The troposphere is the lowest layer of Earth's atmosphere, is where nearly all weather conditions take place. It contains 75% of the atmosphere's mass and 99% of the total mass of water vapor and aerosols; the average height of the troposphere is 18 km in the tropics, 17 km in the middle latitudes, 6 km in the polar regions in winter. The total average height of the troposphere is 13 km; the lowest part of the troposphere, where friction with the Earth's surface influences air flow, is the planetary boundary layer. This layer is a few hundred meters to 2 km deep depending on the landform and time of day. Atop the troposphere is the tropopause, the border between the troposphere and stratosphere; the tropopause is an inversion layer, where the air temperature ceases to decrease with height and remains constant through its thickness. The word troposphere is derived from the Greek tropos and sphere, reflecting the fact that rotational turbulent mixing plays an important role in the troposphere's structure and behaviour.
Most of the phenomena associated with day-to-day weather occur in the troposphere. By volume, dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, small amounts of other gases. Air contains a variable amount of water vapor. Except for the water vapor content, the composition of the troposphere is uniform; the source of water vapor is at the Earth's surface through the process of evaporation. The temperature of the troposphere decreases with altitude. And, saturation vapor pressure decreases as temperature drops. Hence, the amount of water vapor that can exist in the atmosphere decreases with altitude and the proportion of water vapor is greatest near the surface of the Earth; the pressure of the atmosphere decreases with altitude. This is because the atmosphere is nearly in hydrostatic equilibrium so that the pressure is equal to the weight of air above a given point; the change in pressure with altitude can be equated to the density with the hydrostatic equation d P d z = − ρ g n = − m P g n R T where: gn is the standard gravity ρ is the densityz is the altitude P is the pressure R is the gas constant T is the thermodynamic temperature m is the molar massSince temperature in principle depends on altitude, one needs a second equation to determine the pressure as a function of altitude as discussed in the next section.
The temperature of the troposphere decreases as altitude increases. The rate at which the temperature decreases, is called the environmental lapse rate; the ELR is nothing more than the difference in temperature between the surface and the tropopause divided by the height. The ELR assumes that the air is still, i.e. that there is no mixing of the layers of air from vertical convection, nor winds that would create turbulence and hence mixing of the layers of air. The reason for this temperature difference is that the ground absorbs most of the sun's energy, which heats the lower levels of the atmosphere with which it is in contact. Meanwhile, the radiation of heat at the top of the atmosphere results in the cooling of that part of the atmosphere; the ELR assumes as air is heated it becomes buoyant and rises. The dry adiabatic lapse rate accounts for the effect of the expansion of dry air as it rises in the atmosphere and wet adiabatic lapse rates includes the effect of the condensation of water vapor on the lapse rate.
When a parcel of air rises, it expands. As the air parcel expands, it pushes the surrounding air outward, transferring energy in the form of work from that parcel to the atmosphere; as energy transfer to a parcel of air by way of heat is slow, it is assumed to not exchange energy by way of heat with the environment. Such a process is called an adiabatic process. Since the rising parcel of air is losing energy as it does work on the surrounding atmosphere and no energy is transferred into it as heat from the atmosphere to make up for the loss, the parcel of air is losing energy, which manifests itself as a decrease in the temperature of the air parcel; the reverse, of course, will be true for a parcel of air, sinking and is being compressed. Since the process of compression and expansion of an air parcel can be considered reversible and no energy is transferred into or out of the parcel, such a process is considered isentropic, meaning that there is no change in entropy as the air parcel rises and falls, d S = 0.
Since the heat exchanged d Q = 0 is related to the entropy change d S by d Q = T d S, the equation governing the temperature as a function of height for a mixed atmosphere is d S d z = 0 where S is the entropy. The above equation states; the rate at which temperature decreases with height u
A geographical pole is either of the two points on a rotating body where its axis of rotation intersects its surface. As with Earth's North and South Poles, they are called that body's "north pole" and "south pole", one lying 90 degrees in one direction from the body's equator and the other lying 90 degrees in the opposite direction from the equator; every planet has geographical poles. If, like the Earth, a body generates a magnetic field, it will possess magnetic poles. Perturbations in a body's rotation mean that geographical poles wander on its surface; the Earth's North and South Poles, for example, move by a few metres over periods of a few years. As cartography requires exact and unchanging coordinates, the averaged locations of geographical poles are taken as fixed cartographic poles and become the points where the body's great circles of longitude intersect. Antipodes Equatorial bulge Polar regions of Earth Poles of astronomical bodies Polar wander
An airliner is a type of aircraft for transporting passengers and air cargo. Such aircraft are most operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is defined as an aeroplane intended for carrying multiple passengers or cargo in commercial service; the largest of them are wide-body jets which are called twin-aisle because they have two separate aisles running from the front to the back of the passenger cabin. These are used for long-haul flights between airline hubs and major cities. A smaller, more common class of airliners is the single-aisle; these are used for short to medium-distance flights with fewer passengers than their wide-body counterparts. Regional airliners seat fewer than 100 passengers and may be powered by turbofans or turboprops; these airliners are the non-mainline counterparts to the larger aircraft operated by the major carriers, legacy carriers, flag carriers, are used to feed traffic into the large airline hubs. These regional routes form the spokes of a hub-and-spoke air transport model.
The lightest of short-haul regional feeder airliner type aircraft that carry a small number of passengers are called commuter aircraft, commuterliners and air taxis, depending on their size, how they are marketed, region of the world, seating configurations. The Beechcraft 1900, for example, has only 19 seats; when the Wright brothers made the world’s first sustained heavier-than-air flight, they laid the foundation for what would become a major transport industry. Their flight in 1903 was just 11 years before what is defined as the world’s first airliner; these airliners have had a significant impact on global society and politics. In 1913, Igor Sikorsky developed the first large multi-engine airplane, the Russky Vityaz, refined into the more practical Ilya Muromets with dual controls for a pilot plus copilot and a comfortable cabin with a lavatory, cabin heating and lighting; the large four-engine biplane was derived in a bomber aircraft, preceding subsequent transport and bomber aircraft.
Due to the onset of World War I, it was never used as a commercial airliner. It first flew on December 10, 1913 and took off for its first demonstration flight with 16 passengers aboard on February 25, 1914. In 1915, the first airliner was used by Elliot Air Service; the aircraft was a Curtiss JN 4, a small biplane, used in World War I as a trainer. It was used as a tour and familiarization flight aircraft in the early 1920s. In 1919, after World War I, the Farman F.60 Goliath designed as a long-range heavy bomber, was converted for commercial use into a passenger airliner. It could seat 14 passengers from 1919, around 60 were built. Several publicity flights were made, including one on 8 February 1919, when the Goliath flew 12 passengers from Toussus-le-Noble to RAF Kenley, near Croydon, despite having no permission from the British authorities to land. Another important airliner built in 1919 was the Airco DH.16. In March 1919, the prototype first flew at Hendon Aerodrome. Nine aircraft were built, all but one being delivered to the nascent airline, Aircraft Transport and Travel, which used the first aircraft for pleasure flying, on 25 August 1919, it inaugurated the first scheduled international airline service from London to Paris.
One aircraft was sold to the River Plate Aviation Company in Argentina, to operate a cross-river service between Buenos Aires and Montevideo. Meanwhile, the competing Vickers converted its successful WWI bomber, the Vickers Vimy, into a civilian version, the Vimy Commercial, it was redesigned with a larger-diameter fuselage, first flew from the Joyce Green airfield in Kent on 13 April 1919. The world's first all-metal transport aircraft was the Junkers F.13 from 1919, with 322 built. The Dutch Fokker company produced the Fokker F. II and the F. III; these aircraft were used by the Dutch airline KLM when it reopened an Amsterdam-London service in 1921. The Fokkers were soon flying to destinations across Europe, including Bremen, Brussels and Paris, they proved to be reliable aircraft. The Handley Page company in Britain produced the Handley Page Type W as the company's first civil transport aircraft, it housed two crew in 15 passengers in an enclosed cabin. Powered by two 450 hp Napier Lion engines, the prototype first flew on 4 December 1919, shortly after it was displayed at the 1919 Paris Air Show at Le Bourget.
It was the world's first airliner to be designed with an on-board lavatory. Meanwhile in France, the Bleriot-SPAD S.33 was a great success throughout the 1920s serving the Paris-London route, on continental routes. The enclosed cabin could carry four passengers with an extra seat in the cockpit. By 1921, aircraft capacity needed to be larger for the economics to remain favourable; the English company de Havilland, therefore built the 10-passenger DH.29 monoplane, while starting work on the design of the DH.32, an eight-seater biplane with a less powerful but more economical Rolls-Royce Eagle engine. Owing to the urgent need for more capacity, work on the DH.32 was stopped and the DH.34 biplane was designed, accommodating 10 passengers. The Fokker trimotor was an important and popular transport, manufactured under license in Europe and America. Throughout the 1920s, companies in Britain and France were at the forefront of the civil airliner industry considerably aided by governme
The Celsius scale known as the centigrade scale, is a temperature scale used by the International System of Units. As an SI derived unit, it is used by all countries except the United States, the Bahamas, the Cayman Islands and Liberia, it is named after the Swedish astronomer Anders Celsius. The degree Celsius can refer to a specific temperature on the Celsius scale or a unit to indicate a difference between two temperatures or an uncertainty. Before being renamed to honor Anders Celsius in 1948, the unit was called centigrade, from the Latin centum, which means 100, gradus, which means steps. From 1743, the Celsius scale is based on 0 °C for the freezing point of water and 100 °C for the boiling point of water at 1 atm pressure. Prior to 1743, the scale was based on the boiling and melting points of water, but the values were reversed; the 1743 scale reversal was proposed by Jean-Pierre Christin. By international agreement, since 1954 the unit degree Celsius and the Celsius scale are defined by absolute zero and the triple point of Vienna Standard Mean Ocean Water, a specially purified water.
This definition precisely relates the Celsius scale to the Kelvin scale, which defines the SI base unit of thermodynamic temperature with symbol K. Absolute zero, the lowest temperature possible, is defined as being 0 K and −273.15 °C. The temperature of the triple point of water is defined as 273.16 K. This means that a temperature difference of one degree Celsius and that of one kelvin are the same. On 20 May 2019, the kelvin, along with it the degree Celsius, will be redefined so that its value will be determined by definition of the Boltzmann constant. In 1742, Swedish astronomer Anders Celsius created a temperature scale, the reverse of the scale now known as "Celsius": 0 represented the boiling point of water, while 100 represented the freezing point of water. In his paper Observations of two persistent degrees on a thermometer, he recounted his experiments showing that the melting point of ice is unaffected by pressure, he determined with remarkable precision how the boiling point of water varied as a function of atmospheric pressure.
He proposed that the zero point of his temperature scale, being the boiling point, would be calibrated at the mean barometric pressure at mean sea level. This pressure is known as one standard atmosphere; the BIPM's 10th General Conference on Weights and Measures defined one standard atmosphere to equal 1,013,250 dynes per square centimetre. In 1743, the Lyonnais physicist Jean-Pierre Christin, permanent secretary of the Académie des sciences, belles-lettres et arts de LyonAcadémie des sciences, belles-lettres et arts de Lyon, working independently of Celsius, developed a scale where zero represented the freezing point of water and 100 represented the boiling point of water. On 19 May 1743 he published the design of a mercury thermometer, the "Thermometer of Lyon" built by the craftsman Pierre Casati that used this scale. In 1744, coincident with the death of Anders Celsius, the Swedish botanist Carl Linnaeus reversed Celsius's scale, his custom-made "linnaeus-thermometer", for use in his greenhouses, was made by Daniel Ekström, Sweden's leading maker of scientific instruments at the time, whose workshop was located in the basement of the Stockholm observatory.
As happened in this age before modern communications, numerous physicists and instrument makers are credited with having independently developed this same scale. The first known Swedish document reporting temperatures in this modern "forward" Celsius scale is the paper Hortus Upsaliensis dated 16 December 1745 that Linnaeus wrote to a student of his, Samuel Nauclér. In it, Linnaeus recounted the temperatures inside the orangery at the University of Uppsala Botanical Garden:...since the caldarium by the angle of the windows from the rays of the sun, obtains such heat that the thermometer reaches 30 degrees, although the keen gardener takes care not to let it rise to more than 20 to 25 degrees, in winter not under 15 degrees... Since the 19th century, the scientific and thermometry communities worldwide have used the phrase "centigrade scale". Temperatures on the centigrade scale were reported as degrees or, when greater specificity was desired, as degrees centigrade; because the term centigrade was the Spanish and French language name for a unit of angular measurement and had a similar connotation in other languages, the term centesimal degree was used when precise, unambiguous language was required by international standards bodies such as the BIPM.
More properly, what was defined as "centigrade" would now be "hectograde". To eliminate any confusion, the 9th CGPM and the CIPM formally adopted "degree Celsius" in 1948, formally keeping the recognized degree symbol, rather than adopting the gradian/centesimal degree symbol. For scientific use, "Celsius" is the term used, with "centigrade" remaining in common but decreasing use in informal contexts in English-speaking countries, it was not until February 1985 that the weather forecasts issued by
The Fahrenheit scale is a temperature scale based on one proposed in 1724 by Dutch–German–Polish physicist Daniel Gabriel Fahrenheit. It uses the degree Fahrenheit as the unit. Several accounts of how he defined his scale exist; the lower defining point, 0 °F, was established as the freezing temperature of a solution of brine made from equal parts of ice and salt. Further limits were established as the melting point of ice and his best estimate of the average human body temperature; the scale is now defined by two fixed points: the temperature at which water freezes into ice is defined as 32 °F, the boiling point of water is defined to be 212 °F, a 180 °F separation, as defined at sea level and standard atmospheric pressure. At the end of the 2010s, Fahrenheit was used as the official temperature scale only in the United States, its associated states in the Western Pacific, the Bahamas, the Cayman Islands and Liberia. Antigua and Barbuda and other islands which use the same meteorological service, such as Anguilla, the British Virgin Islands and Saint Kitts and Nevis, as well as Bermuda and the Turks and Caicos Islands, use Fahrenheit and Celsius.
All other countries in the world now use the Celsius scale, named after Swedish astronomer Anders Celsius. On the Fahrenheit scale, the freezing point of water is 32 degrees Fahrenheit and the boiling point is 212 °F; this puts the freezing points of water 180 degrees apart. Therefore, a degree on the Fahrenheit scale is 1⁄180 of the interval between the freezing point and the boiling point. On the Celsius scale, the freezing and boiling points of water are 100 degrees apart. A temperature interval of 1 °F is equal to an interval of 5⁄9 degrees Celsius; the Fahrenheit and Celsius scales intersect at −40°. Absolute zero is −273.15 °C or −459.67 °F. The Rankine temperature scale uses degree intervals of the same size as those of the Fahrenheit scale, except that absolute zero is 0 °R — the same way that the Kelvin temperature scale matches the Celsius scale, except that absolute zero is 0 K; the Fahrenheit scale uses the symbol ° to denote a point on the temperature scale and the letter F to indicate the use of the Fahrenheit scale, as well as to denote a difference between temperatures or an uncertainty in temperature.
For an exact conversion, the following formulas can be applied. Here, f is the value in Fahrenheit and c the value in Celsius: f °Fahrenheit to c °Celsius: °F × 5°C/9°F = /1.8 °C = c °C c °Celsius to f °Fahrenheit: + 32 °F = °F + 32 °F = f °FThis is an exact conversion making use of the identity −40 °F = −40 °C. Again, f is the value in Fahrenheit and c the value in Celsius: f °Fahrenheit to c °Celsius: − 40 = c. C °Celsius to f °Fahrenheit: − 40 = f. Fahrenheit proposed his temperature scale in 1724, basing it on two reference points of temperature. In his initial scale, the zero point was determined by placing the thermometer in a mixture "of ice, of water, of ammonium chloride or of sea salt"; this combination forms a eutectic system which stabilizes its temperature automatically: 0 °F was defined to be that stable temperature. The second point, 96 degrees, was the human body's temperature. According to a story in Germany, Fahrenheit chose the lowest air temperature measured in his hometown Danzig in winter 1708/09 as 0 °F, only had the need to be able to make this value reproducible using brine.
According to a letter Fahrenheit wrote to his friend Herman Boerhaave, his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer's scale, brine freezes at zero, water freezes and melts at 7.5 degrees, body temperature is 22.5, water boils at 60 degrees. Fahrenheit multiplied each value by four in order to eliminate fractions and make the scale more fine-grained, he re-calibrated his scale using the melting point of ice and normal human body temperature. Fahrenheit soon after observed; the use of the freezing and boiling points of water as thermometer fixed reference points became popular following the work of Anders Celsius and these fixed points were adopted by a committee of the Royal Society led by Henry Cavendish in 1776. Under this system, the Fahrenheit scale is redefined so that the freezing point of water is 32 °F, the boiling point is 212 °F or 180 degrees higher, it is for this reason that normal human body temperature is 98° on the revised scale. In the present-day Fahrenheit scale, 0 °F no longer corresponds to the eutectic temperature of ammonium chloride brine as described above.
Instead, that eutectic is at 4 °F on the final Fahrenheit scale. The Rankine temperature s
In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium. An example of such an interface is that between the atmosphere and the ocean, which gives rise to wind waves. A gravity wave results when fluid is displaced from a position of equilibrium; the restoration of the fluid to equilibrium will produce a movement of the fluid back and forth, called a wave orbit. Gravity waves on an air–sea interface of the ocean are called surface gravity waves or surface waves, while gravity waves that are within the body of the water are called internal waves. Wind-generated waves on the water surface are examples of gravity waves, as are tsunamis and ocean tides. Wind-generated gravity waves on the free surface of the Earth's ponds, lakes and oceans have a period of between 0.3 and 30 seconds. Shorter waves are affected by surface tension and are called gravity–capillary waves and capillary waves.
Alternatively, so-called infragravity waves, which are due to subharmonic nonlinear wave interaction with the wind waves, have periods longer than the accompanying wind-generated waves. In the Earth's atmosphere, gravity waves are a mechanism that produce the transfer of momentum from the troposphere to the stratosphere and mesosphere. Gravity waves are generated in the troposphere by frontal systems or by airflow over mountains. At first, waves propagate through the atmosphere without appreciable change in mean velocity, but as the waves reach more rarefied air at higher altitudes, their amplitude increases, nonlinear effects cause the waves to break, transferring their momentum to the mean flow. This transfer of momentum is responsible for the forcing of the many large-scale dynamical features of the atmosphere. For example, this momentum transfer is responsible for the driving of the Quasi-Biennial Oscillation, in the mesosphere, it is thought to be the major driving force of the Semi-Annual Oscillation.
Thus, this process plays a key role in the dynamics of the middle atmosphere. The effect of gravity waves in clouds can look like altostratus undulatus clouds, are sometimes confused with them, but the formation mechanism is different; the phase velocity c of a linear gravity wave with wavenumber k is given by the formula c = g k, where g is the acceleration due to gravity. When surface tension is important, this is modified to c = g k + σ k ρ, where σ is the surface tension coefficient and ρ is the density. Since c = ω / k is the phase speed in terms of the angular frequency ω and the wavenumber, the gravity wave angular frequency can be expressed as ω = g k; the group velocity of a wave is given by c g = d ω d k, thus for a gravity wave, c g = 1 2 g k = 1 2 c. The group velocity is one half the phase velocity. A wave in which the group and phase velocities differ is called dispersive. Gravity waves traveling in shallow water, are nondispersive: the phase and group velocities are identical and independent of wavelength and frequency.
When the water depth is h, c p = c g = g h. Wind waves, as their name suggests, are generated by wind transferring energy from the atmosphere to the ocean's surface, capillary-gravity waves play an essential role in this effect. There are two distinct mechanisms involved, called after their proponents and Miles. In the work of Phillips, the ocean surface is imagined to be flat, a turbulent wind blows over the surface; when a flow is turbulent, one observes a randomly fluctuating velocity field superimposed on a mean flow. The fluctuating velocity field gives rise to fluctuating stresses that act on the air-water interface; the normal stress, or fluctuating pressure acts as a forcing term. If the frequency and wavenumber of this forcing term match a mode of vibration of the capillary-gravity wave there is a resonance, the wave grows in amplitude; as with other resonance effects, the amplitude of this wave grows linearly with time. The air-water interface is now endowed with a surface roughness due to the capillary-gravity waves, a second phase of wave growth takes place.
A wave established on the surface either spontaneously as described above
The mesosphere is the layer of the Earth's atmosphere, directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases; this characteristic is used to define its limits: it begins at the top of the stratosphere, ends at the mesopause, the coldest part of Earth's atmosphere with temperatures below −143 °C. The exact upper and lower boundaries of the mesosphere vary with latitude and with season, but the lower boundary is located at heights from 50 to 65 kilometres above the Earth's surface and the upper boundary is around 85 to 100 kilometres; the stratosphere and the mesosphere are collectively referred to as the "middle atmosphere", which spans heights from 10 kilometres to 100 kilometres. The mesopause, at an altitude of 80–90 km, separates the mesosphere from the thermosphere—the second-outermost layer of the Earth's atmosphere; this is around the same altitude as the turbopause, below which different chemical species are well mixed due to turbulent eddies.
Above this level the atmosphere becomes non-uniform. The term near space is sometimes used; this term does not have a technical definition, but refers the region of the atmosphere up to 100 km between the Armstrong limit up to the Kármán line where astrodynamics must take over from aerodynamics in order to achieve flight. The definition of near space can vary depending on the source, but in general near space comprises the altitudes above where commercial airliners fly but below orbiting satellites; some sources distinguish between the terms "near space" and "upper atmosphere," so that only the layers closest to the Karman line are called near space. Within the mesosphere, temperature decreases with increasing height, due to decreasing absorption of solar radiation by the rarefied atmosphere and increasing cooling by CO2 radiative emission; the top of the mesosphere, called the mesopause, is the coldest part of Earth's atmosphere. Temperatures in the upper mesosphere fall as low as −101 °C, varying according to latitude and season.
The main dynamic features in this region are strong zonal winds, atmospheric tides, internal atmospheric gravity waves, planetary waves. Most of these tides and waves start in the troposphere and lower stratosphere, propagate to the mesosphere. In the mesosphere, gravity-wave amplitudes can become so large that the waves become unstable and dissipate; this dissipation deposits momentum into the mesosphere and drives global circulation. This helps the Earth. Noctilucent clouds are located in the mesosphere; the upper mesosphere is the region of the ionosphere known as the D layer. The D layer is only present during the day when some ionization occurs with nitric oxide being ionized by Lyman series-alpha hydrogen radiation; the ionization is so weak that when night falls, the source of ionization is removed, the free electron and ion form back into a neutral molecule. The mesosphere has been called the "ignorosphere" because it is poorly studied relative to the stratosphere and the thermosphere. A 5 km deep sodium layer is located between 80–105 km.
Made of unbound, non-ionized atoms of sodium, the sodium layer radiates weakly to contribute to the airglow. The sodium has an average concentration of 400,000 atoms per cubic centimetre; this band is replenished by sodium sublimating from incoming meteors. Astronomers have begun utilizing this sodium band to create "guide stars" as part of the adaptive optical correction process used to produce ultra-sharp ground-based observations. Other metal layers, e.g. iron and potassium, exist in the upper mesosphere/lower thermosphere region as well. Millions of meteors enter the Earth's atmosphere, averaging 40 tons per year; the ablated material, called meteoric smoke, is thought to serve as condensation nuclei for noctilucent clouds. The mesosphere lies above altitude records for aircraft, while only the lowest few kilometers are accessible to balloons, for which the altitude record is 53.0 km. Meanwhile, the mesosphere is below the minimum altitude for orbital spacecraft due to high atmospheric drag.
It has only been accessed through the use of sounding rockets, which are only capable of taking mesospheric measurements for a few minutes per mission. As a result, it is the least-understood part of the atmosphere, resulting in the humorous moniker ignorosphere; the presence of red sprites and blue jets, noctilucent clouds, density shears within this poorly understood layer are of current scientific interest. Near space was first explored in the 1930s; the early flights flew to the edge of space without computers and with only crude life support systems. Notable people who flew in near space were Jean Piccard and his wife Jeannette, on the nearcraft The Century of Progress. Exploration was carried out by unmanned craft, although there have been skydiving attempts made from high-altitude balloons; the area is of interest for military surveillance purposes, scientific study, as well as to commercial interests for communications, tourism. Craft that fly in near space include hi