The mesosphere (; ) is the third layer of the

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

, directly above the

stratosphere The stratosphere () is the second-lowest layer of the atmosphere of Earth, located above the troposphere and below the mesosphere. The stratosphere is composed of stratified temperature zones, with the warmer layers of air located higher ...

and directly below the

thermosphere The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the ...

. In the mesosphere,

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

decreases as

altitude Altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum (geodesy), datum and a point or object. The exact definition and reference datum varies according to the context (e.g., aviation, geometr ...

increases. This characteristic is used to define limits: it begins at the top of the stratosphere (sometimes called the stratopause), and ends at the mesopause, which is the coldest part of

Earth's atmosphere The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weathe ...

, with temperatures below . The exact upper and lower boundaries of the mesosphere vary with latitude and with season (higher in winter and at the tropics, lower in summer and at the poles), but the lower boundary is usually located at altitudes from above

sea level Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...

, and the upper boundary (the mesopause) is usually from . The stratosphere and mesosphere are sometimes collectively referred to as the "middle atmosphere", which spans altitudes approximately between above Earth's surface. The mesopause, at an altitude of , separates the mesosphere from the

—the second-outermost layer of Earth's atmosphere. On Earth, the mesopause nearly co-incides with the turbopause, below which different chemical species are well-mixed due to turbulent eddies. Above this level the atmosphere becomes non-uniform because the scale heights of different chemical species differ according to their

molecular mass The molecular mass () is the mass of a given molecule, often expressed in units of daltons (Da). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The derived quan ...

es. The term ''

near space Near space is the upper region of the Earth's atmosphere between airspace and outer space. It is sometimes referred to as the " edge of space". There is no legal definition for this extent, but typically this is the altitude range from . Rang ...

'' is also sometimes used to refer to altitudes within the mesosphere. This term does not have a technical definition, but typically refers to the region roughly between the Armstrong limit (about 62,000 ft or 19 km, above which humans require a pressure suit in order to survive) and the

Kármán line The Kármán line (or von Kármán line ) is a conventional definition of the Outer space#Boundary, edge of space; it is widely but not universally accepted. The international record-keeping body Fédération Aéronautique Internationale, FAI ( ...

(where

astrodynamics Orbital mechanics or astrodynamics is the application of ballistics and celestial mechanics to rockets, satellites, and other spacecraft. The motion of these objects is usually calculated from Newton's laws of motion and the Newton's law of univ ...

must take over from

aerodynamics Aerodynamics () is the study of the motion of atmosphere of Earth, air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dynamics and its subfield of gas dynamics, and is an ...

in order to achieve flight); or, by another definition, to the space between the highest altitude commercial

airliner An airliner is a type of airplane for transporting passengers and air cargo. Such aircraft are most often operated by airlines. The modern and most common variant of the airliner is a long, tube shaped, and jet powered aircraft. The largest ...

s fly at (about 40,000 ft (12.2 km)) and the lowest perigee of

satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

s being able to orbit the Earth (about 45 mi (73 km)). Some sources distinguish between the terms "near space" and "upper atmosphere", so that only the layers closest to the Kármán line are described as "near space".

Temperature

Within the mesosphere,

decreases with increasing

height Height is measure of vertical distance, either vertical extent (how "tall" something or someone is) or vertical position (how "high" a point is). For an example of vertical extent, "This basketball player is 7 foot 1 inches in height." For an e ...

. This is a result of decreasing absorption of solar radiation by the rarefied atmosphere having a diminishing relative ozone concentration as altitude increases (ozone being the main absorber in the UV wavelengths that survived absorption by the thermosphere).Photochemistry of Ozone
/ref> Additionally, this is also a result of 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 about , varying according to

latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...

and

season A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's axial tilt, tilted orbit around the Sun. In temperat ...

Dynamic features

The main most important features in this region are strong zonal (East-West) winds,

atmospheric tide An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmospher ...

s, internal atmospheric gravity waves (commonly called "

gravity waves In fluid dynamics, gravity waves are waves 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 oc ...

"), and planetary waves. Most of these tides and waves start in the

troposphere The troposphere is the lowest layer of the atmosphere of Earth. It contains 80% of the total mass of the Atmosphere, planetary atmosphere and 99% of the total mass of water vapor and aerosols, and is where most weather phenomena occur. From the ...

and lower

, and 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 largely drives global circulation. Noctilucent clouds are located in the mesosphere. The upper mesosphere is also the region of the

ionosphere The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...

known as the ''D layer'', which is only present during the day when some

ionization Ionization or ionisation is the process by which an atom or a molecule acquires a negative or positive Electric charge, charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged at ...

occurs with

nitric oxide Nitric oxide (nitrogen oxide, nitrogen monooxide, or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes den ...

being ionized by Lyman series-alpha hydrogen radiation. The ionization is so weak that when night falls, and the source of ionization is removed, the free electron and ion form back into a neutral molecule. A deep sodium layer is located between . Made of unbound, non-ionized atoms of sodium, the sodium layer radiates weakly to contribute to the

airglow Airglow is a faint emission of light by a planetary atmosphere. In the case of Earth's atmosphere, this optical phenomenon causes the night sky never to be completely dark, even after the effects of starlight and diffuse sky radiation, diffuse ...

. The sodium has an average concentration of 400,000 atoms per cubic centimetre. This band is regularly 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. Beginning in October 2018, a distinct type of

aurora An aurora ( aurorae or auroras), also commonly known as the northern lights (aurora borealis) or southern lights (aurora australis), is a natural light display in Earth's sky, predominantly observed in high-latitude regions (around the Arc ...

has been identified, originating in the mesosphere. Often referred to as 'dunes' due to their resemblance to sandy ripples on a beach, the green undulating lights extend toward the equator. They have been identified as originating about above the surface. Since auroras are caused by ultra-high-speed solar particles interacting with atmospheric molecules, the green color of these dunes has tentatively been explained by the interaction of those solar particles with oxygen molecules. The dunes therefore occur where mesospheric oxygen is more concentrated. Millions of

meteor A meteor, known colloquially as a shooting star, is a glowing streak of a small body (usually meteoroid) going through Earth's atmosphere, after being heated to incandescence by collisions with air molecules in the upper atmosphere, creating a ...

s enter the Earth's atmosphere, averaging 40,000 tons per year. The ablated material, called meteoric smoke, is thought to serve as condensation nuclei for noctilucent clouds.

Exploration

The mesosphere lies above altitude records for

aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...

, while only the lowest few kilometers are accessible to balloons, for which the altitude record is . Meanwhile, the mesosphere is below the minimum altitude for orbital

spacecraft A spacecraft is a vehicle that is designed spaceflight, to fly and operate in outer space. Spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth observation, Weather s ...

due to high atmospheric drag. It has only been accessed through the use of

sounding rocket A sounding rocket or rocketsonde, sometimes called a research rocket or a suborbital rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The rockets are often ...

s, 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 (electrical discharges or

lightning Lightning is a natural phenomenon consisting of electrostatic discharges occurring through the atmosphere between two electrically charged regions. One or both regions are within the atmosphere, with the second region sometimes occurring on ...

within the lower mesosphere), noctilucent clouds, and density shears within this poorly understood layer are of current scientific interest. On February 1, 2003, broke up on reentry at about altitude, in the lower mesosphere, killing all seven crew members.

Phenomena in mesosphere and near space

Airglow Airglow is a faint emission of light by a planetary atmosphere. In the case of Earth's atmosphere, this optical phenomenon causes the night sky never to be completely dark, even after the effects of starlight and diffuse sky radiation, diffuse ...

* Atmospheric tides *

Ionosphere The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...

* Meteors * Noctilucent clouds * Polar aurora * Sprite (lightning) * Upper atmospheric lightning (Transient luminous event)

References

External links