United Kingdom of Ice

Arctic Oscillation in Strong Negative Phase:
Why Northern Hemisphere is So Cold

Image of the Day: United Kingdom, Where the Ice Never Thawed!

Photo Credit: NASA/ MODIS Rapid Response. Click Image to enlarge.

Arctic Oscillation (AO)

The loading pattern of the AO is defined as the leading mode of Empirical Orthogonal Function (EOF) analysis of monthly mean 1000mb height during 1979-2000 period.

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The negative phase of the Arctic Oscillation (AO) has been a contributing factor to the arctic cold weather and blanket snow at the mid-latitudes across much of Northern Hemisphere since December 2009. The Arctic Oscillation Index in December 2009 fell to its lowest monthly value since 1950.

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The daily AO index is constructed by projecting the daily (00UTC) 1000mb height anomalies poleward of 20°N onto the loading pattern of the AO.  Year-round monthly mean anomaly data has been used to obtain the loading pattern of the AO (Methodology).  Since the AO has the largest variability during the cold season, the loading pattern primarily captures characteristics of the cold season AO pattern. Source: NOAA/ National Weather Service

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The daily geopotential height anomalies at 17 pressure levels are shown for the previous 120 days as indicated, and they are normalized by standard deviation using 1979-2000 base period. The anomalies are calculated by subtracting 1979-2000 daily climatology, and then averaged over the polar cap poleward of 65°N.

The blue (red) colors represent a strong (weak) polar vortex. The black solid lines show the zero anomalies.  Source: NOAA/  National Weather Service

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The standardized 3-month running mean value of the AO index. The departures are standardized using the 1950-2000 base period statistics.  Source: NOAA/  National Weather Service

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