# WikiJournal Preprints/Cryometeors

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## Article information

Author: Henry A. Hoff
* ↑ henryhoff@rocketmail.com

## Ices

Def. "any frozen volatile chemical, such as water, ammonia, or carbon dioxide" is called an ice.
The discoveries of water ice on the Moon, Mars and Europa add an extraterrestrial component to the field, as in "astroglaciology".

## Radiation

Def. the "shooting forth of anything from a point or surface, like the diverging rays of light; as, the radiation of heat" is called radiation.
Here is a theoretical definition:
Def. "an action or process of throwing or sending out (splitting) a ray in a line, beam, or stream of small cross section" is called radiation.
Meteorites from the Moon (selenometeorites), Mars (arieometeorites) and the asteroids (astrometeorites) have been found on Earth. Acfer 049, an astrometeorite discovered in Algeria in 1990, was shown to have an ultraporous lithology (UPL) that could be formed by removal of ice from these pores, such that a UPL may "represent fossils of primordial ice".
Matter from the Moon, Mars and the asteroids have been radiated into the Earth perhaps including ice.
Asteroids and larger bodies can be radiated through precession or irradiated through solar activity cycles.

## Carbon dioxide ices

Dry ice sublimates at 194.7 K (−78.5 °C; −109.2 °F) at Earth atmospheric pressure.

## Methane or gas hydrate ices

Methane clathrate, also called methane hydrate, methane ice or "fire ice" is a solid clathrate hydrate in which methane is trapped within a crystal structure of water, forming a solid.

## Ammonia ices

Ammonia is a colourless gas with a characteristically pungent smell, that is lighter than air, its density being 0.589 times that of Earth's atmosphere. It is easily liquefied due to the strong hydrogen bonding between molecules; the liquid boils at −33.1 °C (−27.58 °F), and freezes to white crystals at −77.7 °C (−107.86 °F).
Solid ammonium carbonate and ammonium bicarbonate salts partly dissociate to form NH $_3$, CO $_2$ and H $_2$O vapour as follows:
    (NH $_4$) $_2$CO $_3$ → 2 NH $_3$ + CO $_2$ + H $_2$O.
    NH $_4$HCO $_3$ → NH $_3$ + CO $_2$ + H $_2$O.

## Meteors

Def. "1 : a phenomenon or appearance in the atmosphere (as lightning, a rainbow, or a snowfall) 2 a : one of the small particles of matter in the solar system observable directly only when it falls into the earth's atmosphere where friction may cause its temporary incandescence b : the streak of light produced by the passage of a meteor" is called a meteor.
Def. a "fast-moving streak of light in the night sky caused by the entry of extraterrestrial matter into the earth's atmosphere" is called a meteor.
Def. "any natural object radiating through a portion or all of the Earth's or another natural, astronomical object's atmosphere" is called a meteor.

## Cryometeor theory

Def. "the study of the atmosphere and its phenomena, especially with weather and weather forecasting" or the "atmospheric phenomena in a specific region or period" is called meteorology.
Here are two theoretical definitions:
Def. a single ice crystal (such as a snowflake) or large ice object that is radiated and still moving is called a cryometeor.
Def. a cryometeor that has been stopped from moving (such as by impacting the Earth) is called a cryometeorite.
"Part two [of the book Comet/Asteroid Impacts and Human Society: An Interdisciplinary Approach] contains contributions focused on the status of near-earth object (NEO) surveys, current knowledge of NEO populations in space, physical properties of NEOs, the quantitative risk of impacts and risk reduction scenarios, the physical terrestrial effects of impacts, the atmospheric and oceanic (tsunami) effects of impacts, case studies including the Kaali meteorite and Tunguska events and cryometeors."
"Isotope studies suggest that most of the water did not form on Earth but is the result of the impact of a huge cryometeor that impacted on Earth billions of years ago [Morbidelli et al., 2000]."
"Schwerdtfeger (1970, p. 294) notes "With reference to Antarctica, the term ‘cryometeors’ might be more appropriate than "hydrometeors, but it is not used"."

## Cryomicrometeoroids

The rings of Saturn consist of countless small particles, ranging in size from micrometers to meters, that are made almost entirely of water ice, with a trace component of rocky material.
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, to nickel-iron rich dense rocks.
"It is empirically known that all cooling older stars that possess a global magnetic field have rings. This includes the Earth regardless if they are or not observed with the naked eye."
"[W]ater/ice rings will always be oriented in the direction perpendicular to the magnetic field orientation of the cooling star, unless that said star is changing orbits and undergoing a magnetic reversal."
Jupiter and Saturn have water ice rings.

## Megacryometeors

"A megacryometeor is a very large chunk of ice, weighing at least 10 kg, that are sometimes called huge hailstones, but do not [need] to form in Thunderstorms."
"Over the past decade, over fifty such objects have been recorded worldwide. Some have been as small as about one pound, but one monstrous mass of ice that fell in Brazil weighed about 400 pounds⁠— almost a quarter of a ton⁠— and crashed through the roof of a Mercedes-Benz factory. One recently made headlines in Oakland, California, weighing over 200 pounds and creating a dent in the Earth three feet deep. A similar event occurred in Chicago last February, crashing through the roof of a house."
"The mysterious ice blobs, like hail, have been found to contain air bubbles, onion-like layering, and traces of ammonia and silica. The icy objects also have isotopic distributions of oxygen-18 and deuterium similar to those found in hailstones. Aside from their surprising mass and their tendency to plunge one-at-a-time from clear skies, the ice balls are almost identical to hail."
"They are sometimes confused as meteors, because they can leave impact craters. The difference between a megacryometeor and a hailstone is not clearly defined, mostly because the process that creates megacryometeors is not fully understood, but they have been recorded falling out of a clear sky on a hot summer day. They are also not made from airplane toilets or exhaust streams. All analysis of the ice shows it matches normal rain for the region it fell on."
"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."
Def. "a very large water ice object that falls from the sky, similar in composition to hailstones" is called a megacryometeor.
"LARGE icy conglomerates, occasionally falling from a clear sky even when there are no clouds or precipitation, have recently been termed as megacryometeors$^1$."
"That large blocks of ice fall to the ground is evident enough; they are observed to fall and they are collected, but the central question here is did they enter the Earth’s atmosphere from interplanetary space?"
The "solar system contains numerous bodies that have water-ice as a major compositional component."
It "is a certainty that ice-meteoroids exist. The recent outburst of comet 73P/ Schwassmann- Wachmann 3 [...] provides one example of an event that produced icy-nuclei many tens of meters in diameter, and no-doubt smaller icy meteoroids as well."

## Ice meteorites

Def. "a meteor that reaches the surface of the earth without being completely vaporized" is called a meteorite.
Def. a "metallic or stony object or body that [is the remains of a meteor]oid] [or] has fallen to the surface of the Earth from outer space" is called a meteorite.
"In addition, accepting for the moment that ice meteorites might fall to Earth, the question of their origin must also be addressed – literally, where are the ice fragments from."
"One of the key factors in determining the delivery of a meteorite to the Earth’s surface is the meteoroids initial encounter speed: the lower the encounter speed the better. With respect to known cometary meteoroid streams, the smallest known Earth encounter speed is the 15 km/s of the occasionally active τ-Herculid meteor shower. The next lowest encounter speeds being those for the π-Puppid meteoroids (18 km/s) and the Draconid meteoroids (20 km/s)."
"Firstly, “what is the lifetime of a pure water-ice fragment in the inner solar system”, and second “can water-ice meteoroids survive passage through the Earth’s atmosphere”?"
"While ice-meteoroids must exist within our solar system the more important question at this stage is, how long do they exist for?"
"Once any icy nucleus or ice-meteoroid approaches within about 2.5 AU of the Sun then sublimation will become important."
"For a spherical ice-meteoroid moving in an orbit similar to, for example, Comet 73P/ Schwassmann-Wachmann 3 [Aphelion is 5.211 AU, Perihelion is 0.9722 AU] the radius would decrease due to sublimation at a rate of about 1.4 meters per orbit (or 0.25 m/yr). In other words, a 10-m diameter ice-block would disappear within about 4 orbits of the Sun – a timescale of about 20 years. The same sized meteoroid in an orbit similar to that of the Earth would disappear on an even more rapid timescale of about 2 years. Comet’s that move deep into the outer solar system spend much less time close in towards the Sun, and consequently any ice-meteoroids left in their wake will survive longer. A 10-m diameter ice-block with an orbit similar to that of comet C/1861 G1 (Thatcher) [Aphelion is 110 AU, Perihelion is 0.9207 AU], the parent comet to the April Lyrid meteor shower, which has an aphelion distance of about 109 AU, should survive for about 2000 years – but it would encounter the Earth with an initial speed of 48 km/s."
"The problem with respect to the production of ice-meteorites therefore is that they must encounter the Earth within just a few years of being ejected from their parent body, and this dynamically speaking is highly unlikely to happen."
"The lowest speed that any meteoroid can have at the top of the atmosphere is Earth’s escape velocity of 11.2 km/s."
When "the initial velocity at the top of the atmosphere is 11.5 km/s an ice-meteoroid of mass ~50,000-kg (diameter ≈ 4.8-m) is required to produce a 2-kg meteorite on the ground."
"When the initial velocity is 15 km/s, however, even a 1,000,000-kg (diameter ≈ 15-m) ice-meteoroid will only produce an ice meteorite of a few grams mass on the ground."
If "the Earth did encounter a τ-Herculid fragment of several tens of meters in diameter it would probably produce an air-burst explosion similar to that of the 1908 Tunguska impact."
"Catastrophic fragmentation of all large ice-meteoroids in the Earth’s upper atmosphere is almost inevitable, in fact, because the ram pressure due to the on-coming air flow will easily exceed the tensile strength of solid-ice or that of a cometary nucleus. The tensile strength of comet D/1993 F2 (Shoemaker-Levy 9) was estimated to be about 1000 Pa [Scotti and Melosh, 1993]; the tensile strength of water-ice falls between 10$^6$ to 10$^7$ Pa."
"So, can an ice-meteoroid survive atmospheric passage to hit the ground? Well, the answer is perhaps yes – just maybe! If the encounter velocity is not much greater than the Earth’s escape velocity then a 5 to 10-m diameter ice-meteoroid might just produce a 1 to 10-kg ice-meteorite at the Earth’s surface (provided that the tensile strength of the ice-meteoroid is greater than ~10$^7$ Pa)."
"Two main factors argue against ice meteorites. Firstly the velocity restriction requires that the meteoroids must encounter the Earth with very low velocities – certainly less than 12 – 13 km/s. No currently known cometary meteoroid stream, therefore, can produce ice-meteorites."
"The second reason why ice meteorites must, at best, be exceptionally rare relates to their survival lifetime in space. To get close to the Earth means that an ice-meteoroid must become heated, and once this happens lifetimes against mass-loss by sublimation are typically just a few tens of years. In other words an ice-meteoroid is ‘destroyed’ in space long before it might encounter the Earth to produce an ice-meteorite."
It "has been occasionally noted that meteorite falls can precipitate distinct smells; most often described as sulfurous, or ‘metallic’. Berczi and Lukacs (1997) have picked-up on this point and suggested that odors of sulphuric and ammonia compounds might in fact be released by ‘freshly’ fallen ice-meteorites".
Megacryometeors may "form under a rare, clear-sky variant of the nucleation process responsible for the production of ordinary hail (Bosch, 2002). The ‘meteor’ part of megacryometeors, it should be pointed out, relates to the idea that these objects are considered to be meteorological (that is atmospheric) in origin."

## Selenometeorites

Def. "a meteorite that is known to have originated on the Moon" is called a lunar meteorite, or perhaps a selenometeorite.
About 371 lunar meteorites have been discovered so far (as of July, 2019), perhaps representing more than 30 separate meteorite falls (i.e., many of the stones are "paired" fragments of the same meteoroid). The total mass is more than 190 kilograms (420 lb).
All lunar meteorites have been found in deserts; most have been found in Antarctica, northern Africa, and the Sultanate of Oman, but none have yet been found in North America, South America, or Europe.
Cosmic ray exposure history established with noble gas measurements has shown that all lunar meteorites were ejected from the Moon in the past 20 million years. Most left the Moon in the past 100,000 years.

## Extraterrestrial megacryometeorites

"The theory of an origin [for megacryometeors] within the Troposphere [...] seems unlikely because there would be significant heating due to an increase in CO $_2$ concentration (Fu et al. 2011)."
"[M]egacryometeors have been observed and recorded in the mid 1800s, long before the invention of airplanes".
The "proliferation of reports may be due to increased access to the media, such that, it's not the number of meteors which has increased but the number of people reporting them."
"In March of 2000 [...] large chunks and a substantial amount of smashed ice [of the Pullman ice meteorite was discovered near a residence] on a clear, cloudless day. The ice was stratified ice, transitioning from clear transparent to translucent to opaque ice. This is indicative of laid down layers of frozen precipitation. The directionally increasing density is suggestive [of] glacial ice."
"In July of 2000, [...] two vials of melt-water from the suspected ice meteorite [were sent] to Geochronology Labortories, Cambridge, Massachusetts for stable isotope ratio and tritium analysis. Subsequently, high tritium levels were detected, the most likely source being exposure to cosmic radiation."
An "oval shaped sphere, approximately 300 nm in diameter [was transported] to the Ecloe Polytechnique Surface Analysis Laboratory (LASM), located at the Unversite de Montreal in Montreal, Canada. This sample was bombarded with a pulsed liquid metal ion source at energy of 25 KeV. Both polarities, positive and negative, were registered. The most intense element is the Na (sodium) in positive and Cl (chlorine) in negative [...]. This indicates the presence of sodium chloride salt. Also noticeable is the presence of Ca, K, Si, Al and known and unknown aluminum hydroxides."
"Melt-water from the suspected ice meteorite, was analyzed by the labs of EAG, [in] Raleigh, North Carolina. The melt-water was sonicated for 10 minutes then transferred to a copper mesh TEM grid. Imaging using STEM (Hitachi HD2700 scanning transmission electron microscope) provided various magnifications in atomic number contrast mode (ZC) and transmitted electron mode (TE). Chemical analysis was preformed with a Bruker Quantax EDS system."
"Mass spectra of 7 particles [...] indicates high levels of carbon, and Si and O as highly significant particle constituents, as well as Sodium (Na) and chlorine (Cl), being possible salts. When the carbon and the salts are taken into account, the elemental composition of these particles [is] in agreement with the hydrothermal nano-silica (SiO $_2$) particles found in the E ring of Saturn. However, carbon was also the most abundant contaminate element found in Saturn’s E ring by the Cassini’s CDA. When the carbon is taken into account, the elemental composition of the particles are in agreement with the hydrothermal nano-silica (SiO $_2$) particles found in the E ring of Saturn."
There "is no evidence megacryometeors are formed in the stratosphere. Moreover, it is a fact that ice chunks, weighing over tens of kilograms (22 pounds), do fall to Earth and it seems highly unlikely such large objects could develop in the stratosphere when there is no evidence that they were formed in the stratosphere in the first place."
Growth "and layering was [...] observed. Growth, however, requires a place to grow. Micro-Raman spectroscopy of band profiles has indicated that this growth takes place in a range of temperatures (Ruff et al. (2010); and this suggests that the place where these megacryometeors must have been subject to a range of temperatures over a significant duration of time."
These "ice meteors are formed either in space or they are ejecta from stellar objects consisting of large amounts of water. Be they formed in space or ejecta, these ice meteors would break apart and melt as they enter Earth's atmosphere. Their origin, therefore, could include comets. However, if from a water world, or a planet or moon with ample amounts of water, then the moon Enceladus is one possible candidate."
"Enceladus, the six largest moon of Saturn has Cryovolcanic ice water vapor plumes that replenish the E ring of Saturn with material. The plumes contain ice particles, salts, organic compounds, water vapor and nano-silica. The gravitational return, to the surface of Enceladus, of some of the frozen precipitation, salts, organic compounds, and dust particles will lay down a glacial like ice surface."
The "dominant, if not the sole constituent of most E ring stream particles, are SiO $_2$ (nano-silica) (Hsu et al. 2015)."
The "nano-silica particles with a radius of ~8 nm (~16 nm dia.), observed by the Cassini mission Cosmic Dust Analyzer (DCA) (Srama et al. 2011) may have been formed over a period of months or years before being ejected into E ring (Hsu et al. 2015)."
"These nano-silica particles, initially embedded in icy grains, are presumably emitted from Saturn's moon Enceladus’ subsurface waters. They are released by sputter erosion of the icy grains while in Saturns' E ring."
"Quantitative mass spectra analysis of Saturn’s E ring stream of particles detected by the Cassini mission Cosmic Dust Analyzer (CDA) (Srama et al. 2011), indicates a diameter D$_{max}$ = 12 to 18 nm for the largest observed stream particles. This is in agreement with the upper particle size limit independently inferred by simulations (R$_{max}$= 8 nm) (Hsu et al. 2011)."
"The plumes of icy particles and water vapor ejected from the south pole of Enceladus have been shown to contain simple organic compounds (McKay et al. 2008). Analysis of the composition of freshly ejected plume particles have found that salt-rich ice particles dominate the total mass flux of ejected particles (Postberg et al. 2011). However, the salt-rich ice particles are depleted in the population escaping into Saturn’s E ring, due to sputter erosion."
"Salts are found in the mass spectra [..] of the particles found in the melt-water of this suspected ice meteorite. Sodium chloride and known and unknown aluminum hydroxides were found in this ice. The water in this ice is salt-water. Precipitation here on Earth does not contain salt due to the evaporation cycle of water here on earth."
It "is possible that this suspected ice meteorite [...], is a genuine extraterrestrial ice meteorite because the ice is frozen tritiated salt-water precipitation containing salts and hydrothermal nano-silica, the chemical footprints from the E ring of Saturn."
"The stratigraphic evolution of the south pole Tiger Stripe surface of Enceladus (Jaumann et al. 2008) is indicative of material being laid down in a glacial like process. The suggested episodically active tectonic events and the proposed localized catastrophic overturn of the rigid ice surface (O’Neill & Nimmo 2010) of Enceladus, allows for the possibility of large bodies of ice to periodically be ejected from Enceladus. The surface of Enceladus and the E ring of Saturn are exposed to cosmic radiation that creates tritium in the exposed water."
"The data from the analysis of the Pullman ice meteorite is compatible with the possibility that this ice is a genuine ice meteorite. The data is compatible with the possibility that this ice is of extraterrestrial origin. [And] was formed on the surface of Enceladus and constitutes ejecta which eventually fell to Earth."

## Hail

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. 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] of ice falling as precipitation from the sky [a thunderstorm]" are called hail.
Def. a "single ball of hail" 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.
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.
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

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. Hailstones can grow to 15 centimetres (6 in) and weigh more than 0.5 kilograms (1.1 lb).
Graupel also called soft hail or snow pellets) 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" 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.
"Under some atmospheric conditions, forming and descending snow crystals may encounter and pass through atmospheric supercooled cloud droplets. These droplets, which have a diameter of about 10 µm, can exist in the unfrozen state down to temperatures near -40° C. Contact between the snow crystal and the supercooled droplets results in freezing of the liquid droplets onto the surface of the crystals. This process of crystal growth is know[n] as accretion. Crystals that exhibit frozen droplets on their surfaces are referred to as rimed. When this process continues so that the shape of the original snow crystal is no longer identifiable, the resulting crystal is referred to as graupel. 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 LT-SEM clearly show cloud droplets measuring up to 50 µm 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 or otherwise making surfaces slippery. Graupel tends to compact and stabilise ("weld") approximately one or two days after falling, depending on the temperature and the properties of the graupel.

## Sleet

Ice pellets (also referred to as sleet by the United States National Weather Service) are a form of precipitation consisting of small, translucent balls of ice. Ice pellets are usually smaller than hailstones 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" is called sleet.
Def. "a single pellet of sleet" is called an ice pellet.

## Rime

Def. "ice formed by the rapid freezing of cold water droplets of fog onto a cold surface" 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).

## Snow

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

## Avalanches

Def. a "mass of snow which becomes detached and slides down a slope, often acquiring great bulk by fresh addition as it descends" is called an avalanche.
Both avalanches, left and right, top are avalanches in motion in the USA, the one on the left is in Washington. The one on the right was photographed by Richard Armstrong for the National Snow and Ice Data Center, probably in Colorado.

## Firns

While collecting snow and ice samples from the wall of a snow pit, fresh snow can be seen at the surface and glacier ice at the bottom of the pit wall. The snow layers are composed of progressively denser firn, Taku Glacier, Juneau Icefield.
Def. "a type of old snow which has gone through multiple thaw and refreeze cycles and thus is made of numerous small icy grains, though it is not nearly as saturated with water as snow-cone slush is; can be hard or somewhat soft depending on recent and current weather conditions" is called firn.
Def. "rounded, well-bonded snow that is older than one year; firn has a density greater than 550 kilograms per cubic-meter (35 pounds per cubic-foot); called névé during the first year" is called firn.

## Icefalls

"Crevasses [o]pen because of an acceleration of the glacier."
Def. a "part of a glacier with rapid flow and a chaotic crevassed surface; occurs where the glacier bed steepens or narrows" is called an icefall.
Def. "an area of rapid movement on a steep slope with extensive open crevassing" is called an icefall.

## Ice streams

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" is called an ice stream.

## Brittle ices

"It is well known that bulk brittle ice has a hexagonal stucture, while brittle ice that forms in pores may be cubic in structure [...]. Adjacent surfaces appear to further alter the dynamics and structure of confined liquids and their crystals, leading in the case of a water/ice system to a state of enhanced rotational motion (plastic ice) just below the confined freezing/melting transitions. This plastic ice layer appears to form at both the ice-silica interface and the ice-vapour surface, and reversibly transforms to brittle ice at lower temperatures."
Systems "with larger dimensions (∼10nm) contain brittle cubic ice and also some hexagonal ice (if a vapour interface is present); even larger systems (> ∼30nm) contain predominately hexagonal ice. It is conjectured that this layer of plastic ice at vapour surfaces may be present at the myriad of such interfaces in macroscopic systems, such as snow-packs, glaciers and icebergs".
"The [Greenland] Dye 3 1979 core is not completely intact and is not undamaged."
“Below 600 m, the ice became brittle with increasing depth and badly fractured between 800 and 1,200 m. The physical property of the core progressively improved and below ~1,400 m was of excellent quality.”
“The deep ice core drilling terminated in August 1981. The ice core is 2035 m long and has a diameter of 10 cm. It was drilled with less than 6° deviation from vertical, and less than 2 m is missing. The deepest 22 m consists of silty ice with an increasing concentration of pebbles downward. In the depth interval 800 to 1400 m the ice was extremely brittle, and even careful handling unavoidably damaged this part of the core, but the rest of the core is in good to excellent condition.”
The depth interval 800 to 1400 m would be a period approximately from about two thousand years ago to about five or six thousand years ago.
"The brittle zone mentioned above [...] corresponds in Dye 3 1979 with the steady state grain size (crystal size) from ~637 - ~1737 m depth range. This is also the Holocene climatic optimum period."
"Nuclear Magnetic Resonance and Neutron Scattering of the dynamics and phase-fractions of water/ice systems in templated porous silicas (SBA-15) indicate that what was believed to be a non-frozen surface water layer is actually plastic ice, the quantity varying (continuously and reversibly) with temperature, and converting to a brittle (mainly cubic) ice at lower temperatures."
"The ice loads on marine structures are affected by the failure process of ice. Brittle failure is one of the important failure modes. Ice fails in a brittle manner when the loading rate is high or the temperature is low."

## Ice flow divides

"Among numerous other findings, new insights using markers of biological material have proved particularly exciting. Methane has been found to change in time with many rapid climate changes. Spikes of ammonium and organic acids have been found to be markers for biomass burning, while background concentrations of these species indicate the advances of vegetation in North America."

## Glaciers

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" is called a glacier.
Def. "a persistent body of [dense] ice [that is] [moving under its own] [weight]" is called a glacier.

## Surging glaciers

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

## Classification of glaciers

"The low reflectivity of snow and glacier ice in the middle infrared part of the spectrum allows glacier classification".
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).
The images are part of the "102 glaciers of the Mischabel mountain range."
The first image on the left is a ratio image from TM4 and TM4, specifically (TM4 / TM5).
The second is a "derived glacier map after thresholding (blue) and overlay with digitized basins (red)."
The third image from the left identifies "[i]ndividual glaciers after basin intersection (colour-coded) ready for [digital elevation model] DEM-fusion."
The thermal emission and reflectivity have been measured "using the sensors ASTER (Advanced Spaceborne Thermal Emission and reflection Radiometer) on board [the] Terra [satellite]".
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 km$^2$)): 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."
"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."

## Alpine glaciers

Def. "a glacier that is confined by surrounding mountain terrain; also called a mountain glacier" 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."

## Maritime glaciers

Def. a glacier that is
* found on or near the sea,
* bordering on the sea,
* in a moist and temperate climate owing to the influence of the sea,
* related to the sea,
* near or in the sea
is called a maritime glacier.
"Maritime glaciers owe their mass balance variations mainly to changes in the accumulation area".

## Tidewater glaciers

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

## Polar glaciers

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."

## Rock glaciers

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" 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" 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."

## Tributary glaciers

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

## Valley glaciers

Def. a "glacier that has one or more tributary glaciers that flow into it" 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."

## Outlet glaciers

"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."

## Isolated glaciers

"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."
Its "location [is] close to [the] equator associated with the existence of permanent glaciers and its almost perfect volcano shape"
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."
Kilimanjaro is located at 3°04.6'S and 37°21.2'E.
"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]."
"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 km$^2$ in 1912 to ~2.6 km$^2$ in 2000 and that since 1989, a hole has developed near the center of the NIF. A nearly linear relationship (R$^2$ = 0.98) suggests that if climatological conditions of the past 88 years continue, the ice on Kilimanjaro will likely disappear between 2015 and 2020."

## Crater glaciers

"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."
"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."

## Cirque glaciers

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

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 fields

Def. "a mass of glacier ice; similar to an ice cap, and usually smaller and lacking a dome-like shape; somewhat controlled by terrain" is called an icefield.
The image at the right of "Kalstenius Icefield, located on Ellesmere Island, Canada, shows vast stretches of ice. The icefield produces multiple outlet glaciers that flow into a larger valley glacier. The glacier in this photograph is three miles wide."
The Juneau Icefield is located just north of Juneau, Alaska, continuing north through the border with British Columbia, extending through an area of 3,900 square kilometres (1,500 sq mi) in the Coast Range 140 km (87 mi) north to south and 75 km (47 mi) east to west.

## Ice caps

Def. "a dome-shaped mass of glacier ice that spreads out in all directions" 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".
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.
"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.
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.
"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 10$^3$ t day$^{-1}$ in 1997 to 38 x 10$^3$ 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."
"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."
"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."
"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."
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."
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.
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.
Although the ice cores from Quelccaya ice cap only go back ~2 ka, others may go back ~5.2 ka. The Quelccaya ice cores correlate with those from the Upper Fremont Glacier.

## Greenland ice sheets

Def. "a dome-shaped mass of glacier ice that covers surrounding terrain and is greater than 50,000 square kilometers (12 million acres)" 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 km$^2$ in 2002 as compared with an average extent of 455,000 km$^2$ from 1979–2003."
"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."
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."
"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."
(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."
"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 km$^2$[(b)] were classified as melting during 2002 that had not previously melted during any other year between 1979 and 2003."
The figure at the left "presents QSCAT backscatter and diurnal signatures, and ETH/CU AWS air temperature." 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.
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."
"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."
"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."

## Antarctic ice sheets

"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."
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."
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."
Subtle "movements of Antarctic ice [were detected] with a kind of measurement called synthetic-aperture radar interferometric phase data."
"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."
"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."
"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]."
"Each brought a little piece of the puzzle."
"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."

## Himalayas ice sheets

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

## Icequakes

"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." 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."
"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.)"
"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."
"We think the crevasses are being activated by the surface waves from this big earthquake coming through, and that's making the icequake."
"Regular icequakes probably occur all the time in Antarctica and other polar regions." "What we found is that they occurred more during the seismic waves of the Maule event."
"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."
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."

## Ice shelves

"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."
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" is called an ice shelf.
"Ice shelves are permanent floating sheets of ice that connect to a landmass."
"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."
"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."
The Ronne Ice Shelf has a nominal location of 78°30'S 61°W.

## Calving

Def. a "process by which ice breaks off a glacier's terminus" is called calving.
Def. the "breaking away of a mass of ice from an iceberg, glacier etc" is called calving.
The image on the right shows calving by the Perito Moreno Glacier, in Los Glaciares National Park, southern Argentina.
"Calving of huge, tabular icebergs is unique to Antarctica, and the process can take a decade or longer. Calving results from rifts that reach across the shelf. In the case of Antarctica's Amery Ice Shelf, the calving area resembles a loose tooth [images on the second right]." per Clare Averill and David J. Diner, and Helen A. Fricker, State of the Cryosphere: Ice calves at .
On a stable ice shelf, calving is a near-cyclical, repetitive process producing large icebergs every few decades. The icebergs drift generally westward around the continent, and as long as they remain in the cold, near-coastline water, they can survive decades or more. However, they eventually are caught up in north-drifting currents where they melt and break apart.
In Greenland, floating ice tongues downstream from large outlet glaciers are more broken up by crevasses. Calving of the ice tongues releases armadas of smaller, steep-sided icebergs that drift south sometimes reaching North Atlantic shipping lanes. Calving of the large glacier, Jacobshavn, on the east coast of Greenland is responsible for the majority of icebergs reaching Atlantic shipping and fishing areas off of Newfoundland and most likely shed the iceberg responsible for the sinking of the Titanic in 1912. The Petermann Glacier in northwestern Greenland also shed a large ice island in August 2010. These denizens of the ocean are now tracked by the National Ice Center in the United States, along with other organizations.
By 2006, the Jacobshavn Glacier, third image on the right, had retreated back to where its two main tributaries join, leading to two fast-flowing glaciers where there had previously been just one.
The rapidly retreating Jakobshavn Glacier in western Greenland drains the central ice sheet. This image, third one on the right, shows the glacier in 2001, flowing from upper right to lower left. Terminus locations before 2001 were determined by surveys and more recent contours were derived from Landsat data. The recent stages of retreat have widened the ice front, placing more of the glacier in contact with the ocean.
In recent years, calving of the largest ice tongues in Greenland (in particular, Jacobshavn, Helheim, and Kangerdlugssuaq) has accelerated probably due to warmer air and/or ocean temperatures. As the ice tongues have retreated, the reduced backpressure against the glacier has allowed these glaciers to accelerate significantly.
The images, fourth set of images on the right, show a tabular iceberg calving from an ice shelf. This iceberg happens to be calving from the remnant piece of the Larsen B ice shelf at the southwestern corner of the embayment. While the Larsen B Ice Shelf underwent disintegration [...], this was a normal calving event.
Large tabular iceberg calvings are natural events that occur under stable climatic conditions, so they are not a good indicator of warming or changing climate. Over the past several decades, however, meteorological records have revealed atmospheric warming on the Antarctic Peninsula, and the northernmost ice shelves on the peninsula have retreated dramatically (Vaughan and Doake 1996).
The most pronounced ice shelf retreat has occurred on the Larsen Ice Shelf, located on the eastern side of the Antarctic Peninsula's northern tip. The shelf is divided into four regions from north to south: A, B, C, and D.

## Icebergs

Def. a "huge mass of ocean-floating ice which has broken off a glacier or ice shelf" is called an iceberg.
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.

## Sea ices

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."
"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."
Def. a "large consolidated mass of floating sea ice" 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."
"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."
"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."

## Lahars

"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."
Def. a "volcanic mudflow" 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

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."
Volcanic lightning arises from colliding, fragmenting particles of volcanic ash (and sometimes ice), which generate static electricity within the volcanic plume. Volcanic eruptions have been referred to as dirty thunderstorms due to moist convection and ice formation that drive the eruption plume dynamics and can trigger volcanic lightning. But unlike ordinary thunderstorms, volcanic lightning can also occur before any ice crystals have formed in the ash cloud.

## Blues

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. 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.

## Glaciations

Def. the "process of covering with a glacier, or the state of being glaciated; the production of glacial phenomena; an ice age" is called a glaciation.
The ice ages or periods of glaciations on Earth have occurred apparently from the early Proterozoic (Huronian), during the late Proterozoic (Cryogenian), into the early Paleozoic (Andean-Saharan) during the Ordovician and Silurian periods, the late Paleozoic (Karoo Ice Age) during the Carboniferous and early Permian periods, and most recently the Late Cenozoic Ice Age (Holarctic-Antarctic).
Although these ice ages are widely separated in geological time, there appear to be types of astronomical or orbital forcings: "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."

## Ice ages

Throughout Earth's climate history or paleoclimate there have been fluctuations between two primary states: greenhouse and icehouse Earth.
Both climate states last for millions of years and should not be confused with glacial and interglacial periods, which occur as alternate phases within an icehouse period and tend to last less than 1 million years.
Def. a "period of long-term reduction in the temperature of Earth's surface and atmosphere, resulting in the presence of major polar ice sheets that reach the ocean and calve icebergs" is called an ice age.
Def. "a period during which no continental glaciers exist anywhere on the planet" is called a greenhouse Earth.
Earth has been in a greenhouse state for about 85% of its history.
There are five known Icehouse periods in Earth's climate history: the Huronian glaciation, Cryogenian, Andean-Saharan glaciation, Late Paleozoic Ice Age (Karoo Ice Age), and Late Cenozoic Ice Age (Holarctic-Antarctic Ice Age).
The Sturtian glaciation and Marinoan glaciation occurred during the Cryogenian Period. These events were formerly considered together as the Varanger glaciations, from their first detection in Norway's Varanger Peninsula. These are the greatest ice ages known to have occurred on Earth.
The Cryogenian Period was ratified in 1990 by the International Commission on Stratigraphy.
In glaciology, ice age implies the presence of extensive ice sheets in both northern and southern hemispheres. By this definition, Earth is currently in an interglacial period—the Holocene.

## Little Ice Ages

The Little Ice Age (LIA) appears to have lasted from about 1218 (782 b2k) to about 1878 (122 b2k).
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."
In the image at the top, "before present" is used in the context of radiocarbon dating, where the "present" has been fixed at 1950. The apparent decreases in solar activity are called the "Maunder Minimum", "Spörer Minimum", "Wolf Minimum", and "Oort Minimum".
"Northern Hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes."
Precisely "dated records of ice-cap growth from Arctic Canada and Iceland [show] that LIA summer cold and ice growth began abruptly between 1275 and 1300 AD, followed by a substantial intensification 1430-1455 AD. Intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium. [Explosive] volcanism produces abrupt summer cooling at these times, and that cold summers can be maintained by sea-ice/ocean feedbacks long after volcanic aerosols are removed. [The] onset of the LIA can be linked to an unusual 50-year-long episode with four large sulfur-rich explosive eruptions, each with global sulfate loading >60 Tg. The persistence of cold summers is best explained by consequent sea-ice/ocean feedbacks during a hemispheric summer insolation minimum; large changes in solar irradiance are not required."

## Venus

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).

## Moon

"The comet hypothesis of the origin of lunar ice, which was recently discovered in the polar regions of the moon by Lunar Prospector, is [...] that a comet impact produces a temporary atmosphere whose volatile component accumulates essentially completely in cold traps - the permanently shadowed regions of the Moon."
"Due to small oblique angle of the Moon׳s spin axis with respect to ecliptic (1.54°), the plausibility of existence of water ice in cold traps was initially discussed by Watson et al. (1961). Cold traps favorably harbor water ice that originates from occasional comets, water-containing meteorites, and solar-wind-induced iron reduction of regolith; yet ice is lost due to solar wind sputter erosion (Arnold, 1979; Crider and Vondrak, 2002, 2003; Klumov and Berezhnoi, 2002). The processes of deposition and sublimation in these regions have been sustained for nearly 2 Gyr, since the Moon׳s orbital evolution became stable (Arnold, 1979; Bills and Ray, 1999)."
"The 31 km diameter and 7.5 km deep de Gerlache crater, located 30 km from the southern pole of the Moon was surveyed. At its bottom a 15 km diameter younger crater can be also found beside many smaller overprinting craters."
"At all locations [these “girland like features” ... which seem to be produced by mass movements on slopes] are superposed by recently formed 10–50 m diameter craters".
"In de Gerlache crater ice occurrences have previously been located on moderately steep slopes, indicating they might be exposed by mass movement processes, where active movements might have happened in the last some 10 Ma using crater statistics based age of the shallow regolith layer."
Impacts on the Moon could send ice chunks toward the Earth.

## Mars

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.
Figure 109 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."
Figure 110 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".
"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."
"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!"
The ice (presumably water ice) is white in the image, but take note of the blue dust or regolith also exposed.
Figure 111 is a subimage of Figure 110. It is natural color and shows in better detail both the ice (white) and the blue material.
Figure 112 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."
"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."
"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."
Figure 113 shows a freshly formed impact crater that occurred on Mars between February 2005 and July 2005. 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.

## 1 Ceres

The detection of water vapor on Ceres, the largest object in the asteroid belt, was made by using the far-infrared of the Herschel Space Observatory.

## 24 Themis

The surface of 24 Themis appears completely covered in ice as detected using NASA's Infrared Telescope Facility, as this ice layer is sublimating, it may be getting replenished by a reservoir of ice under the surface.

## Europa

"Frozen sulfuric acid on Jupiter's moon Europa is depicted in [Figure 114] 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."
"The morphology of chaotic terrain forms a continuum from areas consisting of densely packed blocks with fractures and narrow lanes of matrix between them ([Figure 115]), to areas consisting of almost all matrix and no blocks ([Figure 116]). Conamara Chaos, the most intensely studied chaos area ([Figure 117]), lies near the middle of this continuum, with -60% of its area consisting of matrix and the remainder consisting of blocks [Spaun et 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"."
"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 ([Figure 118])."
"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]."
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."
Figure 119 is a view "of a small region of the thin, disrupted, ice crust in the Conamara region of Jupiter's moon Europa showing the interplay of surface color with ice structures. The white and blue colors outline areas that have been blanketed by a fine dust of ice particles ejected at the time of formation of the large (26 kilometer in diameter) crater Pwyll some 1000 kilometers to the south. A few small craters of less than 500 meters or 547 yards in diameter can be seen associated with these regions. These were probably formed, at the same time as the blanketing occurred, by large, intact, blocks of ice thrown up in the impact explosion that formed Pwyll. The unblanketed surface has a reddish brown color that has been painted by mineral contaminants carried and spread by water vapor released from below the crust when it was disrupted. The original color of the icy surface was probably a deep blue color seen in large areas elsewhere on the moon. The colors in this picture have been enhanced for visibility. North is to the top of the picture and the sun illuminates the surface from the right. The image, centered at 9 degrees north latitude and 274 degrees west longitude, covers an area approximately 70 by 30 kilometers (44 by 19 miles), and combines data taken by the Solid State Imaging (CCD) system on NASA's Galileo spacecraft during three of its orbits through the Jovian system. Low resolution color (violet, green, and infrared) data acquired in September 1996, were combined with medium resolution images from December 1996, to produce synthetic color images. These were then combined with a high resolution mosaic of images acquired on February 20th, 1997 at a resolution of 54 meters (59 yards) per picture element and at a range of 5340 kilometers (3320 miles)."
Figure 120 is another "image of Jupiter's icy satellite Europa shows surface features such as domes and ridges, as well as a region of disrupted terrain including crustal plates which are thought to have broken apart and "rafted" into new positions. The image covers an area of Europa's surface about 250 by 200 kilometer (km) and is centered at 10 degrees latitude, 271 degrees longitude. The color information allows the surface to be divided into three distinct spectral units. The bright white areas are ejecta rays from the relatively young crater Pwyll, which is located about 1000 km to the south (bottom) of this image. These patchy deposits appear to be superposed on other areas of the surface, and thus are thought to be the youngest features present. Also visible are reddish areas which correspond to locations where non-ice components are present. This coloring can be seen along the ridges, in the region of disrupted terrain in the center of the image, and near the dome-like features where the surface may have been thermally altered. Thus, areas associated with internal geologic activity appear reddish. The third distinct color unit is bright blue, and corresponds to the relatively old icy plains."
"This product combines data taken by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft during three separate flybys of Europa. Low resolution color data (violet, green, and 1 micron) acquired in September 1996 were combined with medium resolution images from December 1996, to produce synthetic color images. These were then combined with a high resolution mosaic of images acquired in February 1997."
Figure 121 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."
"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."
"Chaotic terrain on Europa is interpreted to be the result of the breakup of brittle surface materials over a mobile substrate."
At Figure 122, "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."

## Technology

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. 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.

## Cryosats

CryoSat-2 is a European Space Agency (ESA) Earth Explorer Mission that launched on 8 April 2010, dedicated to measuring land and polar sea ice thickness and monitoring changes in ice sheets.
The primary payload of the mission is a synthetic aperture radar (SAR) Interferometric Radar Altimeter (SIRAL), which measures surface elevation. By subtracting the difference between the surface height of the ocean and the surface height of sea ice, the sea ice freeboard (the portion of ice floating above the sea surface) can be calculated. Freeboard can be converted to sea ice thickness by assuming the sea ice is floating in hydrostatic equilibrium.

## Global Precipitation Measurement

"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." The launch occurred on February 28, 2014 at 3:37am JST on the first attempt.

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### Acknowledgements

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### Competing interests

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### Ethics statement

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