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structure of atmosphereEdit

Name Altitude(km) Pressure Temperature Remark
Troposphere ~8/15 1~1/3 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. pole~equ.
Tropopause
Stratosphere ~50/60 1/10~1/1000  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.
Stratopause 50~55 1/1000
Mesosphere ~95/120 1/10000~1/100000 Temperatures in the upper mesosphere fall as low as −100 °C (170 K; −150 °F), varying according to Latitude latitude and Season.
Mesopause Due to the lack of solar heating and very strong Radiative cooling from Carbon dioxide, the mesopause is the coldest place on Earth with temperatures as low as -100°C (-146°F or 173 K) .
Thermosphere ~600 The highly diluted gas in this layer can reach 2,500 °C (4532° F) during the day.
Thermopause 250~500 Exobase
Exosphere 500~1000
Magnetosphere ~70,000 km (10-12 Earth radii or R, where 1 R=6371 km)/Tail
Magnatopause roughly bullet shaped, about 15 RE abreast of Earth and on the night side (in the "magnetotail" or "geotail") approaching a cylinder with a radius 20-25 RE. The tail region stretches well past 200 RE, and the way it ends is not well-known.

Altitude atmospheric pressure variation Edit

File:Air pressure crushing a plastic bottle p1180559.jpg

Pressure varies smoothly from the Earth's surface to the top of the mesosphere. Although the pressure changes with the weather, NASA has averaged the conditions for all parts of the earth year-round. The following is a list of air pressures (as a fraction of one atmosphere) with the corresponding average altitudes. The table gives a rough idea of air pressure at various altitudes.

fraction of 1 atm average altitude
(m) (ft)
1 0 0
1/2 5,486 18,000
1/e 7,915 25,970
1/3 8,376 27,480
1/10 16,132 52,926
1/100 30,901 101,381
1/1000 48,467 159,013
1/10000 69,464 227,899
1/100000 86,282 283,076

Subscript textInsert non-formatted text here== Calculating variation with altitude ==

There are two different equations for computing the average pressure at various height regimes below 86 km (Template:Convert/mi ft). Equation 1 is used when the value of standard temperature lapse rate is not equal to zero and equation 2 is used when standard temperature lapse rate equals zero.

Equation 1:

{P}=P_b \cdot \left[\frac{T_b}{T_b + L_b\cdot(h-h_b)}\right]^{\textstyle \frac{g_0 \cdot M}{R^* \cdot L_b}}

Equation 2:

{P}=P_b \cdot \exp \left[\frac{-g_0 \cdot M \cdot (h-h_b)}{R^* \cdot T_b}\right]

where

P_b = Static pressure (pascals, Pa)
T_b = Standard temperature (kelvin, K)
L_b = Standard temperature lapse rate (kelvin per meter, K/m)
h = Height above sea level (meters, m)
h_b = Height at bottom of layer b (meters; e.g., h_1 = 11,000 m)
R^* = Universal gas constant: 8.31432 Nm/(K·mol)
g_0 = Standard gravity (9.80665 m/s2)
M = Molar mass of Earth's air (0.0289644 kg/mol)

Or converted to Imperial units:[1]

where

P_b = Static pressure (inches of mercury, inHg)
T_b = Standard temperature ([[kelvin]s, K)
L_b = Standard temperature lapse rate (kelvin per foot, K/ft)
h = Height above sea level (feet, ft)
h_b = Height at bottom of layer b (feet; e.g., h_1 = 36,089 ft)
R^* = Universal gas constant; using feet, kelvin, and (SI) moles: 8.9494596×104 gft2/(mol·Ks2)
g_0 = Standard gravity (32.17405 ft/s2)
M = Molar mass of Earth's air (0.0289644 kg/mol)

The value of subscript b ranges from 0 to 6 in accordance with each of seven successive layers of the atmosphere shown in the table below. In these equations, g0, M and R* are each single-valued constants, while P, L, T, and h are multivalued constants in accordance with the table below. (Note that according to the convention in this equation, L0, the tropospheric lapse rate, is negative.) It should be noted that the values used for M, g0, and R^* are in accordance with the U.S. Standard Atmosphere, 1976, and that the value for R^* in particular does not agree with standard values for this constant.[2] The reference value for Pb for b = 0 is the defined sea level value, P0 = 101325 pascals or 29.92126 inHg. Values of Pb of b = 1 through b = 6 are obtained from the application of the appropriate member of the pair equations 1 and 2 for the case when h = h_{b+1}.:[2]

Subscript b Height Above Sea Level Static Pressure Standard Temperature
(K)
Temperature Lapse Rate
(m) (ft) (pascals) (inHg) (K/m) (K/ft)
0 0 0 101325 29.92126 288.15 -0.00649 -0.0019812
1 11,000 36,089 22632 6.683245 216.65 0.0 0.0
2 20,000 65,617 5474 1.616734 216.65 0.001 0.0003048
3 32,000 104,987 868 0.2563258 228.65 0.0028 0.00085344
4 47,000 154,199 110 0.0327505 270.65 0.0 0.0
5 51,000 167,323 66 0.01976704 270.65 -0.0028 -0.00085344
6 71,000 232,940 4 0.00116833 214.65 -0.002 -0.0006097

Pressure and thicknessEdit

Main article: Atmospheric pressure
Barometric Formula: (used for airplane flight) barometric formula
One mathematical model: NRLMSISE-00

The average atmospheric pressure, at sea level, is about 101.3 kilopascals (about 14.7 psi); total atmospheric mass is 5.1480×1018 kg [3].

Atmospheric pressure is a direct result of the total weight of the air above the point at which the pressure is measured. This means that air pressure varies with location and time, because the amount (and weight) of air above the earth varies with location and time. However the average mass of the air above a square meter of the earth's surface is known to the same high accuracy as the total air mass of 5148.0 teratonnes and area of the earth of 51007.2 megahectares, namely 5148.0/510.072 = 10.093 metric tonnes per square meter or 14.356 lbs (mass) per square inch. This is about 2.5% below the officially standardized unit atmosphere (1 atm) of 101.325 kPa or 14.696 psi, and corresponds to the mean pressure not at sea level but at the mean base of the atmosphere as contoured by the earth's terrain.

Were atmospheric density to remain constant with height the atmosphere would terminate abruptly at 7.81 km (25,600 ft). Instead it decreases with height, dropping by 50% at an altitude of about 5.6 km (18,000 ft). For comparison: the highest mountain, Mount Everest, is higher, at 8.8 km, which is why it is so difficult to climb without supplemental oxygen. This pressure drop is approximately exponential, so that pressure decreases by approximately half every 5.6 km (whence about 50% of the total atmospheric mass is within the lowest 5.6 km) and by 63.2 % (1 - 1/e = 1 - 0.368 = 0.632) every 7.64 km, the average scale height of Earth's atmosphere below 70 km. 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 (as can be seen for example by the effects of atmospheric drag on satellites).

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: [4]

  • 50% of the atmosphere by mass is below an altitude of 5.6 km.
  • 90% of the atmosphere by mass is below an altitude of 16 km. The common altitude of commercial airliners is about 10 km.
  • 99.99997% of the atmosphere by mass is below 100 km. The highest X-15 plane flight in 1963 reached an altitude of 354,300 ft (108.0 km).

Therefore, most of the atmosphere (99.9997%) is below 100 km, although in the rarefied region above this there are auroras and other atmospheric effects.

Density and mass Edit

Atmosphere model

Temperature and mass density against altitude from the NRLMSISE-00 standard atmosphere model

Main 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 to predict 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."

Earth's magnetosphere Edit

Structure of the magnetosphere mod

Schematic of Earth's magnetosphere. The solar wind flows from left to right.

Main article: Earth's magnetic field

The magnetosphere of Earth is a region in space whose shape is determined by the extent of Earth's internal magnetic field, the solar wind plasma, and the interplanetary magnetic field (IMF). In the magnetosphere, a mix of free ions and electrons from both the solar wind and the Earth's ionosphere is confined by magnetic and electric forces that are much stronger than gravity and collisions. In spite of its name, the magnetosphere is distinctly non-spherical. On the side facing the Sun, the distance to its boundary (which varies with solar wind intensity) is about 70,000 km (10-12 Earth radii or RE, where 1 RE=6371 km; unless otherwise noted, all distances here are from the Earth's center). The boundary of the magnetosphere ("magnetopause") is roughly bullet shaped, about 15 RE abreast of Earth and on the night side (in the "magnetotail" or "geotail") approaching a cylinder with a radius 20-25 RE. The tail region stretches well past 200 RE, and the way it ends is not well-known.

The outer neutral gas envelope of Earth, or geocorona, consists mostly of the lightest atoms, hydrogen and helium, and continues beyond 4-5 RE, with diminishing density. The hot plasma ions of the magnetosphere acquire electrons during collisions with these atoms and create an escaping "glow" of fast atoms that have been used to image the hot plasma clouds by the IMAGE mission. The upward extension of the ionosphere, known as the plasmasphere, also extends beyond 4-5 RE with diminishing density, beyond which it becomes a flow of light ions called the polar wind that escapes out of the magnetosphere into the solar wind. Energy deposited in the ionosphere by auroras strongly heats the heavier atmospheric components such as oxygen and molecules of oxygen and nitrogen, which would not otherwise escape from Earth's gravity. Owing to this highly variable heating, however, a heavy atmospheric or ionospheric outflow of plasma flows during disturbed periods from the auroral zones into the magnetosphere, extending the region dominated by terrestrial material, known as the fourth or plasma geosphere, at times out to the magnetopause.

Atmospheric densityEdit

Temperature and mass density against altitude from the NRLMSISE-00 standard atmosphere model shows nearly exponential dependence of density.


See alsoEdit


ReferencesEdit

  1. Mechtly, E. A., 1973: The International System of Units, Physical Constants and Conversion Factors. NASA SP-7012, Second Revision, National Aeronautics and Space Administration, Washington, D.C.
  2. 2.0 2.1 U.S. Standard Atmosphere, 1976, U.S. Government Printing Office, Washington, D.C., 1976. (Linked file is very large.)
  3. The Mass of the Atmosphere: A Constraint on Global Analyses
  4. Lutgens, Frederick K. and Edward J. Tarbuck (1995) The Atmosphere, Prentice Hall, 6th ed., pp14-17, ISBN 0-13-350612-6

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