Troposphere

Atmosphere diagram showing the troposphere and other layers. The layers are not to scale.

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

View of Earth's troposphere from an airplane. NRLMSISE-00 is an Empirical, global model of the Earth's atmosphere from ground to space Overview Fixed-wing aircraft range from small training and recreational aircraft to Wide-body aircraft and military cargo aircraft.

The troposphere is the lowest portion of Earth's atmosphere. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five It contains approximately 75% of the atmosphere's mass and almost all of its water vapor and aerosols. General properties of water vapor Evaporation/sublimation Whenever a water molecule leaves a surface it is said to have evaporated Particulates, alternatively referred to as particulate matter (PM or fine particles, are tiny particles of solid or liquid suspended in a gas

The average depth of the troposphere is about 11 km (7 miles) in the middle latitudes. It is deeper in the tropical regions (up to 20 km (12 miles)) and shallower near the poles (about 7 km (4 miles) in summer, indistinct in winter). The lowest part of the troposphere, where friction with the Earth's surface influences air flow, is the planetary boundary layer. Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e The planetary boundary layer ( PBL) also known as the atmospheric boundary layer ( ABL) or peplosphere, is the lowest part of the Atmosphere This layer is typically a few hundred meters to 2 km (1. 2 miles) deep depending on the landform and time of day. The border between the troposphere and stratosphere, called the tropopause, is a temperature inversion. The tropopause is in the atmosphere between the Troposphere and the Stratosphere. In meteorology an inversion is a deviation from the normal change of an atmospheric property with altitude ^[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. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly In Fluid dynamics, turbulence or turbulent flow is a fluid regime characterized by chaotic Stochastic property changes Most of the phenomena we associate with day-to-day weather occur in the troposphere. The weather is a set of all the phenomena occurring in a given Atmosphere at a given Time. ^[1]

1 Pressure and temperature structure
2 See also
3 References
4 External links

Pressure and temperature structure

Composition

The chemical composition of the troposphere is essentially uniform, with the notable exception of water vapor. General properties of water vapor Evaporation/sublimation Whenever a water molecule leaves a surface it is said to have evaporated The source of water vapor is at the surface through the processes of evaporation and transpiration. Evaporation is the process by which Molecules in a Liquid state (e Transpiration is the Evaporation of water from the aerial parts of Plants especially leaves but also stems Flowers and Roots Furthermore the temperature of the troposphere decreases with height, and saturation vapor pressure decreases strongly with temperature, so the amount of water vapor that can exist in the atmosphere decreases strongly with height. Vapor pressure (also known as equilibrium vapor pressure or saturation vapor pressure) is the Pressure of a Vapor in equilibrium Thus the proportion of water vapor is normally greatest near the surface and decreases with height.

Pressure

The pressure of the atmosphere is maximum at the surface 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. Hydrostatic equilibrium occurs when compression due to Gravity is balanced by a Pressure gradient which creates a Pressure gradient force in the opposite The change in pressure with height therefore can be equated to the density with this hydrostatic equation:^[2]

$\frac{dp}{dz} = -\rho g_n = - \frac {mpg}{RT}$

where:

g_n 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. Fluid statics (also called hydrostatics) is the Science of Fluids at rest and is a sub-field within Fluid mechanics. Standard gravity, usually denoted by g 0 or g n is the nominal acceleration due to gravity at the Earth's surface at sea level The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Relationship with the Boltzmann constant The Boltzmann constant kB (often abbreviated k) may be used in place of the gas constant by working The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic

Temperature

Main article: Lapse rate

The temperature of the troposphere generally decreases with altitude. The lapse rate is defined as the negative of the rate of change in an atmospheric variable usually Temperature, with height in an atmosphere Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The rate at which the temperature decreases, $- d T / d z$ , is called the lapse rate. The lapse rate is defined as the negative of the rate of change in an atmospheric variable usually Temperature, with height in an atmosphere 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). In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat. This article covers adiabatic processes in Thermodynamics. For adiabatic processes in Quantum mechanics, see Adiabatic process (quantum mechanics Since the parcel does work and gains no heat, it loses energy, and so its temperature decreases. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός (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

$\frac{dS}{dz} = 0$

where S is the entropy. In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy The rate at which temperature decreases with height under such conditions is called the adiabatic lapse rate. The lapse rate is defined as the negative of the rate of change in an atmospheric variable usually Temperature, with height in an atmosphere

For dry air, which is approximately an ideal gas, we can proceed further. These four properties that constitute an ideal gas can be easily remembered by the acronym RIPE which stands for - R andom Motion (molecules are in constant random motion The adiabatic equation for an ideal gas is ^[3]

$p(z)T(z)^{-\frac{\gamma}{\gamma-1}}=constant$

where $γ$ is the heat capacity ratio ( $γ$ =7/5, for air). Ideal gas relations For an ideal gas the heat capacity is constant with temperature Combining with the equation for the pressure, one arrives at the dry adiabatic lapse rate,^[4]

$\frac{dT}{dz}=- \frac{mg}{R} \frac{\gamma-1}{\gamma}=-9.8^{\circ}\mathrm{C}/\mathrm{km}$

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. The lapse rate is defined as the negative of the rate of change in an atmospheric variable usually Temperature, with height in an atmosphere General properties of water vapor Evaporation/sublimation Whenever a water molecule leaves a surface it is said to have evaporated 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. Vapor pressure (also known as equilibrium vapor pressure or saturation vapor pressure) is the Pressure of a Vapor in equilibrium The lapse rate is defined as the negative of the rate of change in an atmospheric variable usually Temperature, with height in an atmosphere More generally, the actual rate at which the temperature drops with altitude is called the environmental lapse rate. The lapse rate is defined as the negative of the rate of change in an atmospheric variable usually Temperature, with height in an atmosphere 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, $d T / d z$ ) is not usually equal to the adiabatic lapse rate (or correspondingly, $dS/dz \ne 0$ ). If the upper air is warmer than predicted by the adiabatic lapse rate ( $d S / d z > 0$ ), 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. The tropopause is in the atmosphere between the Troposphere and the Stratosphere. 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. A geographical pole, or geographic pole, is either of two fixed points on the surface of a spinning body or Planet, at 90 degrees from the Equator, based The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the

Tropopause

Main article: Tropopause

The tropopause is the boundary region between the troposphere and the stratosphere. The tropopause is in the atmosphere 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. In meteorology an inversion is a deviation from the normal change of an atmospheric property with altitude

An idealised view of three large circulation cells.

References

^ ^a ^b ^c ^d ^e ^f Danielson, Levin, and Abrams, Meteorology, McGraw Hill, 2003
^ ^a ^b Landau and Lifshitz, Fluid Mechanics, Pergamon, 1979
^ Landau and Lifshitz, Statistical Physics Part 1, Pergamon, 1980
^ Kittel and Kroemer, Thermal Physics, Freeman, 1980; chapter 6, problem 11

External links

The vertical structure of the atmosphere
Composition of the Atmosphere, from the University of Tennessee Physics dept. Notes on Usage This table is a reference tool for rapidly locating Wikipedia articles on Global Climate System Components Transition altitude is the maximum Altitude at which an aircraft should use an altimeter pressure setting indicating height above mean sea level (QNH. Tropospheric scatter (or troposcatter) is the scattering of distant TV and FM radio stations by the Troposphere so that they travel farther than
Chemical Reactions in the Atmosphere

Dictionary

-noun

The lower levels of the atmosphere extending from the earth's surface up to the tropopause. It is characterized by convective air movements and a large vertical temperature change.

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