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35-618: The " Ridiculously Resilient Ridge ", sometimes shortened to " Triple R " or " RRR ", is the nickname given to a persistent anticyclone that occurred over the far northeastern Pacific Ocean , contributing to the 2011–2017 California drought . The "Ridiculously Resilient Ridge" nickname was originally coined in December 2013 by Daniel Swain on the Weather West Blog, but has since been used widely in popular media as well as in peer-reviewed scientific literature. The Ridiculously Resilient Ridge

70-471: A positive feedback loop develops between the convective tropical cyclone and the upper level high, the two systems are strengthened. This loop stops once ocean temperatures cool to below 26.5 °C (79.7 °F), reducing the thunderstorm activity, which then weakens the upper-level high-pressure system. When the subtropical ridge in the Northwest Pacific is stronger than in other areas, it leads to

105-597: A tripoint . Various examples are found in the list below. A number of major cities, such as Chongqing , St. Louis , and Khartoum , arose at confluences; further examples appear in the list. Within a city, a confluence often forms a visually prominent point, so that confluences are sometimes chosen as the site of prominent public buildings or monuments, as in Koblenz , Lyon , and Winnipeg . Cities also often build parks at confluences, sometimes as projects of municipal improvement, as at Portland and Pittsburgh . In other cases,

140-621: A buildup of particulates in urban areas under the high pressure, leading to widespread haze . If the surface level relative humidity rises towards 100 percent overnight, fog can form. The movement of continental arctic air masses to lower latitudes produces strong but vertically shallow high-pressure systems. These systems affect their pressure. The surface level, sharp temperature inversion can lead to areas of persistent stratocumulus or stratus cloud , colloquially known as anticyclonic gloom. The type of weather brought about by an anticyclone depends on its origin. For example, extensions of

175-414: A confluence can be divided into six distinct features which are commonly called confluence flow zones (CFZ). These include The broader field of engineering encompasses a vast assortment of subjects which concern confluences. In hydraulic civil engineering , where two or more underground culverted / artificially buried watercourses intersect, great attention should be paid to the hydrodynamic aspects of

210-619: A confluence is an industrial site, as in Philadelphia or Mannheim . Often a confluence lies in the shared floodplain of the two rivers and nothing is built on it, for example at Manaus , described below. One other way that confluences may be exploited by humans is as sacred places in religions . Rogers suggests that for the ancient peoples of the Iron Age in northwest Europe, watery locations were often sacred, especially sources and confluences. Pre-Christian Slavic peoples chose confluences as

245-482: A corresponding shift in habitat characteristics." Another science relevant to the study of confluences is chemistry , because sometimes the mixing of the waters of two streams triggers a chemical reaction, particularly in a polluted stream. The United States Geological Survey gives an example: "chemical changes occur when a stream contaminated with acid mine drainage combines with a stream with near-neutral pH water; these reactions happen very rapidly and influence

280-545: A larger river ( main stem ); or where two streams meet to become the source of a river of a new name (such as the confluence of the Monongahela and Allegheny rivers, forming the Ohio River ); or where two separated channels of a river (forming a river island ) rejoin at the downstream end. The point of confluence where the channel flows into a larger body of water may be called the river mouth . Confluences are studied in

315-443: A variety of sciences. Hydrology studies the characteristic flow patterns of confluences and how they give rise to patterns of erosion, bars, and scour pools. The water flows and their consequences are often studied with mathematical models . Confluences are relevant to the distribution of living organisms (i.e., ecology ) as well; "the general pattern [downstream of confluences] of increasing stream flow and decreasing slopes drives

350-516: A wet monsoon season for Asia . The subtropical ridge position is linked to how far northward monsoon moisture and thunderstorms extend into the United States . Typically, the subtropical ridge across North America migrates far enough northward to begin monsoon conditions across the Desert Southwest from July to September. When the subtropical ridge is farther north than normal towards

385-416: Is a significant problem in large urban centers during summer months such as Los Angeles, California and Mexico City . The existence of upper-level (altitude) high pressure allows upper level divergence which leads to surface convergence . If a capping mid-level ridge does not exist, this leads to free convection and the development of showers and thunderstorms if the lower atmosphere is humid. Because

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420-625: Is evidence that the occurrence of persistent North Pacific geopotential height anomalies and anomalously dry California winters, will increase due to global warming, although uncertainty remains regarding the magnitude of these future changes. Anticyclone Mid-tropospheric systems, such as the subtropical ridge , deflect tropical cyclones around their periphery and cause a temperature inversion inhibiting free convection near their center, building up surface-based haze under their base. Anticyclones aloft can form within warm-core lows such as tropical cyclones , due to descending cool air from

455-468: Is sometimes referred to as cum sole . Subtropical high-pressure zones form under the descending portion of the Hadley cell circulation. Upper-level high-pressure areas lie over tropical cyclones due to their warm core nature. Surface anticyclones form due to downward motion through the troposphere, the atmospheric layer where weather occurs. Preferred areas within a synoptic flow pattern in higher levels of

490-469: Is the case of other storms that include Anne's Spot on Saturn and the Great Dark Spot on Neptune . Anticyclones had also been detected near the poles of Venus . Confluence In geography , a confluence (also: conflux ) occurs where two or more watercourses join to form a single channel . A confluence can occur in several configurations: at the point where a tributary joins

525-735: Is used to describe the meeting of tidal or other non-riverine bodies of water, such as two canals or a canal and a lake. A one-mile (1.6 km) portion of the Industrial Canal in New Orleans accommodates the Gulf Intracoastal Waterway and the Mississippi River-Gulf Outlet Canal ; therefore those three waterways are confluent there. The term confluence can also apply to the process of merging or flowing together of other substance. For example, it may refer to

560-678: The Four Corners , thunderstorms of the New Mexican Monsoon can spread northward into Arizona and New Mexico . When suppressed to the south, the atmosphere dries out across the Desert Southwest, causing a break in the monsoon regime. On weather maps, high-pressure centers are associated with the letter H in English, within the isobar with the highest pressure value. On constant-pressure upper-level charts, anticyclones are located within

595-682: The monsoon trough or Intertropical Convergence Zone . The divergence over the near-equatorial trough leads to air rising and moving away from the equator and to the poles aloft. As air moves towards the mid-latitudes, it cools and sinks leading to subsidence near the 30° parallel of both hemispheres. This circulation known as the Hadley cell forms the subtropical ridge. Many of the world's deserts are caused by these climatological high-pressure areas . Because these anticyclones strengthen with height, they are known as warm core ridges. The development of anticyclones aloft occurs in warm core cyclones such as tropical cyclones when latent heat caused by

630-461: The Azores high pressure may bring about anticyclonic gloom during the winter because they pick up moisture as they move over the warmer oceans. High pressures that build to the north and move southwards often bring clear weather because they are cooled at the base (as opposed to warmed) which helps prevent clouds from forming. Once arctic air moves over an unfrozen ocean, the air mass modifies greatly over

665-571: The North Pacific storm track during the winters of 2012–13, 2013–14, and 2014–15, resulting in extremely dry and warm conditions in California and along much of the West Coast. The Ridge comprised the western half of a well-defined atmospheric ridge-trough sequence associated with an unusually amplified "North American winter dipole" pattern, which brought persistent anomalous cold and precipitation to

700-436: The air subsidence at their center, act to steer tropical cyclones around and out their periphery. Due to the subsidence within this type of system, a cap can develop which inhibits free convection and hence mixing of the lower with the middle level troposphere. This limits thunderstorms and other low-pressure weather activity near their centers and traps low-level pollutants such as ozone as haze under their base, which

735-469: The backside of upper troughs such as polar highs , or from large-scale sinking such as a subtropical ridge . The evolution of an anticyclone depends upon variables such as its size, intensity, and extent of moist convection , as well as the Coriolis force . Sir Francis Galton first discovered anticyclones in the 1860s. High-pressure systems are alternatively referred to as anticyclones. Their circulation

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770-431: The day, there is more incoming solar radiation and heating so temperatures rise rapidly near the surface. At night, the absence of clouds means that outgoing longwave radiation (i.e. heat energy from the surface) is not blocked, allowing the escape of heat and giving cooler diurnal low temperatures in all seasons. When surface winds become light, the subsidence produced directly under a high-pressure system can lead to

805-522: The eastern half of North America in addition to record-breaking warmth and drought conditions in California. This ridge of high pressure was also associated with a blob of high water temperatures in the Pacific Ocean, which resulted in substantial warming along the western coast of North America as well as adverse ecological impacts. However, it is generally thought that " The Blob " of warm ocean water

840-587: The form of structural bracing. The velocities and hydraulic efficiencies should be meticulously calculated and can be altered by integrating different combinations of geometries, components such a gradients, cascades and an adequate junction angle which is sympathetic to the direction of the watercourse’s flow to minimise turbulent flow, maximise evacuation velocity and to ultimately maximise hydraulic efficiency. Since rivers often serve as political boundaries, confluences sometimes demarcate three abutting political entities, such as nations, states, or provinces, forming

875-413: The formation of clouds is released aloft increasing the air temperature; the resultant thickness of the atmospheric layer increases high pressure aloft which evacuates their outflow. In the absence of rotation, the wind tends to blow from areas of high pressure to areas of low pressure . The stronger the pressure difference (pressure gradient) between a high-pressure system and a low-pressure system,

910-455: The highest height line contour. On Jupiter , there are two examples of an extraterrestrial anticyclonic storm; the Great Red Spot and the recently formed Oval BA on Jupiter. They are powered by smaller storms merging unlike any typical anticyclonic storm that happens on Earth where water powers them. Another theory is that warmer gases rise in a column of cold air, creating a vortex as

945-448: The sites for fortified triangular temples, where they practiced human sacrifice and other sacred rites. In Hinduism , the confluence of two sacred rivers often is a pilgrimage site for ritual bathing. In Pittsburgh, a number of adherents to Mayanism consider their city's confluence to be sacred. Mississippi basin Atlantic watersheds Pacific watersheds Occasionally, "confluence"

980-424: The stronger the wind. The coriolis force caused by Earth 's rotation gives winds within high-pressure systems their clockwise circulation in the northern hemisphere (as the wind moves outward and is deflected right from the center of high pressure) and anticlockwise circulation in the southern hemisphere (as the wind moves outward and is deflected left from the center of high pressure). Friction with land slows down

1015-613: The subsequent transport of metals downstream of the mixing zone." A natural phenomenon at confluences that is obvious even to casual observers is a difference in color between the two streams; see images in this article for several examples. According to Lynch, "the color of each river is determined by many things: type and amount of vegetation in the watershed, geological properties, dissolved chemicals, sediments and biologic content – usually algae ." Lynch also notes that color differences can persist for miles downstream before they finally blend completely. Hydrodynamic behaviour of flow in

1050-401: The system to ensure the longevity and efficiency of the structure. Engineers have to design these systems whilst considering a list of factors that ensure the discharge point is structurally stable as the entrance of the lateral culvert into the main structure may compromise the stability of the structure due to the lack of support at the discharge, this often constitutes additional supports in

1085-448: The troposphere are beneath the western side of troughs. On weather maps, these areas show converging winds (isotachs), also known as confluence , or converging height lines near or above the level of non-divergence, which is near the 500 hPa pressure surface about midway up the troposphere. Because they weaken with height, these high-pressure systems are cold. Heating of the earth near the equator forces upward motion and convection along

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1120-416: The warmer water and takes on the character of a maritime air mass, which reduces the strength of the high-pressure system. When extremely cold air moves over relatively warm oceans, polar lows can develop. However, warm and moist (or maritime tropical) air masses which move poleward from tropical sources are slower to modify than arctic air masses. The circulation around mid-level (altitude) ridges, and

1155-470: The wind flowing out of high-pressure systems and causes wind to flow more outward (more ageostrophically ) from the center. High-pressure systems are frequently associated with light winds at the surface and subsidence of air from higher portions of the troposphere . Subsidence will generally warm an air mass by adiabatic (compressional) heating. Thus, high pressure typically brings clear skies. Because no clouds are present to reflect sunlight during

1190-506: Was caused by the persistence of the ridge and subsequent reduction in vertical ocean mixing due to storms, rather than the reverse. On the other hand, recent research suggests that unusual oceanic warmth in the western tropical Pacific Ocean may have played a role in triggering and maintaining the Triple R over successive seasons. High amplitude atmospheric ridge patterns similar to the Triple R have occurred more frequently in recent decades and there

1225-600: Was characterized by a broad region of anomalously positive geopotential height on monthly to annual timescales. This persistent high pressure system acted to " block " the prevailing mid-latitude westerlies , shifting the storm track northward and suppressing extratropical cyclone (winter storm) activity along the West Coast of the United States. Such a pattern is similar to—but of greater magnitude and longevity than—atmospheric configurations noted during previous California droughts. This anomalous atmospheric feature disrupted

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