SIBERIAN ANTICYCLONE

also called the Siberian High, or Asiatic High, semipermanent system of high atmospheric pressure centred in northeastern Siberia during the colder half of the year. The anticyclone forms because of the intense cooling of the surface layers of air over the continent during this season. It is usually quite shallow in vertical extent, rarely persisting to altitudes of 3,000 m (10,000 feet). The Siberian anticyclone is one of the principal sources of polar air masses. Mean January temperatures at certain locations within this pressure system are the lowest in the Northern Hemisphere: many stations have averages lower than -46 C (-51 F). Outbreaks of polar air westward from this high-pressure area cause occasional severe cold spells in parts of the European continent. In the summer, heating over the vast Asian land mass causes the anticyclone to dissipate.