A strong phase reversal of the Arctic Oscillation in midwinter 2015/2016: Role of the stratospheric polar vortex and tropospheric blocking

In January 2016, Asia and North America experienced unusual cold temperatures, although the global average of surface air temperature broke the warmest record during a strong El Niño event. This was closely related to the remarkable phase transition of the Arctic Oscillation (AO), which can be expla...

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Bibliographic Details
Published in:Journal of geophysical research. Atmospheres 2016-11, Vol.121 (22), p.13,443-13,457
Main Authors: Cheung, Hoffman H. N., Zhou, Wen, Leung, Marco Y. T., Shun, C. M., Lee, S. M., Tong, H. W.
Format: Article
Language:English
Subjects:
Aerodynamics
Air temperature
Anticyclones
Arctic Oscillation
Barotropic mode
Biennial
blocking
Blocking anticyclones
Coastal environments
Coexistence
Cold spells
Displacement
El Nino
El Nino events
Elongation
Equivalence
Extreme low temperatures
Fluid flow
Geophysics
Interactions
Marine
Meteorology
Phase transformations
Phase transitions
Polar environments
Polar vortex
Propagation
Quasi-biennial oscillation
Snowfall
Stratosphere
Stratospheric polar vortexes
Summer
Surface temperature
Temperature
Temperature effects
Troposphere
Vortices
Wave number
Wavelengths
Winter
Zonal waves
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Summary:In January 2016, Asia and North America experienced unusual cold temperatures, although the global average of surface air temperature broke the warmest record during a strong El Niño event. This was closely related to the remarkable phase transition of the Arctic Oscillation (AO), which can be explained by stratosphere‐troposphere interactions. First, the quasi‐biennial oscillation changed to its westerly phase in summer 2015 and the stratospheric polar vortex was stronger in early to midwinter 2015/2016. As blocking did not occur in December, the associated downward propagation signal resulted in a strongly positive AO in late December 2015. Second, after late December, the positive phase of Pacific‐North America pattern became apparent in El Niño event, which strengthened the Aleutian anticyclone in the stratosphere. In addition, an equivalent barotropic (“blocking”) anticyclone was established in the troposphere over Asia. The coexistence of blocking over Asia and North America characterized the negative AO and a strong zonal wave number 2 pattern. Due to stronger zonal wave number 2 signals from the troposphere, the stronger stratospheric polar vortex was elongated, with two cyclonic centers over Asia and the North Atlantic in January. The resultant southward displacement of polar vortices was followed by rare snowfall in the subtropical region of East Asia and a heavy snowstorm on the East Coast of the United States. Key Points The strongly positive Arctic Oscillation was due to the westerly quasi‐biennial oscillation and no blocking An El Niño event and the Asian blocking coincided with the elongation of the stratospheric polar vortex in January 2016 Blocking and the elongated polar vortex were linked to the strongly negative Arctic Oscillation and extreme cold spells
ISSN:2169-897X
2169-8996
DOI:10.1002/2016JD025288