In fluid dynamics, the baroclinity (often called baroclinicity) of a stratified fluid is a measure of how misaligned the gradient of pressure is from the gradient of density in a fluid. In meteorology a baroclinic atmosphere is one for which the density depends on both the temperature and the pressure; contrast this with a barotropic atmosphere, for which the density depends only on the pressure. In atmospheric terms, the barotropic zones of the Earth are generally found in the central latitudes, or tropics, whereas the baroclinic areas are generally found in the mid-latitude/polar regions.
Baroclinity is proportional to:
which is proportional to the sine of the angle between surfaces of constant pressure and surfaces of constant density. Thus, in a barotropic fluid (which is defined by zero baroclinity), these surfaces are parallel.
Baroclinic instability is a fluid dynamical instability of fundamental importance in the atmosphere and in the oceans. In the atmosphere it is the dominant mechanism shaping the cyclones and anticyclones that dominate weather in mid-latitudes. In the ocean it generates a field of mesoscale (100 km or smaller) eddies that play various roles in oceanic dynamics and the transport of tracers. Baroclinic instability is a concept relevant to rapidly rotating, strongly stratified fluids.
Whether a fluid counts as rapidly rotating is determined in this context by the Rossby number, which is a measure of how close the flow is to solid body rotation. More precisely, a flow in solid body rotation has vorticity that is proportional to its angular velocity. The Rossby number is a measure of the departure of the vorticity from that of solid body rotation. The Rossby number must be small for the concept of baroclinic instability to be relevant. When the Rossby number is large, other kinds of instabilities, often referred to as inertial, become more relevant.
The simplest example of a stably stratified flow is an incompressible flow with density decreasing with height.
In a compressible gas such as the atmosphere, the relevant measure is the vertical gradient of the entropy, which must increase with height for the flow to be stably stratified.
The strength of the stratification is measured by asking how large the vertical shear of the horizontal winds has to be in order to destabilize the flow and produce the classic Kelvin–Helmholtz instability. This measure is called the Richardson number. When the Richardson number is large, the stratification is strong enough to prevent this shear instability.
Before the classic work of Jule Charney and Eric Eady on baroclinic instability in the late 1940s, most theories trying to explain the structure of mid-latitude eddies took as their starting points the high Rossby number or small Richardson number instabilities familiar to fluid dynamicists at that time. The most important feature of baroclinic instability is that it exists even in the situation of rapid rotation (small Rossby number) and strong stable stratification (large Richardson's number) typically observed in the atmosphere.
The energy source for baroclinic instability is the potential energy in the environmental flow. As the instability grows, the center of mass of the fluid is lowered. In growing waves in the atmosphere, cold air moving downwards and equatorwards displaces the warmer air moving polewards and upwards.
Baroclinic instability can be investigated in the laboratory using a rotating, fluid filled annulus. The annulus is heated at the outer wall and cooled at the inner wall, and the resulting fluid flows give rise to baroclinically unstable waves.
The term "baroclinic" refers to the mechanism by which vorticity is generated. Vorticity is the curl of the velocity field. In general, the evolution of vorticity can be broken into contributions from advection (as vortex tubes move with the flow), stretching and twisting (as vortex tubes are pulled or twisted by the flow) and baroclinic vorticity generation, which occurs whenever there is a density gradient along surfaces of constant pressure. Baroclinic flows can be contrasted with barotropic flows in which density and pressure surfaces coincide and there is no baroclinic generation of vorticity.
The study of the evolution of these baroclinic instabilities as they grow and then decay is a crucial part of developing theories for the fundamental characteristics of midlatitude weather.
Beginning with the equation of motion for a frictionless fluid (the Euler equations) and taking the curl, one arrives at the equation of motion for the curl of the fluid velocity, that is to say, the vorticity.
In a fluid that is not all of the same density, a source term appears in the vorticity equation whenever surfaces of constant density (isopycnic surfaces) and surfaces of constant pressure (isobaric surfaces) are not aligned. The material derivative of the local vorticity is given by:
This vector, sometimes called the solenoidal vector, is of interest both in compressible fluids and in incompressible (but inhomogeneous) fluids. Internal gravity waves as well as unstable Rayleigh–Taylor modes can be analyzed from the perspective of the baroclinic vector. It is also of interest in the creation of vorticity by the passage of shocks through inhomogeneous media, such as in the Richtmyer–Meshkov instability.
Experienced divers are familiar with the very slow waves that can be excited at a thermocline or a halocline, which are known as internal waves. Similar waves can be generated between a layer of water and a layer of oil. When the interface between these two surfaces is not horizontal and the system is close to hydrostatic equilibrium, the gradient of the pressure is vertical but the gradient of the density is not. Therefore the baroclinic vector is nonzero, and the sense of the baroclinic vector is to create vorticity to make the interface level out. In the process, the interface overshoots, and the result is an oscillation which is an internal gravity wave. Unlike surface gravity waves, internal gravity waves do not require a sharp interface. For example, in bodies of water, a gradual gradient in temperature or salinity is sufficient to support internal gravity waves driven by the baroclinic vector.
The 1932 Atlantic hurricane season was the period during 1932 in which tropical cyclones formed in the Atlantic Basin. It was a relatively active season, with fifteen known storms, six hurricanes, and four major hurricanes. Two storms attained Category 5 intensity, the first known occurrence in which multiple Category 5 hurricanes formed in the same year. The season began with the formation of Tropical Storm One on May 5, and ended with the dissipation of Hurricane Fourteen, also known as the 1932 Cuba hurricane, on November 14. Tropical cyclones that did not approach populated areas or shipping lanes, especially if they were relatively weak and of short duration, may have remained undetected. Because technologies such as satellite monitoring were not available until the 1960s, historical data on tropical cyclones from this period are often not reliable. The Atlantic hurricane reanalysis project discovered four new tropical cyclones, all of which were tropical storms, that occurred during the year. These storms were later added to the HURDAT database.In total, the season resulted in at least 3,384 fatalities and at least $77.706 million in damages. A strong hurricane struck Freeport, Texas in mid–August, severely affecting a large swath of the coast. A Category 5 hurricane, the first of the season, devastated areas of The Bahamas, especially the Abaco Islands. Another strong Category 4 hurricane struck Puerto Rico in late September, leaving catastrophic damage and causing $30 million in damages. A second Category 5 hurricane in early November became one of the deadliest hurricanes of the 20th century after making landfall on Cuba and killing at least 3,103 people. A hurricane and four other tropical storms made landfalls during the season.1966 Atlantic hurricane season
The 1966 Atlantic hurricane season featured the tropical cyclone with the longest track in the Atlantic basin – Hurricane Faith. Also during the year, the Miami, Florida Weather Office was re-designated the National Hurricane Center. The season officially began on June 1, and lasted until November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. It was a near average season in terms of tropical storms, with a total of 11 named storms. The first system, Hurricane Alma, developed over eastern Nicaragua on June 4. Alma brought severe flooding to Honduras and later to Cuba, after crossing the western Caribbean Sea. The storm also brought relatively minor impact to the Southeastern United States. Alma caused 91 deaths and about $210.1 million (1966 USD) in damage.
Hurricanes Becky, Celia, and Dorothy, and Tropical Storm Ella all resulted in minimal or no impact on land. The next system, Hurricane Faith, developed near Cape Verde on August 21. It tracked westward across the Atlantic Ocean until north of Hispaniola. After paralleling the East Coast of the United States, Faith moved northeastward across the open Atlantic and later became extratropical near Scotland on September 6. Overall, Faith traveled about 6,850 mi (11,020 km) across the Atlantic. Although it never made landfall, the storm generated rough seas that resulted in five deaths. The two next tropical storms – Greta and Hallie – caused negligible impact.
The strongest tropical cyclone of the season was Hurricane Inez, a powerful Category 4 hurricane that devastated a large majority of the Caribbean, the Florida Keys, and parts of Mexico. Throughout its path, the storm caused about $226.5 million in damage and more than 1,000 deaths. Tropical Storm Judith left only minor impacts in the Windward Islands. The final system, Hurricane Lois, developed east of Bermuda on November 4. Later in its duration, Lois passed west of the Azores, bringing gale-force winds to Corvo Island. The storm became extratropical northeast of the islands on November 11. A possible tropical cyclone in June and July and another in July brought minor damage to Florida and Louisiana, respectively. Overall, the storms of this season collectively caused at least 1,096 fatalities and about $436.6 million in damage.1971 Atlantic hurricane season
The 1971 Atlantic hurricane season was fairly active with several notable storms. Hurricane Edith, the strongest of the season, was a Category 5 on the Saffir-Simpson scale, the highest category on the scale. It struck Nicaragua at peak intensity, killing dozens, and later hit southern Louisiana. Until 2003, Hurricane Ginger held the record for the longest known duration of a North Atlantic tropical cyclone, lasting 27.25 days from early September to early October; it is currently the second longest-lasting Atlantic hurricane. Ginger moved ashore in North Carolina, producing heavy rains and damaging winds. An unnamed storm in August attained hurricane status further north than any other Atlantic hurricane. Between 11 and 12 September five tropical cyclones were active at the same time, the record for the Atlantic basin.The season officially began on June 1, and lasted until November 30, 1971; these dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. With thirteen tropical storms, of which six became hurricanes, the season was active. Despite the activity, damage in the United States totaled about $235 million (1971 USD, $1.45 billion 2019 USD), which National Hurricane Center forecaster Paul Hebert noted was "pretty small considering we had five storms in a row strike the U.S." Most of the damage came from Tropical Storm Doria, which affected much of the East Coast of the United States. Hurricane Fern struck Texas after executing an unusual track, dropping heavy rainfall and producing flooding. The first storm, Arlene, developed on July 4 off the coast of North Carolina. Activity was steady through most of the season, and the last storm, Laura, dissipated on November 22.Bahama Banks
The Bahama Banks are the submerged carbonate platforms that make up much of the Bahama Archipelago. The term is usually applied in referring to either the Great Bahama Bank around Andros Island, or the Little Bahama Bank of Grand Bahama Island and Great Abaco, which are the largest of the platforms, and the Cay Sal Bank north of Cuba. The islands of these banks are politically part of the Bahamas. Other banks are the three banks of the Turks and Caicos Islands, namely the Caicos Bank of the Caicos Islands, the bank of the Turks Islands, and wholly submerged Mouchoir Bank. Further southeast are the equally wholly submerged Silver Bank and Navidad Bank north of the Dominican Republic.Carbonate platform
A carbonate platform is a sedimentary body which possesses topographic relief, and is composed of autochthonic calcareous deposits. Platform growth is mediated by sessile organisms whose skeletons build up the reef or by organisms (usually microbes) which induce carbonate precipitation through their metabolism. Therefore, carbonate platforms can not grow up everywhere: they are not present in places where limiting factors to the life of reef-building organisms exist. Such limiting factors are, among others: light, water temperature, transparency and pH-Value. For example, carbonate sedimentation along the Atlantic South American coasts takes place everywhere but at the mouth of the Amazon River, because of the intense turbidity of the water there. Spectacular examples of present-day carbonate platforms are the Bahama Banks under which the platform is roughly 8 km thick, the Yucatan Peninsula which is up to 2 km thick, the Florida platform, the platform on which the Great Barrier Reef is growing, and the Maldive atolls. All these carbonate platforms and their associated reefs are confined to tropical latitudes. Today's reefs are built mainly by scleractinian corals, but in the distant past other organisms, like archaeocyatha (during the Cambrian) or extinct cnidaria (tabulata and rugosa) were important reef builders.Glossary of meteorology
This glossary of meteorology is a list of terms and concepts relevant to meteorology and atmospheric science, their sub-disciplines, and related fields.Glossary of tornado terms
The following is a glossary of tornado terms. It includes scientific as well as selected informal terminology.Gustnado
A gustnado is a short-lived, shallow surface-based vortex which forms within the downburst emanating from a thunderstorm. The name is a portmanteau by elision of "gust front tornado", as gustnadoes form due to non-tornadic straight-line wind features in the downdraft (outflow), specifically within the gust front of strong thunderstorms. Gustnadoes tend to be noticed when the vortices loft sufficient debris or form condensation cloud to be visible although it is the wind that makes the gustnado, similarly to tornadoes. As these eddies very rarely connect from the surface to the cloud base, they are very rarely considered as tornadoes. The gustnado has little in common with tornadoes structurally or dynamically in regard to vertical development, intensity, longevity, or formative process --as classic tornadoes are associated with mesocyclones within the inflow (updraft) of the storm, not the outflow.The average gustnado lasts a few seconds to a few minutes, although there can be several generations and simultaneous swarms. Most have the winds of an EF-0 or EF-1 tornado (up to 110 mph or 177 km/h), and are commonly mistaken for tornadoes. However, unlike tornadoes, the rotating column of air in a gustnado usually does not extend all the way to the base of the thundercloud. Gustnadoes actually have more in common with (minor) whirlwinds. They are not considered true tornadoes (unless they connect the surface to the ambient cloud base) by most meteorologists and are not included in tornado statistics in most areas. Sometimes referred to as spin-up tornadoes, that term more correctly describes the rare tornadic gustnado that connects the surface to the ambient clouded base, or more commonly to the relatively brief but true tornadoes that are associated with a mesovortex.The most common setting for a gustnado is along the gust front of a severe thunderstorm (by many definitions, containing wind speeds of at least 93 km/h or 58 mph), along which horizontal shear of the wind may be large. A particularly common location is along the rear-flank gust front of supercell storms. Gustnadoes probably form owing to shear instability associated with the strong horizontal shear; a relative maximum in vertical vorticity must exist in order for shear instability to be present. The bigger question is probably what the dynamical origin(s) of the vertical vorticity is (are), such as the tilting of horizontal vorticity into the vertical or vertical vorticity in the ambient environment that preexists the storm. Along the rear-flank gust front of supercell storms, vertical vorticity very likely has its origins in the upward tilting of vorticity that can occur within descending air in the presence of baroclinity.While injuries or deaths are rare from gustnadoes, strong ones can cause damage and they are hazardous to drivers. There is some speculation that a gustnado might have been responsible for the collapse of a stage at the Indiana State Fair on August 13, 2011 which killed 7 people and injured 58.Haida Eddies
Haida Eddies are episodic, clockwise rotating ocean eddies that form during the winter off the west coast of British Columbia’s Haida Gwaii and Alaska’s Alexander Archipelago. These eddies are notable for their large size, persistence, and frequent recurrence. Rivers flowing off the North American continent supply the continental shelf in the Hecate Strait with warmer, fresher, and nutrient-enriched water. Haida eddies are formed every winter when this rapid outflow of water through the strait wraps around Cape St. James at the southern tip of Haida Gwaii, and meets with the cooler waters of the Alaska Current. This forms a series of plumes which can merge into large eddies that are shed into the northeast Pacific Ocean by late winter, and may persist for up to two years.Haida eddies can be more than 250 km in diameter, and transport a mass of coastal water approximately the volume of Lake Michigan over 1,000 km offshore into the lower nutrient waters of the northeast Pacific Ocean. These "warm-core rings" transport heat out to sea, supplying nutrients (particularly nitrate and iron) to nutrient depleted areas of lower productivity. Consequently, primary production in Haida eddies is up to three times higher than in ambient waters, supporting vast phytoplankton-based communities, as well as influencing zooplankton and icthyoplankton community compositions.The Haida name is derived from the Haida people native to the region, centered on the islands of Haida Gwaii (formerly known as the Queen Charlotte Islands).Index of meteorology articles
This is a list of meteorology topics. The terms relate to meteorology, the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting. (see also: List of meteorological phenomena)
y708Index of physics articles (B)
The index of physics articles is split into multiple pages due to its size.
To navigate by individual letter use the table of contents below.List of submarine volcanoes
A list of active and extinct submarine volcanoes and seamounts located under the world's oceans. There are estimated to be 40,000 to 55,000 seamounts in the global oceans. Almost all are not well-mapped and many may not have been identified at all. Most are unnamed and unexplored. This list is therefore confined to seamounts that are notable enough to have been named and/or explored.Meteorological history of Hurricane Mitch
Hurricane Mitch's meteorological history began with its origins over Africa as a tropical wave and lasted until its dissipation as an extratropical cyclone north of the United Kingdom. Tropical Depression Thirteen formed on October 22, 1998, over the southwestern Caribbean Sea from a tropical wave that exited Africa on October 10. It executed a small loop, and while doing so intensified into Tropical Storm Mitch. A weakness in a ridge allowed the storm to track slowly to the north. After becoming disorganized due to wind shear from a nearby upper-level low, Mitch quickly intensified in response to improving conditions which included warm waters and good outflow. It became a hurricane on October 24 and developed an eye. After turning to the west, Mitch rapidly intensified, first into a major hurricane on October 25 and then into a Category 5 on the Saffir-Simpson Hurricane Scale the next day.
At peak intensity, Mitch maintained maximum sustained winds of 180 mph (285 km/h) while off the northern coast of Honduras. Hurricane Hunters reported a minimum barometric pressure of 905 mbar (26.7 inHg), which at the time was the lowest in the month of October and tied for the fourth lowest for any Atlantic hurricane. Initially, the National Hurricane Center (NHC) and various tropical cyclone forecast models anticipated a turn to the north, threatening the Yucatán Peninsula. Instead, Mitch turned to the south due to a ridge that was not observed while the storm was active. Land interaction imparted weakening, and the hurricane made landfall on Honduras on October 29 with winds of 80 mph (130 km/h). Turning westward, Mitch slowly weakened over land and maintained deep convection over adjacent waters. After moving across mountainous terrain in Central America, the surface circulation of Mitch dissipated on November 1. The next day, the remnants reached the Gulf of Mexico and reorganized into a tropical storm on November 3. Mitch accelerated to the northeast ahead of a cold front, moving across the Yucatán Peninsula before striking southwestern Florida on November 5. Shortly thereafter, the storm became an extratropical cyclone, which was tracked by the NHC until November 9.Oceanic plateau
An oceanic or submarine plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides.There are 184 oceanic plateaus covering an area of 18,486,600 km2 (7,137,700 sq mi), or about 5.11% of the oceans. The South Pacific region around Australia and New Zealand contains the greatest number of oceanic plateaus (see map).
Oceanic plateaus produced by large igneous provinces are often associated with hotspots, mantle plumes, and volcanic islands — such as Iceland, Hawaii, Cape Verde, and Kerguelen. The three largest plateaus, the Caribbean, Ontong Java, and Mid-Pacific Mountains, are located on thermal swells. Other oceanic plateaus, however, are made of rifted continental crust, for example Falkland Plateau, Lord Howe Rise, and parts of Kerguelen, Seychelles, and Arctic ridges.
Plateaus formed by large igneous provinces were formed by the equivalent of continental flood basalts such as the Deccan Traps in India and the Snake River Plain in the United States.
In contrast to continental flood basalts, most igneous oceanic plateaus erupt through young and thin (6–7 km (3.7–4.3 mi)) mafic or ultra-mafic crust and are therefore uncontaminated by felsic crust and representative for their mantle sources.
These plateaus often rise 2–3 km (1.2–1.9 mi) above the surrounding ocean floor and are more buoyant than oceanic crust. They therefore tend to withstand subduction, more-so when thick and when reaching subduction zones shortly after their formations. As a consequence, they tend to "dock" to continental margins and be preserved as accreted terranes. Such terranes are often better preserved than the exposed parts of continental flood basalts and are therefore a better record of large-scale volcanic eruptions throughout Earth's history. This "docking" also means that oceanic plateaus are important contributors to the growth of continental crust. Their formations often had a dramatic impact on global climate, such as the most recent plateaus formed, the three, large, Cretaceous oceanic plateaus in the Pacific and Indian Ocean: Ontong Java, Kerguelen, and Caribbean.Physical oceanography
Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters.
Physical oceanography is one of several sub-domains into which oceanography is divided. Others include biological, chemical and geological oceanography.
Physical oceanography may be subdivided into descriptive and dynamical physical oceanography.Descriptive physical oceanography seeks to research the ocean through observations and complex numerical models, which describe the fluid motions as precisely as possible.
Dynamical physical oceanography focuses primarily upon the processes that govern the motion of fluids with emphasis upon theoretical research and numerical models. These are part of the large field of Geophysical Fluid Dynamics (GFD) that is shared together with meteorology. GFD is a sub field of Fluid dynamics describing flows occurring on spatial and temporal scales that are greatly influenced by the Coriolis force.Stratification (water)
Water stratification is when water masses with different properties - salinity (halocline), oxygenation (chemocline), density (pycnocline), temperature (thermocline) - form layers that act as barriers to water mixing which could lead to anoxia or euxinia. These layers are normally arranged according to density, with the least dense water masses sitting above the more dense layers.
Water stratification also creates barriers to nutrient mixing between layers. This can affect the primary production in an area by limiting photosynthetic processes. When nutrients from the benthos cannot travel up into the photic zone, phytoplankton may be limited by nutrient availability. Lower primary production also leads to lower net productivity in waters.Undersea mountain range
Undersea mountain ranges are mountain ranges that are mostly or entirely underwater, and specifically under the surface of an ocean. If originated from current tectonic forces, they are often referred to as a mid-ocean ridge. In contrast, if formed by past above-water volcanism, they are known as a seamount chain. The largest and best known undersea mountain range is a mid-ocean ridge, the Mid-Atlantic Ridge. It has been observed that, "similar to those on land, the undersea mountain ranges are the loci of frequent volcanic and earthquake activity".Wave base
The wave base, in physical oceanography, is the maximum depth at which a water wave's passage causes significant water motion. For water depths deeper than the wave base, bottom sediments and the seafloor are no longer stirred by the wave motion above.Weather
Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the lowest level of the atmosphere, the troposphere, just below the stratosphere. Weather refers to day-to-day temperature and precipitation activity, whereas climate is the term for the averaging of atmospheric conditions over longer periods of time. When used without qualification, "weather" is generally understood to mean the weather of Earth.
Weather is driven by air pressure, temperature and moisture differences between one place and another. These differences can occur due to the sun's angle at any particular spot, which varies with latitude. The strong temperature contrast between polar and tropical air gives rise to the largest scale atmospheric circulations: the Hadley Cell, the Ferrel Cell, the Polar Cell, and the jet stream. Weather systems in the mid-latitudes, such as extratropical cyclones, are caused by instabilities of the jet stream flow. Because the Earth's axis is tilted relative to its orbital plane, sunlight is incident at different angles at different times of the year. On Earth's surface, temperatures usually range ±40 °C (−40 °F to 100 °F) annually. Over thousands of years, changes in Earth's orbit can affect the amount and distribution of solar energy received by the Earth, thus influencing long-term climate and global climate change.
Surface temperature differences in turn cause pressure differences. Higher altitudes are cooler than lower altitudes, as most atmospheric heating is due to contact with the Earth's surface while radiative losses to space are mostly constant. Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. The Earth's weather system is a chaotic system; as a result, small changes to one part of the system can grow to have large effects on the system as a whole. Human attempts to control the weather have occurred throughout history, and there is evidence that human activities such as agriculture and industry have modified weather patterns.
Studying how the weather works on other planets has been helpful in understanding how weather works on Earth. A famous landmark in the Solar System, Jupiter's Great Red Spot, is an anticyclonic storm known to have existed for at least 300 years. However, weather is not limited to planetary bodies. A star's corona is constantly being lost to space, creating what is essentially a very thin atmosphere throughout the Solar System. The movement of mass ejected from the Sun is known as the solar wind.
Meteorological data and variables