While the Arctic Oscillation and North
Atlantic Oscillation Indices (NO & NOA) can change without
notice, it is still useful to see how they are trending. The AO Index
measures the degree to which Arctic air penetrates into middle
latitudes is related to the AO index, which is defined by surface
atmospheric pressure patterns. When the AO index is positive, surface
pressure is low in the polar region. This helps the middle latitude
jet stream to blow strongly and consistently from west to east, thus
keeping cold Arctic air locked in the polar region. When the AO index
is negative, there tends to be high pressure in the polar region,
weaker zonal winds, and greater movement of frigid polar air into
middle latitudes. Right now it's positive.
The NOA Index can also
swing towards a positive or negative value with the positive side
tending to be associated
with above average temperatures in the eastern United States! And
that's a good thing!
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