Methodology

• The basic element of the multifield analog approach is the definition of a climate state vector which traces the time evolution of the analysed climate system in a multi-dimensional state space (Barnett and Presisendorfer, 1978)
• The climate state vector components: anomalies of temperature at 1000 hPa, geopotential height at the 700 hPa over the Northern Hemisphere, zonal wind at 200 hPa and sea surface temperature have been used to compute a multifield correlation matrix for November.
•  Predictand: the NAO phase (50% percentile of the NAO index built as the diffrerence between Iceland and Azores.
• Hindcast period: 1986-2002.
• The analogs are selected by searching the smallest distance between the actual and past states in the climate hyperspace spanned by the first 3 EOFs of the correlation matrix associated to the climate vector components.

Results: 12 correct matches from 17 predictions (significant at 92%)

References:

Barnett, T.P. and R.W. Preisendorfer. 1978. Multifield analog prediction of short-term climate fluctuations using a climate state vector. J. Atmos. Sci., 35(10), 1771–1787.