Noctilucent clouds, are tenuous
cloud-likeA cloud is a visible mass of droplets or frozen crystals suspended in the atmosphere above the surface of the Earth or another planetary body. A cloud is also a visible mass attracted by gravity, such as masses of material in space called interstellar clouds and nebulae...
phenomena that are the "ragged-edge" of a much brighter and pervasive polar cloud layer called
polar mesospheric cloudsPolar mesospheric clouds , are a diffuse scattering layer of water ice crystals near the summer polar mesopause.-Description:Observed from the ground, this phenomenon is known as noctilucent clouds...
in the upper atmosphere, visible in a deep
twilightTwilight is the time between dawn and sunrise, and the time between sunset and dusk. Sunlight scattered in the upper atmosphere illuminates the lower atmosphere, and the surface of the Earth is neither completely lit nor completely dark. The sun itself is not actually visible because it is below...
. They are made of crystals of
water iceIce is a solid phase, usually crystalline, of a non-metallic substance that is liquid or gas at room temperature, such as carbon dioxide ice , ammonia ice, or methane ice. However, the predominant use of the term ice is for water ice, technically restricted to one of the 15 known crystalline phases...
. The name means roughly
night shining in
LatinLatin is an Italic language originally spoken in Latium and Ancient Rome. Through the Roman conquest, Latin spread throughout the Mediterranean and a large part of Europe...
. They are most commonly observed in the summer months at
latitudeLatitude, usually denoted by the Greek letter phi gives the location of a place on Earth north or south of the equator. Lines of Latitude are the imaginary horizontal lines shown running east-to-west on maps that run either north or south of the equator...
s between 50° and 70° north and south of the
equatorThe equator is the intersection of the Earth's surface with the plane perpendicular to the Earth's axis of rotation and containing the Earth's center of mass. In simpler language, it is an imaginary line on the Earth's surface equidistant from the North Pole and South Pole that divides the Earth...
.
They are the highest
cloudA cloud is a visible mass of droplets or frozen crystals suspended in the atmosphere above the surface of the Earth or another planetary body. A cloud is also a visible mass attracted by gravity, such as masses of material in space called interstellar clouds and nebulae...
s in the
Earth's atmosphereThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
, located in the
mesosphereThe mesosphere is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. The mesosphere is located about 50 to 85 kilometers above the Earth's surface.The stratosphere and mesosphere are referred to as the middle atmosphere...
at altitudes of around . They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in the Earth's shadow. Noctilucent clouds are not fully understood and are a recently discovered
meteorological phenomenonMeteorology is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting . Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the eighteenth century...
; there is no evidence that they were observed before 1885.
Noctilucent clouds can form only under very restrictive conditions; their occurrence can be used as a sensitive guide to changes in the upper atmosphere. Since their relatively recent classification, the occurrence of noctilucent clouds appears to be increasing in frequency, brightness and extent. It is theorized that this increase is connected to
climate changeClimate change is a change in the statistical distribution of weather over periods of time that range from decades to millions of years. It can be a change in the average weather or a change in the distribution of weather events around an average...
.
Formation
Noctilucent clouds are composed of tiny crystals of
water iceIce is a solid phase, usually crystalline, of a non-metallic substance that is liquid or gas at room temperature, such as carbon dioxide ice , ammonia ice, or methane ice. However, the predominant use of the term ice is for water ice, technically restricted to one of the 15 known crystalline phases...
40 to 100 nanometers in diameter and exist at a height of about , higher than any other clouds in Earth's atmosphere. Much like the more familiar lower altitude clouds, the noctilucent clouds are formed from water
collectingCloud condensation nuclei or CCNs are small particles about which cloud droplets coalesce. Water requires a non-gaseous surface to make the transition from a vapour to a liquid. In the atmosphere, this surface presents itself as tiny solid or liquid particles called CCNs...
on the surface of dust particles.
The sources of both the dust and the water vapour in the upper atmosphere are not known with certainty. The dust is believed to come from
micrometeorsMETEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...
, although
volcano3. Conduit
4. Base
5. Sill
6. Dike
7. Layers of ash emitted by the volcano
8. Flank| 9. Layers of lava emitted by the volcano
10. Throat
11. Parasitic cone
12. Lava flow
13. Vent
14. Crater
15...
es and dust from the
troposphereThe troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75 percent of the atmosphere's mass and 99 percent of its water vapor and aerosols....
are also possibilities. The moisture could be lifted through gaps in the
tropopauseThe tropopause is the atmospheric boundary between the troposphere and the stratosphere. Going upward from the surface, it is the point where air ceases to cool with height, and becomes almost completely dry. More formally, it is the region of the atmosphere where the lapse rate changes from...
, as well as forming from the reaction of
methaneMethane is a chemical compound with the chemical formula . It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees. Burning methane in the presence of oxygen produces carbon dioxide and water. The relative abundance of methane and its clean...
with
hydroxyl radicalThe hydroxyl radical, OH·, is the neutral form of the hydroxide ion . Hydroxyl radicals are highly reactive and consequently short-lived; however, they form an important part of radical chemistry...
s in the
stratosphereThe stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
.
The exhaust from
Space ShuttleThe Space Shuttle, part of the Space Transportation System , is a spacecraft operated by NASA for orbital human spaceflight missions. It began operations in the 1980s and is scheduled to be retired from service in 2010 after 134 launches...
s, which is almost entirely water vapour, has been found to generate minuscule individual clouds. About half of the vapor is released into the
thermosphereThe thermosphere is biggest of all the layers of the earth's atmosphere directly above the mesosphere and directly below the exosphere. Within this layer, ultraviolet radiation causes ionization. The International Space Station has a stable orbit within the upper part of the thermosphere, between...
, usually at altitudes of .
This exhaust can be transported to the
ArcticThe Arctic is the region around the Earth's North Pole, opposite the Antarctic region around the South Pole. The Arctic includes the Arctic Ocean and parts of Canada, Greenland , Russia, the United States , Iceland, Norway, Sweden and Finland.The word Arctic comes from the Greek αρκτικός , "near...
region in little over a day, although the exact mechanism of this very high-speed transport is unknown. As the water migrates northward, it falls from the thermosphere down into the colder mesosphere, which occupies the region of the atmosphere just below. Although this mechanism is the cause of individual noctilucent clouds, it is not thought to be a major contributor to the phenomenon as a whole.
As the
mesosphereThe mesosphere is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. The mesosphere is located about 50 to 85 kilometers above the Earth's surface.The stratosphere and mesosphere are referred to as the middle atmosphere...
contains very little moisture, approximately one hundred millionth that of air from the Sahara desert, and is extremely thin, the ice crystals can only form at temperatures below about . This means that noctilucent clouds form predominantly during summer when, counterintuitively, the mesosphere is coldest. Noctilucent clouds form mostly near the polar regions, because the mesosphere is coldest there. Clouds in the southern hemisphere are about 1 km higher up than those in the northern hemisphere.
Ultraviolet radiation from the Sun breaks water molecules apart, reducing the amount of water available to form noctilucent clouds. The radiation is known to vary cyclically with the
solar cycleThe solar cycle, or the solar magnetic activity cycle, is the main source of periodic solar variation driving variations in space weather. The cycle is observed by counting the frequency and placement of sunspots visible on the Sun...
and satellites have been tracking the decrease in brightness of the clouds with the increase of ultraviolet radiation for the last two solar cycles. It has been found that changes in the clouds follow changes in the intensity of ultraviolet rays by about a year, but the reason for this long lag is not yet known.
Noctilucent clouds are known to exhibit high
radarRadar is an object detection system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, and terrain. The term RADAR was coined in 1941 as an acronym for RAdio Detection And...
reflectivity, in a frequency range of 50
MHzThe hertz is a unit of frequency. It is defined as the number of complete cycles per second. It is the basic unit of frequency in the International System of Units , and is used worldwide in both general-purpose and scientific contexts...
to 1.3 GHz. This behavior is not well understood but
CaltechThe California Institute of Technology is a private research university located in Pasadena, California, United States. The Institute maintains a strong emphasis on the natural sciences and engineering, and operates and manages NASA's neighboring Jet Propulsion Laboratory...
's Prof. Paul Bellan has proposed a possible explanation: that the ice grains become coated with a thin metal film composed of
sodiumSodium is a metallic element with a symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals within "group 1"...
and
ironIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
, which makes the cloud far more reflective to radar. Sodium and iron atoms are stripped from incoming
micrometeorA meteorite is a natural object originating in outer space that survives an impact with the Earth's surface. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s and settle into a layer just above the altitude of noctilucent clouds, and measurements have shown that these elements are severely depleted when the clouds are present. Other experiments have demonstrated that, at the extremely cold temperatures of a noctilucent cloud, sodium vapor can rapidly be deposited onto an ice surface.
Discovery and investigation
Noctilucent clouds are first known to have been observed in 1885, two years after the
1883 eruption of KrakatoaThe 1883 eruption of Krakatoa began in May 1883 and culminated with the destruction of Krakatoa in August 1883. Minor seismic activity continued to be reported until February 1884, though reports after October 1883 were later dismissed by Rogier Verbeek's investigation.-Early eruption phase:In the...
. It remains unclear whether their appearance had anything to do with the volcano, or whether their discovery was due to more people observing the spectacular sunsets caused by the volcanic debris in the atmosphere. Studies have shown that noctilucent clouds are not caused solely by volcanic activity, although dust and water vapour could be injected into the upper atmosphere by eruptions and contribute to their formation. Scientists at the time assumed the clouds were another manifestation of volcanic ash but, after the ash had settled out of the atmosphere, the noctilucent clouds persisted. The theory that the clouds were composed of volcanic dust was finally disproved by Malzev in 1926.
In the years following their discovery the clouds were studied extensively by Otto Jesse of
GermanyGermany , officially the Federal Republic of Germany , is a country in Central Europe. It is bordered to the north by the North Sea, Denmark, and the Baltic Sea; to the east by Poland and the Czech Republic; to the south by Austria and Switzerland; and to the west by France, Luxembourg, Belgium,...
, who was the first to photograph them, in 1887, and seems to have been the one to coin the term "noctilucent cloud", which means "night-shining cloud". His notes provide evidence that noctilucent clouds first appeared in 1885. He had been doing detailed observations of the unusual sunsets caused by the Krakatoa eruption the previous year and firmly believed that, if the clouds had been visible then, he would undoubtedly have noticed them. Systematic photographic observations of the clouds were organized in 1887 by Jesse,
FoersterWilhelm Julius Foerster was a German astronomer, father of the pacifist and ethicist Friedrich Wilhelm Foerster. His name can also be written Förster, but is usually written "Foerster" even in most German sources where 'ö' is otherwise used in the text.A native of Grünberg, Silesia, he worked as...
and Dr. Stolze and, after that year, continuous observations were carried out at the
Berlin ObservatoryThe Berlin Observatory has its origins in 1700 when Gottfried Leibniz initiated the Societät der Wissenschaften which would later become the Preußischen Akademie der Wissenschaften...
. During this research the height of the clouds was first determined, via
triangulationIn trigonometry and geometry, triangulation is the process of determining the location of a point by measuring angles to it from known points at either end of a fixed baseline, rather than measuring distances to the point directly...
. The project was discontinued in 1896.
In the decades after Otto Jesse's death in 1901, there were few new insights into the nature of noctilucent clouds. Wegener's conjecture that they were composed of water ice was later shown to be correct. Study was limited to ground-based observations and scientists had very little knowledge of the mesosphere until the 1960s, when direct rocket measurements began. These showed for the first time that the occurrence of the clouds coincided with very low temperatures in the mesosphere.
Noctilucent clouds were first detected from space by an instrument on the
OGOOrbiting Geophysical Observatory refers to the six satellites launched by the United States that were in use from September 1964 to 1972, designed to study the Earth's magnetosphere. The satellites successfully studied the intreactions between the Earth and the Sun, despite a number of technical...
-6 satellite in 1972. The OGO-6 observations of a bright scattering layer over the polar caps were identified as poleward extensions of these clouds. A later satellite, the
Solar Mesosphere ExplorerThe Solar Mesosphere Explorer was an United States unmanned spacecraft to investigate the processes that create and destroy ozone in Earth's upper atmosphere. The mesosphere is a layer of the atmosphere extending from the top of the stratosphere to an altitude of about 80 kilometers...
, mapped the distribution of the clouds between 1981 and 1986 with its ultraviolet spectrometer. The clouds were detected with a
lidarLIDAR is an optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target. The prevalent method to determine distance to an object or surface is to use laser pulses...
in 1995 at
Utah State UniversityUtah State University is a public land-grant university whose main campus is located in Logan, Utah.It was established in 1888, after Anthon H. Lund introduced a bill for its creation. Originally known as the Agricultural College of Utah, its name was subsequently changed to Utah State...
, even when they were not visible with the naked eye. The first physical confirmation that water ice is indeed the primary component of noctilucent clouds came from the HALOE instrument on the
UARSUARS may refer to:*Upper Atmosphere Research Satellite*Upper airway resistance syndrome...
satellite in 2001. In 2001 the
SwedishSweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe...
OdinOdin is a Swedish satellite working in two disciplines; astrophysics and aeronomy. Within the field of astrophysics, Odin is used in the study of star formation...
satellite performed spectral analyses on the clouds, and produced daily global maps that revealed large patterns in their distribution.
On April 25, 2007, the AIM satellite (
Aeronomy of Ice in the MesosphereAeronomy of Ice in the Mesosphere is a NASA-funded satellite being used to conduct a 26-month study of noctilucent clouds . On April 25, 2007 AIM was boosted into a 600 km high polar orbit by a Pegasus-XL rocket, which was air-launched from a Lockheed L-1011 aircraft.The noctilucent clouds AIM is...
) was launched. It is the first satellite dedicated to studying noctilucent clouds, and made its first observations on May 25, 2007. Images taken by the satellite show shapes in the clouds that are similar to shapes in tropospheric clouds, hinting at similarities in their dynamics.
On August 28, 2006, scientists with the
Mars ExpressMars Express is a space exploration mission being conducted by the European Space Agency . The Mars Express mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally referred to the speed and efficiency with which the spacecraft was...
mission announced that they found clouds of
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
crystals over
MarsMars is the fourth planet from the Sun in the Solar System. The planet is named after Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddish appearance, due to iron oxide prevalent on its surface....
that extended up to 100 km above the surface of the planet. They are the highest clouds discovered over the surface of a planet. Like noctilucent clouds on Earth, they can only be observed when the Sun is below the horizon.
Research published in the journal Geophysical Research Letters in June of 2009 suggests that noctilucent clouds observed following the
Tunguska EventThe Tunguska Event, or Tunguska explosion, was a powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai of Russia, at around 7:14 a.m...
are evidence that the impact was caused by a comet.
The
United States Naval Research LaboratoryThe United States Naval Research Laboratory is the corporate research laboratory for the United States Navy and the United States Marine Corps and conducts a broad program of scientific research and advanced development. NRL has existed since 1923, when it opened at the instigation of Thomas Edison...
(NRL) and the
United States Department of DefenseThe United States Department of Defense is the federal department charged with coordinating and supervising all agencies and functions of the government relating directly to national security and the military...
Space Test ProgramThe Space Test Program is the primary provider of spaceflight for the United States Department of Defense space science and technology community. STP is conducted by the Space Development and Test Wing of the United States Air Force...
(STP) conducted the Charged Aerosol Release Experiment (CARE) on September 19, 2009, using exhaust particles from a
Black BrantThe Black Brant is a Canadian-designed sounding rocket built by Bristol Aerospace in Winnipeg, Manitoba. Over 800 Black Brants of various versions have been launched since they were first produced in 1961, and the type remains one of the most popular sounding rockets ever built...
XII suborbital sounding rocket launched from
NASAThe National Aeronautics and Space Administration is an agency of the United States government, responsible for the nation's public space program. NASA was established by the National Aeronautics and Space Act on July 29, 1958, replacing its predecessor, the National Advisory Committee for...
's
Wallops Flight FacilityWallops Flight Facility , located on the Eastern Shore of Virginia, is operated by the National Aeronautics and Space Administration’s Goddard Space Flight Center primarily as a rocket launch site to support science and exploration missions for NASA and other federal agencies...
to create an artificial noctilucent cloud. The cloud will be observed over a period of weeks or months by ground instruments and the Spatial Heterodyne IMager for MEsospheric Radicals (SHIMMER) instrument on the NRL/STP STPSat-1 spacecraft. The rocket's exhaust plume was observed and reported to news organizations in the United States from
New JerseyNew Jersey is a state in the Mid-Atlantic region of the United States. It is bordered on the north by New York, and to the east by the Hudson River, Upper New York Bay, the Kill Van Kull, Newark Bay, the Arthur Kill, Raritan Bay, Sandy Hook Bay, Westchester County, New York City, Long Island, and...
to
MassachusettsThe Commonwealth of Massachusetts is a state in the New England region of the northeastern United States. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. Most of its population of...
.
Observation
Noctilucent clouds are generally colourless or pale blue although occasionally other colours including red and green occur. The characteristic blue colour comes from absorption by
ozoneOzone or trioxygen is a simple triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic O
2. Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals...
in the path of the sunlight illuminating the noctilucent cloud. They can appear as featureless bands but frequently show distinctive patterns such as streaks, wave-like undulations and whirls. They are considered a "beautiful natural phenomenon". Noctilucent clouds can be confused with
cirrus cloudCirrus clouds generally refer to atmospheric clouds that are characterized by thin, wisplike strands, often accompanied by tufts, leading to their common name of mare's tail. Sometimes these clouds are so extensive that they are virtually indistinguishable from one another, forming a sheet of...
s, but appear sharper under magnification. Those caused by rocket exhausts tend to show colours other than silver or blue because of iridescence caused by the uniform size of the water droplets produced.
Noctilucent clouds can be seen by observers at a
latitudeLatitude, usually denoted by the Greek letter phi gives the location of a place on Earth north or south of the equator. Lines of Latitude are the imaginary horizontal lines shown running east-to-west on maps that run either north or south of the equator...
of 50 to 65 degrees. They seldom occur at lower latitudes (although there have been sightings as far south as
UtahUtah is a western state of the United States. It was the 45th state admitted to the Union, on January 4, 1896. Approximately 80 percent of Utah's 2,736,424 people live along the Wasatch Front, centering around Salt Lake City. In contrast, vast expanses of the state are nearly uninhabited, making...
and
ItalyItaly , officially the Italian Republic , is a country located on the Italian Peninsula in Southern Europe and on the two largest islands in the Mediterranean Sea, Sicily and Sardinia. Italy shares its northern, Alpine boundary with France, Switzerland, Austria and Slovenia...
) and, closer to the poles, it does not get dark enough for the clouds to become visible. They occur during summer, from mid-May to mid-August in the northern hemisphere and between mid-November and mid-February in the southern hemisphere. They are very faint and tenuous, and can only be observed in
twilightTwilight is the time between dawn and sunrise, and the time between sunset and dusk. Sunlight scattered in the upper atmosphere illuminates the lower atmosphere, and the surface of the Earth is neither completely lit nor completely dark. The sun itself is not actually visible because it is below...
around sunrise and sunset when the clouds of the lower atmosphere are in shadow but the noctilucent cloud is illuminated by the
sunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
. They are best seen when the sun is between 6 and 16 degrees below the horizon. Although noctilucent clouds occur in both
hemisphereHemisphere may refer to:*Half of a sphereAs half of the Earth:*Any half of the Earth*Eastern Hemisphere*Western Hemisphere*Northern Hemisphere*Southern Hemisphere...
s, they have been observed thousands of times in the northern hemisphere but less than 100 times in the southern. Southern hemisphere noctilucent clouds are fainter and occur less frequently; additionally the southern hemisphere has a lower population and less land area from which to make observations.
The clouds can show a large variety of different patterns and forms. An identification scheme was developed by Fogle in 1970 that classified five different forms. These classifications have since been modified and subdivided.
They can be studied from the ground, from space, and directly by
sounding rocketA sounding rocket, sometimes called a research rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The origin of the term comes from nautical vocabulary, it refers to to sound, which means to throw a weighted...
. Also, some noctilucent clouds are made of smaller crystals, 30 nm or less, which are invisible to observers on the ground because they do not scatter enough light.
Connection to climate change
There is evidence that the relatively recent appearance of noctilucent clouds, and their gradual increase, may be linked to
climate changeClimate change is a change in the statistical distribution of weather over periods of time that range from decades to millions of years. It can be a change in the average weather or a change in the distribution of weather events around an average...
. Atmospheric scientist Gary Thomas of the
Laboratory for Atmospheric and Space PhysicsThe Laboratory for Atmospheric and Space Physics is a research organization at the University of Colorado at Boulder. LASP is a research institute with over 100 research scientists ranging in fields from solar influences, to Earth's and other planetary atmospherics processes, space weather, space...
at the
University of ColoradoThe University of Colorado at Boulder is a public research university located in Boulder, Colorado. It is the flagship university of the University of Colorado system and was founded five months before Colorado was admitted to the union in 1876...
has pointed out that the first sightings coincide with the
Industrial RevolutionThe Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, and transport had a profound effect on the socioeconomic and cultural conditions in the United Kingdom. The changes subsequently spread throughout Europe, North...
and they have become more widespread and frequent throughout the 20th century. The connection remains controversial however. In general it must be pointed out that Wilfried Schröder was the first who explained noctilucent clouds as "indicators" for atmospheric processes (Gerlands Beiträge zur Geophysik, 1971, Meteorologische Rundschau 1968-1970).
Climate models predict that increased greenhouse gas emissions cause a cooling of the mesosphere,
which would lead to more frequent and widespread occurrences of noctilucent clouds.
A competing theory is that larger methane emissions from intensive farming activities produce more water vapour in the upper atmosphere- methane concentrations have more than doubled in the past 100 years.
Tromp et al. suggest that a transition to a
hydrogen economyThe hydrogen economy is a proposal for the distribution of energy by using hydrogen. Hydrogen releases energy when it is combined with oxygen; however in practice, production of hydrogen from water requires more energy than is released when the hydrogen is used as fuel...
could increase the number of noctilucent clouds through increased emissions of free hydrogen.
See also
- Iridescent Cloud
- Polar Mesospheric Clouds
Polar mesospheric clouds , are a diffuse scattering layer of water ice crystals near the summer polar mesopause.-Description:Observed from the ground, this phenomenon is known as noctilucent clouds...
- Polar stratospheric cloud
Polar stratospheric clouds , also known as nacreous clouds, are clouds in the winter polar stratosphere at altitudes of 15,000–25,000 meters...
s
- Aeronomy
Aeronomy is the science of the upper region of the atmosphere, where dissociation and ionization are important. The term aeronomy was introduced by Sydney Chapman, and the above definition stems from 1960. Today the term also includes the science of the corresponding regions of the atmospheres of...
- Aeronomy of Ice in the Mesosphere
Aeronomy of Ice in the Mesosphere is a NASA-funded satellite being used to conduct a 26-month study of noctilucent clouds . On April 25, 2007 AIM was boosted into a 600 km high polar orbit by a Pegasus-XL rocket, which was air-launched from a Lockheed L-1011 aircraft.The noctilucent clouds AIM is...
External links