The Arctic dipole anomaly is a pressure pattern characterized by high pressure on the arctic regions of North America and low pressure on those of Eurasia.This pattern sometimes replaces the Arctic oscillation and the North Atlantic oscillation. It was observed for the first time in the first decade of 2000s and is perhaps linked to recent climate change. The Arctic dipole lets more southern winds into the Arctic Ocean resulting in more ice melting. The summer 2007 event played an important role in the record low sea ice extent which was recorded in September. The Arctic dipole has also been linked to changes in arctic circulation patterns that cause drier winters in Northern Europe, but much wetter winters in Southern Europe and colder winters in East Asia, Europe and the eastern half of North America.
North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere; it is also considered by some to be a northern subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, and to the southeast by South America and the Caribbean Sea.
Eurasia is the combined continental landmass of Europe and Asia. The term is a portmanteau of its constituent continents. Located primarily in the Northern and Eastern Hemispheres, it is bordered by the Atlantic Ocean to the west, the Pacific Ocean to the east, the Arctic Ocean to the north, and by Africa, the Mediterranean Sea, and the Indian Ocean to the south. The division between Europe and Asia as two different continents is a historical social construct, with no clear physical separation between them; thus, in some parts of the world, Eurasia is recognized as the largest of the six, five, or even four continents on Earth. In geology, Eurasia is often considered as a single rigid megablock. However, the rigidity of Eurasia is debated based on paleomagnetic data.
The Arctic oscillation (AO) or Northern Annular Mode/Northern Hemisphere Annular Mode (NAM) is a weather phenomenon at the Arctic and Antarctic poles north of 20 degrees latitude. The index varies over time with no particular periodicity, and is characterized by non-seasonal sea-level pressure anomalies of one sign in the Arctic, balanced by anomalies of opposite sign centered at about 37–45N.
In the 1990s and early 2000s, many studies of Arctic sea ice export focused on the Arctic Oscillation and North Atlantic Oscillation as the primary drivers of export.However, other studies, such as those by Watanabe and Hasumi and Vinje, suggested that the Arctic Oscillation and North Atlantic Oscillation did not always explain the variability in sea ice export.
In 2006, the Arctic dipole anomaly was formally proposed by Bingyi Wu, Jia Wang, and John Walsh, using the NCEP/NCAR reanalysis datasets spanning 1960–2002.It is defined as the spatial distribution of the second leading EOF mode of monthly mean sea level pressure north of 70°N, where the first leading mode corresponds to the Arctic Oscillation. When defined for the winter season (October through March), the first leading mode (Arctic Oscillation) accounts for 61% of the total variance, while the second leading mode (Arctic dipole anomaly) accounts for 13%.
The NCEP/NCAR Reanalysis data set is a continually updated (1948–present) globally gridded data set that represents the state of the Earth's atmosphere, incorporating observations and numerical weather prediction (NWP) model output from 1948 to present. It is a joint product from the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR).
In statistics and signal processing, the method of empirical orthogonal function (EOF) analysis is a decomposition of a signal or data set in terms of orthogonal basis functions which are determined from the data. It is similar to performing a principal components analysis on the data, except that the EOF method finds both time series and spatial patterns. The term is also interchangeable with the geographically weighted PCAs in geophysics.
While the Arctic Oscillation has an annular structure centered over and covering the entire Arctic,the Arctic dipole anomaly has two poles of opposite sign: one over the Canadian Arctic Archipelago and northern Greenland, the other over the Kara and Laptev Seas. This dipole structure leads to a pressure gradient with a zero isopleth oriented from the Bering Strait, across the Arctic to the Greenland and Barents Seas. As a result, anomalous winds are generally directed parallel to the zero isopleth either towards the Greenland and Barents Seas (positive Arctic dipole anomaly) or toward the Bering Strait (negative Arctic dipole anomaly).
Greenland is an autonomous constituent country of the Kingdom of Denmark between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for more than a millennium. The majority of its residents are Inuit, whose ancestors began migrating from the Canadian mainland in the 13th century, gradually settling across the island.
The Kara Sea is part of the Arctic Ocean north of Siberia. It is separated from the Barents Sea to the west by the Kara Strait and Novaya Zemlya, and the Laptev Sea to the east by the Severnaya Zemlya archipelago. It is named after the Kara River, which is now relatively insignificant but which played an important role in the Russian conquest of northern Siberia. The Kara River name is derived from Nenets word meaning "hummocked ice".
The Laptev Sea is a marginal sea of the Arctic Ocean. It is located between the northern coast of Siberia, the Taimyr Peninsula, Severnaya Zemlya and the New Siberian Islands. Its northern boundary passes from the Arctic Cape to a point with co-ordinates of 79°N and 139°E, and ends at the Anisiy Cape. The Kara Sea lies to the west, the East Siberian Sea to the east.
Although the Arctic Oscillation is responsible for more of the total variance in mean sea level pressure over the Arctic, the meridional winds anomalies that arise as a result of the spatial structure of the Arctic dipole anomaly make it the primary driver of Arctic sea ice export variability.During the positive phase of the Arctic dipole anomaly, anomalous winds drive sea ice from the central Arctic out the Fram Strait and into the Greenland Sea via the transpolar drift stream. In contrast, during the negative phase, anomalous winds reduce the removal of sea ice through the Fram Strait. This is supported by Watanabe et al., as well as Wang et al., which show that sea ice export is enhanced during the positive phase of the Arctic dipole anomaly, while export is reduced during the negative phase.
The Fram Strait is the passage between Greenland and Svalbard, located roughly between 77°N and 81°N latitudes and centered on the prime meridian. The Greenland and Norwegian Seas lie south of Fram Strait, while the Nansen Basin of the Arctic Ocean lies to the north. Fram Strait is noted for being the only deep connection between the Arctic Ocean and the World Oceans. The dominant oceanographic features of the region are the West Spitsbergen Current on the east side of the strait and the East Greenland Current on the west.
The Transpolar Drift Stream is a major ocean current of the Arctic Ocean, transporting sea ice from the Laptev Sea and the East Siberian Sea towards Fram Strait. Drift experiments with ships like Fram or Tara showed that the drift takes between two and four years.
However, the Arctic Oscillation cannot be ignored when considering sea ice export from the Arctic. By itself, circulation associated with a positive phase Arctic Oscillation results in an increase in sea ice export, while the negative phase of the Arctic Oscillation is associated with reduced Arctic sea ice export.When considering sea ice export in connection with the Arctic dipole anomaly, the Arctic Oscillation determines the sign of the dominant mean sea level pressure anomaly, while the Arctic dipole anomaly determines the location of the dominant mean sea level pressure anomaly (over the Canadian Arctic Archipelago and northern Greenland, or over the Kara and Laptev Seas). Therefore, while the Arctic dipole anomaly determines whether the overall export of sea ice will be promoted or restricted, the Arctic Oscillation will either enhance or diminish the influence of the Arctic dipole anomaly.
The Arctic dipole anomaly has also been suggested to play an important role in the occurrence of several extreme sea ice minima that have occurred since the mid-1990s, including the minimum in 2007.Wang et al. suggest that in addition to anomalous winds driving sea ice out of the Arctic through the Fram Strait, the positive phase of the Arctic dipole anomalies may also increase the flow of relatively warm waters from the North Pacific through the Bering Strait into the Arctic Ocean. Warmer waters, in addition to increased sea ice export, could result in reduced sea ice areal extent. Additionally, “preconditioning” of sea ice from the previous winter and summer seasons, as well as multidecadal trends, plays a role in determining the minimum sea ice extent for a given year.
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 be close to four years, however, records demonstrate the cycles have lasted between two and seven years. During the development of El Niño, rainfalls develop between September–November. The cool phase of ENSO is la Niña with SST in the eastern Pacific below average and air pressure high in the eastern and low in western Pacific. The ENSO cycle, both el Niño and la Niña, causes global changes in temperature and rainfall.
La Niña is a coupled ocean-atmosphere phenomenon that is the 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. In the United States, an appearance of La Niña persists for at least five months. It has extensive effects on the weather in North America, even affecting the Atlantic and Pacific hurricane seasons.
The quasi-biennial oscillation (QBO) is a quasiperiodic oscillation of the equatorial zonal wind between easterlies and westerlies in the tropical stratosphere with a mean period of 28 to 29 months. The alternating wind regimes develop at the top of the lower stratosphere and propagate downwards at about 1 km (0.6 mi) per month until they are dissipated at the tropical tropopause. Downward motion of the easterlies is usually more irregular than that of the westerlies. The amplitude of the easterly phase is about twice as strong as that of the westerly phase. At the top of the vertical QBO domain, easterlies dominate, while at the bottom, westerlies are more likely to be found. At the 30mb level, with regards to monthly mean zonal winds, the strongest recorded easterly was 29.55 m/s in November 2005, while the strongest recorded westerly was only 15.62 m/s in June 1995.
A sudden stratospheric warming (SSW) is an event in which the observed stratospheric temperature rises by several tens of kelvins, over the course of a few days. The change is preceded by a situation in which the Polar jet stream of westerly winds in the winter hemisphere is disturbed by natural weather patterns or disturbances in the lower atmosphere.
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 their effects vary in intensity.
The North Atlantic Oscillation (NAO) is a weather phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level (SLP) between the Icelandic Low and the Azores High. Through fluctuations in the strength of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds and location of storm tracks across the North Atlantic. It is part of the Arctic oscillation, and varies over time with no particular periodicity.
Dansgaard–Oeschger events are rapid climate fluctuations that occurred 25 times during the last glacial period. Some scientists say that the events occur quasi-periodically with a recurrence time being a multiple of 1,470 years, but this is debated. The comparable climate cyclicity during the Holocene is referred to as Bond events.
The East Greenland Current (EGC) is a cold, low salinity current that extends from Fram Strait (~80N) to Cape Farewell (~60N). The current is located off the eastern coast of Greenland along the Greenland continental margin. The current cuts through the Nordic Seas and through the Denmark Strait. The current is of major importance because it directly connects the Arctic to the Northern Atlantic, it is a major contributor to sea ice export out of the Arctic, and it is a major freshwater sink for the Arctic.
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 Siberian High is a massive collection of cold dry air that accumulates in the northeastern part of Eurasia from September until April. It is usually centered on Lake Baikal. It reaches its greatest size and strength in the winter when the air temperature near the center of the high-pressure area is often lower than −40 °C (−40 °F). The atmospheric pressure is often above 1,040 millibars (31 inHg). The Siberian High is the strongest semi-permanent high in the northern hemisphere and is responsible for both the lowest temperature in the Northern Hemisphere, of −67.8 °C (−90.0 °F) on 15 January 1885 at Verkhoyansk, and the highest pressure, 1083.8 mbar at Agata, Krasnoyarsk Krai on 31 December 1968, ever recorded. The Siberian High is responsible both for severe winter cold and attendant dry conditions with little snow and few or no glaciers across Siberia, Mongolia, and China. During the summer, the Siberian High is largely replaced by the Asiatic low.
Cluster II is a space mission of the European Space Agency, with NASA participation, to study the Earth's magnetosphere over the course of nearly two solar cycles. The mission is composed of four identical spacecraft flying in a tetrahedral formation. As a replacement for the original Cluster spacecraft which were lost in a launch failure in 1996, the four Cluster II spacecraft were successfully launched in pairs in July and August 2000 onboard two Soyuz-Fregat rockets from Baikonur, Kazakhstan. In February 2011, Cluster II celebrated 10 years of successful scientific operations in space. As of November 2018 its mission has been extended until the end of 2020 with a likely extension lasting until 2022. China National Space Administration/ESA Double Star mission operated alongside Cluster II from 2004 to 2007.
The Global Geospace Science (GGS) Wind satellite is a NASA science spacecraft launched on November 1, 1994, at 09:31 UTC, from launch pad 17B at Cape Canaveral Air Force Station (CCAFS) in Merritt Island, Florida, aboard a McDonnell Douglas Delta II 7925-10 rocket. Wind was designed and manufactured by Martin Marietta Astro Space Division in East Windsor, New Jersey. The satellite is a spin-stabilized cylindrical satellite with a diameter of 2.4 m and a height of 1.8 m.
Greenlandic: Sermeq Kujalleq, also known as Ilulissat Glacier or Jakobshavn Glacier, and the Danish: Jakobshavn Isbræ, is a large outlet glacier in West Greenland. It is located near the Greenlandic town of Ilulissat and ends at the sea in the Ilulissat Icefjord.
The Atlantic Multidecadal Oscillation (AMO) is a climate cycle that affects the sea surface temperature (SST) of the North Atlantic Ocean based on different modes on multidecadal timescales. While there is some support for this mode in models and in historical observations, controversy exists with regard to its amplitude, and in particular, the attribution of sea surface temperature change to natural or anthropogenic causes, especially in tropical Atlantic areas important for hurricane development. The Atlantic multidecadal oscillation is also connected with shifts in hurricane activity, rainfall patterns and intensity, and changes in fish populations.
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.
Polar amplification is the phenomenon that any change in the net radiation balance tends to produce a larger change in temperature near the poles than the planetary average. On a planet with an atmosphere that can restrict longwave radiation to space, surface temperatures will be warmer than a simple planetary equilibrium temperature calculation would predict. Where the atmosphere or an extensive ocean is able to transport heat polewards, the poles will be warmer and equatorial regions cooler than their local net radiation balances would predict.
The West Spitsbergen Current (WSC) is a warm, salty current that runs poleward just west of Spitsbergen,, in the Arctic Ocean. The WSC branches off the Norwegian Atlantic Current in the Norwegian Sea. The WSC is of importance because it drives warm and salty Atlantic Water into the interior Arctic. The warm and salty WSC flows north through the eastern side of Fram Strait, while the East Greenland Current (EGC) flows south through the western side of Fram Strait. The EGC is characterized by being very cold and low in salinity, but above all else it is a major exporter of Arctic sea ice. Thus, the EGC combined with the warm WSC makes the Fram Strait the northernmost ocean area having ice-free conditions throughout the year in all of the global ocean.
The Subtropical Indian Ocean Dipole (SIOD) is featured by the oscillation of sea surface temperatures (SST) in which the southwest Indian Ocean i.e. south of Madagascar is warmer and then colder than the eastern part i.e. off Australia. It was first identified in the studies of the relationship between the SST anomaly and the south-central Africa rainfall anomaly; the existence of such a dipole was identified from both observational studies and model simulations .
Global terrestrial stilling is the decrease of wind speed observed near the Earth's surface over the last three decades, originally termed "stilling". This slowdown of near-surface terrestrial winds has mainly affected mid-latitude regions of both hemispheres, with a global average reduction of −0.140 m s−1 dec−1 or between 5 and 15% over the past 50 years. With high-latitude showing increases in both hemispheres. In contrast to the observed weakening of winds over continental surfaces, winds have tended to strengthen over ocean regions. In the last few years, a break in this terrestrial decrease of wind speed has been detected suggesting a recovery at global scales since 2013.