Winter '12 / '13 - North Atlantic Oscillation - Trends

Chart 1 - meteorological winter/s average NAO and 9-point binomial filter.
Binomial filter removes noise from signal to reveal trends.

1950s through 1970s...predominantly negative
1980 ...period of transition toward positive
1990s through 2000s...predominantly positive...trending toward negative in the 2010s.



Chart 2 - tally of all monthly NAO sign by calender year.

Noisy signal during most decades; however...positive index began to prevail during the late 1990s.

Value of '6' are years where positive and negative months during the calender year were equal.



Chart 3 (above) - tally of the monthly NAO sign by half-decade.

Slight advantage for negative index during the 1960s through mid-1970s...alternating during late 1970s through the 1980s...strong positive index prevailed during the late 1980s through the early 2000s...and negative ever since.

Value of '30' are periods where positive and negative months were equal.

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Chart 4 - tally of the monthly NAO sign by decade.

Positive decadal index between the 1970s until 2000s after which negative has been the trend.
Value of '60' are periods where positive and negative months were equal.



The 5-year moving average during meteorological winter turned negative in 2009 has been negative ever since.  The last time the 5-year moving average was negative occurred between 1977 - 1981 and 1954 - 1972.

Trending:  negative NAO.