Jean:
The Arctic oscillation (AO) is not directly related to global warming.
The geographical extent of arctic air is less than it was a few decades
ago, and it is not as cold as it was either, and that is an effect of
global warming. For the last month, temperatures in places like
Greenland and over the Arctic Ocean have been well above average,
because the negative AO cycle sent the arctic air south into the eastern
U.S. and Europe.
There is only so much arctic air to go around, and all the AO does is to
push the existing arctic air masses to different places. The AO is
somewhat like squeezing a balloon full of cold air, when the AO is
positive it squeezes the balloon in one place, and causes cold air to
bulge southwards in certain places, when the AO is negative, it squeezes
in a different place, resulting in arctic air bulging southwards in
different places compared to a positive AO.
There is, however, a slight trend towards positive AO values as the
climate warms, which would lead to fewer cold snaps such as the one we
are experiencing now in the eastern U.S., but it is a very slight trend,
and not something people are likely to notice unless they have a good
memory of cold snap frequency over several decades.
Lee
Wilma Jean Kinsey wrote:
----- Original Message ----- From: "Lee Frelich" <[email protected]>
To: <[email protected]>
Sent: Wednesday, January 06, 2010 6:13 PM
Subject: Re: [ENTS] Impact of cold snap?
James:
I don't think so. Emerald ash borer survived last winters cold spell
in Minnesota, which was much colder than the current cold spell.
Temperatures of -15 to -20 F seem necessary to kill hemlock woolly
adelgid. It might get that cold in MA, but it doesn't seem likely to
get that cold in the Smokies.
The current cold snap is being caused by the Arctic Oscillation,
which has reached the most negative reading recorded (since recording
began in the 1950s). It basically is a change in air pressure that
squeezes the polar vortex in such a way that cold air bulges south in
the eastern U.S. and western Europe, while Greenland is much warmer
than normal. The opposite pattern occurs when the AO is positive.
Lee
JamesRobertSmith wrote:
Will this relatively long cold snap here in the South have an effect
on the insect pests that have been plaguing our forests during the
recent years of warm winters? Will it be enough to stunt or kill off
the populations of rampant native and introduce insect pests?
A question from an interested fan of this site: is the bulge of the
polar vortex
a part of global warming? any relationship? We did study forestry
in my geomorphology class, that got me interested in Old Growth
Forests, (geography major) and backpacking enhanced my love of
trees. Jean Kinsey
