Waghorn wrote:
I think it's worth pointing out that the regime in the North Atlantic sector
depends on the strength of the polar vortex.When the vortex is strong there
is a single strong zonal jet across the NA,during times of weak vortex there
tends to be two weaker jets-eastern and western in the sector.The
statistical dependence on SST distributions differs entirely for the two
different regimes,

--
regards,
David

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Also worth noting that the 97 chart shows an 'intense' El Nino which
would have invigorated the polar vortex and reduced the chance of a
negative NAO - IMO.