# Liquids/Liquid objects/Rains

Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated.
"So-called secondary organic aerosols form from oxidation of airborne organic gases and play key roles in weather and climate by seeding clouds and absorbing or scattering sunlight".

## Thunderstorms

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.
"Thunderstorms are small, intense weather systems that make strong winds, heavy rain, lightning, and thunder."
"Sudden flash floods that happen because of heavy rains is the biggest reason for weather-related deaths."
"Plants receive lots of life-giving rain when they need it."
"Clouds give us shades, and rain can cool down a hot day."
"Rain from thunderstorms washes away many of these pollutants out of the air."

## Hydrometeors

Def. "[a]ny or all of the forms of water particles, whether liquid or solid, that fall from the atmosphere" are called precipitation.
Def. "precipitation products of the condensation of atmospheric water vapour" are called hydrometeors.
"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. very "small, numerous, and uniformly dispersed water drops, mist, or sprinkle ... that falls to the ground" is called drizzle.
Def. "precipitation that evaporates before reaching the ground" is called virga.

## Precipitation detection

"Precipitation detection (PD) is often, but not always, regarded as the first essential step in the estimation of precipitation from remote sensing platforms. The basic purpose of detection is two-fold:
* To make an initial determination of which sensor pixels may contain precipitation, so that a more sophisticated rain rate retrieval algorithm may be brought to bear on those pixels while avoiding unnecessary computational effort elsewhere.
* To prevent the retrieval algorithm from attempting retrievals in situations where it is likely give spurious false-positives; e.g., due to problem background types.
"Launched by NASA and JAXA in 1997, [the Tropical Rainfall Measuring Mission] TRMM carries the first on-orbit active/passive instrument package to study the intensity and structure of tropical rainfall."
"An international satellite mission to be launched by NASA and JAXA in 2014 that will set new standards for precipitation measurements worldwide using a network of satellites united by the [Global Precipitation Measurement] GPM Core Observatory."

## Rainfall

Def. "the amount of rain that falls on a single occasion" is called rainfall.

## Cryometeors

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

## Lithometeors

"The tephra that rained down caused the roofs of many homes near the eruption site to collapse when it crushed them with massive weight and force."

## Plasma meteors

A coronal cloud is a cloud, or cloud-like, natural astronomical entity, composed of plasma and usually associated with a star or other astronomical object where the temperature is such that X-rays are emitted. While small coronal clouds are above the photosphere of many different visual spectral type stars, others occupy parts of the interstellar medium (ISM), extending sometimes millions of kilometers into space, or thousands of light-years, depending on the size of the associated object such as a galaxy.
"[A] medium-strength flare erupted from the sun on July 19, 2012. The blast also generated the enormous, shimmering plasma loops, which are an example of a phenomenon known as "coronal rain," agency officials said."
"Hot plasma in the corona cooled and condensed along strong magnetic fields in the region" slowly falling back to the solar surface as plasma "rain".

## Meteors

Def. liquid moisture that falls visibly in separate drops is called rain.
The Kerala red rain phenomenon was a blood rain (red rain) event that occurred from July 25 to September 23, 2001, when heavy downpours of red-coloured rain fell sporadically on the southern Indian state of Kerala, staining clothes pink. Yellow, green, and black rain was also reported. Colored rain was also reported in Kerala in 1896 and several times since, most recently in June 2012.
Red rains were also reported from November 15, 2012 to December 27, 2012 occasionally in eastern and north-central provinces of Sri Lanka, where scientists from the Sri Lanka Medical Research Institute (MRI) are investigating to ascertain their cause.
The colored rain of Kerala began falling on July 25, 2001, in the districts of Kottayam and Idukki in the southern part of the state. Yellow, green, and black rain was also reported. Many more occurrences of the red rain were reported over the following ten days, and then with diminishing frequency until late September.
According to locals, the first colored rain was preceded by a loud thunderclap and flash of light, and followed by groves of trees shedding shriveled grey "burnt" leaves. Shriveled leaves and the disappearance and sudden formation of wells were also reported around the same time in the area. It typically fell over small areas, no more than a few square kilometers in size, and was sometimes so localized that normal rain could be falling just a few meters away from the red rain. Red rainfalls typically lasted less than 20 minutes. Each milliliter of rain water contained about 9 million red particles, and each liter of rainwater contained approximately 100 milligrams of solids. Extrapolating these figures to the total amount of red rain estimated to have fallen, it was estimated that 50,000 kilograms (110,000 lb) of red particles had fallen on Kerala.
The brownish-red solid separated from the red rain consisted of about 90% round red particles and the balance consisted of debris. The particles in suspension in the rain water were responsible for the color of the rain, which at times was strongly colored red. A small percentage of particles were white or had light yellow, bluish gray and green tints. The particles were typically 4 to 10 µm across and spherical or oval. Electron microscope images showed the particles as having a depressed center. At still higher magnification some particles showed internal structures.
In November 2001, commissioned by the Government of India's Department of Science & Technology, the Center for Earth Science Studies (CESS) and the Tropical Botanical Garden and Research Institute (TBGRI) issued a joint report which concluded that:
"The color was found to be due to the presence of a large amount of spores of a lichen-forming alga belonging to the genus Trentepohlia. Field verification showed that the region had plenty of such lichens. Samples of lichen taken from Changanacherry area, when cultured in an algal growth medium, also showed the presence of the same species of algae. Both samples (from rainwater and from trees) produced the same kind of algae, indicating that the spores seen in the rainwater most probably came from local sources."

## Infrareds

"Tiny crystals of a green mineral called olivine [forsterite is the magnesium end-member of the solid solution] are falling down like rain on a burgeoning star, according to observations from NASA's Spitzer Space Telescope [graph at right]. ... Spitzer's infrared detectors spotted the crystal rain around a distant, sun-like embryonic star, or protostar, referred to as HOPS-68, in the constellation Orion."
"You need temperatures as hot as lava to make these crystals, ... We propose that the crystals were cooked up near the surface of the forming star, then carried up into the surrounding cloud where temperatures are much colder, and ultimately fell down again like glitter."
"If you could somehow transport yourself inside this protostar's collapsing gas cloud, it would be very dark, ... But the tiny crystals might catch whatever light is present, resulting in a green sparkle against a black, dusty backdrop."

## Astrophysics

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.
Rain is measured in units of length per unit time, typically in millimeters per hour, or in countries where imperial units are more common, inches per hour. The "length", or more accurately, "depth" being measured is the depth of rain water that would accumulate on a flat, horizontal and impermeable surface during a given amount of time, typically an hour. One millimeter of rainfall is the equivalent of one liter of water per square meter.
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.

## Climatology

Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and numerous other meteorological elements in a given region over long periods of time.

## Craters

In the majority of typical volcanoes, the crater is situated atop the mountain formed from the erupted volcanic deposits such as lava flows and tephra. Volcanoes that terminate in such a summit crater are usually of a conical form. Other volcanic craters may be found on the flanks of volcanoes, and these are commonly referred to as flank craters. Some volcanic craters may fill either fully or partially with rain and/or melted snow, forming a crater lake.

## Sun

"Coronal clouds, type IIIg, form in space above a [sunspot] area and rain streamers upon it."

## Earth

"Common objects falling from the sky are rain drops, snow flakes, and hail."
Def. A "forest in a climate with high annual rainfall and no dry season" is called a rainforest, or rain forest.
Def. "a meteor that reaches the surface of the Earth without being completely vaporized" is called a meteorite.
"The dominant group of lichens in tropical rain forests are crustose microlichens, a highly diverse assemblage that lacks detailed taxonomic and ecological studies, among them the families Graphidaceae and Thelotremataceae (Wirth and Hale 1963, 1978; Hale 1974, 1978"
"[T]he statement by the famous French scientist, Francis Castlenau, ... he had seen fishes rain down in Singapore in such numbers that the natives went about picking them up by the basketful".
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.
Chondrite falls range from single stones to extraordinary showers consisting of thousands of individual stones, as occurred in the Holbrook fall of 1912, where an estimated 14,000 stones rained down on northern Arizona.

## Titan

"As spring continues to unfold at Saturn, April showers on the planet's largest moon, Titan, have brought methane rain to its equatorial deserts ... Extensive rain from large cloud systems ... has apparently darkened the surface of the moon."
“It's amazing to be watching such familiar activity as rainstorms and seasonal changes in weather patterns on a distant, icy satellite".
"Clouds on Titan are formed of methane as part of an Earth-like cycle that uses methane instead of water. On Titan, methane fills lakes on the surface, saturates clouds in the atmosphere, and falls as rain. Though there is evidence that liquids have flowed on the surface at Titan's equator in the past, liquid hydrocarbons, such as methane and ethane, had only been observed on the surface in lakes at polar latitudes. The vast expanses of dunes that dominate Titan's equatorial regions require a predominantly arid climate."
"An arrow-shaped storm appeared in the equatorial regions on Sept. 27, 2010 -- the equivalent of early April in Titan's “year” -- and a broad band of clouds appeared the next month. ... A 193,000-square-mile (500,000-square-kilometer) region along the southern boundary of Titan’s Belet dune field, as well as smaller areas nearby, had become darker. ... this change in brightness is most likely the result of surface wetting by methane rain."
“These outbreaks may be the Titan equivalent of what creates Earth's tropical rainforest climates, even though the delayed reaction to the change of seasons and the apparently sudden shift is more reminiscent of Earth's behavior over the tropical oceans than over tropical land areas”.
At right is an image that shows clouds over the equatorial region of Titan.
"Methane clouds in the troposphere, the lowest part of the atmosphere, appear white here and are mostly near Titan's equator. The darkest areas are surface features that have a low albedo, meaning they do not reflect much light. Cassini observations of clouds like these provide evidence of a seasonal shift of Titan's weather systems to low latitudes following the August 2009 equinox in the Saturnian system. (During equinox, the sun lies directly over the equator. See PIA11667 to learn how the sun's illumination of the Saturnian system changed during the equinox transition to spring in the northern hemispheres and to fall in the southern hemispheres of the planet and its moons.)"
"In 2004, during Titan's late southern summer, extensive cloud systems were common in Titan's south polar region (see PIA06110, PIA06124 and PIA06241). Since 2005, southern polar systems have been observed infrequently, and one year after the equinox, extensive near-equatorial clouds have been seen. This image was taken on Oct. 18, 2010, a little more than one Earth year after the Saturnian equinox, which happens once in roughly 15 Earth years."
"The cloud patterns observed from late southern summer to early southern fall on Titan suggest that Titan's global atmospheric circulation is influenced by both the atmosphere and the surface. The temperature of the surface responds more rapidly to changes in illumination than does the thick atmosphere. Outbreaks such as the clouds seen here may be the Titan equivalent of what creates the Earth's tropical rainforest climates, even though the delayed reaction to the change of seasons and the apparently sudden shift is more reminiscent of the behavior over Earth's tropical oceans than over tropical land areas."
The climate—including wind and rain—creates surface features similar to those of Earth, such as sand dunes, rivers, lakes and seas (probably of liquid methane and ethane), and deltas, and is dominated by seasonal weather patterns as on Earth. With its liquids (both surface and subsurface) and robust nitrogen atmosphere, Titan's methane cycle is viewed as an analog to Earth's water cycle, although at a much lower temperature.
"These mosaics [at second right] of the south pole of Saturn's moon Titan, made from images taken almost one year apart, show changes in dark areas that may be lakes filled by seasonal rains of liquid hydrocarbons."
"The images on the left (unlabeled at top and labeled at bottom) were acquired July 3, 2004. Those on the right were taken June 6, 2005. In the 2005 images, new dark areas are visible and have been circled in the labeled version. The very bright features are clouds in the lower atmosphere (the troposphere). Titan's clouds behave similarly to those on Earth, changing rapidly on timescales of hours and appearing in different places from day to day. During the year that elapsed between these two observations, clouds were frequently observed at Titan's south pole by observers on Earth and by Cassini's imaging science subsystem (see PIA06124)."
"It is likely that rain from a large storm created the new dark areas that were observed in June 2005. Some features, such as Ontario Lacus, show differences in brightness between the two observations that are the result of differences in illumination between the two observations. These mosaics use images taken in infrared light at a wavelength of 938 nanometers. The images have been oriented with the south pole in the center (black cross) and the 0 degree meridian toward the top. Image resolutions are several kilometers (several miles) per pixel."
"Evidence from Cassini's imaging science subsystem, radar, and visual and infrared mapping spectrometer instruments strongly suggests that dark areas near the poles are lakes of liquid hydrocarbons-an analysis affirmed by images capturing those changes in the lakes thought to be brought on by rainfall."

## Technology

"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 GPM Core Observatory is scheduled for launch in early 2014."

## Hypotheses

* Rain is a liquid meteor of any kind.