Radiation astronomy/Cryometeors

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Malaspina Glacier in southeastern Alaska is considered the classic example of a piedmont glacier. Credit: NASA.{{free media}}

A cryometeor is a meteor of variable size that has been radiated and is still moving composed of ice, e.g. water or methane ice.

A cryometeor that has stopped moving has become a cryometeorite.

Def. a glacier that occurs on a gentle slope leading from the base of mountains to a region of flat land, any region of foothills of a mountain range, or formed or lying at the foot of a mountain range is called a piedmont glacier.

Ices[edit | edit source]

This is an image of columnar ice crystals. Credit: DrAlzheimer.

Def. any frozen "volatile chemical, such as water, ammonia, or carbon dioxide"[1] is called an ice.

Megacryometeors[edit | edit source]

A megacryometeor is a very large chunk of ice sometimes called huge hailstones, but do not need to form in thunderstorms.

A megacryometeor is a very large chunk of ice which, despite sharing many textural, hydro-chemical and isotopic features detected in large hailstones, is formed under unusual atmospheric conditions which clearly differ from those of the cumulonimbus cloud scenario (i.e. clear-sky conditions). They are sometimes called huge hailstones, but do not need to form in thunderstorms. Jesus Martinez-Frias, a planetary geologist at the Center for Astrobiology in Madrid, pioneered research into megacryometeors in January 2000 after ice chunks weighing up to 6.6 pounds (3.0 kg) rained on Spain out of cloudless skies for ten days.

Def. "a very large water ice object that falls from the sky, similar in composition to hailstones"[2] is called a megacryometeor.

Hail[edit | edit source]

A large hailstone (clear and white) with concentric rings is shown. Credit: ERZ.
The image shows small hail that has been fractures to show internal structure. Credit: Erbe, Pooley: USDA, ARS, EMU.
On April 13, 2004, a blanket of hail fell during a storm in Cerro El Pital, El Salvador. Credit: Wanakoo.
The image captures a hailstorm in progress in Bogotá, D.C., Colombia, on March 3, 2006. Credit: Ju98 5.
This is a very large hailstone from the NOAA Photo Library. Credit: NOAA Legacy Photo; OAR/ERL/Wave Propagation Laboratory.
This hailstone was four inches in diameter and weighed seven ounces. Credit: Archival Photography by Steve Nicklas, NOS, NGS.
As of June 22, 2003, this is the largest hailstone ever recovered. Credit: NOAA.
This is a large hailstone, approximately 133 mm (5 1/4 inches) in diameter, that fell in Harper, Kansas on May 14, 2004. Credit: National Weather Service - Wichita, Kansas.
This is a record-setting hailstone that fell in Vivian, South Dakota on July 23, 2010. Credit: NWS Aberdeen, SD.

Hail is a form of solid [water] precipitation. It consists of balls or irregular lumps of ice, each of which is referred to as a hailstone.[3] Unlike graupel, which is made of rime, and ice pellets, which are smaller and translucent, hailstones – on Earth – consist mostly of water ice and measure between 5 and 200 millimetres (0.20 and 7.87 in) in diameter.

Def. "balls [or pieces][4] of ice falling as precipitation from the sky [a thunderstorm][4]"[5] are called hail.

Def. a "single ball of hail"[6] is called a hailstone.

Terminal velocity of hail, or the speed at which hail is falling when it strikes the ground, varies by the diameter of the hail stones. A hail stone of 1 cm (0.39 in) in diameter falls at a rate of 9 metres per second (20 mph), while stones the size of 8 centimetres (3.1 in) in diameter fall at a rate of 48 metres per second (110 mph). Hail stone velocity is dependent on the size of the stone, friction with air it is falling through, the motion of wind it is falling through, collisions with raindrops or other hail stones, and melting as the stones fall through a warmer atmosphere.[7]

Unlike ice pellets, hailstones are layered and can be irregular and clumped together.

A cross-section through a large hailstone shows an onion-like structure. This means the hailstone is made of thick and translucent layers, alternating with layers that are thin, white and opaque.

The image second down on the right shows a blanket of hail precipitated on the ground at Cerro El Pital, El Savador. "Cerro El Pital se encuentra a 12 kilómetros de La Palma, con una altura de 2730 msnm es el punto más alto del territorio Salvadoreño. Es una montaña en medio de un bosque nebuloso que suele tener una temperatura aproximada de 10 ºC. El 13 de abril de 2004, las temperaturas bajaron tanto que el cerro fue cubierto por una escarcha de hielo que causó conmoción entre los pobladores, atribuyendo el fenómeno a una supuesta "nevada"."

The third image at left shows a hailstone that fell at Washington, D. C., on May 26, 1953, that was 4 in in diameter and weighed 7 oz.

In the fourth image at right is the largest hailstone ever recovered in the United States as of June 22, 2003. This hailstone fell in Aurora, Nebraska. It has a 7-inch (17.8 cm) diameter and an approximate circumference of 18.75 inches.[8]

The fourth down on the left hailstone image is one, approximately 133 mm (5 1/4 inches) in diameter, that fell in Harper, Kansas on May 14, 2004.

After 2003, another record-setting hailstone fell in Vivian, South Dakota, on July 23, 2010. Its diameter is 8 inches with a weight of 1 pound 15 ounces. It's in the fifth image down on the right.

Graupel[edit | edit source]

Graupel is shown encasing an unseen snow crystal. Credit: Erbe, Pooley: USDA, ARS, EMU.

The METAR reporting code for hail 5 mm (0.20 in) or greater is GR, while smaller hailstones and graupel are coded GS. ... Hail has a diameter of 5 millimetres (0.20 in) or more.[9] Hailstones can grow to 15 centimetres (6 in) and weigh more than 0.5 kilograms (1.1 lb).[10]

Graupel ... also called soft hail or snow pellets)[11] refers to precipitation that forms when supercooled droplets of water are collected and freeze on a falling snowflake, forming a 2–5 mm (0.079–0.197 in) ball of rime.

Def. a "precipitation that forms when supercooled droplets of water condense on a snowflake"[12] is called graupel.

Strictly speaking, graupel is not the same as hail or ice pellets, although it is sometimes referred to as small hail. However, the World Meteorological Organization defines small hail as snow pellets encapsulated by ice, a precipitation halfway between graupel and hail.[13]

The frozen droplets on the surface of rimed crystals are hard to resolve and the topography of a graupel particle is not easy to record with a light microscope because of the limited resolution and depth of field in the instrument. However, observations of snow crystals with a low-temperature scanning electron microscope (LT-SEM) clearly show cloud droplets measuring up to 50 μm (0.00197 in) on the surface of the crystals. The rime has been observed on all four basic forms of snow crystals, including plates, dendrites, columns and needles. As the riming process continues, the mass of frozen, accumulated cloud droplets obscures the identity of the original snow crystal, thereby giving rise to a graupel particle.

Graupel commonly forms in high altitude climates and is both denser and more granular than ordinary snow, due to its rimed exterior. Macroscopically, graupel resembles small beads of polystyrene. The combination of density and low viscosity makes fresh layers of graupel unstable on slopes, and layers of 20–30 cm (7.9–11.8 in) present a high risk of dangerous slab avalanches. In addition, thinner layers of graupel falling at low temperatures can act as ball bearings below subsequent falls of more naturally stable snow, rendering them also liable to avalanche.[14] Graupel tends to compact and stabilise ("weld") approximately one or two days after falling, depending on the temperature and the properties of the graupel.[15]

Sleet[edit | edit source]

The image shows ice pellets aka sleet in North America, with a United States penny for scale. Credit: Runningonbrains.{{free media}}

Ice pellets (also referred to as sleet by the United States National Weather Service[16]) are a form of precipitation consisting of small, translucent balls of ice. Ice pellets are usually smaller than hailstones[17] and are different from graupel, which is made of rime, or rain and snow mixed, which is soft. Ice pellets often bounce when they hit the ground, and generally do not freeze into a solid mass unless mixed with freezing rain. The METAR code for ice pellets is PL.

Def. rain "which freezes before reaching the ground"[18] is called sleet.

Def. "a single pellet of sleet"[19] is called an ice pellet.

Snow[edit | edit source]

This image is a satellite photo of lake-effect snow bands near the Korean Peninsula. Credit: NASA.

Snow is precipitation in the form of flakes of crystalline water ice that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless subjected to external pressure.

Def. a "crystal of snow, having approximate hexagonal symmetry"[20] is called a snowflake.

Snowflakes come in a variety of sizes and shapes. Types that fall in the form of a ball due to melting and refreezing, rather than a flake, are known as hail, ice pellets or snow grains.

Def. water ice crystals falling as light white flakes are called snow.

Def. "[a]ny or all of the forms of water particles, whether liquid or solid, that fall from the atmosphere"[21] are called precipitation.

"Condensation or sublimation of atmospheric water vapor produces a hydrometeor. It forms in the free atmosphere, or at the earth's surface, and includes frozen water lifted by the wind. Hydrometeors which can cause a surface visibility reduction, generally fall into one of the following two categories:

  1. Precipitation. Precipitation includes all forms of water particles, both liquid and solid, which fall from the atmosphere and reach the ground; these include: liquid precipitation (drizzle and rain), freezing precipitation (freezing drizzle and freezing rain), and solid (frozen) precipitation (ice pellets, hail, snow, snow pellets, snow grains, and ice crystals).
  2. Suspended (Liquid or Solid) Water Particles. Liquid or solid water particles that form and remain suspended in the air (damp haze, cloud, fog, ice fog, and mist), as well as liquid or solid water particles that are lifted by the wind from the earth’s surface (drifting snow, blowing snow, blowing spray) cause restrictions to visibility. One of the more unusual causes of reduced visibility due to suspended water/ice particles is whiteout, while the most common cause is fog."[22]

Def. a "storm consisting of thunder and lightning produced by a cumulonimbus, usually accompanied with rain and sometimes hail, sleet, freezing rain, or snow"[23] is called a thunderstorm.

Rime[edit | edit source]

Rime occurs on both ends of a columnar snow crystal. Credit: Brian0918.{{free media}}
Rime ice is shown after deposition on a window. Credit: Ws47.

Def. "ice formed by the rapid freezing of cold water droplets of fog onto a cold surface"[24] is called rime.

Hard rime is a white ice that forms when the water droplets in fog freeze to the outer surfaces of objects. It is often seen on trees atop mountains and ridges in winter, when low-hanging clouds cause freezing fog. This fog freezes to the windward (wind-facing) side of tree branches, buildings, or any other solid objects, usually with high wind velocities and air temperatures between −2 and −8 °C (28.4 and 17.6 °F).

Cryomicrometeoroids[edit | edit source]

The light spectra [of the Upsilon Pegasid fireball], combined with trajectory and light curve measurements, have yielded various compositions and densities, ranging from fragile snowball-like objects with density about a quarter that of ice,[25] to nickel-iron rich dense rocks.

Ice streams[edit | edit source]

Radarsat image is of ice streams flowing into the Filchner-Ronne Ice Shelf. Credit: Polargeo.{{free media}}

On the right is a radarsat image of ice streams flowing into the Filchner-Ronne ice shelf. Annotations outline the Rutford ice stream.

Def. "a current of ice in an ice sheet or ice cap that flows faster than the surrounding ice"[26] is called an ice stream.

Glaciers[edit | edit source]

This is a radar image of Alfred Ernest Ice Shelf on Ellesmere Island, taken by the ERS-1 satellite. Credit: NASA.{{free media}}

On the right is a radar image of Alfred Ernest Ice Shelf on Ellesmere Island, taken by the ERS-1 satellite.

Def. "a mass of ice that originates on land, usually having an area larger than one tenth of a square kilometer"[26] is called a glacier.

Surging glaciers[edit | edit source]

In 1941, Hole-in-the-Wall Glacier surged. Credit: W.O. Field, World Data Center for Glaciology, Boulder, CO.
The image shows a glacial surge from the Sermersauq Ice Cap. Credit: Robert Gilbert, Niels Nielsen, Henrik Möller, Joseph R. Desloges, and Morten Rasch.

Def. "a glacier that experiences a dramatic increase in flow rate, 10 to 100 times faster than its normal rate; usually surge events last less than one year and occur periodically, between 15 and 100 years"[26] is called a surging glacier.

"In 1941, Hole-in-the-Wall Glacier [imaged at the right] surged, also knocking over trees during its advance."[26]

An "outlet glacier of the Sermersauq Ice Cap [on Disko Island, West Greenland, shown at the left with progressive surges marked] has surged 10.5 km downvalley to within 10 km of the fjord. [...] surging of the glacier, begun in 1995, was undetected until July 1999, when it was discovered during a geomorphic survey of the valley. Mapping from TM, Landsat and SPOT satellite imagery, and subsequent field work have documented the history of the event. On 17 June 1995 the terminus of the glacier was about where it appears in the 1985 air photography [...]. By 24 September 1995 the glacier had advanced 1.25 km and by 12 October another 1.25 km (mean advance during the second period : 70 m day-1). The advance slowed from 18 m day-1 in 1996 to 5 m day-1 in 1997 and <1 m day-1 between 1997 and 1999. By summer 1999 the advance ceased; the maximum extension of the terminus, about 10.5 km down-valley to about 10 km from the head of the fjord, was mapped from imagery on 9 July 1999 [...]."[27]

Classification of glaciers[edit | edit source]

Glacier mapping is performed with Landsat TM and a GIS. Credit: F. Paul, C. Huggel, A. Kääb, T. Kellenberger, and M. Maisch.

"The low reflectivity of snow and glacier ice in the middle infrared part of the spectrum allows glacier classification".[28]

In the set of images at the center top of this section, glacier mapping steps are shown from left to right with the Landsat 7 enhanced Thematic Mapper (TM) and a geographic information system (GIS).[28]

The images are part of the "102 glaciers of the Mischabel mountain range."[28]

The first image on the left is a ratio image from TM4 and TM4, specifically (TM4 / TM5).[28]

The second is a "derived glacier map after thresholding (blue) and overlay with digitized basins (red)."[28]

The third image from the left identifies "[i]ndividual glaciers after basin intersection (colour-coded) ready for [digital elevation model] DEM-fusion."[28]

The thermal emission and reflectivity have been measured "using the sensors ASTER (Advanced Spaceborne Thermal Emission and reflection Radiometer) on board [the] Terra [satellite]".[28]

Glaciers may be classified on the basis of areal extent or size. "With [a standard deviation of] σ = 3% the values obtained [...] are (resolution / minimum useful glacier size (in km2)): 5 m / all, 10 m / 0.01, 15 m / 0.03, 20 m / 0.05, 25 m / 0.1, 30 m / 0.2, 60 m / 0.5."[28]

"The comparison with higher-resolution satellite imagery reveals: (a) an overall good corre- spondence of the TM-derived glacier outlines with the manual delineation, (b) mapping of debris-covered glacier ice is not possible with TM data alone, and (c) also manual glacier delineation is problematic in the case of debris cover or snowfields."[28]

Alpine glaciers[edit | edit source]

The wedgemount alpine glacier is rapidly receding and used to touch the lake as recently as 1990. Credit: McKay Savage from London, UK.

Def. "a glacier that is confined by surrounding mountain terrain; also called a mountain glacier"[26] is called an alpine glacier.

For "alpine glaciers the imbalance [the change of mass balance/altitude profiles from years with positive to those with negative mean balance] is nearly independent of altitude, in dry, continental regions the imbalance is largest near the equilibrium line, where albedo changes are most pronounced."[29]

Maritime glaciers[edit | edit source]

Sawyer Glacier is in the background. Credit: Personnel of the NOAA ship John N. Cobb.

Def. a glacier that is

  1. found on or near the sea,
  2. bordering on the sea,
  3. in a moist and temperate climate owing to the influence of the sea,
  4. related to the sea,
  5. near or in the sea

is called a maritime glacier.

"Maritime glaciers owe their mass balance variations mainly to changes in the accumulation area".[29]

Tidewater glaciers[edit | edit source]

The Jökulsarlón tidewater glacier is in Iceland. Credit: Hansueli Krapf.

Def. a glacier occurring in water affected by the flow of the tide, especially tidal streams is called a tidewater glacier.

Polar glaciers[edit | edit source]

The Pensacola glacier in the Pensacola Range of Antarctica is a polar glacier. Credit: NASA / James Yungel.

Def. a high-latitude glacier that is covered by ice is called a polar glacier, or napajäätikkö.

Polar "glaciers [owe their mass balance variations] to the varying duration of ablation in their lowest parts."[29]

Rock glaciers[edit | edit source]

Frying Pan Glacier is almost entirely covered by rocks and debris. Credit: George L. Snyder.

Def. "looks like a mountain glacier and has active flow; usually includes a poorly sorted mess of rocks and fine material; may include: (1) interstitial ice a meter or so below the surface ("ice-cemented"), (2) a buried core of ice ("ice-cored"), and/or (3) rock debris from avalanching snow and rock"[26] is called a rock glacier.

Def. "a mass of rock fragments and finer material, on a slope, that contains either an ice core or interstitial ice, and shows evidence of past, but not present, movement"[26] is called an inactive rock glacier.

At the right, "Frying Pan Glacier, Colorado, is almost entirely covered by rocks and debris in this photograph from 1966."[26]

Tributary glaciers[edit | edit source]

This shows the many tributary glaciers of the Susitna Glacier, including surge effects. Credit: Brian John.

The photo on the left shows many tributary glaciers coming into the Susitna Glacier, including surge effects.

Valley glaciers[edit | edit source]

In this photograph from 1969, small glaciers flow into the larger Columbia Glacier from mountain valleys on both sides. Credit: United States Geological Survey.

Def. a "glacier that has one or more tributary glaciers that flow into it"[26] is called a branched-valley glacier.

"In this photograph from 1969 [at the right], small glaciers flow into the larger Columbia Glacier from mountain valleys on both sides. Columbia Glacier flows out of the Chugach Mountains into Columbia Bay, Alaska."[26]

Outlet glaciers[edit | edit source]

An outlet glacier flows down the side of Fønfjord (Scoresby Sund), Greenland. Credit: Hannes Grobe, AWI.

"Close to the edges [of an ice sheet], much of the ice flows in narrow and fast-moving outlet glaciers along bedrock troughs [...] Roughly half of the mass loss occurs by iceberg calving from the fronts of these outlets; the other half, by surface melt around the periphery of the whole ice sheet."[30]

Isolated glaciers[edit | edit source]

Annotated NASA image of Mount Kilimanjaro indicates its glaciers. Credit: NASA and MONGO.
This is a panorama of Mount Kilimanjaro showing Kibo peak. Credit: Muhammad Mahdi Karim.
Mount Kilimanjaro is imaged from the air. Credit: Muhammad Mahdi Karim.
The two images show the glacial retreat on Mount Kilimanjaro between February 17, 1993, upper, and February 21, 2000, lower. Credit: NASA and U.S. Government.
This aerial view is from 1938 and shows much more snow than the one above from 2009. Credit:Mary Meader, American Geographical Society Library, University of Wisconsin-Milwaukee Libraries.
Shown are the outlines of the Kibo (Kilimanjaro) ice fields in 1912, 1953, 1976, 1989, and 2000, using the OSU aerial photographs taken on 16 February 2000. Credit: Lonnie G. Thompson, Ellen Mosley-Thompson, Mary E. Davis, Keith A. Henderson, Henry H. Brecher, Victor S. Zagorodnov, Tracy A. Mashiotta, Ping-Nan Lin, Vladimir N. Mikhalenko, Douglas R. Hardy, Jürg Beer.

"Mount Kilimanjaro is the highest [...] "stand-alone" [...] mountain in the world. [...] Mount Kilimanjaro started to be formed about 750000 years ago being currently constituted by three major volcanic cones, Kibo, Mawenzi, and Shira. The first reaches approximately 5900m."[31]

Its "location [is] close to [the] equator associated with the existence of permanent glaciers and its almost perfect volcano shape"[31]

For "the Uhuru Peak with respect to the KILI2008 datum ... a final value of 5890.79m was determined for the orthometric height of the highest point in Africa considering the Tanzanian vertical datum."[32]

Kilimanjaro is located at 3°04.6'S and 37°21.2'E.[32]

"Aerial photographs taken on 16 February 2000 allowed production of a recent detailed map of ice cover extent on the summit plateau [diagram at the lower left]."[32]

"Total ice area calculated from successive maps (1912, 1953, 1976, 1989, and 2000) reveals [diagram at the lower left, inset] that the areal extent of Kilimanjaro’s ice cover has decreased approximately 80% from ~12 km2 in 1912 to ~2.6 km2 in 2000 and that since 1989, a hole has developed near the center of the NIF. A nearly linear relationship (R2 = 0.98) suggests that if climatological conditions of the past 88 years continue, the ice on Kilimanjaro will likely disappear between 2015 and 2020."[32]

Crater glaciers[edit | edit source]

The image shows the crater glacier of the volcano Sollipulli. Credit: Roka1953.
The summit of Sollipulli is occupied by a four-kilometer wide caldera, currently filled with a snow-covered glacier. Credit: International Space Station Expedition 38 crew.

"While active volcanoes are obvious targets of interest because they pose natural hazards, there are some dormant volcanoes that also warrant concern because of their geologic history. One such volcano is Sollipulli, located in central Chile near the border with Argentina. The volcano sits in the southern Andes Mountains within Chile’s Parque Nacional Villarica. This photograph by an astronaut on the International Space Station features the summit (2,282 meters, or 7,487 feet, above sea level) and the bare slopes above the tree line. Lower elevations are covered with green forests indicative of Southern Hemisphere summer."[33]

"The summit of Sollipulli is occupied by a four-kilometer wide caldera, currently filled with a snow-covered glacier. While most calderas form after violent, explosive eruptions, the types of rock and other deposits associated with such events have not been found at Sollipulli. Geologic evidence does indicate explosive activity occurred about 2,900 years ago, and lava flows were produced approximately 700 years ago. Together with the craters and scoria cones along the outer flanks of the caldera, this history suggests Sollipulli could erupt violently again, presenting a potential hazard to towns such as Melipeuco and the wider region."[33]

Cirque glaciers[edit | edit source]

A quarter mile of glacial ice is all that remains from the retreat of the glacier of Southwind Fiord, Baffin Island, Nunavut, Canada. Credit: Mike Beauregard from Nunavut, Canada.
Schematic profile of a cirque and cirque glacier, shows Bergschrund, randkluft and the headwall gap. Credit: Clem Rutter.

Cirques, as diagrammed at the left, are formed by a glacier (the cirque glacier) and usually exhibit a Bergschrund, randkluft and the headwall gap. The image at the right shows a glacier on Baffin Island that has retreated back to a cirque glacier.

Temperate glaciers[edit | edit source]

The canyons of Hafrahvammar are shown. Credit: Friðrik Bragi Dýrfjörð.

At the right is an image of a temperate glacier; i.e., one flowing through a temperate region, as evidenced by the green plants.

Ice caps[edit | edit source]

The most important drill sites on the inland ice and on two small separate ice caps: Hans Tavsen in Peary Land in the north and Renland in the east are indicated. Credit: Willi Dansgaard.
Looking south on Renland is across the Edward Bailey Glacier into the Alpine Bowl. Credit: Silvan Schüpbach.
This is an aerial image of the ice cap on Ellesmere Island, Canada. Credit: National Snow and Ice Data Center.
Vatnajökull, Iceland has an ice cap. Credit: NASA.

Def. "a dome-shaped mass of glacier ice that spreads out in all directions"[26] is called an ice cap.

In addition to many of the ice core drilling sites on Greenland in the image at the right, there are the separate ice caps on Hans Tavsen in Peary Land way to the north and Renland in the east.

In "1985, when [the final version of “the Rolls Royce drill”] penetrated the separate, high-lying Renland ice cap in the Scoresbysund Fiord [...] down to 325 m, world record for this type of drill".[34]

The Renland ice core from East Greenland apparently covers a full glacial cycle from the Holocene into the previous Eemian interglacial. The Renland ice core is 325 m long.[35]

"The δ-profile [...] proved that the Renland ice cap has always been separated from the inland ice. Since all of the δ-leaps revealed by the Camp Century core recurred in the small Renland ice cap, the Renland peninsula cannot have been overrun by ice streams from the inland ice, not even during the glaciation.[34]

The Penny Ice Cap is on Baffin Island, Canada, at 67° 15'N, 65° 45'W, 1900 masl.

In April 1998 on the Devon Ice Cap filtered lamp oil was used as a drilling fluid. In the Devon core it was observed that below about 150 m the stratigraphy was obscured by microfractures.[36]

"Beginning in 1995, a large outlet glacier of the Sermersauq Ice Cap on Disko Island [Greenland] surged 10.5 km downvalley to within 10 km of the head of the fjord, Kuannersuit Sulluat, reaching its maximum extent in summer 1999 before beginning to retreat. Sediment discharge to the fjord increased from 13 x 103 t day-1 in 1997 to 38 x 103 t day-1 in 1999. CTD results, sediment traps and cores from the 2000 melt season document the impact of the surge on the glacimarine environment of the fjord."[27]

"Short gravity cores were taken and CTD profiles were recorded at stations throughout Kuannersuit Sulluat [...]. Positions located by GPS are accurate to ±10 m or less. The stream flowing over the sandur to the head of the fjord was gauged and integrated suspended sediment samples were recovered from primary channels."[27]

"The cores were photographed, X-rayed and logged. X-radiographs provided measures of the number and size of gravel particles interpreted as ice-rafted debris (IRD) and the grey-scale (GS) of the scanned images was plotted as a measure of the properties of the sand and silt."[27]

"The twelve layers in core D4 [imaged at the right] suggest a mean period of about 20 days for these events based on the accumulation rates in the traps [...]. In general, these layers have both higher MS and X-radiographs have lighter toned GS, the former related to lower water content and the latter also related to greater absorption of X-rays by the larger rock and mineral fragments."[27]

There "are notable differences in the surge-generated sediments. The proximal sediments [such as in core D4 at the right] are more clearly laminated and layered in visual examination of the cores and as seen in the X-radiographs [compared to distal sediments as imaged on the left for core D20]. These consist both of the subtle differences in the fine-grained sediments on a millimetre scale, and of the sand layers up to 8 cm thick representing more energetic processes (Ó Cofaigh and Dowdeswell, 2001). Both are a response to greater sediment input to the fjord."[27]

The ice core drilled in Guliya ice cap in western China in the 1990s reaches back to 760,000 b2k; farther back than any other core at the time, though the EPICA core in Antarctica equalled that extreme in 2003.[37]

Ice cores from Sajama in Bolivia span ~25 ka and help present a high resolution temporal picture of the Late Glacial Stage and the Holocene climatic optimum.[38]

Although the ice cores from Quelccaya ice cap only go back ~2 ka,[38] others may go back ~5.2 ka. The Quelccaya ice cores correlate with those from the Upper Fremont Glacier.

Greenland ice sheets[edit | edit source]

Satellite composite image shows the ice sheet of Greenland. Credit: NASA.
Earth's northern hemisphere polar ice sheet includes sea ice. Credit: NASA/Goddard Space Flight Center.
(a) The probability is for of a pixel melting at least as many times as observed during the 1995, 1998 and 2002 melt seasons given the last 25 years of melt observations. (b) Melt extent is for 2002: Pixels are color coded for number of melt days during the season. (c) Slopes of the trend lines are fit to the areas observed to melt between April and November from 1979 to 2003. Credit: K. Steffen, S. V. Nghiem, R. Huff, and G. Neumann.
Half-decade records for ETH/CU Camp station: (a) Top panel is for QSCAT backscatter, (b) middle panel for QSCAT diurnal signature, and (c) bottom panel for air temperature measured at the AWS site. Credit: K. Steffen, S. V. Nghiem, R. Huff, and G. Neumann.
QSCAT melt maps are shown on the climatological peak-melt day (1 August). Red color represents current active melt areas, light blue is for areas that have melted but currently refreeze, white is for areas that will melt later, and magenta is for areas that do not experience any melt throughout the melt season. The dark blue color surrounding Greenland is the ocean mask. Credit: K. Steffen, S. V. Nghiem, R. Huff, and G. Neumann.
QSCAT maps of number of melt days (violet to red for 1 to 31 days) in 2000–2003 with the overlaid black contours representing melt extent derived from PM data are shown. Credit: K. Steffen, S. V. Nghiem, R. Huff, and G. Neumann.

Def. "a dome-shaped mass of glacier ice that covers surrounding terrain and is greater than 50,000 square kilometers (12 million acres)"[26] is called an ice sheet.

At the right is a satellite composite image of the ice sheet over Greenland.

"Active and passive microwave satellite data are used to map snowmelt extent and duration on the Greenland ice sheet. The passive microwave (PM) data reveal the extreme melt extent of 690,000 km2 in 2002 as compared with an average extent of 455,000 km2 from 1979–2003."[39]

"Several PM-based melt assessment algorithms [Mote and Anderson, 1995; Abdalati and Steffen, 1995] are applicable to Scanning Multi-channel, Microwave Radiometer (SMMR) and Special Sensor Microwave/Imager (SSM/I) instruments providing near-continuous coverage since 1979. The PM data as gridded brightness temperatures on polar stereographic grids (25 km resolution) [used] are from the National Snow and Ice Data Center [Maslanik and Stroeve, 2003], containing daily data spanning 25 melt seasons from 1979 to 2003."[39]

In the second image on the right, (a) "shows the probabilities of the observed melt behavior on the Greenland ice sheet for several large melt years and indicates the extreme melt anomaly observed in northeastern Greenland in 2002."[39]

"Prior to 2002, both 1995 and 1998 were extreme melt years in terms of maximum areal extent and total melt. During 1995 melt was dominated by a high frequency of melt along the western margin of the ice sheet. During 1998 melt was spatially diverse with slightly more melt than usual in the northeast and southwest. However, the high frequency melt in 2002 in the northeast and along the western margin is unprecedented in the PM record with a log likelihood of occurrence that is 35% lower than the previous record melt anomaly in 1991."[39]

(c) "depicts the magnitude of the increasing trends in melt extent on a daily basis over the last 25 years. Although there is a large amount of inter-annual variability in melt extent on a given day, 56 days show statistically significant (alpha = 0.1) increasing trends in melt area."[39]

"Melt along the west coast was extensive during 2002 but not atypical for large melt years. However melt in the north and northeast was highly irregular both in terms of extent and frequency. Nearly 3,000 km2[(b)] were classified as melting during 2002 that had not previously melted during any other year between 1979 and 2003."[39]

The figure at the left "presents QSCAT backscatter and diurnal signatures, and ETH/CU AWS air temperature."[39] Half-decade records for ETH/CU Camp station: (a) Top panel is for QSCAT backscatter, (b) middle panel for QSCAT diurnal signature, and (c) bottom panel for air temperature measured at the AWS site.[39]

At the lower right QSCAT melt maps are shown on the climatological peak-melt day (1 August). Red color represents current active melt areas, light blue is for areas that have melted but currently refreeze, white is for areas that will melt later, and magenta is for areas that do not experience any melt throughout the melt season. The dark blue color surrounding Greenland is the ocean mask.

"QSCAT mapping can reveal details of the spatial pattern of surface melt evolution in time. There are large variabilities in melt extent and melt timing over different regions. [The figure at tje lower right] confirms that 2002 has the most extensive areal melt. In 2002, the northeast quadrant of the Greenland ice sheet, extending well into the dry snow zone, experienced at least some melt where melt never happened before (from satellite data records to date). Since the beginning of the QSCAT data record (July 1999), the smallest spatial extent of melt occurred in 2001, and melt extent was similar for years 2000 and 2003."[39]

"To provide a direct comparison of PM and QSCAT results, we overlay results for PM melt extent and QSCAT number of melt days in [the figure at the lower left] for years 2000–2003. PM XPGR melt extent is approximately confined to QSCAT melt areas experiencing 2 weeks or more of melting time [the figure at the lower left]. QSCAT melt areas outside of the PM melt extent represent the surface that has less melt corresponding to about 15 melt days or less. This is consistent with the relationship of relative melt strength measured by active and passive data as discussed above. Note that such areas can total up to a large region in year 2002. Surface albedo can reduce considerably once the snow melts for a period of 2 weeks. The albedo reduction may significantly impact the surface heat balance and thus change the mass balance. The large number of melt days around the northern perimeter of the ice sheet, which is shown as the narrow dark-red band in north Greenland in the 2003 map was an anomalous feature [the figure at the lower left]. This band was wider as defined by the PM melt extent in 2002 than in 2003. However, there were more QSCAT melt days in the 2003 northern melt band."[39]

"The comparison reveals that the PM cross-polarized gradient algorithm classifies melt more conservatively than the scatterometer algorithm. The active microwave identifies melt approximately up to two weeks more than the PM at higher elevation in the percolation zone toward the dry snow zone [the figure at the lower left]. Both methods (active and passive microwave) consistently identify melt areas that have a melt duration of at least 10–14 days. The longer snowmelt duration can be sufficient to decrease surface albedo and affect surface heat and mass balance."[39]

Antarctic ice sheets[edit | edit source]

A satellite composite image shows the ice sheet of Antarctica Credit: Dave Pape.
A satellite composite image shows a global view of the sea ice and ice sheet of Antarctica. Credit: NASA Scientific Visualization Studio Collection.
Velocity of ice flowing across Antarctica varies by location. Credit: Jeremie Mouginot, University of California Irvine.{{fairuse}}

"The only current ice sheets are in Antarctica and Greenland; during the last glacial period at Last Glacial Maximum (LGM) the Laurentide ice sheet covered much of North America, the Weichselian ice sheet covered northern Europe and the Patagonian Ice Sheet covered southern South America."[40]

At the south pole, Antactica, there is also an extensive ice sheet shown in the second image on the right. Seasonally, when the North polar sea ice and ice sheet has been contracting, the South polar sea ice and ice sheet has been expanding.

Apparent global warming that was progressively melting more and more of the north polar ice sheet each year has been countered by progressive expansion of the south polar ice sheet.

"Decades of satellite observations have now provided the most detailed view yet [second image down on the right] of how Antarctica continually sheds ice accumulated from snowfall into the ocean."[41]

The "first comprehensive view of how ice moves across all of Antarctica, [includes] slow-moving ice in the middle of the continent rather than just rapidly melting ice at the coasts."[41]

Subtle "movements of Antarctic ice [were detected] with a kind of measurement called synthetic-aperture radar interferometric phase data."[41]

"By using a satellite to bounce radar signals off a patch of ice, [...] how quickly that ice is moving toward or away from the satellite [can be determined]. Combining observations of the same spot from different angles reveals the speed and direction of the ice’s motion along the ground."[41]

"Inland ice moves incredibly slowly — much of it plods along at fewer than 10 meters per year. Closer to the ocean, ice can travel hundreds to thousands of meters per year."[41]

"To get multiple vantage points of the same swathes of ice, [...] data from about half a dozen satellites launched by Canada, Europe and Japan since the early 1990s [was put together]."[41]

"Each brought a little piece of the puzzle."[42]

"Surface ice velocity is a fundamental characteristic of glaciers and ice sheets that quantifies the transport of ice. Changes in ice dynamics have a major impact on ice sheet mass balance and its contribution to sea level rise. Prior comprehensive mappings employed speckle and feature tracking techniques, optimized for fast‐flow areas, with precision of 2‐5 m/yr, hence limiting our ability to describe ice flow in the slow interior. We present a vector map of ice velocity using the interferometric phase from multiple satellite synthetic aperture radars resulting in ten‐times higher precision in speed (20 cm/yr) and direction (5o) over 80% of Antarctica. Precision mapping over areas of slow motion (< 1 m/yr) improves from 20% to 93%, which helps better constrain drainage boundaries, improve mass balance assessment, evaluate regional atmospheric climate models, reconstruct ice thickness, and inform ice sheet numerical models."[43]

Himalayas ice sheets[edit | edit source]

This is a Landsat 7 image of the Himalayas. NASA.

Often called the third pole, the image on the right shows the rocky ice sheet over the top of the Himalayas.

Glaciations[edit | edit source]

Geologic time is annotated with glacial or ice age periods. Credit: William M. Connolley.
Earth at the last glacial maximum of the current ice age. Credit: Ittiz, based on: "Ice age terrestrial carbon changes revisited" by Thomas J. Crowley (Global Biogeochemical Cycles, Vol. 9, 1995, pp. 377-389.
Recent (black) and maximum (grey) glaciation of the northern hemisphere are during the Quaternary climatic cycles. Credit: Hannes Grobe/AWI.
Recent (black) and maximum (grey) glaciation of the southern hemisphere are during the Quaternary climatic cycles. Credit: Hannes Grobe/AWI.

Def. the "process of covering with a glacier,[44] or the state of being glaciated;[45] the production of glacial phenomena;[45] an ice age[46]" is called a glaciation.

The ice ages or glaciations on Earth occurred from the early Proterozoic (Huronian), late proterozoic (Cryogenian), early Paleozoic (Andean-Saharan) during the Ordovician and Silurian periods, late Paleozoic (Karoo Ice Age) during the Carboniferous and early Permian periods, and lately the Quaternary glaciation.

Although these ice ages are widely separated in geological time, "in most parts of the Earth major climatic and palaeoenvironmental units typically have a duration of the order of half a precession cycle (around 10 ka) rather than half an eccentricity cycle (around 50 ka) so that the level of stratigraphic resolution provided by the Middle Pleistocene [Marine Isotope Stage] MIS (typical duration 50 ka) is not sufficiently fine to constitute a universal stratigraphic template."[47]

Icequakes[edit | edit source]

This map of Antarctica shows the icequakes triggered by Chile's 2010 earthquake. Credit: Zhigang Peng, Georgia Tech.

"Only 12 of Antarctica's 42 seismometers picked up icequakes after the Maule earthquake, but the signals seemed to fit a pattern. The pattern suggests that opening or closing of shallow crevasses generated the tiny tremors. For example, seismic stations near Antarctica's mountain ranges and fast-flowing ice rivers known as ice streams were more likely to see icequakes. These are areas with a lot of crevasses. The high-frequency shaking also fits with cracking of brittle ice."[48] Bold added.

"Antarctica's ice snapped and popped because of a major earthquake in Maule, Chile, halfway around the world [...] Antarctica has been touched by great earthquakes before. In March 2011, Japan's Tohoku tsunami tore off two Manhattan-size icebergs from the Sulzberger Ice Shelf, more than 8,000 miles (13,000 kilometers) south. Sailors also reported a massive Antarctica iceberg-calving event after Chile's 1868 great earthquake."[48]

"Icequakes are seismic tremblings caused by sudden movement within a glacier or ice sheet, such as from a fracturing crevasse. (Anyone who has dropped an ice cube into a glass of water knows ice snaps under stress.)"[48]

"Chile's magnitude-8.8 earthquake on Feb. 27, 2010, set off a flurry of Antarctic icequakes, each lasting from one to 10 seconds, researchers report today (Aug. 10) in the journal Nature Geoscience. The epicenter was 2,900 miles (4,700 km) north of Antarctica."[48]

"We think the crevasses are being activated by the surface waves from this big earthquake coming through, and that's making the icequake."[49]

"Regular icequakes probably occur all the time in Antarctica and other polar regions."[50] "What we found is that they occurred more during the seismic waves of the Maule event."[50]

"Many different kinds of icequakes rumble across Antarctica and Greenland. Known icequake triggers include opening and closing of the fractures called crevasses; glaciers tearing away from sticky bedrock; water runoff; and calving, the breaking off of an iceberg. Spooky underwater sounds from melting, cracking icebergs were once called The Bloop."[48]

Just "one kind of seismic wave, a surface wave, gets the blame for most of Antarctica's icequakes. [...] a Rayleigh wave [...] travels close to the Earth's surface, rolling along like a wave in a lake or the ocean. [...] At some stations, there was also a short icequake burst from a seismic "P wave," which travel through the Earth's interior."[48]

Ice shelves[edit | edit source]

Iceberg A 62 was connected to the Fimbul Ice Shelf by a mere 800-metre-wide bridge. Credit: DLR - German Space Agency.
This is a schematic of glaciological and oceanographic processes along the Antarctic coast. Credit: Hannes Grobe, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany.
Canadian RADARSAT image shows the shelf in August 2002, when a crack made its way down the length of the shelf. Credit: Alaska Satellite Facility, Geophysical Institute, University of Alaska Fairbanks.
This is an image of iceberg A-38 after it detached from the Ronne Ice Shelf. Credit: National Ice Center/National Oceanic and Atmospheric Administration.

"A small island obstructs the constant flow of the ice shelf on Queen Maud Land – it is the lighter area at the bottom left of the image [on the right]. From September 2010 until it broke off, Iceberg A 62 was connected to the Fimbul Ice Shelf by a mere 800-metre-wide bridge. Two fissures in the ice from different sides of the bridge approached one another until the break occurred. The images transmitted by the radar satellite TerraSAR-X over a long period of time should enable researchers to achieve a better understanding of how icebergs calve."[51]

Def. a "thick, floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface"[52] is called an ice shelf.

"Ice shelves are permanent floating sheets of ice that connect to a landmass."[53]

"Ice shelves fall into three categories: (1) ice shelves fed by glaciers, (2) ice shelves created by sea ice, and (3) composite ice shelves (Jeffries 2002). Most of the world's ice shelves, including the largest, are fed by glaciers and are located in Greenland and Antarctica."[53]

"One example of an ice shelf composed of compacted, thickened sea ice is the Ward Hunt Ice Shelf off the coast of Ellesmere Island in northern Canada. Canadian RADARSAT image shows the shelf in August 2002, when a crack made its way down the length of the shelf."[53]

The Ronne Ice Shelf has a nominal location of 78°30'S 61°W.

Sea ices[edit | edit source]

This is an aerial view of the pack ice off the eastcoast of Greenland. Credit: Michael Haferkamp.
This is pack ice off the coast of Vaxholm, Sweden. Credit: Cyberjunkie.
Pack-ice-covered Auke Bay Harbor, Alaska, in winter. Credit: David Csepp, NOAA/NMFS/AKFSC/ABL.
When waves buffet the freezing ocean surface, characteristic "pancake" sea ice forms. Credit: Ted Scambos, NSIDC.

A "climate interpretation was supported by very low δ’s in the 1690’es, a period described as extremely cold in the Icelandic annals. In 1695 Iceland was completely surrounded by sea ice, and according to other sources the sea ice reached half way to the Faeroe Islands."[34]

"The correlation is astonishing, because it implies that the dramatic climate changes during the first more than 50 kyrs of the glaciation elapsed nearly in parallel on both sides of the North Atlantic Ocean, presumably controlled by varying sea ice cover. Thus, the Gulf Stream was not just deflected toward North Africa in cold periods, it was rather turned off."[34]

Def. a "large consolidated mass of floating sea ice"[54] is called pack ice.

Pack ice in the image on the right is drifting southward in the East Greenland current during July 1996.

In the second image on the left, when "waves buffet the freezing ocean surface, characteristic "pancake" sea ice forms."[55]

"Sheets of sea ice form when frazil crystals float to the surface, accummulate and bond together. Depending upon the climatic conditions, sheets can develop from grease and congelation ice, or from pancake ice."[56]

"If the ocean is rough, the frazil crystals accummulate into slushy circular disks, called pancakes or pancake ice, because of their shape. A signature feature of pancake ice is raised edges or ridges on the perimeter, caused by the pancakes bumping into each other from the ocean waves. If the motion is strong enough, rafting occurs. If the ice is thick enough, ridging occurs, where the sea ice bends or fractures and piles on top of itself, forming lines of ridges on the surface. Each ridge has a corresponding structure, called a keel, that forms on the underside of the ice. Particularly in the Arctic, ridges up to 20 meters (60 feet) thick can form when thick ice deforms. Eventually, the pancakes cement together and consolidate into a coherent ice sheet. Unlike the congelation process, sheet ice formed from consolidated pancakes has a rough bottom surface."[56]

Icebergs[edit | edit source]

When the polar sea is calm, the underside of icebergs can easily be observed in the clear waters of the Arctic Ocean. Credit: AWeith.
Black ice growler from a recently calved iceberg is closing in on the shore at the old heliport in Upernavik, Greenland. Credit: Kim Hansen.
Surface texture on a growler of black ice. Credit: Kim Hansen.

The first image on the right shows that when the polar sea is calm, the underside of icebergs can easily be observed in the clear waters of the Arctic Ocean.

Centered in the image second down on the right is a black ice growler from a recently calved iceberg closing in on the shore at the old heliport in Upernavik, Greenland. Such black ice growlers originate from glacial rifts, or crevasses, filled with melting water, which freezes into transparent ice without air bubbles.

On the left is an image of the surface texture on a black ice growler. There are bowl-like depressions in the surface created by the melting process of sea water.

Lahars[edit | edit source]

An explosive eruption of Mount St. Helens on March 19, 1982, sent pumice and ash 9 miles (14 kilometers) into the air, and resulted in a lahar (the dark deposit on the snow) flowing from the crater into the North Fork Toutle River valley. Credit: Tom Casadevall.

"Because the volcano itself is covered by 15 square miles of glaciers, the lava that flows down the side and mixes with ice and snow to form lahars — a mudflow slurry that can move extremely quickly and destroy towns in their path. According to the Smithsonian, "lahars have damaged towns on Villarica's flanks." The BBC reports that more than 100 people are believed to have been killed by the volcano's mudflows in the past century."[57]

Def. a "volcanic mudflow"[58] is called a lahar.

Part of the Mount St. Helens lahar entered Spirit Lake (lower left corner of the image on the right) but most of the flow went west down the Toutle River, eventually reaching the Cowlitz River, 50 miles (80 kilometers) downstream.

Lightning[edit | edit source]

The 1995 eruption of Mount Rinjani in Indonesia exhibits volcanic lightning. Credit: Oliver Spalt.{{free media}}
The slide depicts a spectacular view of lightning strikes during a third eruption on December 3, 1982. Credit: R. Hadian, U.S. Geological Survey.{{free media}}

Many volcanic eruptions put on impressive lightning displays such as during the 1995 eruption of Mount Rinjani in Indonesia shown in the image on the right which exhibits many leaders.

The image on the left shows spectacular lightning strikes around Galunggung, including multiple leaders apparently involved in cloud to cloud lightning.

"This stratovolcano with a lava dome is located in western Java. Its first eruption in 1822 produced a 22-km-long mudflow that killed 4,000 people. The second eruption in 1894 caused extensive property loss. The photo depicts a spectacular view of lightning strikes during a third eruption on December 3, 1982, which resulted in 68 deaths. A fourth eruption occurred in 1984."[59]

Volcanic lightning arises from colliding, fragmenting particles of volcanic ash (and sometimes ice),[60][61] which generate static electricity within the volcanic plume.[62] Volcanic eruptions have been referred to as dirty thunderstorms[63][64] due to moist convection and ice formation that drive the eruption plume dynamics[65][66] and can trigger volcanic lightning.[67][68] But unlike ordinary thunderstorms, volcanic lightning can also occur before any ice crystals have formed in the ash cloud.[69][70]

Blues[edit | edit source]

This image shows the Glacier Castaño Overo spilling blue water ice, or blue ice. Credit: McKay Savage from London, UK.

Blue ice occurs when snow falls on a glacier, is compressed, and becomes part of a glacier ... blue ice was observed in Tasman Glacier, New Zealand in January 2011.[71] Ice is blue for the same reason water is blue: it is a result of an overtone of an oxygen-hydrogen (O-H) bond stretch in water which absorbs light at the red end of the visible spectrum.[72]

Venus[edit | edit source]

While there is little or no water on Venus, there is a phenomenon which is quite similar to snow. The Magellan probe imaged a highly reflective substance at the tops of Venus's highest mountain peaks which bore a strong resemblance to terrestrial snow. This substance arguably formed from a similar process to snow, albeit at a far higher temperature. Too volatile to condense on the surface, it rose in gas form to cooler higher elevations, where it then fell as precipitation. The identity of this substance is not known with certainty, but speculation has ranged from elemental tellurium to lead sulfide (galena).[73]

Mars[edit | edit source]

This Hubble Space Telescope image shows a dust storm, just above center and lighter in contrast than the surface of Mars. Credit: NASA, ESA, The Hubble Heritage Team (STScI/AURA), J. Bell (Cornell University) and M. Wolff (Space Science Institute).
A newly formed impact crater is observed by HiRISE on Mars Reconnaissance Orbiter. Credit: NASA/JPL/University of Arizona.
Another newly formed impact crater is observed by HiRISE on Mars Reconnaissance Orbiter. Credit: NASA/JPL/University of Arizona.
An impact crater on Planum Boreum, or the North Polar Cap, of Mars, is observed by HiRISE on the Mars Reconnaissance Orbiter. Credit: NASA/JPL/University of Arizona.
This freshly formed impact crater occurred on Mars between February 2005 and July 2005. Credit: NASA/JPL/University of Arizona.

Martian meteors are thought to be from Mars because they have elemental and isotopic compositions that are similar to rocks and atmosphere gases analyzed by spacecraft on Mars.[74]

At right is a Hubble Space Telescope image of a dust storm on Mars. The picture was snapped on October 28, 2005. The regional dust storm on Mars had "been growing and evolving over the past few weeks. The dust storm, which is nearly in the middle of the planet in this Hubble view is about 930 miles (1500 km) long measured diagonally, which is about the size of the states of Texas, Oklahoma, and New Mexico combined. No wonder amateur astronomers with even modest-sized telescopes have been able to keep an eye on this storm. The smallest resolvable features in the image (small craters and wind streaks) are the size of a large city, about 12 miles (20 km) across. The occurrence of the dust storm is in close proximity to the NASA Mars Exploration Rover Opportunity's landing site in Sinus Meridiani. Dust in the atmosphere could block some of the sunlight needed to keep the rover operating at full power. ... The large regional dust storm appears as the brighter, redder cloudy region in the middle of the planet's disk. This storm has been churning in the planet's equatorial regions for several weeks now, and it is likely responsible for the reddish, dusty haze and other dust clouds seen across this hemisphere of the planet in views from Hubble, ground based telescopes, and the NASA and ESA spacecraft studying Mars from orbit. Bluish water-ice clouds can also be seen along the limbs and in the north (winter) polar region at the top of the image."[75]

At left is an image of a "newly formed impact crater, observed by HiRISE on Mars Reconnaissance Orbiter. The impact that formed the crater exposed the water ice beneath the surface. Some of the ice can be seen scattered at the adjascent area in the subimages. The blast zone (excavated dark material) is almost 800 meters (half a mile) across. The crater itself is just over 20 meters (66 feet) across".[76]

"This crater is one of a special group that have excavated down to buried ice. This ice gets thrown out of the crater onto the surrounding terrain. Although buried ice is common over about half the Martian surface, we can only easily discover craters in dusty regions. The overlap between areas that both have buried ice and surface dust is unfortunately small. So even though we have discovered over 100 new impact craters we have only discovered 7 new craters that expose buried ice."[76]

"When craters excavate this buried ice it tells us something about the extent and depth of buried ice on Mars (controlled by climate); this information is used by planetary scientists to figure out what the recent climate of Mars was like. It has also been a surprise that this ice is so clean. Scientists expected this buried ice to be a mixture of ice and dirt; instead this ice seems to have formed in pure lenses. Yet another surprise that Mars had in store for us!"[76]

The ice (presumably water ice) is white in the image, but take note of the blue dust or regolith also exposed.

The second image at right is a subimage of the one at left. It is natural color and shows in better detail both the ice (white) and the blue material.

At second left is an image showing an impact crater on Planum Boreum, or the North Polar Cap, of Mars, as observed by HiRISE on Mars Reconnaissance Orbiter in natural color.

"Impact craters on the surface of Planum Boreum, popularly known as the north polar cap, are rare. This dearth of craters has lead scientists to suggest that these deposits may be geologically young (a few million years old), not having had much time to accumulate impact craters throughout their lifetime."[77]

"It is also possible that impacts into ice do not retain their shape indefinitely, but instead that the ice relaxes (similar to glass in an old window), and the crater begins to disappear. This subimage shows an example of a rare, small crater ( approximately 115 meters, or 125 yards, in diameter). Scientists can count these shallow craters to attain an estimate of the age of the upper few meters of the Planum Boreum surface."[77]

"The color in the enhanced-color example comes from the presence of dust and of ice of differing grain sizes. The blueish ice has a larger grain size than the ice that has collected in the crater. The reddish material is dust. The smooth area stretching to the upper right, away from the crater may be due to winds being channeled around the crater or to fine-grained ice and frost blowing out of the crater."[77]

The third image at right shows a freshly formed impact crater that occurred on Mars between February 2005 and July 2005.[78] Note the blue material expelled from the crater rock onto the nearby Martian landscape.

Very light snow is known to occur at high latitudes on Mars.[79]

Europa[edit | edit source]

Frozen sulfuric acid on Jupiter's moon Europa is depicted in this image produced from data gathered by NASA's Galileo spacecraft. Credit: NASA/JPL.
This chaotic terrain on Europa has areas consisting of densely packed blocks with fractures and narrow lanes of matrix between them. Credit: G. C. Collins, J. W. Head III, R. T. Pappalardo, and N. A. Spaun.
The image shows areas on Europa consisting of almost all matrix and no blocks. Credit: G. C. Collins, J. W. Head III, R. T. Pappalardo, and N. A. Spaun.
Conamara Chaos, the most intensely studied chaos area, lies near the middle of this continuum. Credit: G. C. Collins, J. W. Head III, R. T. Pappalardo, and N. A. Spaun.
High-resolution (10 m/pixel) image shows a plate surrounded by matrix material within Conamara Chaos. Credit: G. C. Collins, J. W. Head III, R. T. Pappalardo, and N. A. Spaun.
This view from the Galileo spacecraft of a small region of the thin, disrupted, ice crust in the Conamara region of Jupiter's moon Europa shows the interplay of surface color with ice structures. Credit: NASA/JPL/University of Arizona.
This Galileo spacecraft image of Jupiter's icy satellite Europa shows surface features such as domes and ridges. Credit: NASA/Jet Propulsion Laboratory/University of Arizona.
Craggy, 250 m high peaks and smooth plates are jumbled together in a close-up of Conamara Chaos. Credit: NASA/JPL.
Chaotic terrain is typified by the area in the upper right-hand part of the image. Credit: NASA / JPL.

"Frozen sulfuric acid on Jupiter's moon Europa is depicted in this image produced from data gathered by NASA's Galileo spacecraft. The brightest areas, where the yellow is most intense, represent regions of high frozen sulfuric acid concentration. Sulfuric acid is found in battery acid and in Earth's acid rain."[80]

"The morphology of chaotic terrain forms a continuum from areas consisting of densely packed blocks with fractures and narrow lanes of matrix between them ([second image at the right]), to areas consisting of almost all matrix and no blocks ([first image at the left]). Conamara Chaos, the most intensely studied chaos area ([third image at the right]), lies near the middle of this continuum, with -60% of its area consisting of matrix and the remainder consisting of blocks [Spaunet al., 1998]. In addition to these large chaos areas, chaotic terrain also occurs in the interiors of some small (-10 km diameter) features [Spaun et al., 1999] known as "lenticulae.""[81]

"In Conamara Chaos, where data with spatial resolution of up to ten meters per pixel were obtained, the hummocky matrix appears to be a jumbled collection of ice chunks of all sizes, from a kilometer to tens of meters across ([second image on the left])."[81]

"Galileo spacecraft observations of Europa suggest the existence of a brittle ice crust (or lithosphere) at most -2 km thick, and maybe thinner locally, overlying a liquid water or ductile ice layer [Carr et al., 1998; Pappalardo et al., 1998, 1999]. Elastic and viscous models of buckling based on the spacing between possible folds in the Astypalaea Linea region give a thickness for the buckling layer of -2 km [Prockter and Pappalardo, 2000]. Evidence derived from the width troughs (interpreted as possible grabens) in the surroundings of Callanish, a possible impact structure, might denote a brittle-ductile transition locally as shallow as 0.5 km [Moore et al., 1998]. Besides this, study of ice flexion induced by a dome-type structure located close to Conamara Chaos suggests an elastic lithosphere thickness of only -0.1-0.5 km [Williams and Greeley, 1998]."[82]

The "odd surface terrain patterns [of Europa] likely come about due to convection. [...] The ice shell of Jupiter’s moon Europa is marked by regions of disrupted ice known as chaos terrains that cover up to 40% of the satellite’s surface, most commonly occurring within 40° of the equator. Concurrence with salt deposits implies a coupling between the geologically active ice shell and the underlying liquid water ocean at lower latitudes. Europa’s ocean dynamics have been assumed to adopt a two-dimensional pattern, which channels the moon’s internal heat to higher latitudes. [...] heterogeneous heating promotes the formation of chaos features through increased melting of the ice shell and subsequent deposition of marine ice at low latitudes."[83]

The fifth image at the right is a "view of the Conamara Chaos region on Jupiter's moon Europa taken by NASA's Galileo spacecraft shows an area where the icy surface has been broken into many separate plates that have moved laterally and rotated. These plates are surrounded by a topographically lower matrix. This matrix material may have been emplaced as water, slush, or warm flowing ice, which rose up from below the surface. One of the plates is seen as a flat, lineated area in the upper portion of the image. Below this plate, a tall twin-peaked mountain of ice rises from the matrix to a height of more than 250 meters (800 feet). The matrix in this area appears to consist of a jumble of many different sized chunks of ice. Though the matrix may have consisted of a loose jumble of ice blocks while it was forming, the large fracture running vertically along the left side of the image shows that the matrix later became a hardened crust, and is frozen today. The Brooklyn Bridge in New York City would be just large enough to span this fracture."[84]

"North is to the top right of the picture, and the sun illuminates the surface from the east. This image, centered at approximately 8 degrees north latitude and 274 degrees west longitude, covers an area approximately 4 kilometers by 7 kilometers (2.5 miles by 4 miles). The resolution is 9 meters (30 feet) per picture element. This image was taken on December 16, 1997 at a range of 900 kilometers (540 miles) by Galileo's solid state imaging system."[84]

"Chaotic terrain on Europa is interpreted to be the result of the breakup of brittle surface materials over a mobile substrate."[81]

At the third left, "the mottled appearance results from areas of the bright, icy crust that have been broken apart (known as "chaos" terrain), exposing a darker underlying material. This terrain is typified by the area in the upper right-hand part of the image. The mottled terrain represents some of the most recent geologic activity on Europa. Also shown in this image is a smooth, gray band (lower part of image) representing a zone where the Europan crust has been fractured, separated, and filled in with material derived from the interior. The chaos terrain and the gray band show that this satellite has been subjected to intense geological deformation."[85]

Technology[edit | edit source]

The image shows a standard rain gauge. Credit: Bidgee.

The standard way of measuring rainfall or snowfall is the standard rain gauge, which can be found in 100-mm (4-in) plastic and 200-mm (8-in) metal varieties.[86] The inner cylinder is filled by 25 mm (0.98 in) of rain, with overflow flowing into the outer cylinder. Plastic gauges have markings on the inner cylinder down to 0.25 mm (0.0098 in) resolution, while metal gauges require use of a stick designed with the appropriate 0.25 mm (0.0098 in) markings. After the inner cylinder is filled, the amount inside it is discarded, then filled with the remaining rainfall in the outer cylinder until all the fluid in the outer cylinder is gone, adding to the overall total until the outer cylinder is empty.[87]

Global Precipitation Measurement[edit | edit source]

This image depicts the GPM Core Observatory satellite orbiting Earth, with several other satellites from the GPM Constellation in the background. Credit: NASA.

"The Global Precipitation Measurement (GPM) mission is an international network of satellites [shown in the image at right] that provide the next-generation global observations of rain and snow. Building upon the success of the Tropical Rainfall Measuring Mission (TRMM), the GPM concept centers on the deployment of a “Core” satellite carrying an advanced radar / radiometer system to measure precipitation from space and serve as a reference standard to unify precipitation measurements from a constellation of research and operational satellites. Through improved measurements of precipitation globally, the GPM mission will help to advance our understanding of Earth's water and energy cycle, improve forecasting of extreme events that cause natural hazards and disasters, and extend current capabilities in using accurate and timely information of precipitation to directly benefit society. GPM, initiated by NASA and the Japan Aerospace Exploration Agency (JAXA) as a global successor to TRMM, comprises a consortium of international space agencies, including the Centre National d’Études Spatiales (CNES), the Indian Space Research Organization (ISRO), the National Oceanic and Atmospheric Administration (NOAA), the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT), and others."[88] The launch occurred on February 28, 2014 at 3:37am JST on the first attempt.[89]

See also[edit | edit source]

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External links[edit | edit source]