Madden–Julian oscillation

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A Hovmoller diagram of the 5-day running mean of outgoing longwave radiation showing the MJO. Time increases from top to bottom in the figure, so contours that are oriented from upper-left to lower-right represent movement from west to east. MJO 5-day running mean through 1 Oct 2006.png
A Hovmöller diagram of the 5-day running mean of outgoing longwave radiation showing the MJO. Time increases from top to bottom in the figure, so contours that are oriented from upper-left to lower-right represent movement from west to east.

The Madden–Julian oscillation (MJO) is the largest element of the intraseasonal (30- to 90-day) variability in the tropical atmosphere. It was discovered in 1971 by Roland Madden and Paul Julian of the American National Center for Atmospheric Research (NCAR). It is a large-scale coupling between atmospheric circulation and tropical deep atmospheric convection. [1] [2] Unlike a standing pattern like the El Niño–Southern Oscillation (ENSO), the Madden–Julian oscillation is a traveling pattern that propagates eastward at approximately 4 to 8 m/s (14 to 29 km/h, 9 to 18 mph), through the atmosphere above the warm parts of the Indian and Pacific oceans. This overall circulation pattern manifests itself most clearly as anomalous rainfall.

Paul Rowland Julian, a Fellow of the American Meteorological Society, is an American meteorologist who served as a longtime staff scientist at the National Center for Atmospheric Research (NCAR), was co-author with Roland Madden of the study establishing the Madden–Julian oscillation (MJO), and contributed to the international, multi-institutional Global Atmospheric Research Program (GARP), Tropical Wind, Energy Conversion, and Reference Level Experiment (TWERLE), and Tropical Ocean-Global Atmosphere (TOGA) meteorology research programs. The MJO meteorologic phenomenon he co-discovered is the largest element of the intraseasonal variability in the tropical atmosphere, a traveling pattern arising from large-scale coupling between atmospheric circulation and tropical deep convection. Description of the MJO remains an important contribution to climate research with relevance to modern short- and long-term weather and climate modeling.

National Center for Atmospheric Research American research organization

The US National Center for Atmospheric Research is a US federally funded research and development center (FFRDC) managed by the nonprofit University Corporation for Atmospheric Research (UCAR) and funded by the National Science Foundation (NSF). NCAR has multiple facilities, including the I. M. Pei-designed Mesa Laboratory headquarters in Boulder, Colorado. Studies include meteorology, climate science, atmospheric chemistry, solar-terrestrial interactions, environmental and societal impacts.

Atmospheric convection

Atmospheric convection is the result of a parcel-environment instability, or temperature difference layer in the atmosphere. Different lapse rates within dry and moist air masses lead to instability. Mixing of air during the day which expands the height of the planetary boundary layer leads to increased winds, cumulus cloud development, and decreased surface dew points. Moist convection leads to thunderstorm development, which is often responsible for severe weather throughout the world. Special threats from thunderstorms include hail, downbursts, and tornadoes.


The Madden–Julian oscillation is characterized by an eastward progression of large regions of both enhanced and suppressed tropical rainfall, observed mainly over the Indian and Pacific Ocean. The anomalous rainfall is usually first evident over the western Indian Ocean, and remains evident as it propagates over the very warm ocean waters of the western and central tropical Pacific. This pattern of tropical rainfall then generally becomes nondescript as it moves over the cooler ocean waters of the eastern Pacific (except over the region of warmer water off the west coast of Central America) but occasionally reappears at low amplitude over the tropical Atlantic and higher amplitude over the Indian Ocean. The wet phase of enhanced convection and precipitation is followed by a dry phase where thunderstorm activity is suppressed. Each cycle lasts approximately 30–60 days. Because of this pattern, the Madden–Julian oscillation is also known as the 30- to 60-day oscillation, 30- to 60-day wave, or intraseasonal oscillation.

Precipitation product of the condensation of atmospheric water vapour that falls under gravity

In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation include drizzle, rain, sleet, snow, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and "precipitates". Thus, fog and mist are not precipitation but suspensions, 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."

Thunderstorm type of weather

A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are sometimes called thundershowers. Thunderstorms occur in a type of cloud known as a cumulonimbus. They are usually accompanied by strong winds, and often produce heavy rain and sometimes snow, sleet, or hail, but some thunderstorms produce little precipitation or no precipitation at all. Thunderstorms may line up in a series or become a rainband, known as a squall line. Strong or severe thunderstorms include some of the most dangerous weather phenomena, including large hail, strong winds, and tornadoes. Some of the most persistent severe thunderstorms, known as supercells, rotate as do cyclones. While most thunderstorms move with the mean wind flow through the layer of the troposphere that they occupy, vertical wind shear sometimes causes a deviation in their course at a right angle to the wind shear direction.


The structure of the MJO for a period when the enhanced convective phase is centered across the Indian Ocean and the suppressed convective phase is centered over the west-central Pacific Ocean Madden-Julian oscillation diagram.png
The structure of the MJO for a period when the enhanced convective phase is centered across the Indian Ocean and the suppressed convective phase is centered over the west-central Pacific Ocean

Distinct patterns of lower-level and upper-level atmospheric circulation anomalies accompany the MJO-related pattern of enhanced or decreased tropical rainfall across the tropics. These circulation features extend around the globe and are not confined to only the eastern hemisphere. The Madden–Julian oscillation moves eastward at between 4 m/s (14 km/h, 9 mph) and 8 m/s (29 km/h, 18 mph) across the tropics, crossing the Earth's tropics in 30 to 60 days—with the active phase of the MJO tracked by the degree of outgoing long wave radiation, which is measured by infrared-sensing geostationary weather satellites. The lower the amount of outgoing long wave radiation, the stronger the thunderstorm complexes, or convection, is within that region. [3]

Earth Third planet from the Sun in the Solar System

Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.

Tropics region of the Earth surrounding the Equator

The tropics are the region of the Earth surrounding the Equator. They are delimited in latitude by The Tropic of Cancer in the Northern Hemisphere at 23°26′12.4″ (or 23.43678°) N and the Tropic of Capricorn in the Southern Hemisphere at 23°26′12.4″ (or 23.43678°) S; these latitudes correspond to the axial tilt of the Earth. The tropics are also referred to as the tropical zone and the torrid zone. The tropics include all the areas on the Earth where the Sun contacts a point directly overhead at least once during the solar year - thus the latitude of the tropics is roughly equal to the angle of the Earth's axial tilt.

Infrared electromagnetic radiation with longer wavelengths than those of visible light

Infrared radiation (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with longer wavelengths than those of visible light, and is therefore generally invisible to the human eye, although IR at wavelengths up to 1050 nanometers (nm)s from specially pulsed lasers can be seen by humans under certain conditions. IR wavelengths extend from the nominal red edge of the visible spectrum at 700 nanometers, to 1 millimeter (300 GHz). Most of the thermal radiation emitted by objects near room temperature is infrared. As with all EMR, IR carries radiant energy and behaves both like a wave and like its quantum particle, the photon.

Enhanced surface (upper level) westerly winds occur near the west (east) side of the active convection. [4] Ocean currents, up to 100 metres (330 ft) in depth from the ocean surface, follow in phase with the east-wind component of the surface winds. In advance, or to the east, of the MJO enhanced activity, winds aloft are westerly. In its wake, or to the west of the enhanced rainfall area, winds aloft are easterly. These wind changes aloft are due to the divergence present over the active thunderstorms during the enhanced phase. Its direct influence can be tracked poleward as far as 30 degrees latitude from the equator in both northern and southern hemispheres, propagating outward from its origin near the equator at around 1 degree latitude, or 111 kilometres (69 mi), per day. [5]


The MJO's movement around the globe can occasionally slow or stall during the summer and early autumn[ clarification needed ], leading to consistently enhanced rainfall for one side of the globe and consistently depressed rainfall of the other side. [6] [7] [8] [9] [10] [11] [12] [13] This can also happen early in the year. [14] [15] [16] The MJO can also go quiet for a period of time, which leads to non-anomalous storm activity for each region of the globe. [17] [18] [19] [20] [21] [22]

Local effects

Connection to the monsoon

Onset dates and prevailing wind currents of the southwest summer monsoon. India southwest summer monsoon onset map en.svg
Onset dates and prevailing wind currents of the southwest summer monsoon.

During the Northern Hemisphere summer season the MJO-related effects on the Indian and West African summer monsoon are well documented. MJO-related effects on the North American summer monsoon also occur, though they are relatively weaker. MJO-related impacts on the North American summer precipitation patterns are strongly linked to meridional (i.e. north–south) adjustments of the precipitation pattern in the eastern tropical Pacific. A strong relationship between the leading mode of intraseasonal variability of the North American Monsoon System, the MJO and the points of origin of tropical cyclones is also present.

Northern Hemisphere half of Earth that is north of the equator

The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's North Pole.

Monsoon seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea

Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea. Usually, the term monsoon is used to refer to the rainy phase of a seasonally changing pattern, although technically there is also a dry phase. The term is sometimes incorrectly used for locally heavy but short-term rains, although these rains meet the dictionary definition of monsoon.

A period of warming sea surface temperatures are found five to ten days prior to a strengthening of MJO-related precipitation across southern Asia. A break in the Asian monsoon, normally during the month of July, has been attributed to the Madden–Julian oscillation, after its enhanced phase moves off to the east of the region into the open tropical Pacific Ocean. [23]

Influence on tropical cyclogenesis

Tropical cyclones occur throughout the boreal warm season (typically May–November) in both the north Pacific and the north Atlantic basins—but any given year has periods of enhanced or suppressed activity within the season. Evidence suggests that the Madden–Julian oscillation modulates this activity (particularly for the strongest storms) by providing a large-scale environment that is favorable (or unfavorable) for development. MJO-related descending motion is not favorable for tropical storm development. However, MJO-related ascending motion is a favorable pattern for thunderstorm formation within the tropics, which is quite favorable for tropical storm development. As the MJO progresses eastward, the favored region for tropical cyclone activity also shifts eastward from the western Pacific to the eastern Pacific and finally to the Atlantic basin.

An inverse relationship exists between tropical cyclone activity in the western north Pacific basin and the north Atlantic basin, however. When one basin is active, the other is normally quiet, and vice versa. The main reason for this appears to be the phase of the MJO, which is normally in opposite modes between the two basins at any given time. [24] While this relationship appears robust, the MJO is one of many factors that contribute to the development of tropical cyclones. For example, sea surface temperatures must be sufficiently warm and vertical wind shear must be sufficiently weak for tropical disturbances to form and persist. [25] However, the MJO also influences these conditions that facilitate or suppress tropical cyclone formation. The MJO is monitored routinely by both the USA National Hurricane Center and the USA Climate Prediction Center during the Atlantic hurricane (tropical cyclone) season to aid in anticipating periods of relative activity or inactivity. [26]

Downstream effects

There is strong year-to-year (interannual) variability in Madden–Julian oscillation activity, with long periods of strong activity followed by periods in which the oscillation is weak or absent. This interannual variability of the MJO is partly linked to the El Niño–Southern Oscillation (ENSO) cycle. In the Pacific, strong MJO activity is often observed 6 to 12 months prior to the onset of an El Niño episode, but is virtually absent during the maxima of some El Niño episodes, while MJO activity is typically greater during a La Niña episode. Strong events in the Madden–Julian oscillation over a series of months in the western Pacific can speed the development of an El Niño or La Niña but usually do not in themselves lead to the onset of a warm or cold ENSO event. [27] However, observations suggest that the 1982-1983 El Niño developed rapidly during July 1982 in direct response to a Kelvin wave triggered by an MJO event during late May. [28] Further, changes in the structure of the MJO with the seasonal cycle and ENSO might facilitate more substantial impacts of the MJO on ENSO. For example, the surface westerly winds associated with active MJO convection are stronger during advancement toward El Niño and the surface easterly winds associated with the suppressed convective phase are stronger during advancement toward La Nina. [29] Globally, the inter annual variability of the MJO is most determined by atmospheric internal dynamics, rather than surface conditions.[ clarification needed ]

North American winter precipitation

The strongest impacts of intraseasonal variability on the United States occur during the winter months over the western U.S. During the winter this region receives the bulk of its annual precipitation. Storms in this region can last for several days or more and are often accompanied by persistent atmospheric circulation features. Of particular concern are extreme precipitation events linked to flooding. Strong evidence suggests a link between weather and climate in this region from studies that have related the El Niño Southern Oscillation to regional precipitation variability. In the tropical Pacific, winters with weak-to-moderate cold, or La Nina, episodes or ENSO-neutral conditions are often characterized by enhanced 30- to 60-day Madden–Julian oscillation activity. A recent example is the winter of 1996–1997, which featured heavy flooding in California and in the Pacific Northwest (estimated damage costs of $2.0–3.0 billion at the time of the event) and a very active MJO. Such winters are also characterized by relatively small sea surface temperature anomalies in the tropical Pacific compared to stronger warm and cold episodes. In these winters, there is a stronger link between the MJO events and extreme west coast precipitation events.

Pineapple Express events

The Pineapple Express, an MJO effect on North American weather patterns. Mjo north america rain.png
The Pineapple Express, an MJO effect on North American weather patterns.

The typical scenario linking the pattern of tropical rainfall associated with the MJO to extreme precipitation events in the Pacific Northwest features a progressive (i.e. eastward moving) circulation pattern in the tropics and a retrograding (i.e. westward moving) circulation pattern in the mid latitudes of the North Pacific. Typical wintertime weather anomalies preceding heavy precipitation events in the Pacific Northwest are as follows: [30]

  1. 7–10 days prior to the heavy precipitation event: Heavy tropical rainfall associated with the MJO shifts eastward from the eastern Indian Ocean to the western tropical Pacific. A moisture plume extends northeastward from the western tropical Pacific towards the general vicinity of the Hawaiian Islands. A strong blocking anticyclone is located in the Gulf of Alaska with a strong polar jet stream around its northern flank. [30]
  2. 3–5 days prior to the heavy precipitation event: Heavy tropical rainfall shifts eastward towards the date line and begins to diminish. The associated moisture plume extends further to the northeast, often traversing the Hawaiian Islands. The strong blocking high weakens and shifts westward. A split in the North Pacific jet stream develops, characterized by an increase in the amplitude and areal extent of the upper tropospheric westerly zonal winds on the southern flank of the block and a decrease on its northern flank. The tropical and extra tropical circulation patterns begin to "phase", allowing a developing mid latitude trough to tap the moisture plume extending from the deep tropics. [30]
  3. The heavy precipitation event: As the pattern of enhanced tropical rainfall continues to shift further to the east and weaken, the deep tropical moisture plume extends from the subtropical central Pacific into the mid latitude trough now located off the west coast of North America. The jet stream at upper levels extends across the North Pacific with the mean jet position entering North America in the northwestern United States. The deep low pressure located near the Pacific Northwest coast can bring up to several days of heavy rain and possible flooding. These events are often referred to as Pineapple Express events, so named because a significant amount of the deep tropical moisture traverses the Hawaiian Islands on its way towards western North America. [30]

Throughout this evolution, retrogression of the large-scale atmospheric circulation features is observed in the eastern Pacific–North American sector. Many of these events are characterized by the progression of the heaviest precipitation from south to north along the Pacific Northwest coast over a period of several days to more than one week. However, it is important to differentiate the individual synoptic-scale storms, which generally move west to east, from the overall large-scale pattern, which exhibits retrogression. [30]

A coherent simultaneous relationship exists between the longitudinal position of maximum MJO-related rainfall and the location of extreme west coast precipitation events. Extreme events in the Pacific Northwest are accompanied by enhanced precipitation over the western tropical Pacific and the region of Southeast Asia called by meteorologists the Maritime Continent, with suppressed precipitation over the Indian Ocean and the central Pacific. As the region of interest shifts from the Pacific Northwest to California, the region of enhanced tropical precipitation shifts further to the east. For example, extreme rainfall events in southern California are typically accompanied by enhanced precipitation near 170°E. However, it is important to note that the overall link between the MJO and extreme west coast precipitation events weakens as the region of interest shifts southward along the west coast of the United States. [30]

There is case-to-case variability in the amplitude and longitudinal extent of the MJO-related precipitation, so this should be viewed as a general relationship only. [30]

Related Research Articles

El Niño Warm phase of a cyclic climatic phenomenon in the Pacific Ocean

El Niño is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific, including the area off the Pacific coast of South America. The ENSO is the cycle of warm and cold sea surface temperature (SST) of the tropical central and eastern Pacific Ocean. El Niño is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific. El Niño phases are known to occur close to four years, however, records demonstrate that the cycles have lasted between two and seven years. During the development of El Niño, rainfall develops between September–November. The cool phase of ENSO is La Niña, with SSTs in the eastern Pacific below average, and air pressure high in the eastern Pacific and low in the western Pacific. The ENSO cycle, including both El Niño and La Niña, causes global changes in temperature and rainfall.

La Niña A coupled ocean-atmosphere phenomenon that is the counterpart of El Niño

La Niña is a coupled ocean-atmosphere phenomenon that is the colder counterpart of El Niño, as part of the broader El Niño–Southern Oscillation climate pattern. The name La Niña originates from Spanish, meaning "the little girl", analogous to El Niño meaning "the little boy". It has also in the past been called anti-El Niño, and El Viejo. During a period of La Niña, the sea surface temperature across the equatorial Eastern Central Pacific Ocean will be lower than normal by 3 to 5°C. An appearance of La Niña persists for at least five months. It has extensive effects on the weather across the globe, particularly in North America, even affecting the Atlantic and Pacific hurricane seasons.

Climatology The scientific study of climate, defined as weather conditions averaged over a period of time

Climatology or climate science is the scientific study of climate, scientifically defined as weather conditions averaged over a period of time. This modern field of study is regarded as a branch of the atmospheric sciences and a subfield of physical geography, which is one of the Earth sciences. Climatology now includes aspects of oceanography and biogeochemistry. Basic knowledge of climate can be used within shorter term weather forecasting using analog techniques such as the El Niño–Southern Oscillation (ENSO), the Madden–Julian oscillation (MJO), the North Atlantic oscillation (NAO), the Northern Annular Mode (NAM) which is also known as the Arctic oscillation (AO), the Northern Pacific (NP) Index, the Pacific decadal oscillation (PDO), and the Interdecadal Pacific Oscillation (IPO). Climate models are used for a variety of purposes from study of the dynamics of the weather and climate system to projections of future climate. Weather is known as the condition of the atmosphere over a period of time, while climate has to do with the atmospheric condition over an extended to indefinite period of time.

El Niño–Southern Oscillation Irregularly periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean

El Niño–Southern Oscillation (ENSO) is an irregularly periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean, affecting the climate of much of the tropics and subtropics. The warming phase of the sea temperature is known as El Niño and the cooling phase as La Niña. The Southern Oscillation is the accompanying atmospheric component, coupled with the sea temperature change: El Niño is accompanied by high air surface pressure in the tropical western Pacific and La Niña with low air surface pressure there. The two periods last several months each and typically occur every few years with varying intensity per period.

Intertropical Convergence Zone

The Intertropical Convergence Zone (ITCZ), known by sailors as the doldrums or the calms, is the area encircling Earth near the Equator, where the northeast and southeast trade winds converge.

The Antarctic oscillation is a low-frequency mode of atmospheric variability of the southern hemisphere. It is also known as the Southern Annular Mode (SAM). It is defined as a belt of westerly winds or low pressure surrounding Antarctica which moves north or south as its mode of variability. In its positive phase, the westerly wind belt that drives the Antarctic Circumpolar Current intensifies and contracts towards Antarctica, while its negative phase involves this belt moving towards the Equator. Winds associated with the Southern Annular Mode cause oceanic upwelling of warm circumpolar deep water along the Antarctic continental shelf, which has been linked to ice shelf basal melt, representing a possible wind-driven mechanism that could destabilize large portions of the Antarctic Ice Sheet.

Pacific decadal oscillation A robust, recurring pattern of ocean-atmosphere climate variability centered over the mid-latitude Pacific basin

The Pacific Decadal Oscillation (PDO) is a robust, recurring pattern of ocean-atmosphere climate variability centered over the mid-latitude Pacific basin. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20°N. Over the past century, the amplitude of this climate pattern has varied irregularly at interannual-to-interdecadal time scales. There is evidence of reversals in the prevailing polarity of the oscillation occurring around 1925, 1947, and 1977; the last two reversals corresponded with dramatic shifts in salmon production regimes in the North Pacific Ocean. This climate pattern also affects coastal sea and continental surface air temperatures from Alaska to California.

The South Pacific Convergence Zone (SPCZ), a reverse-oriented monsoon trough, is a band of low-level convergence, cloudiness and precipitation extending from the Western Pacific Warm Pool at the maritime continent south-eastwards towards French Polynesia and as far as the Cook Islands. The SPCZ is a portion of the Intertropical Convergence Zone (ITCZ) which lies in a band extending east-west near the Equator but can be more extratropical in nature, especially east of the International Date Line. It is considered the largest and most important piece of the ITCZ, and has the least dependence upon heating from a nearby landmass during the summer than any other portion of the monsoon trough. The SPCZ can affect the precipitation on Polynesian islands in the southwest Pacific Ocean, so it is important to understand how the SPCZ behaves with large-scale, global climate phenomenon, such as the ITCZ, El Niño–Southern Oscillation, and the Interdecadal Pacific oscillation (IPO), a portion of the Pacific decadal oscillation.

Monsoon trough

The monsoon trough is a portion of the Intertropical Convergence Zone in the Western Pacific, as depicted by a line on a weather map showing the locations of minimum sea level pressure, and as such, is a convergence zone between the wind patterns of the southern and northern hemispheres.

Tropical cyclogenesis

Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which temperate cyclogenesis occurs. Tropical cyclogenesis involves the development of a warm-core cyclone, due to significant convection in a favorable atmospheric environment.

United States rainfall climatology

The characteristics of United States rainfall climatology differ significantly across the United States and those under United States sovereignty. Late summer and fall extratropical cyclones bring a majority of the precipitation which falls across western, southern, and southeast Alaska annually. During the winter, and spring, Pacific storm systems bring Hawaii and the western United States most of their precipitation. Nor'easters moving down the East coast bring cold season precipitation to the Carolinas, Mid-Atlantic and New England states. Lake-effect snows add to precipitation potential downwind of the Great Lakes, as well as Great Salt Lake and the Finger Lakes during the cold season. The snow to liquid ratio across the contiguous United States averages 13:1, meaning 13 inches (330 mm) of snow melts down to 1 inch (25 mm) of water.

Indian Ocean Dipole irregular oscillation of sea-surface temperatures in which the western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean

The Indian Ocean Dipole (IOD), also known as the Indian Niño, is an irregular oscillation of sea-surface temperatures in which the western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean.

The Pacific–North American teleconnection pattern (PNA) is a climatological term for a large-scale weather pattern with two modes, denoted positive and negative, and which relates the atmospheric circulation pattern over the North Pacific Ocean with the one over the North American continent.

Effects of the El Niño–Southern Oscillation in the United States

The El Niño–Southern Oscillation affects the location of the jet stream, which alters rainfall patterns across the West, Midwest, the Southeast, and throughout the tropics. The shift in the jet stream also leads to shifts in the occurrence of severe weather, and the number of tropical cyclones expected within the tropics in the Atlantic and Pacific oceans affected by changes in the ocean temperature and the subtropical jet stream. The winter will have a negative phase according to the Arctic oscillation (AO).

The moist static energy is a thermodynamic variable that describes the state of an air parcel, and is similar to the equivalent potential temperature. The moist static energy is a combination of a parcel's enthalpy due to an air parcel's internal energy and energy required to make room for it, its potential energy due to its height above the surface, and the latent energy due to water vapor present in the air parcel. It is a useful variable for researching the atmosphere because, like several other similar variables, it is approximately conserved during adiabatic ascent and descent.

The Atlantic Equatorial Mode or Atlantic Niño is a quasiperiodic interannual climate pattern of the equatorial Atlantic Ocean. It is the dominant mode of year-to-year variability that results in alternating warming and cooling episodes of sea surface temperatures accompanied by changes in atmospheric circulation. The term Atlantic Niño comes from its close similarity with the El Niño-Southern Oscillation (ENSO) that dominates the tropical Pacific basin. The Atlantic Niño is not the same as the Atlantic Meridional (Interhemispheric) Mode that consists of a north-south dipole and operates more on decadal timescales. The equatorial warming and cooling events associated with the Atlantic Niño are known to be strongly related to atmospheric climate anomalies, especially in African countries bordering the Gulf of Guinea. Therefore, understanding of the Atlantic Niño has important implications for climate prediction in those regions. Although the Atlantic Niño is an intrinsic mode to the equatorial Atlantic, there may be a tenuous causal relationship between ENSO and the Atlantic Niño in some circumstances.

A climate oscillation or climate cycle is any recurring cyclical oscillation within global or regional climate, and is a type of climate pattern. These fluctuations in atmospheric temperature, sea surface temperature, precipitation or other parameters can be quasi-periodic, often occurring on inter-annual, multi-annual, decadal, multidecadal, century-wide, millennial or longer timescales. They are not perfectly periodic and a Fourier analysis of the data does not give a sharp spectrum.

2014–16 El Niño event

The 2014–16 El Niño was a warming of the eastern equatorial Pacific Ocean that resulted in unusually warm waters developing between the coast of South America and the International Date Line. These unusually warm waters influenced the world's weather in a number of ways, which in turn significantly affected various parts of the world. These included drought conditions in Venezuela, Australia and a number of Pacific islands while significant flooding was also recorded. During the event, more tropical cyclones than normal occurred within the Pacific Ocean, while fewer than normal occurred in the Atlantic Ocean.

Westerly wind burst

A westerly wind burst is a phenomenon commonly associated with El Niño events whereby the typical east-to-west trade winds across the equatorial Pacific shift to west-to-east. A westerly wind burst is defined by Harrison and Vecchi (1997) as sustained winds of 25 km/h (16 mph) over a period of 5–20 days. However, no concrete definition has been determined, with Tziperman and Yu (2007) defining them as having winds of 14 km/h (8.7 mph) and lasting "at least a few days". On average, three of these events take place each year, but are significantly more common during El Niño years. They have been linked to various mesoscale phenomena, including tropical cyclones, mid-latitude cold surges, and the Madden–Julian oscillation. Their connection with Kelvin waves also indicate a connection with the onset of El Niño events, with every major occurrence since the 1950s featuring a westerly wind burst upon their onset.


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