Description
The ISA model divides the atmosphere into layers with linear temperature distributions. The other values are computed from basic physical constants and relationships. Thus the standard consists of a table of values at various altitudes, plus some formulas by which those values were derived. For example, at sea level the standard gives a pressure of 1013.25 hPa (1 atm) and a temperature of 15 Celsius, and an initial lapse rate of −6.5 °C/km (roughly −2 °C/1,000 ft). The tabulation continues to 11 km where the pressure has fallen to 226.32 hPa and the temperature to −56.5 °C. Between 11 km and 20 km the temperature remains constant.
| Layer | Level Name |
Base Geopotential Height h (in km) |
Base Geometric Height z (in km) |
Lapse Rate (in °C/km) |
Base Temperature T (in °C) |
Base Atmospheric Pressure p (in Pa) |
|---|---|---|---|---|---|---|
| 0 | Troposphere | 0.0 | 0.0 | −6.5 | +15.0 | 101325 |
| 1 | Tropopause | 11.000 | 11.019 | +0.0 | −56.5 | 22632 |
| 2 | Stratosphere | 20.000 | 20.063 | +1.0 | −56.5 | 5474.9 |
| 3 | Stratosphere | 32.000 | 32.162 | +2.8 | −44.5 | 868.02 |
| 4 | Stratopause | 47.000 | 47.350 | +0.0 | −2.5 | 110.91 |
| 5 | Mesosphere | 51.000 | 51.413 | −2.8 | −2.5 | 66.939 |
| 6 | Mesosphere | 71.000 | 71.802 | −2.0 | −58.5 | 3.9564 |
| 7 | Mesopause | 84.852 | 86.000 | — | −86.2 | 0.3734 |
In the above table, geopotential height is calculated from a mathematical model in which the acceleration due to gravity is assumed constant. Geometric height results from the assumption that gravity obeys an inverse square law.
The ISA model is based on average conditions at mid latitudes, as determined by ISO's TC 20/SC 6 technical committee. It has been revised from time to time since the middle of the 20th century.
Read more about this topic: International Standard Atmosphere
Famous quotes containing the word description:
“The great object in life is Sensation—to feel that we exist, even though in pain; it is this “craving void” which drives us to gaming, to battle, to travel, to intemperate but keenly felt pursuits of every description whose principal attraction is the agitation inseparable from their accomplishment.”
—George Gordon Noel Byron (1788–1824)
“I fancy it must be the quantity of animal food eaten by the English which renders their character insusceptible of civilisation. I suspect it is in their kitchens and not in their churches that their reformation must be worked, and that Missionaries of that description from [France] would avail more than those who should endeavor to tame them by precepts of religion or philosophy.”
—Thomas Jefferson (1743–1826)
“It [Egypt] has more wonders in it than any other country in the world and provides more works that defy description than any other place.”
—Herodotus (c. 484–424 B.C.)