Arctic Oscillation | Surface Temperatures | Stratospheric Temperatures | Clouds

The Arctic Oscillation (AO), shown below, is an important Arctic climate index with positive and negative phases, which represents the state of atmospheric circulation over the Arctic. The positive phase (red) brings lower-than-normal pressure over the polar region, steering ocean storms northward, bringing wetter weather to Scotland and Scandinavia, and drier conditions to areas such as Spain and the Middle East. While the value of the AO index was strongly positive in the early 1990's compared to the previous forty years, the value of the AO has been low and variable for the last nine years. The year to year persistence of positive or negative values and the rapid transition from one to the other is often referred to as "regime-like".

The Arctic Oscillation in Winter (November to March). Data from NCEP.

Find more information (references and websites):

• "Why and how do scientists study climate change in the Arctic? What are the Arctic climate Indices?"
• The Polar Vortex - definition, from National Snow and Ice Data Center
• Phases of the Arctic Oscillation, the Polar Vortex and Arctic weather patterns - from National Snow and Ice Data Center
• Atmospheric and Ocean Climate Indices Time Series - from the Climate Diagnostics Center
• Linear Correlations in Atmospheric Seasonal/Monthly Averages - from the Climate Diagnostics Center