This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
WinterNAOIndex. Description North Atlantic Oscillation NAO index Year is on the xaxis and the standardised principalcomponent based winter NAO index on the yaxis The bars show each winter's mean NAO index where for instance winter means the period from December up to and including March The black line is the year running mean