javv (#), havâsepehr
1) The gaseous envelope surrounding a star, planet, or moon.
Several solar system planets
retain considerable atmospheres, due to their strong
gravitational force. The gas motions in the planetary
atmosphere, as a response to the heating, coupled with the rotation
forces, generate the meteorological systems. The planetary satellites
→ Titan and → Triton
also have atmospheres (M.S.: SDE).
New L. atmosphaera, from Gk. atmos "vapor" + spharia "sphere."
Havâsepehr, from Mod.Pers. havâ, → air, + sepehr, → sphere. Javv "air, atmosphere," from Ar. jauw.
javv-e donbâledâr, havâsepehr-e ~
Fr.: atmosphère de comète
The envelope of → gas and → dust around a → comet nucleus, also known as → coma. As the comet approaches the → Sun, the frozen materials → sublimate and give rise to an expanding atmosphere. The atmosphere is composed of dust, → molecules, → radicals, and molecular → ions released from the inner coma with velocities ~ 0.5 to 1 km s-1, well above the → escape velocity for the nucleus. The → chemical species observed in cometary spectra can be divided into several categories: (i) atoms and molecules related to → water (H, O, OH, OH+, H2O, H2O+), (ii) carbon and related molecules (C, C+, CO, CO+, CO2+, C2, CH, CH+, HCO, H2CO), (iii) → nitrogen and related molecules (CN, CN+, HCN, CH3CN, NH, NH2, N2+, NH3, NH4), (iv) → sulphur and related molecules (S, CS, S2, H2S+), (v) → metals (Na, K, Ca, Co, Cr, Cu, V, Fe, Mn, Ni). For a typical average comet the neutral atmosphere is first seen when the heliocentric distance is d ≤ 3 → astronomical units.
→ cometary; → atmosphere.
javv-e âzâd, havâsepehr-e ~
Fr.: atmosphère libre
That part of the atmosphere where the effects of the ground on the → turbulence conditions are negligible.
→ free, → atmosphere.
javv-e xâkestari, havâsepher-e ~
Fr.: atmosphère grise
A simplifying assumption in the models of stellar atmosphere, according to which the absorption coefficient has the same value at all wavelengths.
→ gray; → atmosphere.
javv-e Hormoz, havâsepehr-e ~
Fr.: atmosphère de Jupiter
The gaseous envelope surrounding Jupiter. It is about 90% → hydrogen and 10% → helium (by numbers of atoms, 75/25% by mass) with traces of → methane, → water, and → ammonia. This is very close to the composition of the primordial → solar nebula from which the entire solar system was formed. Saturn has a similar composition, but Uranus and Neptune have much less hydrogen and helium. The outermost layer is composed primarily of ordinary → molecular hydrogen and helium. Visually, Jupiter is dominated by two atmospheric features; a series of ever-changing atmospheric cloud bands arranged parallel to the equator and an oval atmospheric blob called the → Great Red Spot.
→ Jupiter; → atmosphere.
havâsepehr-e zirin, javv-e ~
Fr.: atmosphère inférieure
Generally and quite loosely, that part of the atmosphere in which most weather phenomena occur (i.e., the → troposphere and lower → stratosphere); hence used in contrast to the common meaning for the → upper atmosphere. In other contexts, the term implies the lower troposphere (Meteorology Glossary, American Meteorological Society).
→ lower; → atmosphere.
havâsepehr-e miyâni, javv-e ~
Fr.: atmosphère moyenne
The region lying between the → troposphere and the → thermosphere comprising the → stratosphere and the → mesosphere (Meteorology Glossary, American Meteorological Society).
→ middle; → atmosphere.
havâsepehr-e parâsu-taxthâ, javv-e ~
Fr.: atmosphère plan-parallèle
An approximation used in many stellar atmosphere models that depict the atmosphere as being only one-dimensional and bounded at the top and bottom by horizontal plane surfaces normal to the direction of gravity.
→ plane; → parallel; → atmosphere.
javv-e bâzhâzandé, havâsepehr-e ~
Fr.: atmosphère réductrice
1) An atmospheric condition in which oxidation is prevented by removal
of oxygen and other oxidating gasses or vapours. Usually nitrogen or
hydrogen gas is used in order to produce specific effects, e.g. on
ceramic wares being fired.
Reducing verbal adj. of → reduce; → atmosphere.
javv-e dovomân, havâsepehr-e ~
Fr.: atmosphère secondaire
An atmosphere of a planet that forms after primordial gases had been lost or had failed to accumulate. A secondary atmosphere develops from internal volcanic outgassing, or by accumulation of material from comet impacts. It is characteristic of terrestrial planets, such as Earth, Mercury, Venus, and Mars. → primordial atmosphere.
→ secondary; → atmosphere.
havâsepehr-e estândé (#), javv-e ~ (#)
Fr.: atmosphère standard
A hypothetical vertical distribution of atmospheric temperature, pressure, and density that, by international agreement, is taken to be representative of the atmosphere for purposes of pressure altimeter calibrations, aircraft performance calculations, aircraft and missile design, ballistic tables, etc.
→ standard; → atmosphere.
javv-e setâre-yi, havâsephre ~
Fr.: atmosphère stellaire
The outer envelope of gas and plasma that surrounds a star; characterized by pressure, temperature, density, chemical composition, and opacity at varying altitudes.
→ stellar; → atmosphere.
stellar atmosphere model
model-e javv-e setâré
Fr.: modèle d'atmosphère stellaire
A model that computes the radiation field crossing the boundary layers of a star at all frequencies. The parameters used for the characterization of a stellar atmosphere model are: → effective temperature, → surface gravity, and → metallicity.
→ stellar; → atmosphere; → model.
havâsepehr-e zabarin, javv-e ~
Fr.: atmosphère supérieure
The general term applied to the atmosphere above the → troposphere.
→ upper; → atmosphere.