The North Atlantic Oscillation (NAO) index and Southern
Oscillation Index (SOI), which are derived by meteorological
information and in particular by sea level pressure,
were also used. The NAO index, based on the difference
of normalized sea level pressure between the Azores and
Iceland, is a temporal fluctuation of zonal wind strength
across the Atlantic Ocean due to pressure variation in
both the subtropical anticyclone belt and the subpolar low
near Iceland. In the northern hemisphere the winter NAO
index (December to March) shows a significant relationship
with storm track, temperature, and precipitation (Hurrell
and van Loon 1997). The SOI is a standardized index
based on observed sea level pressure differences beween
Darwin, Australia (lat: 131°; long: -12°) and Papeete, Tahiti
(lat: -149°; long: -17°) and is a measurement of the largescale
fluctuations in air pressure occurring between the
western and eastern tropical Pacific which quantify the
ENSO (El Niño Southern Oscillation) phenomenon