The daily AO index is constructed by projecting the daily (00Z) 1000mb height anomalies poleward of 20°N onto the loading pattern of the AO. Please note that year-round monthly mean anomaly data have 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.

The daily AO index and its forecasts using GFS and Ensemble mean forecast data are shown for the previous 120 days as indicated. Each daily value has been standardized by the standard deviation of the monthly AO index from 1979-2000.

• Vertical cross section of NH polar vortex

• Daily AO index since January 1950

• Monthly mean AO index since January 1950

• Animations (circulations)

• Time-Longitude Sections (circulations)

• GFS AO outlooks
• Ensemble mean AO outlooks

Higgins, R. W., A. Leetmaa, and V. E. Kousky, 2002: Relationships between climate variability and winter temperature extremes in the United States. J. Climate, 15, 1555-1572.

Higgins, R.W., Y. Zhou and H.-K. Kim, 2001: Relationships between El Niño-Southern Oscillation and the Arctic Oscillation: A Climate-Weather Link. NCEP/Climate Prediction Center ATLAS 8. ( Link to Atlas )

Higgins, R. W., A. Leetmaa, Y. Xue, and A. Barnston, 2000: Dominant factors influencing the seasonal predictability of U.S. precipitation and surface air temperature. J. Climate, 13, 3994-4017.

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Zhou, S., A. J. Miller, J. Wang, and J. K. Angell, 2001: Trends of NAO and AO and their associations with stratospheric processes. Geophys. Res. Lett., 28, 4107-4110.