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129-567: Based on changes in position of ice sheet margins dated via terrestrial cosmogenic nuclides and radiocarbon dating , growth of ice sheets in the southern hemisphere commenced 33,000 years ago and maximum coverage has been estimated to have occurred sometime between 26,500 years ago and 20,000 years ago. After this, deglaciation caused an abrupt rise in sea level. Decline of the West Antarctica ice sheet occurred between 14,000 and 15,000 years ago, consistent with evidence for another abrupt rise in

258-605: A biological attack. El Niño-Southern Oscillation (ENSO) influences the average location of upper-level jet streams, and leads to cyclical variations in precipitation and temperature across North America, as well as affecting tropical cyclone development across the eastern Pacific and Atlantic basins. Combined with the Pacific Decadal Oscillation , ENSO can also impact cold season rainfall in Europe. Changes in ENSO also change

387-520: A cold reversal caused a replacement of much of the arboreal vegetation with Magellanic moorland and Alpine species. On Isla Grande de Chiloé , Magellanic moorland and closed-canopy Nothofagus forests were both present during the LGM, but the former disappeared by the late LGM. Little is known about the extent of glaciers during Last Glacial Maximum north of the Chilean Lake District . To the north, in

516-482: A commercial airliner. Scientists are investigating ways to harness the wind energy within the jet stream. According to one estimate of the potential wind energy in the jet stream, only one percent would be needed to meet the world's current energy needs. In the late 2000s it was estimated that the required technology would reportedly take 10–20 years to develop. There are two major but divergent scientific articles about jet stream power. Archer & Caldeira claim that

645-414: A crystallized mineral or has a short enough half-life such that it has decayed since nucleosynthesis , but a long enough half-life such that it has built up measurable concentrations. The former includes measuring abundances of Kr and Ar whereas the latter includes measuring abundances of Be, C, and Al. Three types of cosmic-ray reactions can occur once a cosmic ray strikes matter which in turn produce

774-555: A data set collected from 35 182 weather stations worldwide, including 9116 whose records go beyond 50 years, found a sharp decrease in northern midlatitude cold waves since the 1980s. Moreover, a range of long-term observational data collected during the 2010s and published in 2020 suggests that the intensification of Arctic amplification since the early 2010s was not linked to significant changes on mid-latitude atmospheric patterns. State-of-the-art modelling research of PAMIP (Polar Amplification Model Intercomparison Project) improved upon

903-719: A formal measurement of uncalibrated radiocarbon years , counted from 1950). In New Zealand and neighbouring regions of the Pacific, temperatures may have been further depressed during part of the LGM by the world's most recent supervolcanic eruption , the Oruanui eruption , approximately 25,500 years BP. However, it is estimated that during the LGM, low-to-mid latitude land surfaces at low elevation cooled on average by 5.8 °C relative to their present-day temperatures, based on an analysis of noble gases dissolved in groundwater rather than examinations of species abundances that have been used in

1032-524: A high-energy cosmic ray interacts with the nucleus of an in situ Solar System atom , causing nucleons (protons and neutrons) to be expelled from the atom (see cosmic ray spallation ). These nuclides are produced within Earth materials such as rocks or soil , in Earth's atmosphere , and in extraterrestrial items such as meteoroids . By measuring cosmogenic nuclides, scientists are able to gain insight into

1161-545: A lack of energy from the Sun entering during the polar night . There are wind maxima at lower levels of the atmosphere that are also referred to as jets. A barrier jet in the low levels forms just upstream of mountain chains, with the mountains forcing the jet to be oriented parallel to the mountains. The mountain barrier increases the strength of the low level wind by 45 percent. In the North American Great Plains

1290-479: A local glacial maximum in the region. In northeastern Italy , in the region around Lake Fimon , Artemisia -dominated semideserts, steppes, and meadow-steppes replaced open boreal forests at the start of the LGM, specifically during Heinrich Stadial 3. The overall climate of the region became both drier and colder. In the Sar Mountains , the glacial equilibrium-line altitude was about 450 metres lower than in

1419-580: A meandering shape, and these meanders themselves propagate eastward, at lower speeds than that of the actual wind within the flow. Each large meander, or wave, within the jet stream is known as a Rossby wave (planetary wave). Rossby waves are caused by changes in the Coriolis effect with latitude. Shortwave troughs , are smaller scale waves superimposed on the Rossby waves, with a scale of 1,000 to 4,000 kilometres (600–2,500 mi) long, that move along through

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1548-410: A mixture of grassland and tundra prevailed, and even here, the northern limit of tree growth was at least 20° farther south than today. In the period before the LGM, many areas that became completely barren desert were wetter than they are today, notably in southern Australia, where Aboriginal occupation is believed to coincide with a wet period between 40,000 and 60,000 years Before Present (BP,

1677-520: A powerful air current in the upper air blowing west to east across the United States as an explanation for the behaviour of major storms. After the 1883 eruption of the Krakatoa volcano , weather watchers tracked and mapped the effects on the sky over several years. They labelled the phenomenon the "equatorial smoke stream". In the 1920s Japanese meteorologist Wasaburo Oishi detected the jet stream from

1806-473: A range of geological and astronomical processes. There are both radioactive and stable cosmogenic nuclides. Some of these radionuclides are tritium , carbon-14 and phosphorus-32 . Certain light (low atomic number) primordial nuclides (isotopes of lithium , beryllium and boron ) are thought to have been created not only during the Big Bang , but also (and perhaps primarily) to have been made after

1935-510: A sharp contrast between high temperatures over land and lower temperatures over the sea and play an important role in coastal weather, giving rise to strong coast parallel winds. Most coastal jets are associated with the oceanic high-pressure systems and thermal low over land. These jets are mainly located along cold eastern boundary marine currents, in upwelling regions offshore California, Peru–Chile, Benguela, Portugal, Canary and West Australia, and offshore Yemen–Oman. A valley exit jet

2064-460: A site near Mount Fuji . He tracked pilot balloons ("pibals"), used to measure wind speed and direction, as they rose in the air. Oishi's work largely went unnoticed outside Japan because it was published in Esperanto , though chronologically he has to be credited for the scientific discovery of jet streams. American pilot Wiley Post (1898–1935), the first man to fly around the world solo in 1933,

2193-460: A slow change in vegetation towards a sparsely distributed vegetation dominated by Nothofagus species. Within this parkland vegetation Magellanic moorland alternated with Nothofagus forest, and as warming progressed even warm-climate trees began to grow in the area. It is estimated that the tree line was depressed about 1,000 m relative to present day elevations during the coldest period, but it rose gradually until 19,300 years ago. At that time

2322-466: A southerly low-level jet helps fuel overnight thunderstorm activity during the warm season, normally in the form of mesoscale convective systems which form during the overnight hours. A similar phenomenon develops across Australia, which pulls moisture poleward from the Coral Sea towards cut-off lows which form mainly across southwestern portions of the continent . Coastal low-level jets are related to

2451-590: A type of fire balloon , was designed as a cheap weapon intended to make use of the jet stream over the Pacific Ocean to reach the west coast of Canada and the United States . Relatively ineffective as weapons, they were used in one of the few attacks on North America during World War II , causing six deaths and a small amount of damage. American scientists studying the balloons thought the Japanese might be preparing

2580-499: Is a big part of the amplification story—a big reason the Arctic is warming faster than anywhere else." In a 2017 study conducted by climatologist Judah Cohen and several of his research associates, Cohen wrote that "[the] shift in polar vortex states can account for most of the recent winter cooling trends over Eurasian midlatitudes". A 2018 paper from Vavrus and others linked Arctic amplification to more persistent hot-dry extremes during

2709-504: Is a strong, down-valley, elevated air current that emerges above the intersection of the valley and its adjacent plain. These winds frequently reach speeds of up to 20 m/s (72 km/h; 45 mph) at heights of 40–200 m (130–660 ft) above the ground. Surface winds below the jet tend to be substantially weaker, even when they are strong enough to sway vegetation. Valley exit jets are likely to be found in valley regions that exhibit diurnal mountain wind systems, such as those of

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2838-456: Is closely associated with Jennifer Francis , who had first proposed it in a 2012 paper co-authored by Stephen J. Vavrus. While some paleoclimate reconstructions have suggested that the polar vortex becomes more variable and causes more unstable weather during periods of warming back in 1997, this was contradicted by climate modelling, with PMIP2 simulations finding in 2010 that the Arctic oscillation

2967-455: Is exactly the same. These same nuclides still arrive on Earth in small amounts in cosmic rays, and are formed in meteoroids, in the atmosphere, on Earth, "cosmogenically". However, beryllium ( all of it stable beryllium-9) is present primordially in the Solar System in much larger amounts, having existed prior to the condensation of the Solar System, and thus present in the materials from which

3096-503: Is greater than average across the southern Rockies and Sierra Nevada mountain range, and is well below normal across the Upper Midwest and Great Lakes states. The northern tier of the lower 48 exhibits above normal temperatures during the fall and winter, while the Gulf coast experiences below normal temperatures during the winter season. The subtropical jet stream across the deep tropics of

3225-413: Is most significant during double Rossby wave breaking events. At high altitudes, lack of friction allows air to respond freely to the steep pressure gradient with low pressure at high altitude over the pole. This results in the formation of planetary wind circulations that experience a strong Coriolis deflection and thus can be considered 'quasi-geostrophic'. The polar front jet stream is closely linked to

3354-454: Is often given some credit for discovery of jet streams. Post invented a pressurized suit that let him fly above 6,200 metres (20,300 ft). In the year before his death, Post made several attempts at a high-altitude transcontinental flight, and noticed that at times his ground speed greatly exceeded his air speed. German meteorologist Heinrich Seilkopf is credited with coining a special term, Strahlströmung (literally " jet current"), for

3483-437: Is proportional to the horizontal temperature gradient. If two air masses in the northern hemisphere, one cold and dense to the north and the other hot and less dense to the south, are separated by a vertical boundary and that boundary should be removed, the difference in densities will result in the cold air mass slipping under the hotter and less dense air mass. The Coriolis effect will then cause poleward-moving mass to deviate to

3612-605: Is referred to in Britain as the Dimlington Stadial , dated to between 31,000 and 16,000 years ago. The average global temperature about 21,000 years ago was about 6 °C (11 °F) colder than today. According to the United States Geological Survey (USGS), permanent summer ice covered about 8% of Earth's surface and 25% of the land area during the last glacial maximum. The USGS also states that sea level

3741-742: Is responsible for dust emission from the Bodélé Depression , the world's most important single source of dust emission. The Somali Jet , which forms off the East African coast is an important component of the global Hadley circulation, and supplies water vapour to the Asian Monsoon . Easterly low-level jets forming in valleys within the East African Rift System help account for the low rainfall in East Africa and support high rainfall in

3870-402: Is said to "follow the sun" as it slowly migrates northward as that hemisphere warms, and southward again as it cools. The width of a jet stream is typically a few hundred kilometres or miles and its vertical thickness often less than five kilometres (16,000 feet). Jet streams are typically continuous over long distances, but discontinuities are also common. The path of the jet typically has

3999-463: Is strongest on the cold air side of the jet, next to and just under the axis of the jet. Clear-air turbulence can cause aircraft to plunge and so present a passenger safety hazard that has caused fatal accidents, such as the death of one passenger on United Airlines Flight 826 . Unusual wind speed in the jet stream in late February 2024 pushed commercial jets to excess of 800 mph (1,300 km/h; 700 kn) in their flight path, unheard of for

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4128-481: Is symmetric with respect to longitude. Tropical air rises to the tropopause, and moves poleward before sinking; this is the Hadley cell circulation. As it does so it tends to conserve angular momentum, since friction with the ground is slight. Air masses that begin moving poleward are deflected eastward by the Coriolis force (true for either hemisphere), which for poleward moving air implies an increased westerly component of

4257-443: The 2010 Pakistan floods , and suggested that these patterns were all connected to Arctic amplification. Further work from Francis and Vavrus that year suggested that amplified Arctic warming is observed as stronger in lower atmospheric areas because the expanding process of warmer air increases pressure levels which decreases poleward geopotential height gradients. As these gradients are the reason that cause west to east winds through

4386-648: The Baltic Shield , and in Russia in particular, the LGM ice margin of the Fennoscandian Ice Sheet was highly lobate. The main LGM lobes of Russia followed the Dvina , Vologda and Rybinsk basins respectively. Lobes originated as result of ice following shallow topographic depressions filled with a soft sediment substrate. The northern Ural region was covered in periglacial steppes. Permafrost covered Europe south of

4515-747: The Barents Sea , the Kara Sea , and Novaya Zemlya , ending at the Taymyr Peninsula in what is now northwestern Siberia. Warming commenced in northern latitudes around 20,000 years ago, but it was limited and considerable warming did not take place until around 14,600 year ago. In northwestern Russia , the Fennoscandian ice sheet reached its LGM extent approximately 17,000 years ago, about five thousand years later than in Denmark, Germany and Western Poland. Outside

4644-697: The Big Bang and the Solar System's formation (thus making these primordial nuclides , by definition) are not termed "cosmogenic", even though they were formed by the same process as the cosmogenic nuclides (although at an earlier time). The primordial nuclide beryllium-9, the only stable beryllium isotope, is an example of this type of nuclide. In contrast, even though the radioactive isotopes beryllium-7 and beryllium-10 fall into this series of three light elements (lithium, beryllium, boron) formed mostly by cosmic ray spallation nucleosynthesis , both of these nuclides have half lives too short (53 days and ca. 1.4 million years, resp.) for them to have been formed before

4773-597: The Cantabrian Mountains of the northwestern corner of the Iberian Peninsula , which in the present day have no permanent glaciers, the LGM led to a local glacial recession as a result of increased aridity caused by the growth of other ice sheets farther to the east and north, which drastically limited annual snowfall over the mountains of northwestern Spain. The Cantabrian alpine glaciers had previously expanded between approximately 60,000 and 40,000 years ago during

4902-674: The Congo Basin rainforest. The formation of the thermal low over northern Africa leads to a low-level westerly jet stream from June into October, which provides the moist inflow to the West African monsoon . While not technically a low-level jet, the mid-level African easterly jet (at 3000–4000 m above the surface) is also an important climate feature in Africa. It occurs during the Northern Hemisphere summer between 10°N and 20°N above in

5031-594: The February 2021 North American cold wave . Another 2021 study identified a connection between the Arctic sea ice loss and the increased size of wildfires in the Western United States . However, because the specific observations are considered short-term observations, there is considerable uncertainty in the conclusions. Climatology observations require several decades to definitively distinguish various forms of natural variability from climate trends. This point

5160-672: The Great Plains . During the Dust Bowl, the jet stream weakened and changed course traveling farther south than normal. This starved the Great Plains and other areas of the Midwest of rainfall, causing extraordinary drought conditions. Since the early 2000s, climate models have consistently identified that global warming will gradually push jet streams poleward. In 2008, this was confirmed by observational evidence, which proved that from 1979 to 2001,

5289-649: The Gulf of Oman . Bathymetric data suggests there were two palaeo-basins in the Persian Gulf. The central basin may have approached an area of 20,000 km, comparable at its fullest extent to lakes such as Lake Malawi in Africa. Between 12,000 and 9,000 years ago much of the Gulf's floor was not covered by water, only being flooded by the sea after 8,000 years ago. It is estimated that annual average temperatures in Southern Africa were 6 °C lower than at present during

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5418-593: The Hex River Mountains , in the Western Cape , block streams and terraces found near the summit of Matroosberg evidences past periglacial activity which likely occurred during the LGM. Palaeoclimatological proxies indicate the region around Boomplaas Cave was wetter, with increased winter precipitation. The region of the Zambezi River catchment was colder relative to present and the local drop in mean temperature

5547-631: The Northern Hemisphere is enhanced due to increased convection in the equatorial Pacific, which decreases tropical cyclogenesis within the Atlantic tropics below what is normal, and increases tropical cyclone activity across the eastern Pacific. In the Southern Hemisphere, the subtropical jet stream is displaced equatorward, or north, of its normal position, which diverts frontal systems and thunderstorm complexes from reaching central portions of

5676-420: The atmospheres of the Earth , Venus, Jupiter, Saturn, Uranus, and Neptune. On Earth, the main jet streams are located near the altitude of the tropopause and are westerly winds (flowing west to east). Jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including opposite to the direction of the remainder of the jet. The strongest jet streams are

5805-507: The dry Andes of Central and the Last Glacial Maximum is associated with increased humidity and the verified advance of at least some mountain glaciers. Montane glaciers in the northern Andes reached their peak extent approximately 27,000 years ago. In northwestern Argentina, pollen deposits record the altitudinal descent of the treeline during the LGM. Amazonia was much drier than in the present. δ D values from plant waxes from

5934-454: The frontogenesis process in midlatitudes, as the acceleration/deceleration of the air flow induces areas of low/high pressure respectively, which link to the formation of cyclones and anticyclones along the polar front in a relatively narrow region. A second factor which contributes to a concentrated jet is more applicable to the subtropical jet which forms at the poleward limit of the tropical Hadley cell , and to first order this circulation

6063-560: The polar jets around the polar vortices , at 9–12 km (5.6–7.5 mi; 30,000–39,000 ft) above sea level, and the higher altitude and somewhat weaker subtropical jets at 10–16 km (6.2–9.9 mi; 33,000–52,000 ft). The Northern Hemisphere and the Southern Hemisphere each have a polar jet and a subtropical jet. The northern hemisphere polar jet flows over the middle to northern latitudes of North America , Europe , and Asia and their intervening oceans , while

6192-698: The sea level about 14,500 years ago. Glacier fluctuations around the Strait of Magellan suggest the peak in glacial surface area was constrained to between 25,200 and 23,100 years ago. There are no agreed dates for the beginning and end of the LGM, and researchers select dates depending on their criteria and the data set consulted. Jennifer French, an archeologist specialising in the European Palaeolithic, dates its onset at 27,500 years ago, with ice sheets at their maximum by around 26,000 years ago and deglaciation commencing between 20,000 and 19,000 years ago. The LGM

6321-490: The thermosphere . Meteorologists use the location of some of the jet streams as an aid in weather forecasting . The main commercial relevance of the jet streams is in air travel, as flight time can be dramatically affected by either flying with the flow or against. Often, airlines work to fly 'with' the jet stream to obtain significant fuel cost and time savings. Dynamic North Atlantic Tracks are one example of how airlines and air traffic control work together to accommodate

6450-491: The 2010 findings of PMIP2; it found that sea ice decline would weaken the jet stream and increase the probability of atmospheric blocking, but the connection was very minor, and typically insignificant next to interannual variability. In 2022, a follow-up study found that while the PAMIP average had likely underestimated the weakening caused by sea ice decline by 1.2 to 3 times, even the corrected connection still amounts to only 10% of

6579-468: The 250 hPa (about 1/4 atmosphere) pressure level, or seven to twelve kilometres (23,000 to 39,000 ft) above sea level , while the weaker subtropical jet streams are much higher, between 10 and 16 kilometres (33,000 and 52,000 ft). Jet streams wander laterally dramatically, and change in altitude. The jet streams form near breaks in the tropopause, at the transitions between the polar, Ferrel and Hadley circulation cells , and whose circulation, with

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6708-588: The Andes occupying lacustrine and marine basins where they spread out forming large piedmont glacier lobes . Glaciers extended about 7 km west of the modern Llanquihue Lake , but not more than 2 to 3 km south of it. Nahuel Huapi Lake in Argentina was also glaciated by the same time. Over most of the Chiloé Archipelago , glacier advance peaked 26,000 years ago, forming a long north–south moraine system along

6837-476: The Arctic to heat up faster than other parts of the globe, in what is known as the Arctic amplification . In 2021–2022, it was found that since 1979, the warming within the Arctic Circle has been nearly four times faster than the global average, and some hotspots in the Barents Sea area warmed up to seven times faster than the global average. While the Arctic remains one of the coldest places on Earth today,

6966-478: The Big Bang, but before the condensation of the Solar System, by the process of cosmic ray spallation on interstellar gas and dust. This explains their higher abundance in cosmic dust as compared with their abundances on Earth. This also explains the overabundance of the early transition metals just before iron in the periodic table – the cosmic-ray spallation of iron produces scandium through chromium on

7095-518: The Coriolis force acting on those masses, drives the jet streams. The polar jets, at lower altitude, and often intruding into mid-latitudes, strongly affect weather and aviation. The polar jet stream is most commonly found between latitudes 30° and 60° (closer to 60°), while the subtropical jet streams are located close to latitude 30°. These two jets merge at some locations and times, while at other times they are well separated. The northern polar jet stream

7224-473: The Earth's jet streams could generate a total power of 1700 terawatts (TW) and that the climatic impact of harnessing this amount would be negligible. However, Miller, Gans, & Kleidon claim that the jet streams could generate a total power of only 7.5 TW and that the climatic impact would be catastrophic. Near the end of World War II , from late 1944 until early 1945, the Japanese Fu-Go balloon bomb ,

7353-554: The East, while equatorward-moving mass will deviate toward the west. The general trend in the atmosphere is for temperatures to decrease in the poleward direction. As a result, winds develop an eastward component and that component grows with altitude. Therefore, the strong eastward moving jet streams are in part a simple consequence of the fact that the Equator is warmer than the north and south poles. The thermal wind relation does not explain why

7482-608: The Great Barrier Reef was enhanced due to low atmospheric CO 2 levels. The deep waters of the Indian Ocean were significantly less oxygenated during the LGM compared to the Middle Holocene. The deep South Indian Ocean in particular was an enormous carbon sink, partially explaining the very low p CO 2 of the LGM. The intermediate waters of the southeastern Arabian Sea were poorly ventilated relative to today because of

7611-542: The Holocene. In Greece , steppe vegetation predominated. Megafaunal abundance in Europe peaked around 27,000 and 21,000 BP; this bountifulness was attributable to the cold stadial climate. In Greenland, the difference between LGM temperatures and present temperatures was twice as great during winter as during summer. Greenhouse gas and insolation forcings dominated temperature changes in northern Greenland, whereas Atlantic meridional overturning circulation (AMOC) variability

7740-536: The LGM are significantly more enriched than those in the present and those dating back to MIS 3, evidencing this increased aridity. Eastern Brazil was also affected; the site of Guanambi in Bahia was much drier than today. AMOC was weaker and more shallow during the LGM. Sea surface temperatures in the western subtropical gyre of the North Atlantic were around 5 °C colder compared to today. Intermediate depth waters of

7869-672: The LGM except in transient intervals around 23,200 and 22,300 BP. In the western South Atlantic , where Antarctic Intermediate Water forms, sinking particle flux was heightened as a result of increased dust flux during the LGM and sustained export productivity. The increased sinking particle flux removed neodymium from shallow waters, producing an isotopic ratio change. On the Island of Hawaii , geologists have long recognized deposits formed by glaciers on Mauna Kea during recent ice ages. The latest work indicates that deposits of three glacial episodes since 150,000 to 200,000 years ago are preserved on

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7998-530: The LGM, 21,000 years ago, the sea level was about 125 meters (about 410 feet) lower than it is today. Across most of the globe, the hydrological cycle slowed down, explaining increased aridity in many regions of the world. In Africa and the Middle East, many smaller mountain glaciers formed, and the Sahara and other sandy deserts were greatly expanded in extent. The Atlantic deep sea sediment core V22-196, extracted off

8127-602: The Last Glacial Maximum. This temperature drop alone would however not have been enough to generate widespread glaciation or permafrost in the Drakensberg Mountains or the Lesotho Highlands . Seasonal freezing of the ground in the Lesotho Highlands might have reached depths of 2 meters or more below the surface. A few small glaciers did however develop during the LGM, in particular in south-facing slopes. In

8256-662: The Laurentide Ice Sheet reached 3.2 km in height around Keewatin Dome and about 1.7-2.1 km along the Plains divide. In addition to the large Cordilleran Ice Sheet in Canada and Montana , alpine glaciers advanced and (in some locations) ice caps covered much of the Rocky and Sierra Nevada Mountains further south. Latitudinal gradients were so sharp that permafrost did not reach far south of

8385-627: The North Atlantic was reduced, as measured by the increased proportion of radiogenic isotopes in neodymium isotope ratios. There is controversy whether upwelling off the Moroccan coast was stronger during the LGM compared to today. Though coccolith size increases in Calcidiscus leptoporus suggest stronger trade winds during the LGM caused there to be increased coastal upwelling of the northwestern coast of Africa, planktonic foraminiferal δC records show upwelling and primary productivity were not enhanced during

8514-464: The North Atlantic were better ventilated during the LGM by Glacial North Atlantic Intermediate Water (GNAIW) relative to its present-day ventilation by upper North Atlantic Deep Water (NADW). GNAIW was nutrient poor compared to present day upper NADW. Below GNAIW, southern source bottom water that was very rich in nutrients filled the deep North Atlantic. Due to the presence of immense ice sheets in Europe and North America, continental weathering flux into

8643-426: The North Atlantic, the jet stream is stronger than normal, which directs stronger systems with increased precipitation towards Europe. Evidence suggests the jet stream was at least partly responsible for the widespread drought conditions during the 1930s Dust Bowl in the Midwest United States. Normally, the jet stream flows east over the Gulf of Mexico and turns northward pulling up moisture and dumping rain onto

8772-414: The Solar System formed. To make the distinction in another fashion, the timing of their formation determines which subset of cosmic ray spallation-produced nuclides are termed primordial or cosmogenic (a nuclide cannot belong to both classes). By convention, certain stable nuclides of lithium, beryllium, and boron are thought to have been produced by cosmic ray spallation in the period of time between

8901-451: The U.S. National Oceanic and Atmospheric Administration (NOAA) cited vertical wind shear as evidenced in the photo. On Earth, the northern polar jet stream is the most important one for aviation and weather forecasting, as it is much stronger and at a much lower altitude than the subtropical jet streams and also covers many countries in the Northern Hemisphere , while the southern polar jet stream mostly circles Antarctica and sometimes

9030-413: The atmosphere . The massive sheets of ice locked away water, lowering the sea level, exposing continental shelves , joining land masses together, and creating extensive coastal plains . The ice sheets also changed the atmospheric circulation, causing the northern Pacific and Atlantic oceans to cool and produce more clouds, which amplified the global cooling as the clouds reflected even more sunlight. During

9159-571: The atmosphere, but some are formed in situ in soil and rock exposed to cosmic rays, notably calcium-41 in the table below. As seen in the table above, there are a wide variety of useful cosmogenic nuclides which can be measured in soil, rocks, groundwater, and the atmosphere. These nuclides all share the common feature of being absent in the host material at the time of formation. These nuclides are chemically distinct and fall into two categories. The nuclides of interest are either noble gases which due to their inert behavior are inherently not trapped in

9288-884: The best known being Lake Bonneville in Utah . This also occurred in Afghanistan and Iran , where a major lake formed in the Dasht-e Kavir . In Australia , shifting sand dunes covered half the continent, while the Chaco and Pampas in South America became similarly dry. Present-day subtropical regions also lost most of their forest cover, notably in eastern Australia, the Atlantic Forest of Brazil , and southern China , where open woodland became dominant due to much drier conditions. In northern China – unglaciated despite its cold climate –

9417-548: The coast of Senegal, shows a major southward expansion of the Sahara. The Persian Gulf averages about 35 metres in depth and the seabed between Abu Dhabi and Qatar is even shallower, being mostly less than 15 metres deep. For thousands of years the Ur-Shatt (a confluence of the Tigris - Euphrates Rivers ) provided fresh water to the Gulf, as it flowed through the Strait of Hormuz into

9546-612: The continent. Across North America during La Niña , increased precipitation is diverted into the Pacific Northwest due to a more northerly storm track and jet stream. The storm track shifts far enough northward to bring wetter than normal conditions (in the form of increased snowfall) to the Midwestern states, as well as hot and dry summers. Snowfall is above normal across the Pacific Northwest and western Great Lakes. Across

9675-692: The continents: the Indonesian islands as far east as Borneo and Bali were connected to the Asian continent in a landmass called Sundaland . Palawan was also part of Sundaland, while the rest of the Philippine Islands formed one large island separated from the continent only by the Sibutu Passage and the Mindoro Strait . The environment along the coast of South China was not very different from that of

9804-507: The dry mountain ranges of the US. Deep valleys that terminate abruptly at a plain are more impacted by these factors than are those that gradually become shallower as downvalley distance increases. There are several important low-level jets in Africa. Numerous low-level jets form in the Sahara , and are important for the raising of dust off the desert surface. This includes a low-level jet in Chad , which

9933-620: The east and west extremities of the Sundaland shelf. Only in Central America and the Chocó region of Colombia did tropical rainforests remain substantially intact – probably due to the extraordinarily heavy rainfall of these regions. Most of the world's deserts expanded. Exceptions were in what is the present-day Western United States , where changes in the jet stream brought heavy rain to areas that are now desert and large pluvial lakes formed,

10062-538: The eastern coast of Chiloé Island (41.5–43° S). By that time the glaciation at the latitude of Chiloé was of ice sheet type contrasting to the valley glaciation found further north in Chile. Despite glacier advances much of the area west of Llanquihue Lake was still ice-free during the Last Glacial Maximum. During the coldest period of the Last Glacial Maximum vegetation at this location was dominated by Alpine herbs in wide open surfaces. The global warming that followed caused

10191-513: The flight, it also nets fuel savings for the airline industry. Within North America, the time needed to fly east across the continent can be decreased by about 30 minutes if an airplane can fly with the jet stream, or increased by more than that amount if it must fly west against it. Associated with jet streams is a phenomenon known as clear-air turbulence (CAT), caused by vertical and horizontal wind shear caused by jet streams. The CAT

10320-609: The flow pattern around large scale, or longwave, "ridges" and "troughs" within Rossby waves. Jet streams can split into two when they encounter an upper-level low, that diverts a portion of the jet stream under its base, while the remainder of the jet moves by to its north. The wind speeds are greatest where temperature differences between air masses are greatest, and often exceed 92 km/h (50 kn; 57 mph). Speeds of 400 km/h (220 kn; 250 mph) have been measured. The jet stream moves from West to East bringing changes of weather. Meteorologists now understand that

10449-421: The formation of the Solar System, and thus they cannot be primordial nuclides. Since the cosmic ray spallation route is the only possible source of beryllium-7 and beryllium-10 occurrence naturally in the environment, they are therefore cosmogenic. Here is a list of radioisotopes formed by the action of cosmic rays ; the list also contains the production mode of the isotope. Most cosmogenic nuclides are formed in

10578-692: The ice sheet down to as far south as present-day Szeged in Southern Hungary. Ice covered the whole of Iceland . In addition, ice covered Ireland along with roughly the northern half of the British Isles with the southern boundary of the ice sheet running approximately from the south of Wales to the north east of England, and then across the now submerged land of Doggerland to Denmark . Central Europe had isolated pockets of relative warmth corresponding to hydrothermally active areas, which served as refugia for taxa not adapted to extremely cold climates. In

10707-420: The ice sheets except at high elevations. Glaciers forced the early human populations who had originally migrated from northeast Siberia into refugia , reshaping their genetic variation by mutation and drift . This phenomenon established the older haplogroups found among Native Americans , and later migrations are responsible for northern North American haplogroups. In southeastern North America, between

10836-495: The interface of the polar and Ferrel circulation cells; the subtropical jet forms near the boundary of the Ferrel and Hadley circulation cells. Other jet streams also exist. During the Northern Hemisphere summer, easterly jets can form in tropical regions, typically where dry air encounters more humid air at high altitudes. Low-level jets also are typical of various regions such as the central United States. There are also jet streams in

10965-412: The jet stream and winds aloft that results in the maximum benefit for airlines and other users. Clear-air turbulence , a potential hazard to aircraft passenger safety, is often found in a jet stream's vicinity, but it does not create a substantial alteration of flight times. The first indications of this phenomenon came from American professor Elias Loomis (1811–1889), when he proposed the hypothesis of

11094-407: The jet stream's natural variability. Additionally, a 2021 study found that while jet streams had indeed slowly moved polewards since 1960 as was predicted by models, they did not weaken, in spite of a small increase in waviness. A 2022 re-analysis of the aircraft observational data collected over 2002–2020 suggested that the North Atlantic jet stream had actually strengthened. Finally, a 2021 study

11223-522: The location of the jet stream over South America, which partially affects precipitation distribution over the continent. During El Niño events, increased precipitation is expected in California due to a more southerly, zonal, storm track. During the Niño portion of ENSO, increased precipitation falls along the Gulf coast and Southeast due to a stronger than normal, and more southerly, polar jet stream. Snowfall

11352-486: The measured cosmogenic nuclides. Since the Earth bulges at the equator and mountains and deep oceanic trenches allow for deviations of several kilometers relative to a uniformly smooth spheroid, cosmic rays bombard the Earth's surface unevenly based on the latitude and altitude. Thus, many geographic and geologic considerations must be understood in order for cosmic-ray flux to be accurately determined. Atmospheric pressure , for example, which varies with altitude, can change

11481-445: The midlatitude summers, as well as the midlatitude winter continental cooling. Another 2017 paper estimated that when the Arctic experiences anomalous warming, primary production in North America goes down by between 1% and 4% on average, with some states suffering up to 20% losses. A 2021 study found that a stratospheric polar vortex disruption is linked with extreme cold winter weather across parts of Asia and North America, including

11610-483: The modelling results but fit the Francis-Vavrus hypothesis. Additionally, a 2013 study noted that the then-current CMIP5 tended to strongly underestimate winter blocking trends, and other 2012 research had suggested a connection between declining Arctic sea ice and heavy snowfall during midlatitude winters. In 2013, further research from Francis connected reductions in the Arctic sea ice to extreme summer weather in

11739-415: The northern jet stream moved northward at an average rate of 2.01 kilometres (1.25 mi) per year, with a similar trend in the Southern Hemisphere jet stream. Climate scientists have hypothesized that the jet stream will also gradually weaken as a result of global warming . Trends such as Arctic sea ice decline , reduced snow cover, evapotranspiration patterns, and other weather anomalies have caused

11868-615: The northern mid-latitudes, while other research from that year identified potential linkages between Arctic sea ice trends and more extreme rainfall in the European summer. At the time, it was also suggested that this connection between Arctic amplification and jet stream patterns was involved in the formation of Hurricane Sandy and played a role in the Early 2014 North American cold wave . In 2015, Francis' next study concluded that highly amplified jet-stream patterns are occurring more frequently in

11997-480: The one hand and helium through boron on the other. However, the arbitrary defining qualification for cosmogenic nuclides of being formed "in situ in the Solar System" (meaning inside an already aggregated piece of the Solar System) prevents primordial nuclides formed by cosmic ray spallation before the formation of the Solar System from being termed "cosmogenic nuclides"—even though the mechanism for their formation

12126-435: The past two decades. Hence, continued heat-trapping emissions favour increased formation of extreme events caused by prolonged weather conditions. Studies published in 2017 and 2018 identified stalling patterns of Rossby waves in the northern hemisphere jet stream as the culprit behind other almost stationary extreme weather events, such as the 2018 European heatwave , the 2003 European heat wave , 2010 Russian heat wave or

12255-427: The past. During the Last Glacial Maximum, much of the world was cold, dry, and inhospitable, with frequent storms and a dust-laden atmosphere. The dustiness of the atmosphere is a prominent feature in ice cores; dust levels were as much as 20 to 25 times greater than they are in the present. This was probably due to a number of factors: reduced vegetation, stronger global winds, and less precipitation to clear dust from

12384-527: The path of jet streams affects cyclonic storm systems at lower levels in the atmosphere, and so knowledge of their course has become an important part of weather forecasting. For example, in 2007 and 2012, Britain experienced severe flooding as a result of the polar jet staying south for the summer. In general, winds are strongest immediately under the tropopause (except locally, during tornadoes , tropical cyclones or other anomalous situations). If two air masses of different temperatures or densities meet,

12513-650: The persistence of rainforests in eastern Australia at this time. Rivers maintained their sinuous form in southeastern Australia and there was increased aeolian deposition of sediment in compared to today. The Flinders Ranges likewise experienced humid conditions. In southwestern Western Australia, forests disappeared during the LGM. Between Sahul and Sundaland – a peninsula of South East Asia that comprised present-day Malaysia and western and northern Indonesia – there remained an archipelago of islands known as Wallacea . The water gaps between these islands, Sahul and Sundaland were considerably narrower and fewer in number than in

12642-624: The phenomenon in 1939. Many sources credit real understanding of the nature of jet streams to regular and repeated flight-path traversals during World War II . Flyers consistently noticed westerly tailwinds in excess of 160 km/h (100 mph) in flights, for example, from the US to the UK. Similarly in 1944 a team of American meteorologists in Guam , including Reid Bryson , had enough observations to forecast very high west winds that would slow bombers raiding Japan. Polar jet streams are typically located near

12771-483: The planetary radius, holding all other parameters fixed, the number of jet streams decreases. The subtropical jet stream rounding the base of the mid-oceanic upper trough is thought to be one of the causes most of the Hawaiian Islands have been resistant to the long list of Hawaii hurricanes that have approached. For example, when Hurricane Flossie (2007) approached and dissipated just before reaching landfall,

12900-902: The present day, featuring moist subtropical evergreen forests, despite sea levels in the South China Sea being about 100 metres lower than the present day. The Australian mainland, New Guinea , Tasmania and many smaller islands comprised a single land mass. This continent is now referred to sometimes as Sahul . In the Bonaparte Gulf of northwestern Australia, sea levels were about 125 metres lower than present. Interior Australia saw widespread aridity, evidenced by extensive dune activity and falling lake levels. Eastern Australia experienced two nadirs in temperature. Lacustrine sediments from North Stradbroke Island in coastal Queensland indicated humid conditions. Data from Little Llangothlin Lagoon likewise indicate

13029-561: The present day. The two main islands of New Zealand, along with associated smaller islands, were joined as one landmass. Virtually all of the Southern Alps were under permanent ice cover, with alpine glaciers extending from them into much of the surrounding high country . Northern Europe was largely covered by ice, with the southern boundary of the ice sheets passing through Germany and Poland. This ice extended northward to cover Svalbard and Franz Josef Land and northeastward to occupy

13158-551: The present, with flora diminished to almost the same degree as in glaciated areas of Europe and North America. Even in less affected regions, rainforest cover was greatly diminished, especially in West Africa where a few refugia were surrounded by tropical grasslands . The Amazon rainforest was split into two large blocks by extensive savanna , and the tropical rainforests of Southeast Asia probably were similarly affected, with deciduous forests expanding in their place except on

13287-559: The production rate of nuclides within minerals by a factor of 30 between sea level and the top of a 5 km high mountain. Even variations in the slope of the ground can affect how far high-energy muons can penetrate the subsurface. Geomagnetic field strength which varies over time affects the production rate of cosmogenic nuclides though some models assume variations of the field strength are averaged out over geologic time and are not always considered. Jet stream Jet streams are fast flowing, narrow, meandering air currents in

13416-422: The resulting pressure difference caused by the density difference (which ultimately causes wind) is highest within the transition zone. The wind does not flow directly from the hot to the cold area, but is deflected by the Coriolis effect and flows along the boundary of the two air masses. All these facts are consequences of the thermal wind relation. The balance of forces acting on an atmospheric air parcel in

13545-557: The shutting down of the Oyashio Current and the presence of large east–west mountain ranges were secondary factors that prevented the development of continental glaciation in Asia . All over the world, climates at the Last Glacial Maximum were cooler and almost everywhere drier. In extreme cases, such as South Australia and the Sahel , rainfall could have been diminished by up to 90% compared to

13674-517: The southern Appalachian Mountains and the Atlantic Ocean, there was an enclave of unusually warm climate. In the Southern Hemisphere, the Patagonian Ice Sheet covered the whole southern third of Chile and adjacent areas of Argentina. On the western side of the Andes the ice sheet reached sea level as far north as in the 41 degrees south at Chacao Channel . The western coast of Patagonia

13803-508: The southern hemisphere polar jet mostly circles Antarctica , both all year round. Jet streams are the product of two factors: the atmospheric heating by solar radiation that produces the large-scale polar, Ferrel, and Hadley circulation cells, and the action of the Coriolis force acting on those moving masses. The Coriolis force is caused by the planet's rotation on its axis. On other planets, internal heat rather than solar heating drives their jet streams. The polar jet stream forms near

13932-444: The southern tip of South America . Thus, the term jet stream in these contexts usually implies the northern polar jet stream. The location of the jet stream is extremely important for aviation. Commercial use of the jet stream began on 18 November 1952, when Pan Am flew from Tokyo to Honolulu at an altitude of 7,600 metres (24,900 ft). It cut the trip time by over one-third, from 18 to 11.5 hours. Not only does it cut time off

14061-428: The stratosphere, which, when combined with the Coriolis effect, create the polar night jets, that race eastward at an altitude of about 48 kilometres (30 mi). The polar vortex is circled by the polar night jet. The warmer air can only move along the edge of the polar vortex, but not enter it. Within the vortex, the cold polar air becomes increasingly cold, due to a lack of warmer air from lower latitudes as well as

14190-500: The temperature gradient between it and the warmer parts of the globe will continue to diminish with every decade of global warming as the result of this amplification. If this gradient has a strong influence on the jet stream, then it will eventually become weaker and more variable in its course, which would allow more cold air from the polar vortex to leak mid-latitudes and slow the progression of Rossby waves , leading to more persistent and more extreme weather . The hypothesis above

14319-564: The thermal wind relationship, declining speeds are usually found south of the areas with geopotential increases. In 2017, Francis explained her findings to the Scientific American : "A lot more water vapor is being transported northward by big swings in the jet stream. That's important because water vapor is a greenhouse gas just like carbon dioxide and methane. It traps heat in the atmosphere. That vapor also condenses as droplets we know as clouds, which themselves trap more heat. The vapor

14448-428: The vertical direction is primarily between the gravitational force acting on the mass of the parcel and the buoyancy force, or the difference in pressure between the top and bottom surfaces of the parcel. Any imbalance between these forces results in the acceleration of the parcel in the imbalance direction: upward if the buoyant force exceeds the weight, and downward if the weight exceeds the buoyancy force. The balance in

14577-417: The vertical direction is referred to as hydrostatic . Beyond the tropics, the dominant forces act in the horizontal direction, and the primary struggle is between the Coriolis force and the pressure gradient force. Balance between these two forces is referred to as geostrophic . Given both hydrostatic and geostrophic balance, one can derive the thermal wind relation: the vertical gradient of the horizontal wind

14706-552: The volcano. Glacial moraines on the volcano formed about 70,000 years ago and from about 40,000 to 13,000 years ago. If glacial deposits were formed on Mauna Loa , they have long since been buried by younger lava flows. Low sea surface temperature (SST) and sea surface salinity (SSS) in the East China Sea during the LGM suggests the Kuroshio Current was reduced in strength relative to the present. Abyssal Pacific overturning

14835-649: The weakened thermohaline circulation. Evidence from sediment cores in the Scotia Sea suggests the Antarctic Circumpolar Current was weaker during the LGM than during the Holocene. The Antarctic Polar Front (APF) was located much farther to the north compared to its present-day location. Studies suggest it could have been placed as far north as 43°S, reaching into the southern Indian Ocean. Cosmogenic nuclide Cosmogenic nuclides (or cosmogenic isotopes ) are rare nuclides ( isotopes ) created when

14964-431: The winds (note that deflection is leftward in the southern hemisphere). Jupiter 's atmosphere has multiple jet streams, caused by the convection cells that form the familiar banded color structure; on Jupiter, these convection cells are driven by internal heating. The factors that control the number of jet streams in a planetary atmosphere is an active area of research in dynamical meteorology. In models, as one increases

15093-401: The winds are organized into tight jets, rather than distributed more broadly over the hemisphere. One factor that contributes to the creation of a concentrated polar jet is the undercutting of sub-tropical air masses by the more dense polar air masses at the polar front . This causes a sharp north–south pressure (south–north potential vorticity ) gradient in the horizontal plane, an effect which

15222-454: The winter months when the nights are much longer – hence the name referencing polar nights – in their respective hemispheres at around 60° latitude. The polar night jet moves at a greater height (about 24,000 metres (80,000 ft)) than it does during the summer. During these dark months the air high over the poles becomes much colder than the air over the Equator. This difference in temperature gives rise to extreme air pressure differences in

15351-600: Was a pocket of relative warmth. Following a preceding period of relative retreat from 52,000 to 40,000 years ago, the Laurentide Ice Sheet grew rapidly at the onset of the LGM until it covered essentially all of Canada east of the Rocky Mountains and extended roughly to the Missouri and Ohio Rivers , and eastward to Manhattan , reaching a total maximum volume of around 26.5 to 37 million cubic kilometres. At its peak,

15480-494: Was able to reconstruct jet stream patterns over the past 1,250 years based on Greenland ice cores , and found that all of the recently observed changes remain within range of natural variability: the earliest likely time of divergence is in 2060, under the Representative Concentration Pathway 8.5 which implies continually accelerating greenhouse gas emissions. The polar-night jet stream forms mainly during

15609-739: Was about 125 meters (410 ft) lower than in present times (2012). When comparing to the present, the average global temperature was 15 °C (59 °F) for the 2013–2017 period. As of 2012 about 3.1% of Earth's surface and 10.7% of the land area is covered in year-round ice. Carbon sequestration in the highly stratified and productive Southern Ocean was essential in producing the LGM. The formation of an ice sheet or ice cap requires both prolonged cold and precipitation ( snow ). Hence, despite having temperatures similar to those of glaciated areas in North America and Europe , East Asia remained unglaciated except at higher elevations. This difference

15738-495: Was because the ice sheets in Europe produced extensive anticyclones above them. These anticyclones generated air masses that were so dry on reaching Siberia and Manchuria that precipitation sufficient for the formation of glaciers could never occur (except in Kamchatka where these westerly winds lifted moisture from the Sea of Japan ). The relative warmth of the Pacific Ocean due to

15867-480: Was largely glaciated, but some authors have pointed out the possible existence of ice-free refugia for some plant species. On the eastern side of the Andes, glacier lobes occupied the depressions of Seno Skyring , Seno Otway , Inútil Bay , and Beagle Channel . On the Straits of Magellan, ice reached as far as Segunda Angostura . During the LGM, valley glaciers in the southern Andes (38–43° S) merged and descended from

15996-608: Was much weaker and more negative during the Last Glacial Maximum , and suggesting that warmer periods have stronger positive phase AO, and thus less frequent leaks of the polar vortex air. However, a 2012 review in the Journal of the Atmospheric Sciences noted that "there [has been] a significant change in the vortex mean state over the twenty-first century, resulting in a weaker, more disturbed vortex.", which contradicted

16125-769: Was seasonally uniform. On the island of Mauritius in the Mascarenhas Archipelago , open wet forest vegetation dominated, contrasting with the dominantly closed-stratified-tall-forest state of Holocene Mauritian forests. There were ice sheets in modern Tibet (although scientists continue to debate the extent to which the Tibetan Plateau was covered with ice) as well as in Baltistan and Ladakh . In Southeast Asia , many smaller mountain glaciers formed, and permafrost covered Asia as far south as Beijing . Because of lowered sea levels, many of today's islands were joined to

16254-553: Was similar in spatial extent. The outflow of North Pacific Intermediate Water through the Tasman Sea was stronger during the LGM. In the Great Barrier Reef along the coast of Queensland , reef development shifted seaward due to the precipitous drop in sea levels, reaching a maximum distance from the present coastline as sea levels approached their lowest levels around 20,700-20,500 years ago. Microbial carbonate deposition in

16383-468: Was stressed by reviews in 2013 and in 2017. A study in 2014 concluded that Arctic amplification significantly decreased cold-season temperature variability over the Northern Hemisphere in recent decades. Cold Arctic air intrudes into the warmer lower latitudes more rapidly today during autumn and winter, a trend projected to continue in the future except during summer, thus calling into question whether winters will bring more cold extremes. A 2019 analysis of

16512-496: Was the dominant influence on southern Greenland's climate. Illorsuit Island was exclusively covered by cold-based glaciers. Eastern Beringia was extremely cold and dry. July air temperatures in northern Alaska and Yukon were about 2-3 °C lower compared to today. Equilibrium line altitudes in Alaska suggest summer temperatures were 2-5 °C compared to preindustrial. Sediment core analysis from Lone Spruce Pond in southwestern Alaska show it

16641-512: Was weaker during the LGM than in the present day, although it was temporarily stronger during some intervals of ice sheet retreat. The El Niño–Southern Oscillation (ENSO) was strong during the LGM. Evidence suggests that the Peruvian Oxygen Minimum Zone in the eastern Pacific was weaker than it is in the present day, likely as a result of increased oxygen concentrations in seawater permitted by cooler ocean water temperatures, though it

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