वायुमण्डललाई अङ्ग्रेजीमा Atmosphere जो (ग्रीक भाषाको ἀτμός - atmos "vapor" and σφαῖρα - sphaira "sphere") बाट बनिएको हो र नेपालीमा यो दुई शव्द(वायु+मण्डल)ले बनेकोछ जसको अर्थ हुन्छ- वायु(हावा)को समूह। वायुमण्डलले अपार गुरूत्व(भार) भएको पिण्ड (ग्रह आदि)लाई घेरेको हुन्छ र ग्रहको गुरूत्वाकर्षण शक्तिले वायुमण्डललाई थामेर राख्छ। यदि ग्रहको गुरूत्व धेरै र वायुमण्डलको ताप कम छ भनें वायुमण्डललाई लामो समयसम्म थामेर राख्छ। कुनै-कुनै ग्रह हरू धेरै प्रकारका ग्यासहरू (gases)ले मिलेर बनेका छन् तर ती ग्रहहरूको पनि बाहिरी परतलाई मात्र वायुमण्डल भनिन्छ (हेर्नुहोस् यहाँ).
तारकीय वायुमण्डल(वातावरण) ताराको बाहिरी परत हो ।
पृथ्वीलाई बेरेर राख्ने जुन स्थानमा वायु छ त्यसलाई वायुमंडल भनिन्छ। वायुमंडलका अतिरिक्त पृथ्वीको स्थलमंडल (Litho sphere) ठोस पदार्थोंले बनिएको, र जलमंडल (Hydro sphere) जलले बनिएको छ। वायुमंडल कति टाडासम्म फैलेकोछ यो कुराको सही जानकारी मिल्न नसकेता पनि यो निश्चित छ कि पृथिवीको चारैतिर सयौं मायलसम्म यो फैलेको छ। वायुमंडलको तल्लो भाग (जो प्राय: चारदेखि आठ माइलसम्म फैलेकोछ) क्षोभमंडल (Troposphere), त्यसमाथिको भाग समतापमंडल (Stratosphere) र त्यसमाथि अझ माथिको भागलाई आयनमंडल (Ionosphere) भनिन्छ। क्षोभमंडल र समतापमंडलको बीचको बीच भागलाई "शांतमंडल" (Topopause) र समतापमंडल र आयनमंडलको बीचलाई स्ट्रैटोपज (Stratopause) भनिन्छ। साधारणतया माथिको तह धेरै शान्त रहन्छ।
प्राणी र वनस्पतिको जीवनपोषणका निम्ति वायु अत्यावश्यक हुन्छ। पृथ्वीतलका अपक्षय (weathering)माथि पनि यसको गहिरो प्रभाव पर्छ। 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.
Atmospheric pressure is the force per unit area that is 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 air 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 cm²).
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 e (an irrational number with a value of 2.71828..) is called the scale height and is denoted by H. 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 acceleration. 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.
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 photodissociated 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.
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. These original atmospheres underwent much evolution over time, with the varying properties of each planet resulting in very different outcomes.
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) 78.09% nitrogen, 20.95% oxygen, a variable amount (average around 0.247%, National Center for Atmospheric Research) 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.
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 atmosphere lies 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 10,000 km above the surface, where it interacts with the planet's magnetosphere.
Other astronomical bodies such as these listed have known atmospheres.
हाम्रो सौरमण्डलभित्र[सम्पादन गर्ने]
- Atmosphere of Mercury
- Atmosphere of Venus
- Atmosphere of Earth
- Atmosphere of Mars
- Atmosphere of Jupiter
- Atmosphere of Saturn
- Atmosphere of Uranus
- Atmosphere of Neptune
- Atmosphere of Pluto
हाम्रो सौर मण्डलबाहिर[सम्पादन गर्ने]
- Atmosphere of HD 209458 b
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.
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.
- Atmometer (evaporimeter)
- Edge of space
- Stellar atmosphere
- Table of global climate system components
सन्दर्भ सूचि[सम्पादन गर्ने]
- ἀτμός, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library
- σφαῖρα, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library
- Ontario Science Centre website
- Seki, K.; Elphic, R. C.; Hirahara, M.; Terasawa, T.; Mukai, T. (2001), "On Atmospheric Loss of Oxygen Ions from Earth Through Magnetospheric Processes", Science 291(5510): 1939–1941, PMID 11239148, doi: 10.1126/science.1058913 , <http://www.sciencemag.org/cgi/content/full/291/5510/1939>. Retrieved on ७ मार्च २००७
- Weaver, D.; Villard, R.. "Hubble Probes Layer-cake Structure of Alien World's Atmosphere", Hubble News Center, 2007-01-31. अन्तिम पहुँच मिति:2007-03-11.
बाहिरी लिंकहरू[सम्पादन गर्ने]
- Properties of atmospheric strata - The flight environment of the atmosphere
- Atmosphere - an Open Access journal
|विकिमिडिया कमन्समा अरु धेरै सामग्रीहरू छन्: Planetary atmospheres|