Radiation astronomy/Atmospheres

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The image shows the Upper Atmosphere Research Satellite. Credit: NASA/GSFC.

"The Upper Atmosphere Research Satellite (UARS) is a NASA program aimed at improving our knowledge of the physical and chemical processes controlling the stratosphere, mesosphere, and lower thermosphere, emphasizing those levels that are known to be particularly susceptible to change by human activities. The spacecraft was launched by the Space Shuttle Discovery on September 12, 1991, into a near-circular orbit at 585 km altitude and 57° inclination. Measurements include vertical profiles of temperature, many trace gases, and horizontal wind velocities, as well as solar energy inputs. Many of the limb-scanning instruments can measure to as high as 80° latitude, providing near-global coverage."[1]

Upper Atmosphere Research Satellite
Instruments Description Image Function
1. ACRIM-II Active Cavity Radiometer Irradiance Monitoring
UARS ACRIM II photo.jpg
total solar irradiance (TSI)
2. CLAES Cryogenic Limb Array Etalon Spectrometer
CLAES instrument.png
concentrations and distributions of nitrogen and chlorine compounds, ozone, water vapor and methane
3. HALOE Halogen Occultation Experiment
Uars haloe.gif
solar occultation to measure simultaneous vertical profiles of ozone (O3), hydrogen chloride (HCl), hydrogen fluoride (HF), methane (CH4), water vapor (H2O), nitric oxide (NO), nitrogen dioxide (NO2), temperature, aerosol extinction, aerosol composition and size distribution versus atmospheric pressure at the Earth's limb
4. HRDI High Resolution Doppler Imager
Uars hrdi.jpg
emission and absorption lines of molecular oxygen above the limb of the Earth
5. ISAMS Improved Stratospheric and Mesospheric Sounder
Uars iasms.gif
infrared radiometer for measuring thermal emission from the Earth's limb
6. MLS Microwave Limb Sounder
UARS Microwave Limb Sounder.gif
detected naturally occurring microwave thermal emissions from Earth's limb
7. PEM Particle Environment Monitor
the atmospheric X ray imaging spectrometer (AXIS), the high-energy particle spectrometer (HEPS) at Zenith and Nadir (ZEPS and NEPS), the medium-energy particle spectrometer (MEPS) at Zenith and Nadir (ZEPS and NEPS), and the vector magnetometer (VMAG) above AXIS for magnetic field measurements
8. SOLSTICE Solar Stellar Irradiance Comparison Experiment
solar & stellar UV radiation
9. SUSIM Solar Ultraviolet Spectral Irradiance Monitor
Uars susim.gif
measured UV emissions from the sun through vacuum and through Earth atmosphere occultations
10. WINDII Wind Imaging Interferometer
Uars windii.gif
measured wind, temperature and emission rate from airglow and aurora in the visible and near-infrared

Atmospheric rivers[edit | edit source]

Water vapor imagery of the eastern Pacific Ocean from the GOES 11 satellite, shows a large atmospheric river aimed across California in December 2010. Credit: United States Naval Research Laboratory, Monterey.
NASA Image of the Day October 26, 2017, AR connects Asia to North America. Credit: NASA Earth Observatory.
Layered precipitable water imagery of particularly strong atmospheric rivers on 5 December 2015. Credit: NWS OPC.
An atmospheric river forms over Hawai'i then heads toward California 10-11 April 2017. Credit: UW-CIMSS.{{fairuse}}

The particularly intense storm system in the image on the right produced as much as 26 in (66 cm) of precipitation in California and up to 17 ft (520 cm) of snowfall in the Sierra Nevada during December 17–22, 2010.

Atmospheric rivers consist of narrow bands of enhanced water vapor transport, typically along the boundaries between large areas of divergent surface air flow, including some frontal zones in association with extratropical cyclones that form over the oceans.[2][3][4][5]

Pineapple Express storms are the most commonly represented and recognized type of atmospheric rivers; they are given the name due to the warm water vapor plumes originating over the Hawaiian tropics that follow a path towards California.[6][7]

Atmospheric rivers are typically several thousand kilometers long and only a few hundred kilometers wide, and a single one can carry a greater flux of water than the Earth's largest river, the Amazon River.[3]

The length and width factors in conjunction with an integrated water vapor depth greater than 2.0 cm are used as standards to categorize atmospheric river events.[7][8][9][10]

Integrated water vapor transport (IVT) is more directly attributed to orographic precipitation, a key factor in the production of intense rainfall and subsequent flooding.[10]

On any given day, atmospheric rivers account for over 90% of the global meridional (north-south) water vapor transport, yet they cover less than 10% of the Earth's circumference.[3] Atmospheric rivers are also known to contribute to about 22% of total global runoff.[11]

They also are the major cause of extreme precipitation events that cause severe flooding in many mid-latitude, westerly coastal regions of the world, including the West Coast of North America,[12][13][14][8] Western Europe,[15][16][17] the west coast of North Africa,[4] the Iberian Peninsula, Iran and New Zealand.[11] Equally, the absence of atmospheric rivers has been linked with the occurrence of droughts in several parts of the world including South Africa, Spain and Portugal.[11]

The inconsistency of California's rainfall is due to the variability in strength and quantity of these storms, which can produce strenuous effects on California's water budget, which make California a perfect case study to show the importance of proper water management and prediction of these storms.[7] The significance atmospheric rivers have for the control of coastal water budgets juxtaposed against their creation of detrimental floods can be constructed and studied by looking at California and the surrounding coastal region of the western United States, where atmospheric rivers have contributed 30-50% of total annual rainfall.[18] The Fourth National Climate Assessment (NCA) report, released by the U.S. Global Change Research Program (USGCRP) on November 23, 2018[19] confirmed that along the U.S. western coast, landfalling atmospheric rivers "account for 30%–40% of precipitation and snowpack. These landfalling atmospheric rivers "are associated with severe flooding events in California and other western states."[6][8][20]

"As the world warms, the "landfalling atmospheric rivers on the West Coast are likely to increase" in "frequency and severity" because of "increasing evaporation and higher atmospheric water vapor levels in the atmosphere."[19][21][22][23][24]

Landfalling ARs were "responsible for nearly all the annual peak daily flow (APDF)s in western Washington" from 1998 through 2009.[25]

This AR in the image on the left brought a "stunning" end to the American West's 5-year drought with "some parts of California received nearly twice as much rain in a single deluge as normally falls in the preceding 5 months (October–February)".[26]

"Several times a year an atmospheric river [shown in the image on the bottom right forming over Hawai'i]—a long, narrow conveyor belt of storms that stream in relentlessly from the Pacific Ocean—drops inches of rain or feet of snow on the U.S. west coast. Such a system triggered floods and mudslides in central and southern California this past weekend [2-3 February 2019]."[27]

"Atmospheric rivers flow through the sky about a mile above the ocean surface, and may extend across a thousand miles of ocean to the coast. Some bring routine rain but the more intense systems can carry as much water as 15 Mississippi Rivers. The series of storms striking land can arrive for days or, occasionally, weeks on end. They hit west-facing coastlines worldwide, although the U.S. experiences more than most other national coasts."[27]

The “atmospheric river scale” "ranks severity and impacts, from category 1 (weak) to category 5 (exceptional)."[27]

"Without a scale, we really had no way to objectively communicate what would be a strong storm or a weak one."[28]

"Scientists, the media and the public viewed atmospheric rivers as primarily a hazard, but the weaker ARs are quite beneficial. Water managers made it clear to us that a rating scale would be helpful."[28]

"The scale, published Tuesday in the Bulletin of the American Meteorological Society, ranks atmospheric rivers on five levels:"[27]

  • Category 1: Weak—primarily beneficial
  • Category 2: Moderate—mostly beneficial, but also somewhat hazardous
  • Category 3: Strong—balance of beneficial and hazardous
  • Category 4: Extreme—mostly hazardous, but also beneficial (if persistent drought)
  • Category 5—Exceptional—primarily hazardous

Cyclogenesis[edit | edit source]

Cyclogenesis is the process of cyclone formation and intensification.[29]

Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere (a low-pressure area).[30]

The anticyclonic equivalent, the process of formation of high pressure systems, dealing with surface systems is anticyclogenesis.[31]

Cyclogenesis is the opposite of cyclolysis, which concerns the weakening of surface cyclones. The term has an anticyclonic equivalent—Anticyclogenesis.[31]

Dust devils[edit | edit source]

A large dust devil occurs in Colonia Omega, Saltillo, Coahuila, Mexico. Credit: Dupondt.

A large dust devil measuring about 100 metres (330 ft) across at its base can lift about 15 metric tonnes (17 short tons) of dust into the air in 30 minutes. Giant dust storms that sweep across the world's deserts contribute 8% of the mineral dust in the atmosphere each year during the handful of storms that occur. In comparison, the significantly smaller dust devils that twist across the deserts during the summer lift about three times as much dust, thus having a greater combined impact on the dust content of the atmosphere. When this occurs, they are often called sand pillars.[32]

Jet streams[edit | edit source]

Clouds are shown along a jet stream over Canada. Credit: NASA.

Def. any of the high-speed, high-altitude air currents that circle the Earth in a westerly direction is called a jet stream.

Jet streams are fast flowing, narrow air currents found in the atmospheres of some planets, including Earth. The main jet streams are located near the tropopause, the transition between the troposphere (where temperature decreases with altitude) and the stratosphere (where temperature increases with altitude).[33] The major jet streams on Earth are westerly winds (flowing west to east). Their paths typically have a meandering shape; jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including the opposite direction of most of the jet. The strongest jet streams are the polar jets, at around 7–12 km (23,000–39,000 ft) above sea level, and the higher and somewhat weaker subtropical jets at around 10–16 km (33,000–52,000 ft). The Northern Hemisphere and the Southern Hemisphere each have both a polar jet and a subtropical jet. The northern hemisphere polar jet flows over the middle to northern latitudes of North America, Europe, and Asia and their intervening oceans, while the southern hemisphere polar jet mostly circles Antarctica all year round.

Mesocyclones[edit | edit source]

Storm relative motion of a tornado-producing mesocyclone over Greensburg, Kansas on May 4, 2007. The storm was producing an EF5 tornado at the time of the image. Credit: .
Mesocyclones are sometimes visually identifiable by a rotating wall cloud like the one in this thunderstorm over Texas.
Mesocyclone detection algorithm output on tornadic cells in Northern Michigan on July 3rd, 1999

A mesocyclone is a vortex of air within a convective storm.[34] Mesocyclones are localized, approximately 2 km (1.2 mi) to 10 km (6.2 mi) in diameter within strong thunderstorms.[34]

Mesocyclones form when strong changes of wind speed and/or direction with height ("wind shear") sets parts of the lower part of the atmosphere spinning in invisible tube-like rolls. The convective updraft of a thunderstorm then draw up this spinning air, tilting the rolls' orientation upward (from parallel to the ground to perpendicular) and causing the entire updraft to rotate as a vertical column.[35]

The best way to detect and verify the presence of a mesocyclone is by Doppler weather radar. Nearby high values of opposite sign within velocity data are how they are detected.[36]

Nephology[edit | edit source]

Cumuliform cloudscape is over Swifts Creek, Victoria, Australia. Credit: Fir0002.

In meteorology, a cloud is an aerosol consisting of a visible mass of minute liquid droplets, ice crystals, or other particulates suspended in the atmosphere of a planetary body.[37]

Def. the "branch of meteorology that studies clouds"[38] is called nephology.

Forms and levels Stratiform
mostly non-convective
strong convective
(Extreme level)
Noctilucent clouds
(Polar mesospheric clouds)
(Very high level)
Polar stratospheric clouds
Cirrostratus clouds Cirrus clouds Cirrocumulus clouds
(Mid-level) Altostratus clouds Altocumulus clouds
(Low-level) Stratus clouds Stratocumulus clouds Cumulus humilis
Multi-level/vertical Nimbostratus clouds Cumulus mediocris
Towering vertical Cumulus congestus Cumulonimbus clouds
Surface-level Fog

Noctilucent clouds[edit | edit source]

Noctilucent cloud appears over Estonia. Credit: Martin Koitmäe.

Def. "very high-altitude[39] [shining or glowing at night;[40] nightshining[41]] clouds that reflect sunlight long after sunset"[42] are called noctilucent clouds.

Noctilucent clouds may occasionally take on more of a red or orange hue.[43]

They are not common or widespread enough to have a significant effect on climate.[44]

An increasing frequency of occurrence of noctilucent clouds since the 19th century may be the result of climate change.[45]

Noctilucent clouds are the highest in the atmosphere and form near the top of the mesosphere at about ten times the altitude of tropospheric high clouds.[46]

Convective lift in the mesosphere is strong enough during the polar summer to cause adiabatic cooling of small amount of water vapour to the point of saturation which tends to produce the coldest temperatures in the entire atmosphere just below the mesopause resulting in the best environment for the formation of polar mesospheric clouds.[44]

Smoke particles from burnt-up meteors provide much of the condensation nuclei required for the formation of noctilucent cloud.[47]

Sightings are rare more than 45 degrees south of the north pole or north of the south pole.[43]

"The mesopause occurs, by definition, at the top of the mesosphere and at the bottom of the thermosphere. Noctilucent clouds appear always in the vicinity of the mesopause."[48]

Ionospheres[edit | edit source]

Relationship exits between the atmosphere and ionosphere. Credit: Bhamer.{{free media}}
Diagram of Earth's atmosphere is adapted from NASA document. Credit: Minesweeper.{{free media}}
Ionospheric layers are the E layer and F layer are present at night, during the day, a D layer forms and the E and F layers become much stronger, often during the day the F layer will differentiate into F1 and F2 layers. Credit: Naval Postgraduate School.{{free media}}

From 1972 to 1975 NASA launched the AEROS and AEROS B satellites to study the F region.[49] "The Es layer (sporadic E-layer) is characterized by small, thin clouds of intense ionization, which can support reflection of radio waves, rarely up to 225 MHz."[50]

"The total time for transport of metal ions from the equatorial E region to the higher latitudes (within ± 30" magnetic latitude) of the F region must not exceed about 12 hours if the entire "circulation" process is to occur during the time the fountain effect is operative. This requirement seems unnecessary in that the "reverse fountain effect" which occurs when the daytime eastward E field reverses to the west is weaker than the daytime fountain (WOODMAN et al., 1977) thus leading to an apparent daily net positive flux of metal ions into the equatorial F region from the equatorial E region. Some evidence for this "pulsed" source of metal ions is found in the observed "clouds" of Mg+ reported by MENDE et al., (1985) and possibly by KUMAR and HANSON (1980)."[51]

During solar proton events, ionization can reach unusually high levels in the D-region over high and polar latitudes, known as Polar Cap Absorption (or PCA) events, because the increased ionization significantly enhances the absorption of radio signals passing through the region.[52]

"Dust quite probably plsys a major role in noctilucent cloud formation (TURCO et al., 1982) and possibly modifies D region ion chemistry (eg. PARTHASARATHY, 1976)."[51]

"Dust has long been considered important to the formation of noctiluent clouds at high latitudes. TURCO et al., (1982) extensively treats the problem of noctilucent cloud formation including effects of ion attachment to dust or ice particles. PARTHASARATHY (1976) has considered dust a direct "sink" for D region ionization."[51]

"[N]octilucent clouds are not an aspect of low and mid-laditude D region aeronomy."[51]

Venus[edit | edit source]

Venus in approximately true-color is a nearly uniform pale cream. Credit: NASA/Ricardo Nunes, http://www.astrosurf.com/nunes.
Imaged is the cloud structure in the Venusian atmosphere in 1979, revealed by ultraviolet observations by Pioneer Venus Orbiter. Credit: NASA.

In visual astronomy almost no variation or detail can be seen in the clouds. The surface is obscured by a thick blanket of clouds. Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in visible light. It has thick clouds of sulfur dioxide. There are lower and middle cloud layers. The thick clouds consisting mainly of sulfur dioxide and sulfuric acid droplets.[53][54] These clouds reflect and scatter about 90% of the sunlight that falls on them back into space, and prevent visual observation of the Venusian surface. The permanent cloud cover means that although Venus is closer than Earth to the Sun, the Venusian surface is not as well lit.

Strong 300 km/h winds at the cloud tops circle the planet about every four to five earth days.[55] Venusian winds move at up to 60 times the speed of the planet's rotation, while Earth's fastest winds are only 10% to 20% rotation speed.[56]

Mars[edit | edit source]

These are true color images of Mars taken in 1999. Credit: Antonio Cidadao.
These are Hubble Space Telescope images of Mars prior to the Mars Pathfinder spacecraft and Lander. Credit: Philip James, NASA.
Dust devil on Mars Mars Global Surveyor (MGS).
Dust devils cause twisting dark trails on the Martian surface.
Serpent Dust Devil of Mars (Mars Reconnaissance Orbiter (MRO)).
A dust devil on hilly terrain in the Amazonis quadrangle.
Dust devils in Valles Marineris (Mars Reconnaissance Orbiter (MRO)).
Dust devil on Mars, is photographed by the Mars rover Spirit. The counter in the bottom-left corner indicates time in seconds after the first photo was taken in the sequence. At the final frames, a trail is visible on the Martian surface. Three other dust devils also appear in the background. Credit: .
The Serpent Dust Devil of Mars - video (01:16).

"The [true] color images of Mars [at right] were taken in 1999, across almost 60 million miles (!) by a talented amateur astronomer in Oeiras, Portugal – Antonio Cidadao."[57]

"They were acquired with a modest 10-inch "Schmidt-Cassegrain" reflecting telescope, and a commercially available CCD (charge coupled device) camera. Mr. Cidadao’s total investment in his "Mars imaging system"—commercial telescope and electronic camera, plus computer to process the images, and the appropriate software—was approximately three thousand American dollars."[57]

"In 1997, before the arrival of the Mars Pathfinder spacecraft (the first NASA Lander sent to Mars since Viking), the Hubble Telescope was tasked to acquire a series of "weather forecast Mars images" prior to the landing [at left]."[57]

"This long-distance reconnaissance detected a small dust storm less than a month before the Pathfinder arrival, which (with its potentially high winds) could have posed a serious threat to the Pathfinder entry and landing."[57]

"If dust diffuses to the landing site, the sky could turn out to be pink like that seen by Viking... otherwise [based on the Hubble images - above], Pathfinder will likely show blue sky with bright clouds."[58]

Dust devils also occur on Mars (see dust devil tracks) and were first photographed by the Viking orbiters in the 1970s. In 1997, the Mars Pathfinder lander detected a dust devil passing over it.[59][60] In the image shown here, photographed by the Mars Global Surveyor, the long dark streak is formed by a moving swirling column of Martian atmosphere. The dust devil itself (the black spot) is climbing the crater wall. The streaks on the right are sand dunes on the crater floor.

Martian dust devils can be up to fifty times as wide and ten times as high as terrestrial dust devils, and large ones may pose a threat to terrestrial technology sent to Mars.[61] On 7 November 2016, five such dust devils ranging in heights of 0.5 to 1.9 km were imaged in a single observation by Mars Orbiter Mission in martian southern hemisphere.[62]

Mission members monitoring the Spirit rover on Mars reported on March 12, 2005, that a lucky encounter with a dust devil had cleaned the solar panels of that robot. Power levels dramatically increased and daily science work was anticipated to be expanded.[63] A similar phenomenon (solar panels mysteriously cleaned of accumulated dust) had previously been observed with the Opportunity rover]], and dust devils had also been suspected as the cause.[64]

Saturn[edit | edit source]

A global storm girdles Saturn in 2011. The head of the storm (bright area) passes the tail circling around the left limb. Credit: NASA/JPL-Caltech/SSI.
North polar hexagonal cloud feature, discovered by Voyager 1 and confirmed in 2006 by Cassini is shown. Credit: NASA / JPL-Caltech / Space Science Institute.
This is a closer view of the north polar vortex at the center of the hexagon. Credit: NASA / JPL-Caltech / Space Science Institute.

The upper clouds are composed of ammonia crystals.

In 1990, the Hubble Space Telescope imaged an enormous white cloud near Saturn's equator that was not present during the Voyager encounters and in 1994, another, smaller storm was observed. The 1990 storm was an example of a Great White Spot, a unique but short-lived phenomenon that occurs once every Saturnian year, roughly every 30 Earth years, around the time of the northern hemisphere's summer solstice.[65] Previous Great White Spots were observed in 1876, 1903, 1933 and 1960, with the 1933 storm being the most famous. If the periodicity is maintained, another storm will occur in about 2020.[66]

Wind speeds on Saturn can reach 1,800 km/h (1,100 mph) ... Voyager data indicate peak easterly winds of 500 m/s (1800 km/h).[67]

Infrared imaging has shown that Saturn's south pole has a warm polar vortex, the only known example of such a phenomenon in the Solar System.[68] Whereas temperatures on Saturn are normally −185 °C, temperatures on the vortex often reach as high as −122 °C, believed to be the warmest spot on Saturn.[68]

A persisting hexagonal wave pattern around the north polar vortex in the atmosphere at about 78°N was first noted in the Voyager images.[69][70]

Uranus[edit | edit source]

This is an image of the planet Uranus taken by the spacecraft Voyager 2 in 1986. Credit: NASA/JPL/Voyager mission.
Uranus's southern hemisphere in approximate natural colour (left) and in shorter wavelengths (right), shows its faint cloud bands and atmospheric "hood" as seen by Voyager 2. Credit: NASA.
The first dark spot on Uranus ever observed is in an image obtained by ACS on HST in 2006. Credit: NASA, ESA, L. Sromovsky and P. Fry (University of Wisconsin), H. Hammel (Space Science Institute), and K. Rages (SETI Institute).
Uranus in 2005. Rings, southern collar and a bright cloud in the northern hemisphere are visible (HST ACS image).

In larger amateur telescopes with an objective diameter of between 15 and 23 cm, the planet appears as a pale cyan disk with distinct limb darkening.

"Methane possesses prominent absorption bands in the visible and near-infrared (IR) making Uranus aquamarine or cyan in color."[71]

In 1986 Voyager 2 found that the visible southern hemisphere of Uranus can be subdivided into two regions: a bright polar cap and dark equatorial bands (see figure on the right).[72] Their boundary is located at about -45 degrees of latitude. A narrow band straddling the latitudinal range from -45 to -50 degrees is the brightest large feature on the visible surface of the planet.[72][73] It is called a southern "collar". The cap and collar are thought to be a dense region of methane clouds located within the pressure range of 1.3 to 2 bar (see above).[74] Besides the large-scale banded structure, Voyager 2 observed ten small bright clouds, most lying several degrees to the north from the collar.[72] In all other respects Uranus looked like a dynamically dead planet in 1986. Unfortunately Voyager 2 arrived during the height of the planet's southern summer and could not observe the northern hemisphere. At the beginning of the 21st century, when the northern polar region came into view, the Hubble Space Telescope (HST) and Keck telescope initially observed neither a collar nor a polar cap in the northern hemisphere.[73] So Uranus appeared to be asymmetric: bright near the south pole and uniformly dark in the region north of the southern collar.[73] In 2007, when Uranus passed its equinox, the southern collar almost disappeared, while a faint northern collar emerged near 45 degrees of latitude.[75]

On August 23, 2006, researchers at the Space Science Institute (Boulder, CO) and the University of Wisconsin observed a dark spot on Uranus's surface, giving astronomers more insight into the planet's atmospheric activity.[76] Why this sudden upsurge in activity should be occurring is not fully known, but it appears that Uranus's extreme axial tilt results in extreme seasonal variations in its weather.[77][78] Determining the nature of this seasonal variation is difficult because good data on Uranus's atmosphere have existed for less than 84 years, or one full Uranian year. A number of discoveries have been made. Photometry over the course of half a Uranian year (beginning in the 1950s) has shown regular variation in the brightness in two spectral bands, with maxima occurring at the solstices and minima occurring at the equinoxes.[79] A similar periodic variation, with maxima at the solstices, has been noted in microwave measurements of the deep troposphere begun in the 1960s.[80] Stratospheric temperature measurements beginning in the 1970s also showed maximum values near the 1986 solstice.[81] The majority of this variability is believed to occur owing to changes in the viewing geometry.[82]

There are some reasons to believe that physical seasonal changes are happening in Uranus. While the planet is known to have a bright south polar region, the north pole is fairly dim, which is incompatible with the model of the seasonal change outlined above.[78] During its previous northern solstice in 1944, Uranus displayed elevated levels of brightness, which suggests that the north pole was not always so dim.[79] This information implies that the visible pole brightens some time before the solstice and darkens after the equinox.[78] Detailed analysis of the visible and microwave data revealed that the periodical changes of brightness are not completely symmetrical around the solstices, which also indicates a change in the meridional albedo patterns.[78] Finally in the 1990s, as Uranus moved away from its solstice, Hubble and ground based telescopes revealed that the south polar cap darkened noticeably (except the southern collar, which remained bright),[74] while the northern hemisphere demonstrated increasing activity,[83] such as cloud formations and stronger winds, bolstering expectations that it should brighten soon.[84] This indeed happened in 2007 when the planet passed an equinox: a faint northern polar collar arose, while the southern collar became nearly invisible, although the zonal wind profile remained slightly asymmetric, with northern winds being somewhat slower than southern.[75]

Neptune[edit | edit source]

Combined colour and near-infrared image of Neptune, shows bands of methane in its atmosphere, and four of its moons, Proteus, Larissa, Galatea, and Despina. Credit: .
Bands of high-altitude clouds cast shadows on Neptune's lower cloud deck. Credit: .
The Great Dark Spot (top), Scooter (middle white cloud),[85] and the Small Dark Spot (bottom), with contrast exaggerated. Credit: .
The Great Dark Spot is imaged by Voyager 2. Credit: .
The snapshots of Neptune were taken at roughly 4-hour intervals, offering a full view of the blue-green planet. Credit: NASA/ESA/Hubble Heritage Team (STScI/AURA).

At the time of the 1989 Voyager 2 flyby, the planet's southern hemisphere possessed a Great Dark Spot. In 1989, the Great Dark Spot, an anti-cyclonic storm system spanned 13000×6600 km,[86] was discovered by NASA's Voyager 2 spacecraft. Some five years later, on 2 November 1994, the Hubble Space Telescope did not see the Great Dark Spot on the planet. Instead, a new storm similar to the Great Dark Spot was found in the planet's northern hemisphere.[87]

The Scooter is another storm, a white cloud group farther south than the Great Dark Spot. Its nickname is due to the fact that when first detected in the months before the 1989 Voyager 2 encounter it moved faster than the Great Dark Spot.[88] Subsequent images revealed even faster clouds.

The Small Dark Spot is a southern cyclonic storm, the second-most-intense storm observed during the 1989 encounter. It initially was completely dark, but as Voyager 2 approached the planet, a bright core developed and can be seen in most of the highest-resolution images.[89]

The persistence of companion clouds shows that some former dark spots may continue to exist as cyclones even though they are no longer visible as a dark feature. Dark spots may dissipate when they migrate too close to the equator or possibly through some other unknown mechanism.[90]

The upper-level clouds occur at pressures below one bar, where the temperature is suitable for methane to condense.

High-altitude clouds on Neptune have been observed casting shadows on the opaque cloud deck below. There are also high-altitude cloud bands that wrap around the planet at constant latitude. These circumferential bands have widths of 50–150 km and lie about 50–110 km above the cloud deck.[91]

Because of seasonal changes, the cloud bands in the southern hemisphere of Neptune have been observed to increase in size and albedo. This trend was first seen in 1980 and is expected to last until about 2020. The long orbital period of Neptune results in seasons lasting forty years.[92]

Neptune has the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as 2,100 kilometres per hour (1,300 mph).[93]

On Neptune winds reach speeds of almost 600 m/s—nearly attaining supersonic flow.[93] More typically, by tracking the motion of persistent clouds, wind speeds have been shown to vary from 20 m/s in the easterly direction to 325 m/s westward.[94] At the cloud tops, the prevailing winds range in speed from 400 m/s along the equator to 250 m/s at the poles.[95] Most of the winds on Neptune move in a direction opposite the planet's rotation.[88] The general pattern of winds showed prograde rotation at high latitudes vs. retrograde rotation at lower latitudes. The difference in flow direction is believed to be a "skin effect" and not due to any deeper atmospheric processes.[96] At 70° S latitude, a high-speed jet travels at a speed of 300 m/s.[96] With a large telescope of 25 cm or wider, cloud patterns may be visible.[97]

On July 12, 2011, Neptune "has arrived at the same location in space where it was discovered nearly 165 years ago. To commemorate the event, NASA's Hubble Space Telescope has taken these "anniversary pictures" of the blue-green giant planet."[98]

"Neptune is the most distant major planet in our solar system. German astronomer Johann Galle discovered the planet on September 23, 1846. At the time, the discovery doubled the size of the known solar system. The planet is 2.8 billion miles (4.5 billion kilometers) from the Sun, 30 times farther than Earth. Under the Sun's weak pull at that distance, Neptune plods along in its huge orbit, slowly completing one revolution approximately every 165 years."[98]

"These four Hubble images of Neptune were taken with the Wide Field Camera 3 on June 25-26, during the planet's 16-hour rotation. The snapshots were taken at roughly four-hour intervals, offering a full view of the planet. The images reveal high-altitude clouds in the northern and southern hemispheres. The clouds are composed of methane ice crystals."[98]

"The giant planet experiences seasons just as Earth does, because it is tilted 29 degrees, similar to Earth's 23-degree-tilt. Instead of lasting a few months, each of Neptune's seasons continues for about 40 years."[98]

"The snapshots show that Neptune has more clouds than a few years ago, when most of the clouds were in the southern hemisphere. These Hubble views reveal that the cloud activity is shifting to the northern hemisphere. It is early summer in the southern hemisphere and winter in the northern hemisphere."[98]

"In the Hubble images, absorption of red light by methane in Neptune's atmosphere gives the planet its distinctive aqua color. The clouds are tinted pink because they are reflecting near-infrared light."[98]

"A faint, dark band near the bottom of the southern hemisphere is probably caused by a decrease in the hazes in the atmosphere that scatter blue light. The band was imaged by NASA's Voyager 2 spacecraft in 1989, and may be tied to circumpolar circulation created by high-velocity winds in that region."[98]

"The temperature difference between Neptune's strong internal heat source and its frigid cloud tops, about minus 260 degrees Fahrenheit, might trigger instabilities in the atmosphere that drive large-scale weather changes."[98]

Hypotheses[edit | edit source]

  1. The use of satellites should provide ten times the information as sounding rockets or balloons.

A control group for a radiation satellite would contain

  1. a radiation astronomy telescope,
  2. a two-way communication system,
  3. a positional locator,
  4. an orientation propulsion system, and
  5. power supplies and energy sources for all components.

A control group for radiation astronomy satellites may include an ideal or rigorously stable orbit so that the satellite observes the radiation at or to a much higher resolution than an Earth-based ground-level observatory is capable of.

See also[edit | edit source]

References[edit | edit source]

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External links[edit | edit source]

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