LAPISAN-LAPISAN BUMI dan PENJELASANNYA

Atmosfer Bumi terdiri atas nitrogen (78.17%) dan oksigen (20.97%), dengan sedikit argon (0.9%), karbondioksida (variabel, tetapi sekitar 0.0357%), uap air, dan gas lainnya. Atmosfer melindungi kehidupan di bumi dengan menyerap radiasi sinar ultraviolet dari matahari dan mengurangi suhu ekstrem di antara siang dan malam. 75% dari atmosfer ada dalam 11 km dari permukaan planet.

Atmosfer tidak mempunyai batas mendadak, tetapi agak menipis lambat laun dengan menambah ketinggian, tidak ada batas pasti antara atmosfer dan angkasa luar.

1.Troposfer

Lapisan ini berada pada level yang terrendah, campuran gasnya paling ideal untuk menopang kehidupan di bumi. Dalam lapisan ini kehidupan terlindung dari sengatan radiasi yang dipancarkan oleh benda-benda langit lain. Dibandingkan dengan lapisan atmosfer yang lain, lapisan ini adalah yang paling tipis (kurang lebih 15 kilometer dari permukaan tanah). Dalam lapisan ini, hampir semua jenis cuaca, perubahan suhu yang mendadak, angin tekanan dan kelembaban yang kita rasakan sehari-hari berlangsung.

Ketinggian yang paling rendah adalah bagian yang paling hangat dari troposfer, karena permukaan bumi menyerap radiasi panas dari matahari dan menyalurkan panasnya ke udara. Biasanya, jika ketinggian bertambah, suhu udara akan berkurang secara tunak (steady), dari sekitar 17 sampai℃ -52 . Pada permukaan bumi yang tertentu, seperti daerah pegunungan ℃dan dataran tinggi dapat menyebabkan anomali terhadap gradien suhu tersebut.

Diantara stratosfer dan troposfer terdapat lapisan yang disebut lapisan Tropopouse.

2.Stratosfer

Perubahan secara bertahap dari troposfer ke stratosfer dimulai dari ketinggian sekitar 11 km. Suhu di lapisan stratosfer yang paling bawah relatif stabil dan sangat dingin yaitu – 70oF atau sekitar – 57oC. Pada lapisan ini angin yang sangat kencang terjadi dengan pola aliran yang tertentu. Awan tinggi jenis cirrus kadang-kadang terjadi di lapisan paling bawah, namun tidak ada pola cuaca yang signifikan yang terjadi pada lapisan ini.

Dari bagian tengah stratosfer keatas, pola suhunya berubah menjadi semakin bertambah semakin naik, karena bertambahnya lapisan dengan konsentrasi ozon yang bertambah. Lapisan ozon ini menyerap radiasi sinar ultra ungu. Suhu pada lapisan ini bisa mencapai sekitar 18oC pada ketinggian sekitar 40 km. Lapisan stratopause memisahkan stratosfer dengan lapisan berikutnya.

3.Mesosfer

Kurang lebih 25 mil atau 40km diatas permukaan bumi terdapat lapisan transisi menuju lapisan mesosfer. Pada lapisan ini, suhu kembali turun ketika ketinggian bertambah, sampai menjadi sekitar – 143oC di dekat bagian atas dari lapisan ini, yaitu kurang lebih 81 km diatas permukaan bumi. Suhu serendah ini memungkinkan terjadi awan noctilucent, yang terbentuk dari kristal es.

4.Termosfer

Transisi dari mesosfer ke termosfer dimulai pada ketinggian sekitar 81 km. Dinamai termosfer karena terjadi kenaikan temperatur yang cukup tinggi pada lapisan ini yaitu sekitar 1982oC. Perubahan ini terjadi karena serapan radiasi sinar ultra ungu. Radiasi ini menyebabkan reaksi kimia sehingga membentuk lapisan bermuatan listrik yang dikenal dengan nama ionosfer, yang dapat memantulkan gelombang radio. Sebelum munculnya era satelit, lapisan ini berguna untuk membantu memancarkan gelombang radio jarak jauh.

Fenomena aurora yang dikenal juga dengan cahaya utara atau cahaya selatan terjadi disini.

5.Eksosfer

Adanya refleksi cahaya matahari yang dipantulkan oleh partikel debu meteoritik. Cahaya matahari yang dipantulkan tersebut juga disebut sebagai cahaya Zodiakal

TroposphereFrom Wikipedia, the free encyclopedia

Jump to: navigation, search

Earth atmosphere diagram showing the exosphere and other layers. The layers are to scale. From Earth's surface to the top of the stratosphere (50km) is just under 1% of Earth's radius.

View of Earth's troposphere from an airplane.

Atmospheric circulation shown with three large cells.

The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75 percent of the atmosphere's mass and 99 percent of its water vapor and aerosols.

The average depth of the troposphere is approximately 17 km (11 mi) in the middle latitudes. It is deeper in the tropical regions, up to 20 km (12 mi), and shallower near the poles, at 7 km (4.3 mi) in summer, and indistinct in winter. The lowest part of the troposphere, where friction with the Earth's surface influences air flow, is the planetary boundary layer. This layer is typically a few hundred meters to 2 km (1.2 mi) deep depending on the landform and time of day. The border between the troposphere and stratosphere, called the tropopause, is a temperature inversion.[1]

The word troposphere derives from the Greek: tropos for "turning" or "mixing," reflecting the fact that turbulent mixing plays an important role in the troposphere's structure and behavior. Most of the phenomena we associate with day-to-day weather occur in the troposphere.[1]

Contents

[hide]

1 Pressure and temperature structure o 1.1 Composition o 1.2 Pressure o 1.3 Temperature o 1.4 Tropopause

2 References

3 External links

[edit] Pressure and temperature structure

[edit] Composition

The chemical composition of the troposphere is essentially uniform, with the notable exception of water vapor. The source of water vapor is at the surface through the processes of evaporation and transpiration. Furthermore the temperature of the troposphere decreases with height, and saturation vapor pressure decreases strongly as temperature drops, so the amount of water vapor that can exist in the atmosphere decreases strongly with height. Thus the proportion of water vapor is normally greatest near the surface and decreases with height.

[edit] Pressure

The pressure of the atmosphere is maximum at sea level and decreases with higher altitude. This is because the atmosphere is very nearly in hydrostatic equilibrium, so that the pressure is equal to the weight of air above a given point. The change in pressure with height therefore can be equated to the density with this hydrostatic equation:[2]

where:

gn stands for the standard gravity ρ stands for density z stands for height p stands for pressure R stands for the gas constant T stands for temperature in kelvins m stands for the molar mass

Since temperature in principle also depends on altitude, one needs a second equation to determine the pressure as a function of height, as discussed in the next section.

[edit] Temperature

Main article: Lapse rate

The temperature of the troposphere generally decreases as altitude increases. The rate at which the temperature decreases, − dT / dz, is called the lapse rate. The reason for this decrease is as follows. When a parcel of air rises, it expands, because the pressure is lower at higher altitudes. As the air parcel expands, it pushes on the air around it, doing work; but generally it does not gain heat in exchange from its environment, because its thermal conductivity is low (such a process is called adiabatic). Since the parcel does work and gains no heat, it loses energy, and so its temperature decreases. (The reverse, of course, will be true for a sinking parcel of air.) [1]

Since the heat exchanged dQ is related to the entropy change dS by dQ=T dS, the equation governing the temperature as a function of height for a thoroughly mixed atmosphere is

where S is the entropy. The rate at which temperature decreases with height under such conditions is called the adiabatic lapse rate.

For dry air, which is approximately an ideal gas, we can proceed further. The adiabatic equation for an ideal gas is [3]

where γ is the heat capacity ratio (γ=7/5, for air). Combining with the equation for the pressure, one arrives at the dry adiabatic lapse rate,[4]

If the air contains water vapor, then cooling of the air can cause the water to condense, and the behavior is no longer that of an ideal gas. If the air is at the saturated vapor pressure, then the rate at which temperature drops with height is called the saturated adiabatic lapse rate. More generally, the actual rate at which the temperature drops with altitude is called the environmental lapse rate. In the troposphere, the average environmental lapse rate is a drop of about 6.5 °C for every 1 km (1000 meters) increase in height. [1]

The environmental lapse rate (the actual rate at which temperature drops with height, dT /

dz) is not usually equal to the adiabatic lapse rate (or correspondingly, ). If the upper air is warmer than predicted by the adiabatic lapse rate (dS / dz > 0), then when

a parcel of air rises and expands, it will arrive at the new height at a lower temperature than its surroundings. In this case, the air parcel is denser than its surroundings, so it sinks back to its original height, and the air is stable against being lifted. If, on the contrary, the upper air is cooler than predicted by the adiabatic lapse rate, then when the air parcel rises to its new height it will have a higher temperature and a lower density than its surroundings, and will continue to accelerate upward.[1][2]

Temperatures decrease at middle latitudes from an average of 15°C at sea level to about -55°C at the beginning of the tropopause. At the poles, the troposphere is thinner and the temperature only decreases to -45°C, while at the equator the temperature at the top of the troposphere can reach -75°C.[citation needed]

[edit] Tropopause

Main article: Tropopause

The tropopause is the boundary region between the troposphere and the stratosphere.

Measuring the temperature change with height through the troposphere and the stratosphere identifies the location of the tropopause. In the troposphere, temperature decreases with altitude. In the stratosphere, however, the temperature remains constant for a while and then increases with altitude. The region of the atmosphere where the lapse rate changes from positive (in the troposphere) to negative (in the stratosphere), is defined as the tropopause.[1] Thus, the tropopause is an inversion layer, and there is little mixing between the two layers of the atmosphere.

http://en.wikipedia.org/wiki/Troposphere

Troposphere

The lowest layer of the atmosphere is called the troposphere. It ranges in thickness from 8km at the poles to 16km over the equator. The troposphere is bounded above by the tropopause, a boundary marked by stable temperatures. Above the troposphere is the stratosphere. Although variations do occur, temperature usually declines with increasing altitude in the troposphere. Hill walkers know that it will be several degrees cooler on the top of a mountain than in the valley below.

The troposphere is denser than the layers of the atmosphere above it (because of the weight compressing it), and it contains up to 75% of the mass of the atmosphere. It is primarily composed of nitrogen (78%) and oxygen (21%) with only small concentrations of other trace gases. Nearly all atmospheric water vapour or moisture is found in the troposphere.

The troposphere is the layer where most of the world's weather takes place. Since temperature decreases with altitude in the troposphere, warm air near the surface of the Earth can readily rise, being less dense than the colder air above it. In fact air molecules can travel to the top of the troposphere and back down again in a just a few days. Such vertical movement or convection of air generates clouds and ultimately rain from the moisture within the air, and gives rise to much of the weather which we experience. The troposphere is capped by the tropopause, a region of stable temperature. Air temperature then begins to rise in the stratosphere. Such a temperature increase prevents much air convection beyond the tropopause, and consequently most weather phenomena, including towering cumulonimbus thunderclouds, are confined to the troposphere.

Sometimes the temperature does not decrease with height in the troposphere, but increases. Such a situation is known as a temperature inversion. Temperature inversions limit or prevent the vertical mixing of air. Such atmospheric stability can lead to air pollution episodes with air pollutants emitted at ground level becoming trapped underneath the temperature inversion.

http://www.ace.mmu.ac.uk/eae/atmosphere/older/troposphere.html

Ozone in the Troposphere

Did you know that ozone is found in two different layers of the atmosphere? You may have heard of the ozone hole problem - that is a lack of ozone in the stratosphere (the 2nd layer of the Earth's atomsphere). But ozone is also found in the troposphere, the first layer of the Earth’s atmosphere. In the troposphere, ozone is NOT wanted! It can actually do a lot of damage.

Ozone is released naturally in the troposphere by plants and soil. These are such small amounts that they are not harmful to the health of humans, animals or the environment.

Ozone that increases because of certain human activities does become a

problem at ground level and this is what we think of as 'bad' ozone. With increasing populations, more automobiles, and more industry (power plants and refineries in particular), there's more ozone in the lower atmosphere. Since 1900, the amount of ozone near the Earth's surface has more than doubled. In urban areas in the Northern Hemisphere, high ozone levels usually occur during the warm, sunny, summer months (from May through September). Typically, ozone levels reach their peak in mid to late afternoon, after the Sun has had time to react fully with the exhaust fumes from the morning rush hours. A hot, sunny, still day is the perfect environment for ozone pollution production. In early evening, the sunlight's intensity decreases and ground level ozone begins to decrease again.

When ozone pollution reaches high levels, pollution alerts are issued telling people with breathing problems to take extra precautions or to remain indoors. That's no fun! Smog can damage lung tissues, impair an athlete's performance, create more frequent attacks for individuals with asthma, cause eye irritation, chest pain, coughing, nausea, headaches and chest congestion. It can even worsen heart disease, bronchitis, and emphysema.

Rubber, fibers, and certain paints may be damaged by exposure to ozone. Some elastic materials can become brittle and crack (take a look at old rubber bands!), while paints and fabric dyes may fade more quickly.

So why can't we take all of this "bad" ozone and blast it up into the stratosphere where ozone is wanted? Unfortunately, the vehicle necessary to transport such enormous amounts of ozone into the stratosphere does not exist, and, if it did, it would require so

Ozone peaks in urban areas during late afternoons. Click on image for full size (23K)Courtesy of UCAR

much fuel that the resulting pollution might undo any positive effect. We can turn to simpler solutions though, decreasing the production of those chemicals that create ozone in the troposphere. That means choosing to take public transportation instead of all driving separate cars, walking to school or work, and maybe even buying a new hybrid car!? http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/ozone_tropo.html

StratosphereFrom Wikipedia, the free encyclopedia

Jump to: navigation, searchFor other uses, see Stratosphere (disambiguation).

Atmosphere diagram showing stratosphere. The layers are to scale: from Earth's surface to the top of the stratosphere (50km) is just under 1% of Earth's radius. (click to enlarge)

The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler higher up and warmer farther down. The border of the troposphere and stratosphere, the tropopause, is marked by where this inversion begins, which in terms of atmospheric thermodynamics is the equilibrium level. The stratosphere is situated between about 10 km (6 miles) and 50 km (31 miles) altitude above the surface at moderate latitudes, while at the poles it starts at about 8 km (5 miles) altitude.

The word stratosphere is from the Greek meaning 'stratified layer'and sphaira meaning ball.

Contents

[hide]

1 Temperature 2 Aircraft flight 3 Circulation and mixing 4 Life 5 See also 6 References

7 External links

[edit] Temperature

The stratosphere is layered in temperature because it is heated from above by absorption of ultraviolet radiation from the Sun. Within this layer, temperature increases as altitude increases (see temperature inversion); the top of the stratosphere has a temperature of about 270 K (−3°C or 29.6°F), just slightly below the freezing point of water.[1] This top is called the stratopause, above which temperature again decreases with height. The vertical stratification, with warmer layers above and cooler layers below, makes the stratosphere dynamically stable: there is no regular convection and associated turbulence in this part of the atmosphere. The heating is caused by an ozone layer that absorbs solar ultraviolet radiation, heating the upper layers of the stratosphere. The base of the stratosphere occurs where heating by conduction from above and heating by convection from below (through the troposphere) balance out; hence, the stratosphere begins at lower altitudes near the poles due to the lower ground temperature.The major reason for the

temperature increase with altitude is that most of the ozone (O3) is contained in the stratosphere. High energy ultraviolet light interacts with ozone to cause the temperature increase.

[edit] Aircraft flight

Commercial airliners typically cruise at altitudes of 9–12 km in temperate latitudes, in the lower reaches of the stratosphere.[2] They do this to optimize jet engine fuel burn, mostly thanks to the low temperatures encountered near the tropopause. It also allows them to stay above any hard weather, and avoid atmospheric turbulence from the convection in the troposphere. Turbulence experienced in the cruise phase of flight is often caused by convective overshoot from the troposphere below. Although a few gliders have achieved great altitudes in the powerful thermals in thunderstorms, this is dangerous. Most high altitude flights by gliders use lee waves from mountain ranges and were used to set the current record of 15,447m (50,671 feet).

[edit] Circulation and mixing

This section does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (June 2009)

The stratosphere is a region of intense interactions among radiative, dynamical, and chemical processes, in which horizontal mixing of gaseous components proceeds much more rapidly than vertical mixing.

An interesting feature of stratospheric circulation is the quasi-Biennial Oscillation (QBO) in the tropical latitudes, which is driven by gravity waves that are convectively generated in the troposphere. The QBO induces a secondary circulation that is important for the global stratospheric transport of tracers such as ozone or water vapor.

In northern hemispheric winter, sudden stratospheric warmings can often be observed which are caused by the absorption of Rossby waves in the stratosphere.

[edit] Life

Bacterial life survives in the stratosphere, making it a part of the biosphere.[3]

http://en.wikipedia.org/wiki/Stratosphere

Ozone layerFrom Wikipedia, the free encyclopedia

Jump to: navigation, search

The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of grass and cows (O3). This layer absorbs 93-99% of the sun's high frequency to be used for argiculture ultraviolet light, which is potentially damaging to life on earth.[1] Over 91% of the ozone in Earth's atmosphere is present here.[1] It is mainly located in the lower portion of the stratosphere from approximately 10 km to 50 km above Earth, though the thickness varies seasonally and geographically.[2] The ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson. Its properties were explored in detail by the British meteorologist G. M. B. Dobson, who developed a simple spectrophotometer (the Dobsonmeter) that could be used to measure stratospheric ozone from the ground. Between 1928 and 1958 Dobson established a worldwide network of ozone monitoring stations which continues to operate today. The "Dobson unit", a convenient measure of the total amount of ozone in a column overhead, is named in his honor.

Contents

[hide]

1 Origin of ozone 2 Ultraviolet light and ozone 3 Distribution of ozone in the stratosphere 4 Ozone depletion

o 4.1 Regulation 5 References 6 Further reading

7 External links

[edit] Origin of ozone

Ozone-oxygen cycle in the ozone layer.

The photochemical mechanisms that give rise to the ozone layer were discovered by the British physicist Sidney Chapman in 1930. Ozone in the Earth's stratosphere is created by ultraviolet light striking oxygen molecules containing two oxygen atoms (O2), splitting them into individual oxygen atoms (atomic oxygen); the atomic oxygen then combines with unbroken O2 to create ozone, O3. The ozone molecule is also unstable (although, in the stratosphere, long-lived) and when ultraviolet light hits ozone it splits into a molecule of O2 and an atom of atomic oxygen, a continuing process called the ozone-oxygen cycle, thus creating an ozone layer in the stratosphere, the region from about 10 to 50 km (32,000 to 164,000 feet) above Earth's surface. About 90% of the ozone in our atmosphere is contained in the stratosphere. Ozone concentrations are greatest between about 20 and 40 km, where they range from about 2 to 8 parts per million. If all of the ozone were compressed to the pressure of the air at sea level, it would be only a few millimeters thick.

[edit] Ultraviolet light and ozone

Levels of ozone at various altitudes and blocking of ultraviolet radiation.

Although the concentration of the ozone in the ozone layer is very small, it is vitally important to life because it absorbs biologically harmful ultraviolet (UV) radiation coming from the Sun. UV radiation is divided into three categories, based on its

wavelength; these are referred to as UV-A (400-315 nm), UV-B (315-280 nm), and UV-C (280-100 nm). UV-C, which would be very harmful to humans, is entirely screened out by ozone at around 35 km altitude. UV-B radiation can be harmful to the skin and is the main cause of sunburn; excessive exposure can also cause genetic damage, resulting in problems such as skin cancer. The ozone layer is very effective at screening out UV-B; for radiation with a wavelength of 290 nm, the intensity at the top of the atmosphere is 350 billion times stronger than at the Earth's surface. Nevertheless, some UV-B reaches the surface. Most UV-A reaches the surface; this radiation is significantly less harmful, although it can potentially cause genetic damage.

UV-B energy levels at several altitudes. Blue line shows DNA sensitivity. Red line shows surface energy level with 10% decrease in ozone

[edit] Distribution of ozone in the stratosphere

The thickness of the ozone layer—that is, the total amount of ozone in a column overhead—varies by a large factor worldwide, being in general smaller near the equator and larger towards the poles. It also varies with season, being in general thicker during the spring and thinner during the autumn in the northern hemisphere. The reasons for this latitude and seasonal dependence are complicated, involving atmospheric circulation patterns as well as solar intensity.

Since stratospheric ozone is produced by solar UV radiation, one might expect to find the highest ozone levels over the tropics and the lowest over polar regions. The same argument would lead one to expect the highest ozone levels in the summer and the lowest in the winter. The observed behavior is very different: most of the ozone is found in the mid-to-high latitudes of the northern and southern hemispheres, and the highest levels are found in the spring, not summer, and the lowest in the autumn, not winter in the northern hemisphere. During winter, the ozone layer actually increases in depth. This puzzle is explained by the prevailing stratospheric wind patterns, known as the Brewer-Dobson circulation. While most of the ozone is indeed created over the tropics, the stratospheric circulation then transports it poleward and downward to the lower stratosphere of the high latitudes. However in the southern hemisphere, owing to the ozone hole

phenomenon, the lowest amounts of column ozone found anywhere in the world are over the Antarctic in the southern spring period of September and October.

Brewer-Dobson circulation in the ozone layer.

The ozone layer is higher in altitude in the tropics, and lower in altitude in the extratropics, especially in the polar regions. This altitude variation of ozone results from the slow circulation that lifts the ozone-poor air out of the troposphere into the stratosphere. As this air slowly rises in the tropics, ozone is produced by the overhead sun which photolyzes oxygen molecules. As this slow circulation bends towards the mid-latitudes, it carries the ozone-rich air from the tropical middle stratosphere to the mid-and-high latitudes lower stratosphere. The high ozone concentrations at high latitudes are due to the accumulation of ozone at lower altitudes.

The Brewer-Dobson circulation moves very slowly. The time needed to lift an air parcel from the tropical tropopause near 16 km (50,000 ft) to 20 km is about 4–5 months (about 30 feet (9.1 m) per day). Even though ozone in the lower tropical stratosphere is produced at a very slow rate, the lifting circulation is so slow that ozone can build up to relatively high levels by the time it reaches 26 km.

Ozone amounts over the continental United States (25°N to 49°N) are highest in the northern spring (April and May). These ozone amounts fall over the course of the summer to their lowest amounts in October, and then rise again over the course of the winter. Again, wind transport of ozone is principally responsible for the seasonal evolution of these higher latitude ozone patterns.

The total column amount of ozone generally increases as we move from the tropics to higher latitudes in both hemispheres. However, the overall column amounts are greater in the northern hemisphere high latitudes than in the southern hemisphere high latitudes. In addition, while the highest amounts of column ozone over the Arctic occur in the northern spring (March-April), the opposite is true over the Antarctic, where the lowest amounts of column ozone occur in the southern spring (September-October). Indeed, the highest amounts of column ozone anywhere in the world are found over the Arctic region during the northern spring period of March and April. The amounts then decrease over the course of the northern summer. Meanwhile, the lowest amounts of column ozone anywhere in the world are found over the Antarctic in the southern spring period of September and October, owing to the ozone hole phenomenon.

[edit] Ozone depletion

Main article: Ozone depletion

NASA projections of stratospheric ozone concentrations if chlorofluorocarbons had not been banned.

The ozone layer can be depleted by free radical catalysts, including nitric oxide (NO), nitrous oxide (N2O), hydroxyl (OH), atomic chlorine (Cl), and atomic bromine (Br). While there are natural sources for all of these species, the concentrations of chlorine and bromine have increased markedly in recent years due to the release of large quantities of manmade organohalogen compounds, especially chlorofluorocarbons (CFCs) and bromofluorocarbons.[3] These highly stable compounds are capable of surviving the rise to the stratosphere, where Cl and Br radicals are liberated by the action of ultraviolet light. Each radical is then free to initiate and catalyze a chain reaction capable of breaking down over 100,000 ozone molecules. The breakdown of ozone in the stratosphere results in the ozone molecules being unable to absorb ultraviolet radiation. Consequently, unabsorbed and dangerous ultraviolet-B radiation is able to reach the Earth’s surface.[citation needed] Ozone levels, over the northern hemisphere, have been dropping by 4% per decade. Over approximately 5% of the Earth's surface, around the north and south poles, much larger (but seasonal) declines have been seen; these are the ozone holes.

In 2009, nitrous oxide (N2O) was the largest ozone-depleting substance emitted through human activities. [4]

[edit] Regulation

In 1978, the United States, Canada and Norway, enacted bans on CFC-containing aerosol sprays that are thought to damage the ozone layer. The European Community rejected an analogous proposal to do the same. In the U.S., chlorofluorocarbons continued to be used in other applications, such as refrigeration and industrial cleaning, until after the discovery of the Antarctic ozone hole in 1985. After negotiation of an international treaty (the Montreal Protocol), CFC production was sharply limited beginning in 1987 and phased out completely by 1996.

On August 2, 2003, scientists announced that the depletion of the ozone layer may be slowing down due to the international ban on CFCs.[5] Three satellites and three ground stations confirmed that the upper atmosphere ozone depletion rate has slowed down significantly during the past decade. The study was organized by the American Geophysical Union. Some breakdown can be expected to continue due to CFCs used by nations which have not banned them, and due to gases which are already in the stratosphere. CFCs have very long atmospheric lifetimes, ranging from 50 to over 100 years, so the final recovery of the ozone layer is expected to require several lifetimes.

Compounds containing C–H bonds have been designed to replace the function of CFC's (such as HCFC), since these compounds are more reactive and less likely to survive long enough in the atmosphere to reach the stratosphere where they could affect the ozone layer. However, while being less damaging than CFC's, HCFC's also have a significant negative impact on the ozone layer. HCFC's are therefore also being phased out.[6]

http://en.wikipedia.org/wiki/Ozone_layer

Pentingnya Atmosfer Bumi

Manusia dapat bertahan sampai satu hari tanpa air di daerah gurun yang paling panas, tetapi tanpa udara manusia hanya bertahan beberapa menit saja. Jadi Anda tentu bisa menyimpulkan sendiri betapa pentingnya udara bagi kehidupan di bumi. Karena tanpa udara, maka manusia, hewan dan tumbuh-tumbuhan tidak dapat hidup. Udara untuk kehidupan sehari-hari terdapat di atmosfer.

Struktur Lapisan Atmosfer

Gambar 1: Struktur Lapisan Atmosfer  (Annenberg, 2009)

Bumi yang kita huni ini terdiri dari tiga unsur: padat, cair, gas. Bumi padat disebut juga litosfer, meliputi bagian inti bumi hingga lapisan terluar yang tampak sebagai permukaan tanah. Bumi cair disebut hidrosfer, mencakup air permukaan seperti laut, danau, sungai, juga berupa air di dalam tanah atau disebut air tanah, dan air yang terkandung di dalam atmosfer atau disebut air atmosfer. Bumi gas atau atmosfer merupakan seluruh gas yang menyelubungi bumi baik di bagian padat maupun cair. Ketiga unsur tersebut terkait erat dan saling mempengaruhi proses-proses yang terjadi di bumi secara keseluruhan. Atmosfer bumi merupakan lapisan gas yang menyelimuti bumi dan penting bagi kehidupan makhluk hidup.atmosfer setinggi 5.5-5.6 km telah mencakup 50% dari massa total dan pada ketinggian 40 km mencakup 99.99%. Batas bawah atmosfer relatif lebih mudah ditentukan berdasarkan ketinggian permukaan laut. Sedangkan puncaknya sulit ditentukan karena disamping besarnya keragaman ukuran dan massa partikel terdapat pula keragaman suhu permukaan bumi dan kekuatan angin yang mempengaruhi pengangkatan bahan (Nasir, dalam Handoko, 1995). Atmosfer dapat dibedakan berdasarkan parameter-parameter seperti tekanan udara, masa atmosfer dan profil temperatur. Profil temperatur vertikal dapat dibagi menjadi empat lapisan yang berbeda yaitu troposfer, stratosfer, mesosfer, dan termosfer. Puncak dari lapisan-lapisan tersebut adalah tropopause, stratopause, mesopause, dan termopause.

Nasir, dalam Handoko (1995) mengemukakan perubahan suhu udara di atmosfer secara vertikal (menurut ketinggian) berbeda-beda dapat dikelompokkan menjadi tiga hal:

1. dT/dz > 0 Suhu naik, dengan bertambahnya ketinggian. Hal ini disebut inversi suhu

2. dT/dz = 0 Suhu tetap walaupun ketinggian berubah. Hal ini disebut isotermal

3. dT/dz < 0 Suhu udara turun dengan bertambahnya ketinggian disebut lapse rate

Troposfer merupakan lapisan terbawah dari atmosfer terdapat pada ketinggian dari 8 km di daerah kutub dan 16 km di

ekuator. Ruang terjadinya sirkulasi dan turbulensi seluruh bahan atmosfer sehingga menjadi salah satu lapisan yang mengalami pembentukan dan perubahan cuaca seperti angin, awan, presipitasi, badai, kilat dan guntur. Kecepatan angin pada lapisan ini bertambah dengan naiknya ketinggian dan di troposfer ini pemindahan energi berlangsung. Radiasi surya menyebabkan pemanasan permukaan bumi yang selanjutnya panas tersebut diserap oleh air untuk berubah menjadi uap. Akibat proses evaporasi, energi panas diangkat oleh uap ke lapisan atas yang lebih tinggi berupa panas laten. Setelah terjadi pendinginan berlangsung proses kondensasi.

Pada lapisan ini suhu udara turun dengan bertambahnya ketinggian (dT/dz < 0) atau pada keadaan lapse rate. Rata-rata lapse rate seluruh dunia pada keadaan normal adalah      -6.5K setiap kenaikan ketinggian 1 km. Pada atmosfer normal, suhu troposfer berubah dari 150C pada permukaan laut menjadi -600C di puncak troposfer. Tekanan dan kerapatan udara di permukaan laut masing-masing adalah 1013.2 mb dan 1.23 km m-3. Lapisan di atasnya dengan suhu tetap atau meningkat disebut stratofer kisaran ketinggiannya antara 12-50 km diatas permukaan laut. Lapisan ini terdiri dari 3 wilayah antara lain Stratofer bawah krtinggiannya 12-20 km daerah isotermis, Stratosfer tengah ketinggiannya 20-35 km daerah inversi suhu, Stratosfer atas ketinggiannya 35-50 km daerah inversi suhu yang kuat. Lapisan ini tidak mengalami turbulensi maupun sirkulasi. Stratosfer merupakan lapisan atmosfer utama yang mengandung gas ozon.

Lapisan dengan suhu menurun dari 50-80 km disebut mesosfer dengan perubahan suhu terhadap ketinggian adalah lapse rate. Pada lapisan inisuhu udara sekitar -50C pada lapisan hingga -950C pada puncaknya. Tidak mengalami turbuleni atau sirkulasi udara. Merupakan daerah penguraian 02 menjadi atom O. Batas atasnya adalah lapisan mesopause dengan perubahan suhu terhadap ketinggian mulai bersifat isotermal. Lapisan di atasnya dengan suhu yang meningkat disebut termosfer. Lapisan ini ditandai dengan beberapa ciri yaitu memiliki ketinggian 80 km hingga batas yang sulit ditentukan karena sangat jarangnya partikel gas yang mencapai lapisan ini. Lapisan ini merupakan tempat berlangsungnya proses ionisasi gas ionasasi gas N2 dan O2 sehingga lapisan ini disebut ionosfer. Dimana diatas ketinggian 100km pengaruh radiasi uv dan sinar x makin kuat.

Karakteristik Atmosfer

Atmosfer merupakan udara yang menyelubungi bumi dan sangat berguna bagi keberlangsungan kehidupan di bumi karena beberapa sebab.  Pertama, atmosfer melindungi bumi dari pancaran radiasi matahari yang bersuhu 6000

derajat Kelvin. Kedua, atmosfer berperan penting dalam siklus hidrologi pada proses penampungan air dari permukaan bumi (daratan dan lautan). Ketiga, atmosfer mengandung oksigen yang dibutuhkan makhluk hidup untuk bernapas.

Keempat, atmosfer merupakan medium tempat bercampurnya beraneka unsur kimia yang berdampak pada kualitas udara.

 

 

 

 

Atmosfer terdiri dari beberapa lapisan dari yang terdekat dengan bumi: troposfer, stratosfer, mesosfer, termosfer. Lapisan tersebut dibedakan antara satu dan lainnya berdasarkan profil temperaturnya. Pada lapisan troposfer, ketinggian 10-12 km, profil temperaturnya berkurang terhadap ketinggian. Di stratosfer, ketinggian 50 km, profil temperaturnya bertambah terhadap ketinggian. Dan di termosfer, ketinggian 1000 km, profil temperaturnya kembali bertambah terhadap ketinggian.

Di atas termosfer adalah ionosfer merupakan puncak atmosfer yang langsung bersentuhan dengan ruang hampa udara. Lapisan terdekat bumi, troposfer, mengandung 6/7 bagian dari massa total atmosfer yang relatif tercampur secara sempurna, sangat basah, dan merupakan pusat aktivitas dan pembentukan awan maupun hujan.

http://www.dirgantara-lapan.or.id/moklim/edukasiatmosfer.html

Cuaca: Menimbulkan Kepanikan?24-Apr-2007 | 11:13

Selasa, 24/04/2007 jika semua bahan bakar yang telah diproduksi terbakar untuk beberapa jam,konsentrasi karbondioksida akan meningkat sekitar 800 parts per million(ppm). Menurut pendapat saya, kepanikan yang timbul atas isu pemanasan global sangatlah tidak adil.Tidak ada tindakan serius terhadap perubahan cuaca ini.Tidak perlu mendramatisasi dampak yang mungkin ditimbulkan secara berlebihan karena cuaca sendiri selalu berubah-ubah di bawah pengaruh alam,bahkan ketika manusia belum ada sekalipun. Institut kami telah melakukan perhitungan bahwa jika semua bahan bakar yang telah diproduksi terbakar untuk beberapa jam,konsentrasi karbondioksida akan meningkat sekitar 800 parts per million(ppm).

Ini adalah batas atas yang tak akan mudah terlampaui.Akan tetapi,sekalipun angka ini tidak sensasional pada era karbon 350 juta tahun lalu,bumi telah memiliki beberapa ribu ppm (10 kali lebih banyak).Kondisi saat ini ditandai oleh cepatnya pertumbuhan vegetasi yang menyisakan sejumlah besar cadangan batu bara.Penelitian terhadap inti es yang telah dilakukan oleh ilmuwan Rusia dari kedalaman Antartika membuktikan bahwa pada 450 ribu tahun,bumi telah empat kali mengalami perubahan suhu yang berfluktuasi pada kisaran 10 hingga 1 derajat. Kami juga telah mengetahui batas terendah yaitu lapisan es,dengan dasar putih yang konsentrasi CO2-nya tidak signifikan kurang dari 200 ppm.

Menimbang contoh yang didapatkan dari inti Antartika tersebut,proses pembentukan es terjadi sekali dalam 100 ribu tahun.Indikator-indikator CO2 berubah dari 200 ppm menjadi 350 ppm.Yang cukup menarik,dengan kondisi saat ini yang telah mencapai 379 ppm itu,bumi telah mendekati batas terendah.Secara teori,manusia lebih diserang oleh suhu dingin dibandingkan dengan pemanasan global. Namun,tampaknya dunia sangat menaruh perhatian pada pemanasan global dan potensi yang mungkin ditimbulkannya.Perkiraan atas prediksi cuaca abad ini menunjukkan peningkatan sekitar 2,5 C–3 C (dengan batas ekstrem dari 1,4 C–5,8 C).

Dengan demikian,ketinggian laut seharusnya naik 47 cm. Saya tidak melihat hal ini sebagai sebuah hal yang dapat mengakibatkan dampak serius bagi umat manusia.Tentu saja,beberapa dataran rendah dan pelabuhan pasti akan menghadapi masalah,tapi wilayah baru akan dibangun dan manusia akan tinggal di tempat yang lebih tinggi. Ilmuwan dari British Hadley Center telah berusaha membedakan bahaya global yang ditimbulkan pada es Greenland yang mencair.Mereka percaya bahwa jika suhu naik tiga derajat,dunia akan mengering dalam tiga ribu tahun.

Dalam perhitungan terbaru,kemungkinan cairnya es di Antartika barat dan Greenland akan terjadi dalam beberapa abad atau beberapa ribu tahun.Bahkan,beberapa ilmuwan memprediksikan perubahan di wilayah teluk akan menurunkan suhu di Skandinavia,tetapi kelompok ahli cuaca antar pemerintahan (IGEC) dan kelompok panel perubahan cuaca antar pemerintahan (IPCC) belum dapat mengonfirmasi hipotesis ini. Dalam perhitungan

terbaru ini,ratarata peningkatan suhu berada pada kisaran 0,74 C.Angka ini dipercaya cukup dapat menimbulkan efek negatif, tapi tetap saja belum ada bukti ilmiah untuk mendukung pernyataan ini. Sementara itu,pada 1974,ilmuwan Rusia Mikhail Budyko muncul dengan ide yang mungkin dapat memecahkan masalah pemanasan global dalam beberapa tahun.Idenya adalah untuk mengubah ’’kekuatan pancaran sinar matahari”dengan memenuhi stratosfer (lapisan pada ketinggian 12–16 km) dengan asam sulfur,sebagai contoh.

Hal ini diperkirakan dapat menurunkan radiasi solar pada permukaan bumi dan mengurangi suhu di troposfer beberapa derajat.Ini adalah salah satu instrumen yang dapat dipakai. Dapat saya tambahkan di sini bahwa pada musim gugur 2005 lalu,saya telah memublikasikan artikel dengan proposal yang konkret berdasarkan metode tersebut dan saya telah memberikan serangkaian wawancara. Beberapa rekan saya bahkan mendukung ide tersebut,sementara rekan lainnya masih cukup skeptis.Akan tetapi,pada akhir 2006,saya membaca artikel yang ditulis oleh pemenang Nobel Paul J Crutzen,ahli kimia dan meteorologi asal Belanda,yang menuliskan proposal yang sama tanpa merujuk referensi dari Yury Izrael.

Saat ini,tujuan utama yang ingin dicapai adalah menstabilisasikan cuaca atau pada tingkat masa preantropogenik (sebelum revolusi industri) pada kisaran 280 ppm. Terdapat banyak sekali perubahan parameter yang memengaruhi arus radiasi,dalam hal ini,cuaca.Emisi rumah panas memiliki efek terkuat. Emisi ini telah meningkatkan arus radiasi,yang dipercaya telah menaikkan rata-rata suhu di permukaan bumi hingga mencapai 0,6 C–0,7 C.

Ada juga penyebab lain yang dapat memanaskan udara atau mendinginkannya sekalipun.Kemungkinan terburuk adalah adanya partikelpartikel aerosol keras yang dihasilkan dari pabrik-pabrik,pesawat,gunung berapi,dan badai debu.Saya menyarankan agar kita tidak terlalu peduli dengan CO2 yang tidak terlalu memberikan dampak serius pada cuaca.Bahkan,lebih masuk akal untuk berusaha menurunkan radiasi solar 0,3%–0,5%. Aerosol di lapisan stratosfer memiliki kapasitas terbesar dalam mengurangi radiasi solar.Dalam perkiraan sementara,untuk dapat menurunkan suhu di troposfer hingga satu derajat, sangatlah penting untuk memenuhi lapisan ini dengan jutaan ton aerosol atau 300 ribu ton sulfur yang dibakar. Kita dapat saja menyebarkan sulfur pada troposfer melalui beberapa metode atau menerbangkan pesawat pada ketinggian tertentu dengan membawa bahan bakar sulfur.

Langkah ini akan menurunkan suhu troposfer dengan cepat dalam dua atau tiga tahun. Akan tetapi,apa yang akan terjadi pada aerosol tiruan ini terkait dengan masa hidup stratosfer dalam satu hingga dua tahun? Mereka akan beterbangan di angkasa,membentang pada lintang 30 hingga 70 derajat. Bentangan ini akan memberikan perlindungan pada bumi dari radiasi solar.Akankah ada dampak terhadap biosfer dan kesehatan manusia? Perhitungan menunjukkan bahwa penurunan radiasi solar akan kurang dari 1% mendekati permukaan bumi. Hal ini biasa terjadi setelah adanya ledakan gunung berapi dan dapat dipastikan tidak akan mematikan kehidupan di bumi.

Jumlah aerosol yang jatuh ke tanah akan mencapai 0,2 mg Sulfur per meter persegi per tahun atau sekitar 1.000 kali lebih sedikit dibandingkan yang biasa dihasilkan oleh emisi industri pada hujan dan salju yang turun. Yang lebih penting,tindakan semacam ini akan berkaitan erat dengan perjanjian internasional, seperti Konvensi 1978 antara Soviet dan Amerika mengenai pelarangan penggunaan teknik modifikasi lingkungan untuk tujuan militer atau tujuan lain.

Sekalipun langkah ini tidak ditujukan untuk menyerang negara lain,tetapi didesain untuk menangani masalah perubahan cuaca tantangan global. PBB telah mengadopsi sebuah kerangka kerja bagi Konvensi mengenai perubahan cuaca di Rio de Janeiro pada 1992.Tujuan utamanya adalah menstabilisasi emisi rumah kaca di udara pada level yang tidak berbahaya akibat revolusi industri. Pada 1997,konvensi ini didukung oleh protokol Kyoto,yaitu negara-negara industrialis memutuskan untuk mengurangi efek rumah kaca dengan sukarela hingga mencapai rata-rata 5,3% dari 2008 hingga 2012.

Dokumen ini memfokuskan pada emisi rumah kaca yang mempunyai dampak terbesar pada cuaca. Tapi,pastinya,akan memerlukan waktu yang panjang untuk menurunkan CO2 dan emisi rumah kaca dengan tujuan menstabilkan tingkat atmosfer.Ini adalah sebuah tugas yang kurang disukai negaranegara industrialis.Lebih jauh lagi, IGECC memperkirakan bahwa sejumlah besar dana akan dikeluarkan telah mencapai 18 triliun dolar pada abad ini.

Metode dengan memakai efek aerosol pada stratosfer tentunya akan lebih murah,seratus kali lebih cepat dan mudah dihentikan jika berdampak buruk. Semua ini berjalan tanpa harus dikatakan bahwa metode ini harus disetujui oleh komunitas dunia.Untuk sementara,ilmuwan Rusia masih bekerja sendiri dengan membuat detail bagi perhitungan lebih jauh.( YURY IZRAEL (RIA NOVOSTI) Akademisi dari Akademi Ilmu Pengetahuan Rusia dan mengepalai Institut Ekologi dan Cuaca Global)

http://library.pelangi.or.id/?pilih=arsip&topik=7&nid=2632

.:: Profil Suhu dan Tekanan terhadap Ketinggian ::.

1. TroposferPada lapisan troposfer, semakin ke atas suhu dan tekanan semakin rendah.Lapisan yang membatasi antara Troposfer dengan Stratosfer dinamakan Lapisan Tropopause.Di lapisan troposfer ketinggian pada ekuator + 17 – 20 Km, dan pada kutub + 8 Km.Suhu di lapisan troposfer pada daerah ekuator mencapai – 80 derajat celcius dan pada daerah kutub mencapai – 60 derajat celcius. Tekanan pada tropopause mencapai + 100 mb. Lapisan Troposfer pada ketinggian lebih dari 5 Km, suhu mencapai 0 derajat celcius pada tekanan + 500 – 600 mb.

2. StratosferPada lapisan stratosfer, semakin ke atas suhu semakin tinggi dan tekanan semakin rendah.Lapisan yang membatasi antara Stratosfer dengan Mesosfer dinamakan Stratopause.Tekanan pada lapisan stratopause mencapai + 0 mb dan ketinggiannya mencapai + 50 Km.Pada lapisan stratosfer terdapat partikel – partikel ringan. Suhu di lapisan stratopause sekitar 17 derajat celcius.

3. MesosferPada lapisan ini, semakin ke atas suhu semakin rendah hingga mencapai – 90 derajat celcius. Pada lapisan mesosfer tidak terdapat tekanan atau ruang hampa udara. Lapisan yang membatasi antara mesosfer dengan thermosfer dinamakan mesopause.Ketinggian mesopause mencapai +80 km.

4. ThermosferPada lapisan thermosfer suhunya mencapai ribuan derajat celcius.Dan lapisan yang membatasi thermosfer dengan lapisan di atasnya dinamakan lapisan thermopause.

http://meteorologi43-d.blogspot.com/2009/01/profil-suhu-dan-tekanan-terhadap.html

Tentang Atmosfer

Friday, November 21, 2008 — danangekonuryanto

Berbicara tentang atmosfer, samakah atmosfer dengan langit. Bahasa Al Qur’an pada Surah tersebut di bwah ini membicarakan tentang penciptaan langit.

(Al Baqoroh (2):29)

29. Dia-lah Allah, yang menjadikan segala yang ada di bumi untuk kamu dan Dia berkehendak (menciptakan) langit, lalu dijadikan-Nya tujuh langit. dan Dia Maha mengetahui segala sesuatu.

(Fushshilat (41):11-12)

11. kemudian Dia menuju kepada penciptaan langit dan langit itu masih merupakan asap, lalu Dia berkata kepadanya dan kepada bumi: “Datanglah kamu keduanya menurut perintah-Ku dengan suka hati atau terpaksa”. keduanya menjawab: “Kami datang dengan suka hati”.

12. Maka Dia menjadikannya tujuh langit dalam dua masa. Dia mewahyukan pada tiap-tiap langit urusannya. dan Kami hiasi langit yang dekat dengan bintang-bintang yang cemerlang dan Kami memeliharanya dengan sebaik-baiknya. Demikianlah ketentuan yang Maha Perkasa lagi Maha mengetahui.

Kalau menurut tante wiki, berbicara tentang atmosfer menyebutkan bahwa atmosfer adalah lapisan gas yang melingkupi sebuah planet, termasuk bumi, dari permukaan planet tersebut sampai jauh di luar angkasa. Di bumi, atmosfer terdapat dari ketinggian 0 km di atas permukaan tanah, sampai dengan sekitar 560 km dari atas permukaan bumi. Atmosfer tersusun atas beberapa lapisan, yang dinamai menurut fenomena yang terjadi di lapisan tersebut. Transisi antara lapisan yang satu dengan yang lain berlangsung bertahap. Studi tentang atmosfer mula-mula dilakukan untuk memecahkan masalah cuaca, fenomena pembiasan sinar matahari saat terbit dan tenggelam, serta kelap-kelipnya bintang. Dengan peralatan yang sensitif yang dipasang di wahana luar angkasa, kita dapat memperoleh pemahaman yang lebih baik tentang atmosfer berikut fenomena-fenomena yang terjadi di dalamnya.

Atmosfer Bumi terdiri atas nitrogen (78.17%) dan oksigen (20.97%), dengan sedikit argon (0.9%), karbondioksida (variabel, tetapi sekitar 0.0357%), uap air, dan gas lainnya. Atmosfer melindungi kehidupan di bumi dengan menyerap radiasi sinar ultraviolet dari matahari dan mengurangi suhu ekstrem di antara siang dan malam. 75% dari atmosfer ada dalam 11 km dari permukaan planet.

Atmosfer tidak mempunyai batas mendadak, tetapi agak menipis lambat laun dengan menambah ketinggian, tidak ada batas pasti antara atmosfer dan angkasa luar.

Berikut nama-nama lapisat atmosfer dikenal :TroposferLapisan ini berada pada level yang paling rendah, di mana campuran gas-gasnya adalah yang paling ideal untuk menopang kehidupan di bumi. Di lapisan ini kehidupan juga terlindung dari sengatan radiasi yang dipancarkan oleh benda-benda langit lain. Dibandingkan dengan lapisan atmosfer yang lain, lapisan ini adalah yang paling tipis (kurang lebih 15 kilometer dari permukaan tanah). Di dalam lapisan ini, hampir semua jenis cuaca, perubahan suhu yang mendadak, angin tekanan dan kelembaban yang kita rasakan sehari-hari terjadi.Ketinggian yang paling rendah adalah bagian yang paling hangat dari troposfer, karena permukaan bumi menyerap radiasi panas dari matahari dan menyalurkan panasnya ke udara. Biasanya, jika ketinggian bertambah, maka suhu udara akan berkurang secara tunak (steady), dari sekitar 17 sampai -52 . Namun topografi di permukaan bumi, ℃ ℃seperti pegunungan dan plato (dataran tinggi) dapat menyebabkan anomali terhadap gradien suhu tersebut.Diantara stratosfer dan troposfer terdapat lapisan yang biasanya dilewati/digunakan pesawat Komersil mengudara yang disebut lapisan Tropopouse.

StratosferPerubahan secara bertahap dari troposfer ke stratosfer dimulai dari ketinggian sekitar 11 km. Suhu di lapisan stratosfer yang paling bawah relatif stabil dan sangat dingin yaitu – 70oF atau sekitar – 57oC. Pada lapisan ini angin yang sangat kencang terjadi dengan pola aliran yang tertentu. Awan tinggi jenis cirrus kadang-kadang terjadi di lapisan paling bawah, namun tidak ada pola cuaca yang signifikan yang terjadi pada lapisan ini.Dari bagian tengah stratosfer keatas, pola suhunya berubah menjadi semakin bertambah semakin naik, karena bertambahnya lapisan dengan konsentrasi ozon yang bertambah. Lapisan ozon ini menyerap radiasi sinar ultra ungu. Suhu pada lapisan ini bisa mencapai sekitar 18oC pada ketinggian sekitar 40 km. Lapisan stratopause memisahkan stratosfer dengan lapisan berikutnya.

MesosferKurang lebih 25 mil atau 40km diatas permukaan bumi terdapat lapisan transisi menuju lapisan mesosfer. Pada lapisan ini, suhu kembali turun ketika ketinggian bertambah, sampai menjadi sekitar – 143oC di dekat bagian atas dari lapisan ini, yaitu kurang lebih 81 km diatas permukaan bumi. Suhu serendah ini memungkinkan terjadi awan noctilucent, yang terbentuk dari kristal es.

TermosferTransisi dari mesosfer ke termosfer dimulai pada ketinggian sekitar 81 km. Dinamai termosfer karena terjadi kenaikan temperatur yang cukup tinggi pada lapisan ini yaitu sekitar 1982oC. Perubahan ini terjadi karena serapan radiasi sinar ultra ungu. Radiasi ini menyebabkan reaksi kimia sehingga membentuk lapisan bermuatan listrik yang dikenal dengan nama ionosfer, yang dapat memantulkan gelombang radio. Sebelum munculnya

era satelit, lapisan ini berguna untuk membantu memancarkan gelombang radio jarak jauh.Fenomena aurora yang dikenal juga dengan cahaya utara atau cahaya selatan terjadi disini.

EksosferAdanya refleksi cahaya matahari yang dipantulkan oleh partikel debu meteoritik. Cahaya matahari yang dipantulkan tersebut juga disebut sebagai cahaya Zodiakal

Cahaya matahari merupakan fenomena yang penting, karena walaupun tidak terlihat secara langsung, tetapi memberikan pengaruh pada lingkungan bumi. Atmosfer bumi, walaupun secara tidak signifikan terganggu, tetapi memberikan pengaruh pada kondisi iklim, dan teknologi satelit, serta teknologi komunikasi saat ini.

Meskipun atmosfer bumi yang mendukung kehidupan hanyalah setinggi 10 km dari permukaan, lapisan atmosfer yang lebih di atas lagi mencapai ratusan kilometer, menipis seiring ketinggian. Pada fase solar maksimum, radiasi dengan panjang gelombang ultraviolet ekstrim memanaskan lapisan atas atmosfer ini, (disebut sebagai termosfer, dan berada pada ketinggian lebih dari 100 km). Banyak satelit yang terletak pada ketinggian ini. Meskipun termosfer sangatlah tidak rapat dibandingkan lapisan atmosfer bawah, tetapi kerapatannya tetap saja memberikan pengaruh hambatan pada lintasan orbit satelit yang berada disana.

Selama periode matahari minimum, temperatur termosfer mencapai 700 derajat celsius, dan meningkat pada periode matahari maksimum. Panas berlebih ini menyebabkan termosfer mengembang. Pengembangan akan menyebabkan kerapatan meningkat, sehingga lintasan satelit di daerah tersebut mengalami gangguan. Dengan mengamati perubahan lintasan satelit, dapat ditentukan kerapatan udara di daerah tersebut, dan dengan dengan demikian dapat dilihat dinamika atmosfer pada saat tersebut.

Saat ini teknologi komunikasi memanfaatkan ribuan satelit yang diluncurkan, dan kebergantungan manusai sangat besar pada komunikasi yang semakin canggih, seperti komputer yang online, telepon selular, perbankan real-time online, dan sistem elektronik yang lainnya. Tetapi ketika, matahari melepaskan radiasi energi tinggi-nya, (yang mengarah ke bumi), maka lapisan atmosfer terluar bumi mengalami hujan partikel bermuatan tinggi, yang dayanya bisa mencapai 1500 gigawatts (mencapai empat kali pembangkit tenaga di seluruh amerika), maka interferensi dengan semua peralatan elektronik yang berada pada lingkungan itu (satelit) tidak terelakkan. Dan semua transmisi elektronik yang memanfaatkan penjalaran sinyal melalui satelit-satelit tersebut tentulah mengalami gangguan. Dengan demikian, maka terjadi gangguan pada aktivitas manusia di permukaan bumi yang terbiasa memanfaatkan teknologi tersebut. Meskipun kita tidak menyadari secara langsung keberadaan gangguan tersebut, tetapi telah menjadi pekerjaan besar bagi mereka yang mengurusi pengaturan daya dan tenaga elektronik di seluruh dunia, dalam mengatasi gangguan signfikan dari antariksa ini. http://dimensi5.wordpress.com/2008/11/21/tentang-atmosfer/

Earth's atmosphereFrom Wikipedia, the free encyclopedia

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"Air" redirects here. For other uses, see Air (disambiguation).

Blue light is scattered more than other wavelengths by the gases in the atmosphere, giving the Earth a blue halo when seen from space

The Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. 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. Dry air contains roughly (by volume) 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, and trace amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%.

The atmosphere has a mass of about five quadrillion (5x1015) tonnes, three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface. The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. An altitude of 120 km (75 mi) is where atmospheric effects become noticeable during atmospheric reentry of spacecraft. The Kármán line, at 100 km (62 mi), also is often regarded as the boundary between atmosphere and outer space.

Contents

[hide] 1

Composition 2 Structure of

the atmosphere

2.1 Principal layers

2.2 Other layers

3 Physical properties

3.1 Pressure and thickness

3.2 Density and mass

4 Optical properties

4.1 Scattering

4.2 Absorption

4.3 Emission

4.4 Refractive index

5 Circulation 6 Evolution

of Earth's atmosphere

6.1 Earliest atmosphere

6.2 Second atmosphere

6.3 Third atmosphere

6.4 Air pollution

7 See also 8 References 9 External

links

[edit] Composition

Main article: Atmospheric chemistry

Composition of Earth's atmosphere as of Dec. 1987. The lower pie represents the trace gases which together compose 0.038% of the atmosphere. Values normalized for illustration.

Mean atmospheric water vapor

Air is mainly composed of nitrogen, oxygen, and argon, which together constitute the "major gases" of the atmosphere. The remaining gases often are referred to as "trace gases,"[1] among which are the greenhouse gases such as water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Filtered air includes trace amounts of many other chemical compounds. Many natural substances may be present in tiny amounts in an unfiltered air sample, including dust, pollen and spores, sea spray, volcanic ash, and meteoroids. Various industrial pollutants also may be present, such as chlorine (elementary or in compounds), fluorine (in compounds), elemental mercury, and sulfur (in compounds such as sulfur dioxide [SO2]).

Composition of dry atmosphere, by volume[2]ppmv: parts per million by volume (note: volume fraction is equal to mole fraction for ideal gas only, see Gas volume#Partial volume)Gas VolumeNitrogen (N2) 780,840 ppmv (78.084%)

Oxygen (O2) 209,460 ppmv (20.946%)

Argon (Ar) 9,340 ppmv (0.9340%)Carbon dioxide (CO2) 383 ppmv (0.0383%)

Neon (Ne) 18.18 ppmv (0.001818%)Helium (He) 5.24 ppmv (0.000524%)Methane (CH4) 1.745 ppmv (0.0001745%)

Krypton (Kr) 1.14 ppmv (0.000114%)Hydrogen (H2) 0.55 ppmv (0.000055%)

Nitrous oxide (N2O) 0.3 ppmv (0.00003%)

Xenon (Xe) 0.09 ppmv (9x10−6%)Ozone (O3) 0.0 to 0.07 ppmv (0% to 7x10−6%)

Nitrogen dioxide (NO2) 0.02 ppmv (2x10−6%)

Iodine (I) 0.01 ppmv (1x10−6%)Carbon monoxide (CO) 0.1 ppmvAmmonia (NH3) trace

Not included in above dry atmosphere:Water vapor (H2O) ~0.40% over full atmosphere, typically 1%-4% at surface

[edit] Structure of the atmosphere

[edit] Principal layers

Layers of the atmosphere (not to scale)

Earth's atmosphere can be divided into five main layers. These layers are mainly determined by whether temperature increases or decreases with altitude. From lowest to highest, these layers are:

Troposphere The troposphere begins at the surface and extends to between 7 km (23,000 ft) at the poles and 17 km (56,000 ft) at the equator, with some variation due to weather. The troposphere is mostly heated by transfer of energy from the surface, so on average the lowest part of the troposphere is warmest and temperature decreases with altitude. This promotes vertical mixing (hence the origin of its name in the Greek word "τροπή", trope, meaning turn or overturn). The troposphere contains roughly 80% of the mass of the atmosphere. The tropopause is the boundary between the troposphere and stratosphere.

Stratosphere The stratosphere extends from the tropopause to about 51 km (32 mi; 170,000 ft). Temperature increases with height, which restricts turbulence and mixing. The stratopause, which is the boundary between the stratosphere and mesosphere, typically is at 50 to 55 km (31 to 34 mi; 160,000 to 180,000 ft). The pressure here is 1/1000th sea level.

Mesosphere The mesosphere extends from the stratopause to 80–85 km (50–53 mi; 260,000–280,000 ft). It is the layer where most meteors burn up upon entering the atmosphere. Temperature decreases with height in the mesosphere. The mesopause, the temperature minimum that marks the top of the mesosphere, is the coldest place on Earth and has an average temperature around −100 °C (−148.0 °F; 173.1 K).

Thermosphere Temperature increases with height in the thermosphere from the mesopause up to the thermopause, then is constant with height. The temperature of this layer can rise to 1,500 °C (2,730 °F), though the gas molecules are so far apart that temperature in the usual sense is not well defined. The International Space Station orbits in this layer, between 320 and 380 km (200 and 240 mi). The top of the thermosphere is the bottom of the exosphere, called the exobase. Its height varies with solar activity and ranges from about 350–800 km (220–500 mi; 1,100,000–2,600,000 ft).

Exosphere The outermost layer of Earth's atmosphere extends from the exobase upward. Here the particles are so far apart that they can travel hundreds of km without colliding with one another. Since the particles rarely collide, the atmosphere no longer behaves like a fluid. These free-moving particles follow ballistic trajectories and may migrate into and out of the magnetosphere or the solar wind. The exosphere is mainly composed of hydrogen and helium.

[edit] Other layers

Within the five principal layers determined by temperature are several layers determined by other properties.

The ozone layer is contained within the stratosphere. In this layer ozone concentrations are about 2 to 8 parts per million, which is much higher than in the lower atmosphere but still very small compared to the main components of the atmosphere. It is mainly located in the lower portion of the stratosphere from about 15–35 km (9.3–22 mi; 49,000–110,000 ft), though the thickness varies seasonally and geographically. About 90% of the ozone in our atmosphere is contained in the stratosphere.

The ionosphere, the part of the atmosphere that is ionized by solar radiation, stretches from 50 to 1,000 km (31 to 620 mi; 160,000 to 3,300,000 ft) and typically overlaps both the exosphere and the thermosphere. It forms the inner edge of the magnetosphere. It has practical importance because it influences, for example, radio propagation on the Earth. It is responsible for auroras.

The homosphere and heterosphere are defined by whether the atmospheric gases are well mixed. In the homosphere the chemical composition of the atmosphere does not depend on molecular weight because the gases are mixed by turbulence.[3] The homosphere includes the troposphere, stratosphere, and mesosphere. Above the turbopause at about 100 km (62 mi; 330,000 ft) (essentially corresponding to the mesopause), the composition varies with altitude. This is because the distance that particles can move without colliding with one another is large compared with the size of motions that cause mixing. This allows the gases to stratify by molecular weight, with the heavier ones such as oxygen and nitrogen present only near the bottom of the heterosphere. The upper part of the heterosphere is composed almost completely of hydrogen, the lightest element.

The planetary boundary layer is the part of the troposphere that is nearest the Earth's surface and is directly affected by it, mainly through turbulent diffusion. During the day the planetary boundary layer usually is well-mixed, while at night it becomes stably stratified with weak or intermittent mixing. The depth of the planetary boundary layer ranges from as little as about 100 m on clear, cold nights to 3000 m or more during the afternoon in dry regions.

The average temperature of the atmosphere at the surface of Earth is 14 °C (57 °F; 287 K)[4] or 15 °C (59 °F; 288 K)[5], depending on the reference.[6] [7] [8]

[edit] Physical properties

[edit] Pressure and thickness

Main article: Atmospheric pressure

The average atmospheric pressure at sea level is about 1 atmosphere (atm) = 101.3 kPa (kilopascals) = 14.7 psi (pounds per square inch) = 760 torr = 29.9 inches of mercury (symbol Hg). Total atmospheric mass is 5.1480×1018 kg (1.135×1019 lb).[9] Atmospheric pressure is the total weight of the air above the point at which the pressure is measured. Thus air pressure varies with location and time, because the amount of air above the Earth's surface varies with location and time.

Were atmospheric density to remain constant with height the atmosphere would terminate abruptly at 8.50 km (27,900 ft). Instead, density decreases with height, dropping by 50% at an altitude of about 5.6 km (18,000 ft). As a result the pressure decrease is approximately exponential with height, so that pressure decreases by approximately half every 5.6 km (18,000 ft) and by 63.2% (1 − 1 / e = 1 − 0.368 = 0.632) every 7.64 km (25,100 ft), the average scale height of Earth's atmosphere below 70 km (43 mi; 230,000 ft). However, because of changes in temperature, average molecular weight, and gravity throughout the atmospheric column, the dependence of atmospheric pressure on altitude is modeled by separate equations for each of the layers listed above. Even in the exosphere, the atmosphere is still present. This can be seen by the effects of atmospheric drag on satellites.

In summary, the equations of pressure by altitude in the above references can be used directly to estimate atmospheric thickness. However, the following published data are given for reference:[10]

50% of the atmosphere by mass is below an altitude of 5.6 km (18,000 ft). 90% of the atmosphere by mass is below an altitude of 16 km (52,000 ft). The

common altitude of commercial airliners is about 10 km (33,000 ft) and Mt. Everest's summit is 8,848 m (29,030 ft) above sea level.

99.99997% of the atmosphere by mass is below 100 km (62 mi; 330,000 ft), although in the rarefied region above this there are auroras and other atmospheric effects. The highest X-15 plane flight in 1963 reached an altitude of 354,300 ft (108.0 km).

[edit] Density and mass

Temperature and mass density against altitude from the NRLMSISE-00 standard atmosphere modelMain article: Density of air

The density of air at sea level is about 1.2 kg/m3 (1.2 g/L). Density is not measured directly but is calculated from measurements of temperature, pressure and humidity using the equation of state for air (a form of the ideal gas law). Atmospheric density decreases as the altitude increases. This variation can be approximately modeled using the barometric formula. More sophisticated models are used by meteorologists and space agencies to predict weather and orbital decay of satellites.

The average mass of the atmosphere is about 5 quadrillion (5x1015) tonnes or 1/1,200,000 the mass of Earth. According to the National Center for Atmospheric Research, "The total mean mass of the atmosphere is 5.1480 × 1018 kg with an annual range due to water vapor of 1.2 or 1.5 × 1015 kg depending on whether surface pressure or water vapor data are used; somewhat smaller than the previous estimate. The mean mass of water vapor is estimated as 1.27 × 1016 kg and the dry air mass as 5.1352 ±0.0003 × 1018 kg."

[edit] Optical properties

See also: Sunlight

Earth's atmosphere from space. The blue color of the atmosphere is due to Rayleigh scattering; shorter (blue) wavelengths of light are scattered more easily than longer (red) wavelengths.

Solar radiation (or sunlight) is the energy the Earth receives from the Sun. The Earth also emits radiation back into space, but at longer wavelengths that we cannot see. Depending on its condition, the atmosphere can block radiation from coming in or going out. Important examples of this are clouds and the greenhouse effect.

[edit] Scattering

Main article: Scattering

When light passes through our atmosphere, photons interact with it through scattering. If the light does not interact with the atmosphere, it is called direct radiation and is what you see if you were to look directly at the sun. Indirect radiation is light that has been scattered in the atmosphere. For example, on an overcast day when you can't see your shadow there is no direct radiation reaching you, it has all been scattered. As another example, due to a phenomenon called Rayleigh scattering, shorter (blue) wavelengths

scatter more easily than longer (red) wavelengths. This is why the sky looks blue, you are seeing scattered blue light. This is also why sunsets are red. Because the sun is close to the horizon, the sun rays pass through more atmosphere than normal to reach your eye. Much of the blue light has been scattered out, leaving the red light in a sunset.

[edit] Absorption

Main article: Absorption (electromagnetic radiation)

Different molecules absorb different wavelengths of radiation. For example, O2 and O3

absorb almost all wavelengths shorter than 300 nanometers. Water (H2O) absorbs many

wavelengths above 700 nm. When a molecule absorbs a photon, it increases the energy of the molecule. We can think of this as heating the atmosphere, but the atmosphere also cools by emitting radiation, as discussed below.

Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light.

The combined absorption spectra of the gasses in the atmosphere leave "windows" of low opacity, allowing the transmission of only certain bands of light. The optical window runs from around 300 nm (ultraviolet-C) up into the range humans can see, the visible spectrum (commonly called light), at roughly 400–700 nm and continues to the infrared to around 1100 nm. There are also infrared and radio windows that transmit some infrared and radio waves at longer wavelengths. For example, the radio window runs from about one centimeter to about eleven-meter waves.

[edit] Emission

Main article: Emission (electromagnetic radiation)

Emission is the opposite of absorption, it is when an object emits radiation. Objects tend to emit amounts and wavelengths of radiation depending on their "black body" emission curves, therefore hotter objects tend to emit more radiation, with shorter wavelengths. Colder objects emit less radiation, with longer wavelengths. For example, the sun is approximately 6,000 K (5,730 °C; 10,340 °F), its radiation peaks near 500 nm, and is visible to the human eye. The Earth is approximately 290 K (17 °C; 62 °F), so its radiation peaks near 10,000 nm, and is much too long to be visible to humans.

Because of its temperature, the atmosphere emits infrared radiation. For example, on clear nights the Earth's surface cools down faster than on cloudy nights. This is because clouds (H2O) are strong absorbers and emitters of infrared radiation. This is also why it

becomes colder at night at higher elevations. The atmosphere acts as a "blanket" to limit the amount of radiation the Earth loses into space.

The greenhouse effect is directly related to this absorption and emission (or "blanket") effect. Some chemicals in the atmosphere absorb and emit infrared radiation, but do not interact with sunlight in the visible spectrum. Common examples of these chemicals are

CO2 and H2O. If there are too much of these greenhouse gasses, sunlight heats the

Earth's surface, but the gases block the infrared radiation from exiting back to space. This imbalance causes the Earth to warm, and thus climate change.

[edit] Refractive index

The refractive index of air is close to, but just greater than 1. Systematic variations in refractive index can lead to the bending of light rays over long optical paths. One example is that under some circumstances ships can see other vessels just over the horizon because light is refracted in the same direction as the curvature of the Earth's surface.

See also: Scintillation (astronomy)

[edit] Circulation

Main article: Atmospheric circulation

An idealised view of three large circulation cells.

Atmospheric circulation is the large-scale movement of air, and the means (with ocean circulation) by which heat is distributed around the Earth. The large-scale structure of the atmospheric circulation varies from year to year, but the basic structure remains fairly constant as it is determined by the Earth's rotation rate and the difference in solar radiation between the equator and poles.

[edit] Evolution of Earth's atmosphere

See also: History of Earth, Gaia hypothesis, and Paleoclimatology

[edit] Earliest atmosphere

The outgassings of the Earth were stripped away by solar wind early in the history of the planet until a steady state was established, the first atmosphere. Based on today's volcanic evidence, this atmosphere would have contained 80% water vapor, 10% carbon dioxide, 5 to 7% hydrogen sulfide, and smaller amounts of nitrogen, carbon monoxide, hydrogen, methane and inert gases.

A major rainfall led to the buildup of a vast ocean, enriching the other agents, first carbon dioxide and later nitrogen and inert gases. A major part of carbon dioxide exhalations were soon dissolved in water and built up carbonatic sediments.

[edit] Second atmosphere

Water related sediments have been found dating from as early as 3.8 billion years ago [11]. About 3.4 billion years ago, nitrogen was the major part of the then stable "second atmosphere." An influence of life has to be taken into account rather soon in the history of the atmosphere, since hints of early life forms are to be found as early as 3.5 billion years ago[12]. The fact that this is not perfectly in line with the - compared to today 30% lower - solar radiance of the early sun has been described as the "Faint young Sun paradox".

The geological record however shows a continually relatively warm surface during the complete early temperature record of the Earth with the exception of one cold glacial phase about 2.4 billion years ago. Sometime during the late Archaean era an oxygen-containing atmosphere began to develop, apparently from photosynthesizing algae which have been found as stromatolite fossils from 2.7 billion years ago. The early basic carbon isotopy (isotope ratio proportions) is very much in line with what is found today,[13] suggesting that the fundamental features of the carbon cycle were established as early as 4 billion years ago.

[edit] Third atmosphere

Oxygen content of the Atmosphere since one Billion years

The accretion of continents about 3.5 billion years ago[14] added plate tectonics, constantly rearranging the continents and also shaping long-term climate evolution by allowing the transfer of carbon dioxide to large land-based carbonate storages. Free oxygen did not exist until about 1.7 billion years ago and this can be seen with the development of the red beds and the end of the banded iron formations. This signifies a shift from a reducing atmosphere to an oxidising atmosphere. O2 showed major ups and

downs until reaching a steady state of more than 15%[15]. The following time span was the Phanerozoic era, during which oxygen-breathing metazoan life forms began to appear.

Currently, anthropogenic greenhouse gases are increasing in the atmosphere. According to the Intergovernmental Panel on Climate Change, this increase is the main cause of global warming.[16]

[edit] Air pollution

Main article: Air pollution

Air pollution is the human introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to organisms, into the atmosphere.[17] Stratospheric ozone depletion is believed to be caused by air pollution (chiefly from chlorofluorocarbons).[citation needed]

Worldwide, air pollution is responsible for large numbers of deaths and respiratory disease.[citation needed] Enforced air quality standards, like the Clean Air Act in the United States, have reduced the presence of some pollutants.[citation needed] While

major stationary sources are often identified with air pollution, the greatest source of emissions is actually mobile sources, principally the automobile.[citation needed]