A rain gauge (also known as udometer, pluviometer,ombrometer, and hyetometer) is an instrument used by meteorologists and hydrologists to gather and measure the amount of liquid precipitation over a predefined area, over a period of time. [1] It is used to determine the depth of precipitation (usually in mm) that occurs over a unit area and measure rainfall amount.
The first known rainfall records were kept by the Ancient Greeks, at around 500 BCE. [ citation needed ]
People living in India began to record rainfall in 400 BCE [2] The readings were correlated against expected growth. In the Arthashastra, used for example in Magadha, precise standards were set as to grain production. Each state storehouse was equipped with a rain gauge to classify land for taxation purposes. [3] Rainfall measurement was also mentioned in the Jewish text in Palestine. [4] In 1247, the Song Chinese mathematician and inventor Qin Jiushao invented Tianchi basin rain and snow gauges to reference rain, and snowfall measurements, as well as other forms of meteorological data. [5] [6]
In 1441, the Cheugugi was invented during the reign of Sejong the Great of the Joseon Dynasty of Korea as the first standardized rain gauge. [7] [8] [9] In 1662, Christopher Wren created the first tipping-bucket rain gauge in Britain in collaboration with Robert Hooke. [7] Hooke also designed a manual gauge with a funnel that made measurements throughout 1695.
Richard Towneley was the first to make systematic rainfall measurements over a period of 15 years from 1677 to 1694, publishing his records in the Philosophical Transactions of the Royal Society . Towneley called for more measurements elsewhere in the country to compare the rainfall in different regions, [10] although only William Derham appears to have taken up Towneley's challenge. They jointly published the rainfall measurements for Towneley Park and Upminster in Essex for the years 1697 to 1704. [11]
The naturalist Gilbert White took measurements to determine the mean rainfall from 1779 to 1786, although it was his brother-in-law, Thomas Barker, who made regular and meticulous measurements for 59 years, recording temperature, wind, barometric pressure, rainfall and clouds. His meteorological records are a valuable resource for knowledge of the 18th-century British climate. He was able to demonstrate that the average rainfall varied greatly from year to year with little discernible pattern. [12]
The meteorologist George James Symons published the first annual volume of British Rainfall in 1860. This pioneering work contained rainfall records from 168 land stations in England and Wales. He was elected to the council of the British Meteorological Society in 1863 and made it his life's work to investigate rainfall within the British Isles. He set up a voluntary network of observers, who collected data which were returned to him for analysis. So successful was he in this endeavour that by 1866 he was able to show results that gave a fair representation of the distribution of rainfall and the number of recorders gradually increased until the last volume of British Rainfall which he lived to edit, for 1899, contained figures from 3,528 stations — 2,894 in England and Wales, 446 in Scotland, and 188 in Ireland. He also collected old rainfall records going back over a hundred years. In 1870 he produced an account of rainfall in the British Isles starting in 1725.
Due to the ever-increasing numbers of observers, standardisation of the gauges became necessary. Symons began experimenting with new gauges in his own garden. He tried different models with variations in size, shape, and height. In 1863 he began a collaboration with Michael Foster Ward [13] from Calne, Wiltshire, who undertook more extensive investigations. By including Ward and various others around Britain, the investigations continued until 1890. The experiments were remarkable for their planning, execution, and drawing of conclusions. The results of these experiments led to the progressive adoption of the well-known standard gauge, still used by the UK Meteorological Office today, namely, one made of "... copper, with a five-inch funnel having its brass rim one foot above the ground ..." [14]
Most modern rain gauges generally measure the precipitation in millimetres in height collected during a certain period, equivalent to litres per square metre. Previously rain was recorded as inches or points, where one point is equal to 0.254 mm or 0.01 of an inch. [15]
Rain gauge amounts are read either manually or by automatic weather station (AWS). The frequency of readings will depend on the requirements of the collection agency. Some countries will supplement the paid weather observer with a network of volunteers to obtain precipitation data (and other types of weather) for sparsely populated areas.
In most cases the precipitation is not retained, but some stations do submit rainfall and snowfall for testing, which is done to obtain levels of pollutants.
Rain gauges have their limitations. Attempting to collect rain data in a tropical cyclone can be nearly impossible and unreliable (even if the equipment survives) due to wind extremes. Also, rain gauges only indicate rainfall in a localized area. For virtually any gauge, drops will stick to the sides or funnel of the collecting device, such that amounts are very slightly underestimated, and those of .01 inches or .25 mm may be recorded as a "trace".
Another problem encountered is when the temperature is close to or below freezing. Rain may fall on the funnel and ice or snow may collect in the gauge, blocking subsequent rain. To alleviate this, a gauge may be equipped with an automatic electric heater to keep its moisture-collecting surfaces and sensor slightly above freezing.
Rain gauges should be placed in an open area where there are no buildings, trees, or other obstacles to block the rain. This is also to prevent the water collected on the roofs of buildings or the leaves of trees from dripping into the rain gauge after a rain, resulting in inaccurate readings.
Types of rain gauges include graduated cylinders, weighing gauges, tipping bucket gauges, and simply buried pit collectors. Each type has its advantages and disadvantages while collecting rain data.
The standard United States National Weather Service rain gauge, developed at the start of the 20th century, consists of an 8 in (200 mm) funnel emptying into a graduated cylinder, 2.525 in (64.1 mm) in diameter, which fits inside a larger container that is 8 in (200 mm) in diameter and 20 in (510 mm) tall. If the rainwater overflows the graduated inner cylinder, then the larger outer container will catch it. When measurements are taken, then the height of the water in the small graduated cylinder is measured, and the excess overflow in the large container is carefully poured into another graduated cylinder and measured to give the total rainfall. A cone meter is sometimes used to prevent leakage that can result in alteration of the data. In locations using the metric system, the cylinder is usually marked in mm and will measure up to 250 mm (9.8 in) of rainfall. Each horizontal line on the cylinder is 0.5 mm (0.02 in). In areas using Imperial units, each horizontal line represents 0.01 in (0.25 mm) inches.
The pluviometer of intensities (or Jardi's pluviometer) is a tool that measures the average intensity of rainfall in a certain interval of time. It was initially designed to record the rainfall regime in Catalonia but eventually spread throughout the world. [16]
It employs the principle of feedback ... the incoming water pushes the buoy upwards, making the lower "adjusting conic needle" to let pass the same amount of water that enters into the container, this way ... the needle records on the drum the amount of water flowing through it at every moment—in mm of rainfall per square meter.
It consists of a rotating drum that rotates at constant speed, this drum drags a graduated sheet of cardboard, which has the time at the abscissa while the y-axis indicates the height of rainfall in mm of rain. This height is recorded with a pen that moves vertically, driven by a buoy, marking on the paper the rainfall over time. Each cardboard sheet is usually used for one day.
As the rain falls, the water collected by the funnel falls into the container and raises the buoy that makes the pen arm rise in the vertical axis, marking the cardboard accordingly. If the rainfall does not vary, the water level in the container remains constant, and while the drum rotates, the pen's mark is more or less a horizontal line, proportional to the amount of water that has fallen. When the pen reaches the top edge of the recording paper, it means that the buoy is "up high in the tank" leaving the tip of the conical needle in a way that uncovers the regulating hole, i.e., the maximum flow that the apparatus is able to record. If the rain suddenly decreases, making the container (as it empties) quickly lower the buoy, that movement corresponds to a steep slope line that can reach the bottom of the recorded cardboard if it stops raining.
The rain gauge of intensities allowed precipitation to be recorded over many years, particularly in Barcelona (95 years), apart from many other places around the world, such as Hong Kong. [16] [17]
A weighing-type precipitation gauge consists of a storage bin, which is weighed to record the mass. Certain models measure the mass using a pen on a rotating drum, or by using a vibrating wire attached to a data logger. [8] The advantages of this type of gauge over tipping buckets are that it does not underestimate intense rain, and it can measure other forms of precipitation, including rain, hail, and snow. These gauges are, however, more expensive and require more maintenance than tipping bucket gauges.
The weighing-type recording gauge may also contain a device to measure the number of chemicals contained in the location's atmosphere. This is extremely helpful for scientists studying the effects of greenhouse gases released into the atmosphere and their effects on the levels of the acid rain. Some Automated Surface Observing System (ASOS) units use an automated weighing gauge called the AWPAG (All Weather Precipitation Accumulation Gauge).
The tipping bucket rain gauge consists of a funnel that collects and channels the precipitation into a small seesaw-like container. After a pre-set amount of precipitation falls, the lever tips, dumping the collected water and sending an electrical signal. An old-style recording device may consist of a pen mounted on an arm attached to a geared wheel that moves once with each signal sent from the collector. In this design, as the wheel turns the pen arm moves either up or down leaving a trace on the graph and at the same time making a loud "click".
The tipping bucket rain gauge is not as accurate as the standard rain gauge, because the rainfall may stop before the lever has tipped. When the next period of rain begins it may take no more than one or two drops to tip the lever. This would then indicate that a pre-set amount has fallen when only a fraction of that amount has actually fallen. Tipping buckets also tend to underestimate the amount of rainfall, particularly in snowfall and heavy rainfall events. [18] [19] The advantage of the tipping bucket rain gauge is that the character of the rain (light, medium, or heavy) may be easily obtained. Rainfall character is decided by the total amount of rain that has fallen in a set period (usually 1 hour) by counting the number of pulses during that period. Algorithms may be applied to the data as a method of correcting the data for high-intensity rainfall.
Modern tipping rain gauges consist of a plastic collector balanced over a pivot. When it tips, it actuates a switch (such as a reed switch) which is then electronically recorded or transmitted to a remote collection station.
Tipping gauges can also incorporate elements of weighing gauges whereby a strain gauge is fixed to the collection bucket so that the exact rainfall can be read at any moment. Each time the collector tips, the strain gauge (weight sensor) is re-zeroed to null out any drift.
To measure the water equivalent of frozen precipitation, a tipping bucket may be heated to melt any ice and snow that is caught in its funnel. Without a heating mechanism, the funnel often becomes clogged during a frozen precipitation event, and thus no precipitation can be measured. Many Automated Surface Observing System (ASOS) units use heated tipping buckets to measure precipitation. [20]
This type of gauge has a row of collection funnels. In an enclosed space below each is a laser diode and a photo transistor detector. When enough water is collected to make a single drop, it drops from the bottom, falling into the laser beam path. The sensor is set at right angles to the laser so that enough light is scattered to be detected as a sudden flash of lights. The flashes from these photodetectors are then read and transmitted or recorded. Different type of optical range gauges have been used throughout the decades. The technology has also improved.
Acoustic disdrometers, also referred to as hydrophones, are able to sense the sound signatures for each drop size as rain strikes a water surface within the gauge. Since each sound signature is unique, it is possible to invert the underwater sound field to estimate the drop-size distribution within the rain. Selected moments of the drop-size distribution yield rainfall rate, rainfall accumulation, and other rainfall properties. [21]
A weather station is a facility, either on land or sea, with instruments and equipment for measuring atmospheric conditions to provide information for weather forecasts and to study the weather and climate. The measurements taken include temperature, atmospheric pressure, humidity, wind speed, wind direction, and precipitation amounts. Wind measurements are taken with as few other obstructions as possible, while temperature and humidity measurements are kept free from direct solar radiation, or insolation. Manual observations are taken at least once daily, while automated measurements are taken at least once an hour. Weather conditions out at sea are taken by ships and buoys, which measure slightly different meteorological quantities such as sea surface temperature (SST), wave height, and wave period. Drifting weather buoys outnumber their moored versions by a significant amount.
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and "precipitates" or falls. Thus, fog and mist are not precipitation but colloids, because the water vapor does not condense sufficiently to precipitate. Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called showers.
Sea surface temperature (SST), or ocean surface temperature, is the ocean temperature close to the surface. The exact meaning of surface varies in the literature and in practice. It is usually between 1 millimetre (0.04 in) and 20 metres (70 ft) below the sea surface. Sea surface temperatures greatly modify air masses in the Earth's atmosphere within a short distance of the shore. Local areas of heavy snow can form in bands downwind of warm water bodies within an otherwise cold air mass. Warm sea surface temperatures can develop and strengthen cyclones over the Ocean. Experts call this process tropical cyclogenesis. Tropical cyclones can also cause a cool wake. This is due to turbulent mixing of the upper 30 metres (100 ft) of the ocean. Sea surface temperature changes during the day. This is like the air above it, but to a lesser degree. There is less variation in sea surface temperature on breezy days than on calm days. Ocean currents, such as the Atlantic Multidecadal Oscillation, can affect sea surface temperatures over several decades. Thermohaline circulation has a major impact on average sea surface temperature throughout most of the world's oceans.
A snow gauge is a type of instrument used by meteorologists and hydrologists to gather and measure the amount of solid precipitation over a set period of time.
A lysimeter are cylindrical containers filled with soil, which can be used to study the transport of water and material through the soil. Lysimeters can be equipped with different measuring probes at different depth. The soil contained in the lysimeter can either be collected as a monolith or be reconstructed from the different layers present at the sampling site. Most lysimeters contain an opening at the bottom allowing the leachate to be collected and analyzed over time.
In hydrology, stemflow is the flow of intercepted water down the trunk or stem of a plant. Stemflow, along with throughfall, is responsible for the transferral of precipitation and nutrients from the canopy to the soil. In tropical rainforests, where this kind of flow can be substantial, erosion gullies can form at the base of the trunk. However, in more temperate climates stemflow levels are low and have little erosional power.
The Tropical Rainfall Measuring Mission (TRMM) was a joint space mission between NASA and JAXA designed to monitor and study tropical rainfall. The term refers to both the mission itself and the satellite that the mission used to collect data. TRMM was part of NASA's Mission to Planet Earth, a long-term, coordinated research effort to study the Earth as a global system. The satellite was launched on 27 November 1997 from the Tanegashima Space Center in Tanegashima, Japan. TRMM operated for 17 years, including several mission extensions, before being decommissioned on 15 April 2015. TRMM re-entered Earth's atmosphere on 16 June 2015.
Pan evaporation is a measurement that combines or integrates the effects of several climate elements: temperature, humidity, rain fall, drought dispersion, solar radiation, and wind. Evaporation is greatest on hot, windy, dry, sunny days; and is greatly reduced when clouds block the sun and when air is cool, calm, and humid. Pan evaporation measurements enable farmers and ranchers to understand how much water their crops will need.
Meteorological instruments, including meteorological sensors, are the equipment used to find the state of the atmosphere at a given time. Each science has its own unique sets of laboratory equipment. Meteorology, however, is a science which does not use much laboratory equipment but relies more on on-site observation and remote sensing equipment. In science, an observation, or observable, is an abstract idea that can be measured and for which data can be taken. Rain was one of the first quantities to be measured historically. Two other accurately measured weather-related variables are wind and humidity. Many attempts had been made prior to the 15th century to construct adequate equipment to measure atmospheric variables.
The quantitative precipitation forecast is the expected amount of melted precipitation accumulated over a specified time period over a specified area. A QPF will be created when precipitation amounts reaching a minimum threshold are expected during the forecast's valid period. Valid periods of precipitation forecasts are normally synoptic hours such as 00:00, 06:00, 12:00 and 18:00 GMT. Terrain is considered in QPFs by use of topography or based upon climatological precipitation patterns from observations with fine detail. Starting in the mid-to-late 1990s, QPFs were used within hydrologic forecast models to simulate impact to rivers throughout the United States. Forecast models show significant sensitivity to humidity levels within the planetary boundary layer, or in the lowest levels of the atmosphere, which decreases with height. QPF can be generated on a quantitative, forecasting amounts, or a qualitative, forecasting the probability of a specific amount, basis. Radar imagery forecasting techniques show higher skill than model forecasts within 6 to 7 hours of the time of the radar image. The forecasts can be verified through use of rain gauge measurements, weather radar estimates, or a combination of both. Various skill scores can be determined to measure the value of the rainfall forecast.
Airport weather stations are automated sensor suites which are designed to serve aviation and meteorological operations, weather forecasting and climatology. Automated airport weather stations have become part of the backbone of weather observing in the United States and Canada and are becoming increasingly more prevalent worldwide due to their efficiency and cost-savings.
Richard Towneley was an English mathematician, natural philosopher and astronomer, resident at Towneley Hall, near Burnley in Lancashire. His uncle was the antiquarian and mathematician Christopher Towneley (1604–1674).
The following outline is provided as an overview of and topical guide to the field of Meteorology.
Surface weather observations are the fundamental data used for safety as well as climatological reasons to forecast weather and issue warnings worldwide. They can be taken manually, by a weather observer, by computer through the use of automated weather stations, or in a hybrid scheme using weather observers to augment the otherwise automated weather station. The ICAO defines the International Standard Atmosphere (ISA), which is the model of the standard variation of pressure, temperature, density, and viscosity with altitude in the Earth's atmosphere, and is used to reduce a station pressure to sea level pressure. Airport observations can be transmitted worldwide through the use of the METAR observing code. Personal weather stations taking automated observations can transmit their data to the United States mesonet through the Citizen Weather Observer Program (CWOP), the UK Met Office through their Weather Observations Website (WOW), or internationally through the Weather Underground Internet site. A thirty-year average of a location's weather observations is traditionally used to determine the station's climate. In the US a network of Cooperative Observers make a daily record of summary weather and sometimes water level information.
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water for hydroelectric power plants, crop irrigation, and suitable conditions for many types of ecosystems.
The Prediction and Research Moored Array in the Atlantic (PIRATA) is a system of moored observation buoys in the tropical Atlantic Ocean which collect meteorological and oceanographic data. The data collected by the PIRATA array helps scientists to better understand climatic events in the Tropical Atlantic and to improve weather forecasting and climate research worldwide. Climatic and oceanic events in the tropical Atlantic, such as the Tropical Atlantic SST Dipole affect rainfall and climate in both West Africa and Northeast Brazil. The northern tropical Atlantic is also a major formation area for hurricanes affecting the West Indies and the United States. Alongside the RAMA array in the Indian Ocean and the TAO/TRITON network in the Pacific Ocean, PIRATA forms part of the worldwide system of tropical ocean observing buoys.
Ramon Jardí i Borras was a Catalan meteorologist, astronomer and seismologist. He participated in the foundation of the Meteorological Service of Catalonia (1921–1939). He was member of the Academy of Sciences and Arts (1914), professor of electricity at Industrial School University (1917), professor at the University of Barcelona (1930–1951) and a member of the Institut d'Estudis Catalans (1926–1931).
Snow science addresses how snow forms, its distribution, and processes affecting how snowpacks change over time. Scientists improve storm forecasting, study global snow cover and its effect on climate, glaciers, and water supplies around the world. The study includes physical properties of the material as it changes, bulk properties of in-place snow packs, and the aggregate properties of regions with snow cover. In doing so, they employ on-the-ground physical measurement techniques to establish ground truth and remote sensing techniques to develop understanding of snow-related processes over large areas.
Tianchi basins were meteorological measuring instruments used to gather and measure the amount of liquid precipitation over a period of time during the Song Dynasty. The instrument was devised by the Song Chinese mathematician and inventor Qin Jiushao in 1247.
In meteorology, a trace denotes an amount of precipitation, such as rain or snow, that is greater than zero, but is too small to be measured by standard units or methods of measurement. The designation of a trace rather than zero is used to indicate that precipitation did fall, but not enough to be measured reliably. This is important for both weather forecasting and climatological purposes, because even precipitation amounts too small to be measured can have significant societal impacts.
