| Siberian High | |
|---|---|
| Area of occurrence | Northeastern part of Eurasia |
| Season | September–April |
| Effect | Severe winter cold and attendant dry conditions with little snow and few or no glaciers |
TheSiberian High (alsoSiberian Anticyclone;Russian:Азиатский антициклон (Aziatsky antitsiklon);Chinese:西伯利亞高壓;PinyinXībólìyǎ gāoyā;Kazakh Азия антициклоны (Aziya antitsiklonı)) is a massive collection of cold dry air that accumulates in the northeastern part ofEurasia from September until April. It is usually centered onLake Baikal.[1] It reaches its greatest size and strength in thewinter when the air temperature near the center of thehigh-pressure area is often lower than −40 °C (−40 °F). Theatmospheric pressure is often above 1,040millibars (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 outsideGreenland, of −67.8 °C (−90.0 °F) on 15 January 1885 atVerkhoyansk, and the highest pressure, 1083.8mbar (108.38kPa, 32.01inHg) atAgata,Krasnoyarsk Krai, on 31 December 1968, ever recorded.[2] The Siberian High is responsible both forsevere winter cold and attendant dry conditions with little snow and few or no glaciers acrossthe Asian part of Russia,Mongolia, andChina. During thesummer, the Siberian High is largely replaced by theAsiatic low.
The Siberian High affects the weather patterns in most parts of theNorthern Hemisphere: its influence extends as far west asItaly,[3] bringing freezing conditions also in the warm South,[4] and as far southeast asMalaysia,[5] where it is a critical component of the northeastmonsoon. Occasionally a strong Siberian High can bring unusually cold weather into the tropics as far southeast as thePhilippines.[6] It may block or reduce the size oflow-pressure cells and generate dry weather across much of the Asian landscape with the exception of regions such asHokuriku and theCaspian Sea coast ofIran that receiveorographic rainfall from the winds it generates. As a result of the Siberian High, coastal winters in the main city of Pacific RussiaVladivostok are very cold in relation to its latitude and proximity to the ocean.
Siberian air is generally colder than Arctic air, because unlike Arctic air which forms over thesea ice around theNorth Pole, Siberian air forms over the cold tundra of Siberia, which does not radiate heat the same way the ice of the Arctic does.[7]
In general, the Siberian High-pressure system begins to build up at the end of August, reaches its peak in the winter, and remains strong until the end of April. Its genesis at the end of the Arctic summer is caused by the convergence of summer air flows being cooled over interiornortheast Asia as days shorten. In the process of the Siberian High's formation, the upper-level jet is transferred across northern Eurasia by adiabatic cooling and descendingadvection, which in extreme cases creates "cold domes" that outbreak over warmer parts ofEast Asia.
In spite of its immense influence on the weather experienced by a large proportion of the world's population, scientific studies of the Siberian High have been late in coming, though variability of its behavior was observed as early as the 1960s.[1] However, recent studies of observedglobal warming overAsia have shown that weakening of the Siberian High is a prime driver of warmer winters in almost all of inland extra-tropical Asia and even over most parts ofEurope,[1] with the strongest relationship over theWest Siberian Plain and significant relationships as far west asHungary and as far southeast asGuangdong.Precipitation has also been found to be similarly inversely related to the mean central pressure of the Siberian High over almost all ofEastern Europe during theboreal winter, and similar relationships are found in southern China, whilst the opposite correlation exists over theCoromandel Coast andSri Lanka. Other studies have suggested that the strength of the Siberian High shows an inverse correlation with the high-pressure systems over North Africa.Another correlation has been noted, a connection of a weaker Siberian High andArctic oscillation when theAntarctic oscillation (AAO) is stronger.[8]
Because increased snow and ice cover enhances the Siberian High,[9] the Siberian High was both more intense and located further west during the earlyMiddle Pleistocene as a result of the extensive glaciation ofmountain ranges across Central Asia.[10] The decrease in magnitude of the Siberian High during the Holocene enabled eastward encroachment of westerlies enriched withwater vapour, precipitating an increase in low altitudeafforestation of Central Asia.[11]
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