Revised Values for Vorticity Area Index

Many studies of possible links between solar activity and the terrestrial atmosphere and climate system have been based on the Vorticity Area Index (VAI). The VAI is an index describing cyclonic activity, and is typically specified for the Northern Hemisphere and the 500 mb level. Nearly all studies of VAI have been based on the original Olson, Roberts and Gerety data set for VAI, which was based on the NMC data grid, or extensions thereof. The reanalysis data which are now available since 1948 can be used to calculate a new dataset for vorticities and VAI. As the reanalysis data is more homogeneous than the NMC grid expected improvements in the VAI dataset should be investigated. This poster presents such a new VAI dataset, based on NCEP reanalysis data. We find changes in the VAI which are mainly related to large jumps in the old VAI dataset which no longer are evident, as well as changes on shorter time scale. The new dataset is made available over the Internet.