Franklin Fact Archive
Back to Franklin Facts homepage.
Back to TV12
WEDNESDAY MARCH 28 - NORTH ATLANTIC OSCILLATION: PART 1
One climate cycle has received a lot of attention in the last few years. That's the
El Nino/La Nina cycle, a variation between unusually warm and unusually cool waters
in the tropical Pacific Ocean.
But there are other cycles that get less publicity but plenty of attention from
meteorologists. One that impacts our area, especially in winter, is called the
North Atlantic Oscillation - NAO for short. The NAO is based on pressure differences
from north to south in the North Atlantic Ocean, approximately between the
Islands to the south and Iceland to the north. At one extreme of the NAO, called
Positive phase, air pressure is unusually high near the Azores, and unusually
low near Iceland. This large pressure difference leads to a strong westerly jet
stream blowing across the Atlantic. At the other extreme, called the
the pressure difference is much less, so these upper-air winds tend to be weaker,
and the jet stream pattern tends to have lots of dips and bends in it.
Now all this is happening out over the Atlantic Ocean. But with the East Coast of the
U.S. just to the west, it's not much of a stretch to think that this cycle over the
ocean can affect our weather. Weíll look at that tomorrow night.