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Precipitation (meteorology)

Precipitation (meteorology)

In meteorology, precipitation is any kind of water that falls from the sky as part of the weather. This includes snow, rain, sleet, freezing rain, hail, and virga. Precipitation is a major part of the hydrologic cycle, and is responsible for depositing most of the fresh water on the planet. Precipitation is generated in clouds, which reach a point of saturation; at this point larger and larger droplets (or pieces of ice) form, which then fall to the earth under gravity. It is possible to 'seed' clouds to induce precipitation by releasing a fine dust or appropriate chemical (commonly silver nitrate) into a cloud, encouraging droplets to form, and increasing the probability of precipitation.

Orographic precipitation

Orographic precipitation, also known as relief precipitation, is precipitation generated by a forced upward movement of air upon encountering a physiographic upland (see anabatic wind). This upwards movement cools the air, resulting in a cloud formation and rainfall. In parts of the world subjected to relatively consistent winds (for example the trade winds), a wetter climate prevails on the windward side of a mountain than on the leeward (downwind) side as moisture is removed by orographic precipitation, leaving drier air (see katabatic wind) on the descending (generally warming), leeward side where a rain shadow is formed. Orographic precipitation is well known on oceanic islands, such as the Hawaiian Islands, where much of the rainfall received on an island is on the windward side, and the leeward side tends to be quite dry, almost desert-like, by comparison. This phenomenon results in substantial local gradients of average rainfall, with coastal areas receiving on the order of 20 to 30 inches (500 to 750 mm) per year, and interior uplands receiving over 100 inches (2.5 m) per year. Leeward coastal areas are especially dry (<20 in (500 mm) per year at Waik&#299;k&#299;), and the tops of moderately high uplands are especially wet (~475 in (12 m) per year at Wai'ale'ale on Kaua'i).

Convectional rainfall

Convectional rainfall occurs when the air is heated up, usually by the land below it (land tends to heat up faster than air or water bodies). As the air heats up it rises. Inevitably cooling will result, and water vapor will condense out of the air to form droplets, and eventually clouds, if there is enough vapour. This kind of precipitation is most commonly found in tropical areas.

Frontal Rainfall

Frontal rainfall occurs at both warm fronts and cold fronts. At a warm front the warm air, being lighter, rides up over the cold air. As it rises it also cools down (adiabatic process). Moisture in the air condenses to form clouds, and precipitation occurs. At a cold front the warm air is forced up by the cold and the same process occurs.

Rainfall Patterns

Western

Major elements are prevailing westerlies and ocean currents moving equatorward. At high lattitudes the current is warmer than land, westerlies pick up moisture and cool when moving over land. When the land is warmer than the ocean clouds don't drop precipitation, but pick up additional moisture; it rains in the mountains. When the land is cooler than the ocean, then westerlies cool as they move inland and rain occurs in the lowlands.

Eastern and Central

Polar air masses (above 50° latitudes) are distinct from lower latitude air masses. The westerlies are warm air masses that move poleward from 30°N. In Eastern US the westernlies are often laden with moisture from Gulf of Mexico and Atlantic. When polar and westernlie air masses meet, precipitation occurs.

Inland Continental Areas

Areas not proximate to large bodies of water, warm faster than surrounding areas. Hot air masses rise from the center of the continent forming a low pressure area. This low pressure draws water laden clouds from the coasts. This area is heated & rises, this causes cooling adiabatically and precipitation. Resulting in summer rain, and less winter precipitation.

Water

:This article focuses on water as it is experienced in everyday life. See water (molecule) for information on the chemical and physical properties of pure water (H₂O, hydrogen oxide). Water (from the Old English word wæter; c.f German "Wasser", from PIE
- wod-or, "water") is a tasteless, odorless, and nearly colorless (it has a slight hint of blue) substance in its pure form that is essential to all known forms of life and is known also as the most universal solvent. Water is an abundant substance on Earth. It exists in many places and forms. It appears mostly in the oceans and polar ice caps, but also as clouds, rain water, rivers, freshwater aquifers, and sea ice. On the planet, water is continuously moving through the cycle involving evaporation, precipitation, and runoff to the sea. Water fit for human consumption is called potable water. This natural resource is becoming more scarce in certain places as human population in those places increases, and its availability is a major social and economic concern.

Molecular properties

Forms of water

potable water] Water takes many different shapes on earth: water vapor and clouds in the sky, waves and icebergs in the sea, glaciers in the mountain, aquifers in the ground, to name but a few. Through evaporation, precipitation, and runoff, water is continuously flowing from one form to another, in what is called the water cycle. Because of the importance of precipitation to agriculture, and to mankind in general, different names are given to its various forms: while rain is common in most countries, other phenomena are quite surprising when seen for the first time. Hail, snow, fog or dew are examples. When appropriately lit, water drops in the air can refract sunlight to produce rainbows. Similarly, water runoffs have played major roles in human history as rivers and irrigation brought the water needed for agriculture. Rivers and seas offered opportunity for travel and commerce. Through erosion, runoffs played a major part in shaping the environment providing river valleys and deltas which provide rich soil and level ground for the establishment of population centers. Water also infiltrates the ground and goes into aquifers. This groundwater later flows back to the surface in springs, or more spectacularly in hot springs and geysers. Groundwater is also extracted artificially in wells. Because water can contain many different substances, it can taste or smell very differently. In fact, humans and other animals have developed their senses to be able to evaluate the drinkability of water: animals generally dislike the taste of salty sea water and the putrid swamps and favor the purer water of a mountain spring or aquifer.

Water in biology

From a biological standpoint, water has many distinct properties that are critical for the proliferation of life that set it apart from other substances. Water carries out this role by allowing organic compounds to react in ways that ultimately allows replication. It is a good solvent and has a high surface tension, and thus allows organic compounds and living things to be transported in it. Fresh water has its greatest density at 4°C, then becoming less dense as it freezes or heats up from this point. As a stable, polar molecule prevalent in the atmosphere, it plays an important atmospheric role as an absorber of infrared radiation, crucial in the atmospheric greenhouse effect without of which, the average surface temperature would be −18° Celsius. Water also has an unusually high specific heat, which plays many roles in regulating global and regional climate, such as the Gulf Stream climate, allowing life to survive. Water is a very good solvent, chemically not unlike ammonia, and dissolves many types of substances, such as various salts and sugar, and facilitates their chemical interaction, which aids complex metabolisms. Some substances, however, do not mix well with water, including oils and other hydrophobic substances. Cell membranes, composed of lipids and proteins, take advantage of this property to carefully control interactions between their contents and external chemicals. This is facilitated somewhat by the surface tension of water. Water drops are stable due to the high surface tension of water caused by the strong intermolecular forces called cohesive forces. This can be seen when small quantities of water are put onto a nonsoluble surface such as polythene: the water stays together as drops. On extremely clean glass the water may form a thin film because the molecular forces between glass and water molecules (adhesive forces) are stronger than the cohesive forces. This property plays a key role in plant transpiration. A simple but environmentally important and unique property of water is that its common solid form, ice, floats on the liquid. This solid phase is less dense than liquid water, due to the geometry of the strong hydrogen bonds which are formed only at lower temperatures. For almost all other substances and for all other 11 uncommon phases of water ice except ice-XI, the solid form is more dense than the liquid form. Fresh water is most dense at 4°C, and will sink by convection as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4°C. This effectively insulates a lake floor from the cold. While this behavior may seem obvious, even intuitive, it should be noted that almost all other chemicals are denser as solids than they are as liquids, and freeze from the bottom up. Life on earth has evolved with and adapted itself to the important features of water. The existence of abundant liquid, vapor and solid forms of water on Earth has been an important factor in the abundant colonization of Earth's various environments by life-forms adapted to those varying and often extreme conditions. Civilizations have historically flourished around rivers and major waterways; Mesopotamia, the so-called cradle of civilization, is situated between two major rivers. Large metropolises like London, Paris, New York, and Tokyo owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore and Hong Kong, have flourished for precisely this reason. In places such as North Africa and the Middle East, where water is scarcer, access to clean drinking water was and is a major factor in human development.

Astronomical position of Earth and impact on its water

Mesopotamia The coexistence of the solid, liquid, and gaseous phases of water on Earth is vital to the origin, evolution, and continued existence of life on Earth. However, if the Earth's location in the solar system were even marginally closer or further from the Sun (ie, a million miles or so), the conditions which allow the three forms to be present simultaneously would be far less likely to exist. Earth's mass allows gravity to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provides a greenhouse effect which helps maintain a relatively steady surface temperature. If Earth were less massive, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in polar ice caps (as on Mars). According to the solar nebula model of the solar system's formation, Earth's mass may be largely due to its distance from the Sun. The distance between Earth and the Sun and the combination of solar radiation received and the greenhouse effect of the atmosphere ensures that its surface is neither too cold nor too hot for liquid water. If Earth were more distant, most water would be frozen. If Earth were nearer to the Sun, its higher surface temperature would limit the formation of ice caps, or cause water to exist only as vapor. In the former case, the low albedo of oceans would cause Earth to absorb more solar energy. In the second case, a runaway greenhouse effect and inhospitable conditions similar to Venus would result. It has been proposed that life itself may maintain the conditions that have allowed its continued existence. The surface temperature of Earth has been relatively constant through geologic time despite varying solar flux, indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.

Human uses of water

Gaia hypothesis All known forms of life depend on water. Water is a vital part of many metabolic processes within the body. Significant quantities of water are used during the digestion of food. (Note however that some bacteria and plant seeds can enter a cryptobiotic state for an indefinite period when dehydrated, and come back to life when returned to a wet environment) About 72% of the fat free mass of the human body is made of water. To function properly the body requires between one and seven litres of water per day to avoid dehydration, the precise amount depending on the level of activity, temperature, humidity, and other factors. It is not clear how much water intake is needed by healthy people. However, for those who do not have kidney problems, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) dangerous to drink too little. People do often drink far more water than necessary while exercising, however, putting them at risk of water intoxication, which is frequently fatal. The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source. However, leading dieticians and nutritionists will tell you that this is the RDI (Recommended Daily Intake) of water. [http://ajpregu.physiology.org/cgi/content/full/283/5/R993]. The latest dietary reference intake report by the National Research Council recommended 2.7 liters of water total (including food sources) for women and 3.7 liters for men[http://www.iom.edu/report.asp?id=18495]. Water is lost from the body in urine and feces, through sweating, and by exhalation of water vapor in the breath. Humans require water that does not contain too much salt or other impurities. Common impurities include chemicals and/or harmful bacteria, such as crypto sporidium. Some solutes are acceptable and even desirable for perceived taste enhancement and to provide needed electrolytes.

Water as a precious resource

:See water resources for information about fresh water supplies. fresh water Because of the growth of world population and other factors, the availability of drinking water per capita is shrinking. The issue of water shortage can be solved through more production, better distribution and less waste of it. For this reason, water is a strategic resource for many countries. Many battles and wars, such as the Six-Day War in the Middle East, have been fought to gain access to it. Experts predict more trouble ahead because of the world's growing population, increasing contamination through pollution, and global warming. UNESCO's World Water Development Report (WWDR, 2003) from its World Water Assessment Program indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30%. 40% of the world's inhabitants currently have insufficient fresh water for minimal hygiene. More than 2.2 million people died in 2000 from diseases related to the consumption of contaminated water or drought. In 2004, the UK charity WaterAid reported that a child dies every 15 seconds due to easily preventable water-related diseases. Some have predicted that clean water will become the "next oil", making Canada, with this resource in abundance, possibly the richest country in the world.

Regulating water distribution

Drinking water is often collected at springs or extracted from artificial borings in the ground, or wells. Building more wells in adequate places is thus a possible way to produce more water assuming the aquifers can supply an adequate flow. Other water sources are the rainwater and river or lake water. This surface water, however, must be purified for human consumption. This may involve removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant ocean or seawater is a more expensive solution used in coastal arid climates. The distribution of drinking water is done through municipal water systems or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge. Others argue that the market mechanism and free enterprise are best to manage this rare resource, and to finance the boring of wells or the construction of dams and reservoirs. Reducing waste, that is using drinking water only for human consumption, is another option. In some cities, such as Hong Kong, sea water is extensively used for flushing toilets citywide in order to conserve fresh water resources. Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the pollutor. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable.

The impact of water on human culture

Water is considered a purifier in most religions, including Christianity, Islam, Judaism, and Shinto. For instance, baptism in Christian churches is done with water. In addition, a ritual bath in pure water is performed for the dead in many religions including Judaism and Islam. In Islam, the daily Salah can only be done after ablution (Wodoo), that is, washing parts of the body in clean water. In Shinto, water is used in almost all rituals to cleanse a person or an area. Water is often believed to have spiritual powers. In Celtic mythology, Sulis is the local goddess of thermal springs; in Hinduism, the Ganga is also personified as a goddess. Alternatively, gods can be patrons of particular springs, river or lakes: for example in Greek and Roman mythology, Peneus was a river god, one of the three thousand Oceanids. The Greek philosopher Empedocles held that water is one of the four classical elements along with fire, earth and air, and was regarded as the ylem, or basic stuff of the universe. Water was considered cold and moist. In the theory of the four bodily humours, water was associated with phlegm. Water was also one of the Five Elements in traditional Chinese philosophy, along with earth, fire, wood, and metal. A common misconception about water is that it is a powerful conductor of electricity. Any electrical properties observable in water are due to the ions of mineral salts and carbon dioxide dissolved in it. Water does self-ionize (two water molecules become one hydroxide anion and one hydronium cation), but only at a very slight, almost immeasurable level. Pure water can also be electrolized into oxygen and hydrogen gases but without any dissolved ions, this is a very slow process and thus very little current is conducted. Many bottled water companies exploit another common misconception, advertising both purity and taste, even though pure water is tasteless.

External links

- [http://www.lsbu.ac.uk/water/phase.html Phase diagrams of water]
- [http://www.publicforuminstitute.org/issues/oceans/index.htm Oceans and Water Issues Page]
- [http://www.greenfacts.org/water-disinfectants/index.htm Scientific Facts on Water disinfectants] A faithful summary by GreenFacts of a leading scientific consensus report on Drinking Water Disinfectants published by the International Programme on Chemical Safety of the WHO.
- [http://www.hkc22.com/residentialwater.html Residential water problems and markets] Study paper from Helmut Kaiser Consultancy
- [http://www.hkc22.com/watermarketsworldwide.html Water markets worldwide] Study paper from Helmut Kaiser Consultancy
- [http://www.worldwaterforum.org/ World Water Forum]
- [http://www.unesco.org/water/wwap/ World Water Assessment Program]
- [http://unesdoc.unesco.org/images/0012/001295/129556e.pdf United Nations' World Water Development Report]
- [http://www.gemswater.org/ United Nations GEMS/Water Programme]
- [http://www.lsbu.ac.uk/water/ Water Structure and Behaviour]
- [http://www.wateraid.org/ WaterAid]
- [http://www.sahra.arizona.edu/newswatch/ SAHRA—Global Water Newswatch]
- [http://www.siwi.org/ Stockholm International Water Institute] (SIWI)
- [http://www.c-win.org/ California Water Impact Network (C-WIN)]
- [http://news.bbc.co.uk/2/hi/science/nature/3752590.stm BBC: The water debate]
- [http://www.geocities.com/tapvsbottled/ Tap Water Vs Bottled Water] - Interesting site providing facts about tap and bottled water.
- [http://www.emagazine.com/september-october_2003/0903feat1.html E the Environmental Magazine piece on bottled water] (Oct 2003).
- [http://www.iapws.org/ International Association for the Properties of Water and Steam]
- [http://ga.water.usgs.gov/edu/watercycle.html US Geological Survey: Comprehensive discussion of the water cycle, in many languages]
- [http://www.dartmouth.edu/~etrnsfer/water.htm Why is water blue?]
- [http://www.water.org.uk/home/resources-and-links/water-for-health/ask-about/adults Water requirements in adults]
- [http://www.hkc22.com/environmentaltechnology.html/ Climate change raises markets for environmental technology, drinking water and clean energies]

References

- OA Jones, JN Lester and N Voulvoulis, Pharmaceuticals: a threat to drinking water? TRENDS in Biotechnology 23(4): 163, 2005
- Category:Beverages Category:Hydrology Category:Materials Category:Natural resources Category:Nutrition zh-min-nan:Chúi als:Wasser ko:물 ja:水 ms:Air simple:Water th:น้ำ

Snow

) high forests.]] Snow is precipitation in the form of crystalline water ice, consisting of a multitude of snowflakes. Since it is composed of small rough particles it is a granular material. It has an open and therefore soft structure, unless packed by external pressure. Snow is commonly formed when water vapor undergoes deposition high in the atmosphere at a temperature of less than 0°C (32°F), and then falls to the ground.

Types

Flurries are similar to rainshowers and only last for short periods of time. Snow which has partially thawed while falling is called sleet; if this re-freezes on further descent, the resulting small icy pellets or granules of snow are called soft hail. A related phenomenon is freezing rain, where rain falls on ground sufficiently cold for it to freeze on contact, forming black ice on the ground. A snow squall is a brief, very intense snowstorm while a blizzard is a long-lasting snow storm with intense snowfall and usually high winds. Particularly severe storms can create whiteout conditions where visibility is reduced to less than 1 m, while blizzards can also create large snowdrifts. A ground blizzard occurs when a strong wind drives already fallen snow to create drifts and whiteouts. Snow can be also manufactured using snow cannons, which actually create tiny granules more like soft hail (this is sometimes called "grits" by those in the southern U.S. for its likeness to the texture of the food). In recent years, snow cannons have been produced that create more natural looking snow, but these machines are very expensive and are found only on the most prestigious places.

Occurrence

Snowfall varies by time and location, including geographic latitude, elevation and other factors which affect weather in general. In latitudes closer to the equator, there is less chance of snow fall, 35° N and 40°S are often quoted as a rough delimiter. The western coasts of the major continents remain snowless to much higher latitudes. As temperature decreases with altitude, high mountains, even at or near the Equator, have permanent snow cover on their top. Examples include Mount Kilimanjaro in Tanzania and the Tropical Andes in South America; the only snow actually on the Equator is at 4,690 m altitude on the south slope of Volcán Cayambe in Ecuador (Google Earth images). Conversely, many regions of the Arctic and Antarctic receive very little precipitation and therefore little snow despite the bitter cold (below a certain temperature, air essentially loses its ability to carry water vapor). Although density of fresh snow varies widely, a guide is that the depth of snowfall is 10 times that of a rainfall containing the same mass of water. Substantial snowfall sometimes disrupts infrastructure and services even in regions that are accustomed to them. Traffic may be snarled or even completely stop. Basic infrastructure such as electricity, phones and gas supply can be shut down. This can lead to a snow day, a day on which school or other services are cancelled owing to unusually heavy snowfall. In areas that normally have very little snow, this may occur even with light accumulation — something often made fun of by those people used to colder climates, where streets would remain passable given the same amount of snow. The highest seasonally cumulative precipitation of snow ever measured in the world was on Mount Baker, Washington, U.S.A during 1998–1999 season when they received 28.96 meters (1,140 in); this surpassed the previous record holder, Mount Rainier, Washington, U.S.A which during 1971–1972 season received 28.5 meters (1,122 in) of snow; and the world record daily precipitation was recorded in Silver Lake, Colorado, U.S.A in 1921 1.93 meters (76 in). See also: List of Countries receiving snowfall

Recreation

List of Countries receiving snowfall Forms of recreation dependent on snow:
- Many winter sports, such as skiing, snowmobiling, snowshoeing and snowboarding
- Playing with a sled or riding in a sleigh
- Building a snowman or snow fort
- Throwing snowballs mutually in a snowball fight or at others to tease them. (Humans seem to be the only animal that throw their snowballs. Pygmy chimpanzees have been known to carry snowballs around, but never to throw them.) Where snow is scarce but the temperature is low enough, snow cannons may be used to produce an adequate amount for such sports. Tightly packed snow may be used as a construction material in, for example, Inuit snow houses. The world´s biggest snowcastle is built in Kemi, Finland, every winter.

Geometry

Finland An interesting question is why the arms of snowflakes are symmetrical, and why no two snowflakes appear to be identical. The answer is believed to be due to the fact that the distances between snowflakes are much greater than the distances across snowflakes. The symmetry of snowflake arms is always six-fold, which arises from the hexagonal crystal structure of ordinary ice (known as ice I_h) along its 'basal' plane. There are, broadly, two possible explanations for the symmetry of snowflakes. Firstly, there could be communication (information transfer) between the arms, such that growth in each arm affects the growth in each other arm. Surface tension or phonons are among the ways that such communication could occur. The other explanation, which appears to be the prevalent view, is that the arms of a snowflake grow independently in an environment that is believed to be rapidly varying in temperature, humidity and so on. This environment is believed to be relatively spatially homogenous on the scale of a single flake, leading to the arms growing to a high level of visual similarity by responding in identical ways to identical conditions, much in the same way that unrelated trees respond to environmental changes by growing near-identical sets of tree rings. The difference in the environment in scales larger than a snowflake leads to the observed lack of correlation between the shapes of different snowflakes. tree ring However, the concept that no two snowflakes are alike is incorrect; it is entirely possible, but unlikely, that a pair of snowflakes may be visually identical if their environments were similar enough, either because they grew very near one another, or simply by chance. The American Meteorological Society has reported that matching snow crystals were discovered by Nancy Knight of the National Center for Atmospheric Research. The crystals were not flakes in the usual sense but rather hollow hexagonal prisms. ;High-resolution gallery Image:Snow crystals.png Image:Snow crystals 2.png Image:Snow crystals 2b.png Image:LT-SEM snow crystals.jpg Image:LT-SEM snow crystal magnification series-3.jpg

Media

External links

- [http://www.nsdl.arm.gov/Library/glossary.shtml#snowflake National Science Digital Library - Snowflake]
- [http://www.its.caltech.edu/~atomic/snowcrystals/faqs/faqs.htm Kenneth G. Libbrecht's Snowflake FAQ]
- http://www.its.caltech.edu/~atomic/snowcrystals/photos/photos.htm Category:Snow ko:눈 (날씨) ja:雪 simple:Snow th:หิมะ

Sleet

Sleet refers to snow that has partially melted on its fall to the ground, due to surrounding air that is sufficiently warm to partially melt it while falling, but not warm enough to fully melt droplets into rain. Thus 'sleet' refers to partially melted droplets. It does not tend to form a layer on the ground, other than when the ground has a temperature that is below freezing, when it can form a dangerous layer of invisible ice on surfaces known as 'black ice'. This occurs similarly when rain freezes upon contact with the ground. Sleet is also used colloquially for rain mixed with some frozen droplets. In the British Isles, sleet refers to precipitation which is a mixture of snow and rain.

Misconceptions

Other forms of precipitation, such as so-called 'soft hail' or granular snow, are sometimes mistakenly referred to as sleet.

Hail

Hail is a type of graupel, a form of precipitation. Composed of spears or irregular lumps of ice. It occurs when supercooled water droplets (remaining in a liquid state despite being below the freezing point, 0 °C/32 °F) in a storm cloud aggregates around some solid object, such as a dust particle or an already-forming hailstone. The water then freezes around the object. Depending on the wind patterns within the cloud, the hailstone may continue to circulate for some time, increasing in size. Eventually, the hailstone falls to the ground, when the updraft is no longer strong enough to support its weight. weight Hail often forms in strong thunderstorms, often along a cold front, where the layer of air on top is much colder than that on the bottom. The smaller hailstones can bounce up and down between the warm and cold layers due to updrafts and gravity. The longer the stones bounce around, the larger they grow. For the same reason, larger hail can occur in warmer regions in the world due to stronger updrafts. These strong, severe, or even supercell thunderstorms can also occur in summer, even without a cold front. summer Hail can do serious damage, notably to automobiles, skylights, and glass-roofed structures. Rarely, massive hailstones have been known to cause concussions or fatal head trauma. Hailstones, while most commonly only a few millimetres in diameter, can sometimes grow to several centimetres or occasionally even bigger. Pea or golfball-size hailstones are not uncommon in severe storms. The image to the right shows an aggregate hailstone with smaller stones visible. The ruler shows the size of this hailstone as approximately 6 cm, almost the size of a tennis ball.

Costly or Deadly Hailstorms

- July 11 1990, Denver, Colorado, USA, $625 million, softball-sized hail destroyed roofs and cars.
- May 5 1995, Dallas and Fort Worth, Texas, USA, $2 billion.
- April 12 1999, Sydney, New South Wales, Australia, $190 Million. 15 thousand homes lost power and several people were injured.
- July 19 2002, Henan Province, China, 25 dead and hundreds injured. Category:Precipitation ja:霰 th:ลูกเห็บ

Virga

:This article is about the meteorological term. Virgae are also a type of surface feature found on Titan Titan Virga is a meteorologic term for precipitation that falls from a cloud but evaporates before reaching the ground. At high altitudes the precipitation falls mainly as ice crystals, before melting and finally evaporating. It is very common in desert nations. Virga can cause very interesting weather effects, because as rain changes from liquid to vapour form it takes a lot of heat out of the air due to the high heat of vaporization of water. These small pockets of extremely cold air then descend rapidly, creating a microburst which can be extremely hazardous to aviation. Virga also has a role in seeding storm cells, where light particles from one cloud are blown into neighbouring supersaturated air and act as nucleation particles for the next thunderhead cloud to begin forming. Virga can produce dramatic and beautiful scenes, especially during a red sunset. The red light can be caught by the streamers of falling precipitation, while aloft winds push the bottom ends of the virga so it falls at an angle, making the clouds appear to have commas attached. Virga is a Latin word for a branch or twig, and hence for objects made from it, as a broom, a staff or a rod (hence the English word virge).

External links

- [http://www.nsdl.arm.gov/Library/glossary.shtml#virga National Science Digital Library - Virga]
- [http://wetterchronik.de/mm/niederschlag/20040430fallstreifen.htm Picture: Virga over Düsseldorf, Germany.] Category:Precipitation

Hydrologic cycle

The water cycle—technically known as the hydrologic cycle—is the circulation of water within the earth's hydrosphere, involving changes in the physical state of water between liquid, solid, and gas phases. The hydrologic cycle refers to the continuous exchange of water between atmosphere, land, surface and subsurface waters, and organisms. In addition to storage in various compartments (the ocean is one such "compartment"), the multiple cycles that make up the earth's water cycle involve five main physical actions: evaporation, precipitation, infiltration, runoff, and subsurface flow:
- Evaporation is the transfer of water from bodies of surface water into the atmosphere. This transfer entails a change in the physical nature of water from liquid to gaseous phases. Along with evaporation can be counted transpiration from plants, as well as, to a lesser degree, perspiration from land mammals and marsupials. Thus, this transfer is sometimes referred to as evapotranspiration. 90% of atmospheric water comes from evaporation, while the remaining 10% is from transpiration.
- Precipitation is atmospheric moisture that has previously condensed to form clouds (changed from the gas phases to a liquid or solid phase), falling to the surface of the earth. This mostly occurs as rainfall, but snow, hail, fog drip, and other forms participate as well.
- Interception is precipitation trapped by vegetation instead of falling directly onto the soil.
- Infiltration into the ground is the transition from surface water to groundwater. The infiltration rate will depend upon soil or rock permeability as well as other factors. Infiltrated water may reach another compartment known as groundwater (i.e., an aquifer). Groundwaters tend to move slowly, so the water may return as surface water after storage within an aquifer for a period of time that can amount to thousands of years in some cases. Water returns to the land surface at lower elevation than where it infiltrated, under the force of gravity or gravity induced pressures.
- Runoff includes the variety of ways by which land surface water moves down slope to the oceans. Water flowing in streams and rivers may be delayed for a time in lakes. Not all precipitated water returns to the sea as runoff; much of it evaporates before reaching the ocean or reaching an aquifer.
- Subsurface flow incorporates movement of water within the earth, either within the vadose zone or aquifers. After infiltrating, subsurface water may return to the surface or eventually seep into the ocean.

External links

- [http://www.und.edu/instruct/eng/fkarner/pages/cycle.htm Hydrologic Cycle] from [http://www.und.edu/instruct/eng/fkarner/earth.htm Earthscape]
- [http://www.grow.arizona.edu/water/hydrologiccycle/hydrologiccycle.shtml Hydrologic Cycle] from [http://www.grow.arizona.edu/ GROW]
- [http://ga.water.usgs.gov/edu/watercycle.html United States Geological Survey Water Site] Category:Water Category:Forms of water Category:Hydrology Category:Environmental science simple:Water cycle th:วัฏจักรของน้ำ

Fresh-water

:For the village on the Isle of Wight, see Freshwater, Isle of Wight. Fresh water (also freshwater or fresh-water) is water that contains only minimal quantities of dissolved salts, especially sodium chloride, thus distinguishing it from sea water or brackish water. All freshwater ultimately comes from precipitation of atmospheric water vapor, reaching inland lakes, rivers, and groundwater bodies directly, or after melting of snow or ice (see hydrologic cycle). Access to fresh water is a critical issue for the survival of many species, including humans, especially in desert or otherwise arid areas. See water resources. Even on a ship or island in the ocean, there can be a "water shortage", which means a shortage of fresh water. Seawater is undrinkable directly. For fish, it strongly matters how much dissolved sodium chloride the water they live in has. Most species cannot live in both fresh and salt water, though some species move between the two. Salt water fish have access to an abundance of salt, and try to get as much salt out of their body as possible, while trying to keep the water. Fresh water fish do the opposite: they have too much water, and too little salt. simple:Fresh water

Ice

] Ice is the solid form of water. The phase transition occurs when liquid water is cooled below 0 °C (273.15 K, 32 °F) at standard atmospheric pressure. An unusual feature of ice frozen at a pressure of one atmosphere is that the solid is some 8% less dense than liquid water. Ice has a density of 0.917 g/cm³ at 0 °C, whereas water has a density of 0.9998 g/cm³ at the same temperature. Liquid water is most dense, essentially 1.00 g/cm³, at 4 °C and becomes less dense as the water molecules begin to form the hexagonal crystals of ice as the temperature drops to 0 °C. (In fact, the word "crystal" derives from the Greek word for frost.) This is due to hydrogen bonds forming between the water molecules, which line up molecules less efficiently (in terms of volume) when water is frozen. The result of this is that ice floats on liquid water, an important factor in Earth's climate. When ice melts, it absorbs as much heat energy (the heat of fusion) as it would take to heat an equivalent mass of water by 80 °C, while its temperature remains a constant 0 °C. As a crystalline solid, ice is considered a mineral.

Types of ice

mineral Everyday ice and snow is hexagonal ice (ice I_h). Subjected to higher pressures and varying temperatures, ice can form in roughly a dozen different phases. Only a little less stable (metastable) than I_h is cubic structure ice (I_c). But cooling I_h causes a different arrangement to form in which the protons move, XI. With both cooling and pressure more types exist, each being created depending on the phase diagram of ice. These are II, III, V, VI, VII, VIII, IX, and X. With care all these types can be recovered at ambient pressure. The types are differentiated by their crystalline structure, ordering and density. There are also two metastable phases of ice under pressure, both fully hydrogen disordered, these are IV and XII. Ice XII was discovered in 1996. As well as crystalline forms solid water can exist in amorphous states as amorphous solid water (ASW), low density amorphous ice (LDA), high density amorphous ice (HDA), very high density amorphous ice (VHDA) and hyperquenched glassy water (HGW). Kurt Vonnegut's novel Cat's Cradle features Ice IX as a central element of the plot, although real Ice IX does not have the properties of Vonnegut's fictional ice-nine (i.e. the ability to freeze all water on Earth with the introduction of one granule). Rime is a type of ice formed by fog freezing on cold objects. It contains a high proportion of trapped air, making it appear white rather than transparent, and giving it a density about one quarter of that of pure ice. Ice can also form icicles, similar to stalactites in appearance, as water drips and re-freezes. Clathrate hydrates are forms of ice that contain gas molecules trapped within its crystal lattice. Pancake ice is a formation of ice generally created in areas with less calm conditions. Some other substances (particularly solid forms of those usually found as fluids) are also called "ice": dry ice, for instance, is a popular term for solid carbon dioxide. carbon dioxide, circa 1905.]]

Human relationship with ice

carbon dioxide, Iran, built during the Middle Ages for storing harvested ice.]] Ice has long been valued as a means of cooling. Until recently, the Hungarian Parliament building used ice harvested in the winter from Lake Balaton as its primary source of energy for air conditioning. Icehouses were used to store ice during the winter so as to preserve perishables during the summer, and early refrigerators were known as iceboxes because they had a block of ice in them. In many cities it was not unusual to have a regular ice delivery service during the summer. The advent of artificial refrigeration technology has since made delivery of ice obsolete. In 400 BC Iran, Persian engineers had already mastered the technique of storing ice in the middle of summer in the desert. The ice was brought in during the winters from nearby mountains in bulk amounts, and stored in specially designed, naturally cooled refrigerators, called yakhchal (meaning ice storage). This was a large underground space (up to 5000 m³) that had thick walls (at least two meters at the base) made out of a special mortar called sārooj, composed of sand, clay, egg whites, lime, goat hair, and ash in specific proportions, and which was resistant to heat transfer. This mixture was thought to be completely water impenetrable. The space often had access to a Qanat, and often contained a system of windcatchers that could easily bring temperatures inside the space down to frigid levels in summer days. The ice was then used to chill treats for royalty during hot summer days.

Sports on ice

Ice also plays a role in winter recreation, in sports such as ice skating, ice hockey, ice fishing, ice climbing and sled racing on bobsled and luge. The human quest for excitement has even led to ice racing, where drivers must go fast on lake ice while also controlling the skid of their vehicle (this is similar in some ways to dirt track racing). The sport has even been modified to work on ice rinks.

Ice travel

ice rink, February 2002.]] Ice can also be an obstacle; for harbors near the poles, being ice-free is an important advantage, ideally all-year round. Examples are Murmansk (Russia), Petsamo (Russia, formerly Finland) and Vardø. Harbors that are not ice-free are opened up using icebreakers. Ice forming on roads is a dangerous winter hazard. Black ice is very difficult to see because it lacks the expected glossy surface. Whenever there is freezing rain or snow that occurs at a temperature near the melting point, it is common for ice to build up on the windows of vehicles. Driving safely requires the removal of the ice build-up. Ice scrapers are tools designed to break the ice free and clear the windows, though removing the ice can be a long, labor-intensive, and stressful process—especially when a driver ends up running late for work as a result. Far enough below the freezing point, a thin layer of ice crystals can form on the inside surface of windows. This usually happens when a vehicle has been left alone after being driven for a while, but can happen while driving if the outside temperature is low enough. Moisture from the driver's breath is the source of water for the crystals. It is troublesome to remove this form of ice, so people often open their windows slightly when the vehicle is parked in order to let the moisture dissipate, and it is now common for cars to have rear-window defrosters to combat the problem. A similar problem can happen in homes, which is why many colder regions require double-pane windows for insulation. When the outdoor temperature stays below freezing for extended periods, very thick layers of ice can form on lakes and other bodies of water (although places with flowing water require much colder temperatures). The ice can become thick enough to drive onto with automobiles and trucks. Doing this safely requires a thickness of at least 30 centimeters (one foot).

Other uses of ice

- The manufacture and use of ice cubes or crushed ice is common for drinks.
- Pagophagia, a type of pica eating disorder, is the compulsive consumption of ice.
- Structures are built out of large chunks of ice. They are mostly ornamental (as in the case with ice castles) and not practical for long-term habitation. Ice hotels exist on a seasonal basis in a few cold areas. Igloos are another example of a temporary structure.

Ice at different pressures

Ice can be formed at higher temperatures in pressurized environments, and water will remain a liquid or gas until -30 °C at lower pressures. Ice formed at high pressure has a different crystal structure and density than ordinary ice. Ice, water, and water vapor can coexist at the triple point, which is 273.16 K at a pressure of 611.73 Pa.

Related terms

- A rusticle is a rust formation similar to an icicle.
- Isaz is the Proto-Germanic rune for "ice".

External links

- [http://www.its.caltech.edu/~atomic/snowcrystals/ice/ice.htm The phase diagram of water, including the ice variants]
- [http://www.webmineral.com/data/Ice.shtml Webmineral listing for Ice]
- [http://www.mindat.org/min-2001.html MinDat.org listing and location data for Ice]
- [http://www-2.cs.cmu.edu/~dst/ATG/ice.html The physics of ice]
- [http://www.martin.chaplin.btinternet.co.uk/phase.html The phase diagrams of water with some high pressure diagrams]
- [http://www.livescience.com/forcesofnature/050630_melting_discovery.html A recent discovery about how ice melts] Category:Forms of water Category:Water ice Category:Glaciology Category:Minerals als:Eis ja:氷 simple:Ice

Silver nitrate

| R-phrases | , |- | S-phrases | , , ,
, |- Silver nitrate is a chemical compound with chemical formula Ag N O₃. This nitrate of silver is a light-sensitive ingredient in photographic film and is a poisonous, corrosive compound. Silver nitrate crystals can be produced by dissolving silver in nitric acid and evaporating the solution. The compound notably stains skin a greyish or black color that is made visible after exposure to sunlight. When making photographic film, fine silver nitrate particles are bonded to strips of tri-acetate or polyester. Photons from sunlight, X-rays or other sources, initiate a purported chemical chain reaction: when photons strike silver nitrate molecules, they free electrons from the silver ions. These free electrons roam through the crystal and settle in structural imperfections called sensitivity specks. These specks apparently attract positive silver ions, which are then neutralized to form groups of stable silver atoms, creating a latent image that is chemically developed to reveal a photographic image. Silver nitrate has been used as an antiseptic, dropped into newborn babies' eyes at birth. This is to prevent contraction of gonorrhoea or chlamydia from their mother. A very weak solution is used for this, (about 1%) and there are very few side effects. Mythically, silver nitrate was used as a method of killing vampires, with the silver nitrate generally being injected into a bullet cartrige or used in a hypodermic needle. Fused silver nitrate, shaped into sticks, was traditionally called lunar caustic and used as a cauterizing agent. In histology, silver nitrate is used for silver staining, for demonstrating proteins and nucleic acids. It is also used as a stain in scanning electron microscopy.

Hazards

Silver nitrate is harmful to the environment, is toxic to fish and can discolor skin when exposed.

External links

- [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc11/icsc1116.htm International Chemical Safety Card 1116]
- [http://www.cdc.gov/niosh/npg/npgd0557.html NIOSH Pocket Guide to Chemical Hazards]
-
- [http://www.kodak.com/US/en/corp/aboutKodak/kodakHistory/filmImaging.shtml Film Making] Category:Silver compounds Category:Nitrates Category:Antiseptics Category:Photographic chemicals Category:Staining dyes Category:Electron microscopy stains ja:硝酸銀 nb:Sølvnitrat

Katabatic wind

A katabatic wind, from the Greek word katabatikos meaning "going downhill", is a wind that blows down a topographic incline such as a hill, mountain, or glacier. Such winds, particularly when they occur over a wide area, are sometimes called fall winds. A distinction is drawn between winds that are warmer than their surroundings (generally called Föhn or regionally, Chinook, Santa Ana or Diablo) and those that are cooler (for instance the Mistral in the Mediterranean, the Bura (or Bora) in the Adriatic or the Oroshi in Japan). In more recent times, however, the term katabatic wind usually refers to the cold variant. The cold form of katabatic wind originates in a cooling, either radiatively or through vertical motion, of air at the top of the mountain, glacier, or hill. Since the density of air increases with lower temperature, the air will flow downwards, warming adiabatically as it descends, but still remaining relatively cold. Cold katabatic winds are frequently found in the early hours of the night when the solar heating has ceased and the ground cools by emitting infrared radiation. Cold air from extratropical cyclones may contribute to this effect. Over Antarctica and Greenland, prominent (although unnamed) cold katabatic winds exist, blowing for most of the year. Winds which blow up a slope are called anabatic winds.

References

- McKnight, TL & Hess, Darrel (2000). Katabatic Winds. In , Physical Geography: A Landscape Appreciation, pp. 131-2. Upper Saddle River, NJ: Prentice Hall. ISBN 0130202630

Links

- [http://www.bbc.co.uk/weather/features/az/alphabet31.shtml Weather A-Z - Katabatic Winds By Bill Giles OBE] Category:Winds

Hawaiian Islands

The Hawaiian Islands, once known as the Sandwich Islands, form an archipelago of nineteen islands and atolls, numerous smaller islets, and undersea seamounts trending northwest by southeast in the North Pacific Ocean between latitudes 19° N and 29° N. The archipelago takes its name from the largest island in the group and extends some 1500 miles (2400 km) from the Island of Hawai‘i in the south to northernmost Kure Atoll. The archipelago represents the exposed peaks of a great undersea mountain range known as the Hawaiian-Emperor seamount chain, formed by volcanic activity over a hotspot in the earth's mantle. At about 3,000 km (1,860 miles) from the nearest continent, the Hawaiian Island archipelago is the most isolated grouping of islands on Earth (Macdonald, Abbott, and Peterson, 1984).

Islands and reefs of the Hawaiian archipelago

Earth A total of 19 islands and atolls comprise the Hawaiian Islands, with a total land area of 16,636 km² (6,423.4 square miles). The eight main Hawaiian islands (all inhabited except for Kaho‘olawe) are, listed here from south to north:
- Hawai‘i (also known as the Big Island)
- Maui
- Kaho‘olawe (uninhabited; temporary residential facilities)
- Lāna‘i
- Moloka‘i
- O‘ahu
- Kaua‘i
- Ni‘ihau Smaller islands, atolls, and reefs (beyond Ni‘ihau and all uninhabited); called the Northwestern Hawaiian Islands:
- Ka‘ula
- Nihoa
- Necker (Mokumanamana)
- French Frigate Shoals (Mokupāpapa)
- Gardner Pinnacles (Pūhāhonu)
- Maro Reef (Nalukakala)
- Laysan (Kauō)
- Lisianski (Papa‘āpoho)
- Pearl and Hermes Reef (Holoikauaua)
- Midway (Pihemanu) (temporary residential facilities)
- Kure (Kānemiloha‘i)

Islets

Some information sources state that there are 137 "islands" in the Hawaiian chain. This number includes all minor islands and islets offshore of the main islands (listed above) and individual islets in each atoll. (Hawai‘i state government, undated). Following is a list of islets and small offshore islands that make up the total count beyond 19:
- Ford Island (Moku‘ume‘ume)
- Kaohikaipu
- Manana Island
- Mōkōlea Rock
- Nā Mokulua
- Molokini Except for Midway, which is an unincorporated territory of the United States, these islands and islets are administered as the State of Hawaii — the 50th state of the United States of America.

Geology

United States of America) and blue to light gray (shallowest). Historical lava flows are shown in red, erupting from the summits and rift zones of Mauna Loa, Kilauea, and Hualalai volcanoes on Hawai‘i .]] The chain of islands or archipelago formed as the Pacific plate moves slowly northwestward over a hotspot in the earth's crust. Hence the islands in the northwest of the archipelago are older and typically smaller (have been eroding far longer). Because of the composition of the magma in the hotspot, the composition of Hawaiian volcanoes is basaltic. The majority of eruptions in Hawai‘i are Hawaiian-type eruptions because basaltic magma is relatively fluid compared with andesitic eruptions. Hawai‘i (the Big Island) is the largest and youngest island in the chain, built from seven different volcanoes. Mauna Loa, comprising over half of the Big Island, is the largest shield volcano on the planet. The measurement from the base locally depressing the sea floor to its peak is about 17 km (56,000 feet; [http://wwwhvo.wr.usgs.gov/maunaloa/ USGS]) See also: List of Hawaii rivers

Ecology

:Related article: Endemism in the Hawaiian Islands. The Hawaiian Islands are home to a large number of endemic species. The plant and animal life of the Hawaiian Islands developed in nearly complete isolation over about 70 million years. Human contact, first by Polynesians, introduced new trees, plants and animals. The growing population also brought deforestation, forest degradation, treeless grasslands, and environmental degradation. As a result, many species which depended on forest habitats and food went extinct. Agriculture began to increase, with monocultual crop production replacing multi-species systems. The arrival of the Europeans had a significant impact, with the promotion of large-scale single-species export agriculture and livestock grazing. In turn, this led to the increased clearing of forests, and the development of towns, driving more species to extinction. Today, many of the remaining endemic species are considered endangered. [http://www.agroforestry.net/afg/]

Climate

The islands receive most rainfall from the trade winds on their north and east flanks (called the windward side) as a result of orographic precipitation. Coastal areas in general and especially the south and west flanks or leeward sides, tend to be drier. Because of the frequent build-up of Tradewind clouds and potential showers, most tourist areas have been built on the leeward coasts of the islands. In general, the Hawaiian Islands receive most of their precipitation during the winter months (October to April). Drier conditions generally prevail from May to September, but the warmer temperatures increase the risk of hurricanes (see below). Temperatures at sea level generally range from high temperatures of 85-90°F (29-32°C) during the summer months to low temperatures of 65-70°F (18-21°C) during the winter months. Very rarely does the temperature rise above 90°F (32°C) or drop below 60°F (16°C) at lower elevations. Temperatures are lower at higher altitudes; in fact, the three highest mountains of Mauna Kea, Mauna Loa, and Haleakala sometimes receive snowfall during the winter.

Hurricanes

The hurricane season in the Hawaiian Islands is roughly from June through November, when hurricanes and tropical storms are most probable in the North Pacific. These storms tend to originate off the coast of Mexico (particularly the Baja California peninsula) and track west or northwest towards the islands. Hawai‘i is protected by the vastness of the Pacific (i.e. the improbability of a direct hit); as storms cross the Pacific they tend to lose strength if they bear northward and encounter cooler water. It is thought that the topography of the highest islands (Haleakalā on Maui, Mauna Kea and Mauna Loa on the Big Island) may protect these islands, and certainly Kaua‘i has been hit more often in the last 50 years than the others.

Tsunamis

Baja California peninsula The Hawaiian islands can be affected by tsunamis, great waves that strike the shore typically but not exclusively from the north. Tsunamis are movements of the surface layer of the ocean most often caused by earthquakes somewhere in the Pacific. The city of Hilo on the Big Island has historically been most impacted by tsunamis, where the inrushing water is accentuated by the shape of the bay on which the town is situated.

References

- [http://www2.hawaii.gov/DBEDT/images/User_FilesImages/databook/db02/sec05_a254.pdf Hawai‘i state government], Table 05.09 (.pdf file).
- Macdonald, G. A., A. T. Abbott, and F. L. Peterson. 1984. Volcanoes in the Sea. The Geology of Hawaii, 2nd edition. University of Hawaii Press, Honolulu. 517 pp.
- [http://radlab.soest.hawaii.edu/atlas/ The Ocean Atlas of Hawai‘i] - SOEST at University of Hawai‘i.
- Category:Archipelagoes ko:하와이 제도 ja:ハワイ諸島

Kauai

Kauai (usually called Kauai outside the Hawaiian Islands) is the oldest and fourth largest of the main Hawaiian Islands, having an area of 1,446 km² . Known also as the "Garden Isle", Kauai lies 105 miles (170 kilometers) across the Kauai Channel, northwest of Oahu. Of volcanic origin, the highest peak on this mountainous island is Kawaikini at 1,598 m (5,243 ft). The second highest peak is Mount Waialeale near the center of the island, 1,570 m (5,148 ft) above sea level. The wettest spot on Earth, with an annual average rainfall of 460 inches (11,700 millimeters), is located on the east side of Mount Waialeale. The high annual rainfall has eroded deep valleys in the central mountain, carving out canyons with many scenic waterfalls. There is no known meaning behind the name of Kauai. Native Hawaiian tradition indicates the name's origin in the legend of Hawaiiloa — the Polynesian navigator attributed with discovery of the Hawaiian Islands. The story relates how he named the island of Kauai after a son. During the reign of King Kamehameha, the islands of Kauai and Niihau were the last Hawaiian Islands to join his Kingdom of Hawaii. Their ruler, Kaumualii, resisted Kamehameha for years, until the king arrived with a huge armada of ships to take the islands by force. Kaumualii decided to join the kingdom without bloodshed, and became Kamehameha's vassal in 1810. 1810]] The city of Līhue, on the island's southeast coast, is the seat of Kauai County and the largest city on the island. Waimea, on the island's southwest side and once the capital of Kauai, was the first place visited by explorer Captain James Cook in 1778. Waimea town is located at the mouth of the Waimea River, whose flow formed one of the most scenic canyons in the world: 3000 ft (900 m) deep Waimea Canyon. The island of Kauai was featured in Disney's 2002 animated feature film Lilo & Stitch. Waimea Canyon was used in the filming of the 1993 film Jurassic Park. Kauai is home to the U.S. Navy's Pacific Missile Range Facility. Kauai was known for its distinct dialect of the Hawaiian language before it went extinct there. Whereas the standard language today is based on the dialect of Hawaii island (also extinct), the Kauai dialect was known for pronouncing /k/ as /t/. Therefore, the native name for Kauai was Tauai, and the major settlement of Kapaa would have been called Tapaa.

Important towns and cities

Līhue Hanalei Poipū Princeville Wailua

Places of interest

Hanalei Bay Nā Pali Coast Waimea Canyon Iraivan temple

Bibliography

- Edward Joestring. Kauai, the Separate Kingdom. University of Hawaii Press and Kauai Museum Association. Honolulu. 1984. ISBN 0824811623

External links

- [http://www.kauaichamber.org/ Kauai Chamber of Commerce] - Essential business information
- [http://www.gregoryferdinandsen.com/HNL2003/Waterfalls.htm Waterfalls on Kauai]
- [http://www.kauaiexplorer.com/ Kauai Beaches] ja:カウアイ島 simple:Kauai Kauai Kauai

Water vapor

Water vapor or water vapour, also aqueous vapour, is the gas phase of water. On the Earth, water vapor is one state of the water cycle within the hydrosphere. Water vapor can be produced from the evaporation of liquid water or from the sublimation of ice. Under normal atmospheric conditions, water vapor is continuously evaporating and condensing. Normally, water vapor is invisible to the naked eye.

General properties of water vapor

Evaporation/sublimation

condensing Whenever a water molecule leaves a surface, it is said to have evaporated. Each water molecule that becomes water vapor takes a parcel of heat with it. This process is called evaporative cooling. The amount of water vapor in the air will determine how fast each molecule will return back to the surface or not. So, when a net evaporation occurs, that body of water will undergo a net cooling directly related to the loss of water. Evaporative cooling is restricted by atmospheric conditions. The amount of water vapor in the air is referred to as humidity. Measurement of the vapor content of air is accomplished with devices known as hygrometers. The measurements are expressed as specific humidity or percent relative humidity. The temperature of the atmosphere and the water surface determines the equilibrium vapor pressure, 100% relative humidity occurs when the partial pressure of water vapor is equal to the equilibrium vapor pressure. This is often referred to as complete saturation. Another form of evaporation is sublimation, in which water molecules become gaseous from ice instead of liquid water. Under the same principle, when ice has a higher temperature than the surrounding atmosphere, sublimation occurs. It is sublimation that accounts for the slow, mid-winter disappearance of ice and snow at temperatures too low to cause melting.

Condensation

Water vapor will only condense onto another surface when that surface is cooler than the temperature of the water vapor, or when the water vapor equilibrium in air has been exceeded. When water vapor condenses onto a surface, a net warming occurs on that surface. The water molecule brings a parcel of heat with it. In turn, the temperature of the atmosphere drops slightly. In the atmosphere, condensation produces clouds, fog and precipitation--usually only when facilitated by cloud condensation nuclei. The dew point of an air parcel is the temperature to which it must cool before condensation in the air begins to form. Also, a net condensation of water vapor occurs on surfaces when the temperature of the surface is at or below the dew point temperature of the atmosphere. Deposition is a type of condensation. Frost and snow are examples of deposition (or sublimation). Deposition is the direct formation of ice from water vapor.

General Discussion

The amount of water vapor in an atmosphere exists due to the restrictions of partial pressures and temperature. Dew point temperature and relative humidity act as guidelines for the process of water vapor in the water cycle. Energy input, such as sunlight, can trigger more evaporation on an ocean surface or more sublimation on a chunk of ice on top of a mountain. The balance between condensation and evaporation gives the quantity called vapor partial pressure (abbreviated to Vapor pressure). The maximum partial pressure (saturation pressure) of water vapor in air varies with temperature of the air and water vapor mixture. A variety of empirical formulae exist for this quantity; the most used reference formula is the Goff-Gratch equation for the SVP over liquid water: :

\log_ p =  -7.90298 (373.16/T-1) + 5.02808 \log_(373.16/T) - 1.3816 . 10^ (10^ -1) + 8.1328 . 10^ (10^ -1) + \log_(1013.246)

Where T, temperature of the moist air, is given in units of kelvins, and p is given in units of millibars (hectopascals). The formula is valid from about −50 to 102 °C; however there are a very limited number of measurements of the vapor pressure of water over supercooled liquid water. A number of other formulae are listed and compared at [http://cires.colorado.edu/~voemel/vp.html]. Under adverse conditions, such as when the boiling temperature of water is reached, a net evaporation will always occur during standard atmospheric conditions regardless of the percent of relative humidity. This immediate process will dispel massive amounts of water vapor into a cooler atmosphere. Exhaled air is almost fully at equilibrium with water vapor at the body temperature. In the cold air the exhaled vapor quickly condenses, thus showing up as a fog or mist of water droplets and as condensation or frost on surfaces. Supermarket buildings that utilise open chiller cabinets are able to significantly lower vapor pressure (lowering humidity). This practice delivers several benefits and other problems.

Water vapor in Earth's atmosphere

Gaseous water represents a small but environmentally significant constituent of the atmosphere. Most of it is contained in the troposphere. Besides accounting for most of Earth's natural greenhouse effect, which warms the planet, gaseous water also condenses to form clouds, which may act to warm or cool, depending on the circumstances. In general terms, atmospheric water strongly influences, and is strongly influenced by weather, and weather is modified by climate. Fog and clouds form through condensation around cloud condensation nuclei. In the absence of nuclei, condensation will only occur at much lower temperatures. Under persistent condensation or deposition, cloud droplets or snowflakes form, which precipitate when they reach a critical mass. precipitate The average residence time of water molecules in the troposphere is about 1 week. Water depleted by precipitation is replenished by evaporation from the seas, lakes, rivers and the transpiration of plants, and other biological and geological processes. Measurements of vapor concentration are expressed as specific humidity or percent relative humidity. The annual mean global concentration of water vapor would yield about 25 mm of liquid water over the entire surface of the Earth if it were to instantly condense. However, the mean annual precipitation for the planet is about 1 meter, which indicates a rapid turnover of water in the air.

Radar and satellite imaging

relative humidity global mean atmospheric water vapor ]] Because water molecules absorb microwaves and other radio wave frequencies, water in the atmosphere attenuates radar signals. In addition, atmospheric water will reflect and refract signals to an extent that depends on whether it is vapor, liquid or solid. Generally, radar signals lose strength progressively the farther they travel through the troposphere. Different frequencies attenuate at different rates, such that some components of air are opaque to some frequencies and transparent to others. Radio waves used for broadcasting and other communication tend to suffer the same effect. Water vapor reflects radar to a less extent than do water's other two phases. In the form of drops and ice crystals, water acts as a prism, which it does not do as a gas. A comparison of GOES-12 satellite images shows the distribution of atmospheric water vapor relative to the oceans, clouds and continents of the Earth. Vapor surrounds the planet but is unevenly distributed.

Lightning generation

Water vapor plays a key role in lightning production in the atmosphere. From cloud physics, usually, clouds are the real generators of static charge as found in Earth's atmosphere. But the ability, or capacity, of clouds to hold massive amounts of electrical energy is directly related to the amount of water vapor present in the local system. The amount of water vapor directly controls the permittivity of the air. During times of low humidity, static discharge is quick and easy. During times of higher humidity, fewer static discharges occur. However, permittivity and capacitance work hand in hand to produce the megawatt outputs of lightning. After a cloud, for instance has started its way to becoming a lightning generator, atmospheric water vapor acts as a substance (or insulator) that decreases the ability of the cloud to discharge its electrical energy. Over a certain amount of time, if the cloud continues to generate more static electricity, the barrier that was created by the atmospheric water vapor will ultimately break down. This energy will be released to a locally, opposite charged region in the form of lightning. The strength of each discharge is directly related to the atmospheric permittivity, capacitance, and the source's charge generating ability. See also, Van de Graaff generator.

Extraterrestrial water vapor

The brilliance of comet tails comes largely from water vapor. On approach to the sun, the ice many comets carry sublimates to vapor, which reflects light from the sun. Knowing a comet's distance from the sun, astronomers may deduce a comet's water content from its brilliance. Bright tails in cold and distant comets suggests carbon monoxide sublimation. Scientists studying Mars hypothesize that if water moves about the planet, it does so as vapor. Most of the water on Mars appears to exist as ice at the northern pole. During Mars' summer, this ice sublimates, perhaps enabling massive seasonal storms to convey significant amounts of water toward the equator.

External links

- [http://www.nsdl.arm.gov/Library/glossary.shtml#water_vapor National Science Digital Library - Water Vapor]
- [http://avc.comm.nsdlib.org/cgi-bin/wiki_grade_interface.pl?Measuring_Water_Vapor Measuring Water Vapor] : A lesson plan from the National Science Digital Library.
- [http://www.ems.psu.edu/~fraser/Bad/BadClouds.html psu.edu science misconceptions - Bad Clouds]
- [http://fermi.jhuapl.edu/people/babin/vapor/index.html Water Vapor Myths: A Brief Tutorial]
- [http://www.agu.org/sci_soc/mockler.html AGU Water Vapor in the Climate System - 1995] Category:Climatology Category:Meteorology Category:greenhouse gases