This dataset contains global 500mb and 300mb vorticity area indices which were compiled by the Aspen Institute. The indices are stored on polar-stereographic grids, one for each hemisphere. For the Northern Hemisphere indices, the 20 and 24 vorticity contour levels were used, and for the Southern Hemisphere, the 16 contour level was used.

The 500mb Northern Hemisphere grids cover the period from January 1946 to February 1979 and the 300mb grids span the period from April 1955 to December 1977. For the Southern Hemisphere at both levels, grids are available from April 1972 to January 1978.