Bar (unit) in the context of Siberian High

Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth; that is, the Earth's atmospheric pressure at sea level is approximately 1 atm.

In most circumstances, atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. As elevation increases, there is less overlying atmospheric mass, so atmospheric pressure decreases with increasing elevation. Because the atmosphere is thin relative to the Earth's radius—especially the dense atmospheric layer at low altitudes—the Earth's gravitational acceleration as a function of altitude can be approximated as constant and contributes little to this fall-off. Pressure measures force per unit area, with SI units of pascals (1 pascal = 1 newton per square metre, 1 N/m). On average, a column of air with a cross-sectional area of 1 square centimetre (cm), measured from the mean (average) sea level to the top of Earth's atmosphere, has a mass of about 1.03 kilogram and exerts a force or "weight" of about 10.1 newtons, resulting in a pressure of 10.1 N/cm or 101 kN/m (101 kilopascals, kPa). A column of air with a cross-sectional area of 1 in would have a weight of about 14.7 lbf, resulting in a pressure of 14.7 lbf/in.

Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than 150 to 200 °C (300 to 400 °F) and, often, elevated pressure of 100 megapascals (1,000 bar) or more, causing profound physical or chemical changes. During this process, the rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition. The protolith may be an igneous, sedimentary, or existing metamorphic rock.

Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by their protolith, their chemical and mineral makeup, and their texture. They may be formed simply by being deeply buried beneath the Earth's surface, where they are subject to high temperatures and the great pressure of the rock layers above. They can also form from tectonic processes such as continental collisions, which cause horizontal pressure, friction, and distortion. Metamorphic rock can be formed locally when rock is heated by the intrusion of hot molten rock called magma from the Earth's interior. The study of metamorphic rocks (now exposed at the Earth's surface following erosion and uplift) provides information about the temperatures and pressures that occur at great depths within the Earth's crust.

Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy for use in industry, and in the residential and commercial sectors. Solar thermal collectors are classified by the United States Energy Information Administration as low-, medium-, or high-temperature collectors. Low-temperature collectors are generally unglazed and used to heat swimming pools or to heat ventilation air. Medium-temperature collectors are also usually flat plates but are used for heating water or air for residential and commercial use.

High-temperature collectors concentrate sunlight using mirrors or lenses and are generally used for fulfilling heat requirements up to 300 °C (600 °F) / 20 bar (300 psi) pressure in industries, and for electric power production. Two categories include Concentrated Solar Thermal (CST) for fulfilling heat requirements in industries, and concentrated solar power (CSP) when the heat collected is used for electric power generation. CST and CSP are not replaceable in terms of application.

Compressed hydrogen (CH₂, CGH₂ or CGH2) is the gaseous state of the element hydrogen kept under pressure. Compressed hydrogen in hydrogen tanks at 350 bar (5,000 psi) and 700 bar (10,000 psi) is used for mobile hydrogen storage in hydrogen vehicles. It is used as a fuel gas.

Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixture and the condensation of the vapors in a still.

Distillation can operate over a wide range of pressures from 0.14 bar (e.g., ethylbenzene/styrene) to nearly 21 bar (e.g.,propylene/propane) and is capable of separating feeds with high volumetric flowrates and various components that cover a range of relative volatilities from only 1.17 (o-xylene/m-xylene) to 81.2 (water/ethylene glycol). Distillation provides a convenient and time-tested solution to separate a diversity of chemicals in a continuous manner with high purity. However, distillation has an enormous environmental footprint, resulting in the consumption of approximately 25% of all industrial energy use. The key issue is that distillation operates based on phase changes, and this separation mechanism requires vast energy inputs.

Ultra-high vacuum (often spelled ultrahigh in American English, UHV) is the vacuum regime characterised by pressure lower than about 1×10 torrs (1×10 mbar; 1×10 Pa). UHV conditions are created by pumping the gas out of a UHV chamber. At these low pressures the mean free path of a gas molecule is greater than approximately 40 km, so the gas is in free molecular flow, and gas molecules will collide with the chamber walls many times before colliding with each other. Almost all molecular interactions therefore take place on various surfaces in the chamber.

UHV conditions are integral to scientific research. Surface science experiments often require a chemically clean sample surface with the absence of any unwanted adsorbates. Surface analysis tools such as X-ray photoelectron spectroscopy and low energy ion scattering require UHV conditions for the transmission of electron or ion beams. For the same reason, beam pipes in particle accelerators such as the Large Hadron Collider are kept at UHV.

Hurricane Wilma was the most intense tropical cyclone in the Atlantic basin and the second-most intense tropical cyclone in the Western Hemisphere, both based on barometric pressure, after Hurricane Patricia in 2015. Wilma's rapid intensification led to a 24-hour pressure drop of 97 mbar (2.9 inHg), setting a new basin record. At its peak, Hurricane Wilma's eye contracted to a record minimum diameter of 2.3 mi (3.7 km). In the record-breaking 2005 Atlantic hurricane season, Wilma was the twenty-second storm, thirteenth hurricane, sixth major hurricane, and fourth Category 5 hurricane, and was the second costliest hurricane in Mexican history, behind Hurricane Otis in 2023.

Its origins came from a tropical depression that formed in the Caribbean Sea near Jamaica on October 15, headed westward, and intensified into a tropical storm two days later, which abruptly turned southward and was named Wilma. Continuing to strengthen, Wilma eventually became a hurricane on October 18. Shortly thereafter, explosive intensification occurred, and in only 24 hours, Wilma became a Category 5 hurricane with wind speeds of 185 mph (295 km/h). Wilma's intensity slowly leveled off after becoming a Category 5 hurricane, and winds had decreased to 150 mph (240 km/h) before it reached the Yucatán Peninsula on October 20 and 21. After crossing the Yucatán, Wilma emerged into the Gulf of Mexico as a Category 2 hurricane. As it began accelerating to the northeast, gradual re-intensification occurred, and the hurricane was upgraded to Category 3 status on October 24. Shortly thereafter, Wilma made landfall in Cape Romano, Florida, with winds of 120 mph (190 km/h). As Wilma was crossing Florida, it briefly weakened back to a Category 2 hurricane, but again re-intensified as it reached the Atlantic Ocean. The hurricane intensified into a Category 3 hurricane for the last time, before weakening while accelerating northeastward. By October 26, Wilma transitioned into an extratropical cyclone southeast of Nova Scotia.

In science and engineering, the study of high pressure examines its effects on materials and the design and construction of devices, such as a diamond anvil cell, which can create high pressure. High pressure usually means pressures of thousands (kilobars) or millions (megabars) of times atmospheric pressure (about 1 bar or 100 kilopascals).

An air blaster or air cannon is a de-clogging device with two main components: a pressure vessel (storing air pressure) and a triggering mechanism (high speed release of compressed air). They are permanently installed on silos, bins and hoppers for powdery materials, and are used to prevent caking and to allow maximum storage capacity. They are also used in the film and theatre industries to project simulated debris from explosions, and as surprise effects in Halloween haunts and other attractions.

Air blasters do not need any specific air supply. Available plant air is enough with a minimum of 4 bar air pressure (60 psi or 400 kPa), although 5 to 6 bar are preferred for better results (75 to 90 psi). The average air consumption is moderate, and depends on the number of firings per hour, size of the pressure vessel, and number of blasters installed. For instance, a 50-liter air blaster consumes 0.60 normal cubic metres per hour at 6 bar air pressure (90 psi or 600 kPa), with 2 firings per hour.

Pressure washing or power washing is the use of high-pressure water spray to remove loose paint, mold, grime, dust, mud, and dirt from surfaces and objects such as buildings, vehicles and concrete surfaces. The volume of a mechanical pressure washer is expressed in gallons or liters per minute, often designed into the pump and not variable. The pressure, expressed in pounds per square inch, pascals, or bar, is designed into the pump but can be varied by adjusting the unloader valve or using specialized nozzle tips. Machines that produce pressures from 750 to 30,000 psi (5 to 200 MPa) or more are available.

The terms pressure washing and power washing are used interchangeably in many scenarios, and there is some debate as to whether they are actually different processes.

A diving cylinder or diving gas cylinder is a gas cylinder used to store and transport high-pressure gas used in diving operations. This may be breathing gas used with a scuba set, in which case the cylinder may also be referred to as a scuba cylinder, scuba tank or diving tank. When used for an emergency gas supply for surface-supplied diving or scuba, it may be referred to as a bailout cylinder or bailout bottle. It may also be used for surface-supplied diving or as decompression gas. A diving cylinder may also be used to supply inflation gas for a dry suit, buoyancy compensator, decompression buoy, or lifting bag. Cylinders provide breathing gas to the diver by free-flow or through the demand valve of a diving regulator, or via the breathing loop of a diving rebreather.

Diving cylinders are usually manufactured from aluminum or steel alloys, and when used on a scuba set are normally fitted with one of two common types of scuba cylinder valve for filling and connection to the regulator. Other accessories such as manifolds, cylinder bands, protective nets and boots and carrying handles may be provided. Various configurations of harness may be used by the diver to carry a cylinder or cylinders while diving, depending on the application. Cylinders used for scuba typically have an internal volume (known as water capacity) of between 3 and 18 litres (0.11 and 0.64 cu ft) and a maximum working pressure rating from 184 to 300 bars (2,670 to 4,350 psi). Cylinders are also available in smaller sizes, such as 0.5, 1.5 and 2 litres; however these are usually used for purposes such as inflation of surface marker buoys, dry suits, and buoyancy compensators rather than breathing. Scuba divers may dive with a single cylinder, a pair of similar cylinders, or a main cylinder and a smaller "pony" cylinder, carried on the diver's back or clipped onto the harness at the side. Paired cylinders may be manifolded together or independent. In technical diving, more than two scuba cylinders may be needed to carry different gases. Larger cylinders, typically up to 50 litre capacity, are used as on-board emergency gas supply on diving bells. Large cylinders are also used for surface supply through a diver's umbilical, and may be manifolded together on a frame for transportation.

The Eoarchean (IPA: /ˌiːoʊ.ɑːrˈkiːən/ EE-oh-ar-KEE-ən; also spelled Eoarchaean) is the first era of the Archean Eon of the geologic record. It spans 431 million years, from the end of the Hadean Eon 4031 Mya to the start of the Paleoarchean Era 3600 Mya. Some estimates place the beginnings of life on Earth in this era, while others place it earlier. Evidence of archaea and cyanobacteria date to 3500 Mya, comparatively shortly after the Eoarchean. At that time, the atmosphere was without oxygen and the pressure values ranged from 10 to 100 bar (around 10 to 100 times the atmospheric pressure today).