Bomb cyclone, polar vortex.
It is freaking freezing outside.
Tonight we take a closer look at the science behind this deep
freeze.
UW-Madison Professor of Atmospheric and Oceanic Sciences
Jonathan Martin is here.
Thanks very much for being here.
- It's my pleasure.
- So exactly what is a bomb cyclone?
- It is sort of a nerdy word that was coined maybe 40 or so
years ago.
Maybe even older than that by somebody.
It got to be in general parlance around 1980 to explain or
describe cyclones, mid-latitude storms that develop really rapidly.
The way we measure their development is their minimum sea level pressure.
So a bomb storm is one where the sea level pressure
drops through the floor at a really rapid rate,
24 or so millibars in one day.
And that represents about 2% of the total column atmospheric
mass in one day disappears from that storm.
- How unusual is it?
- We probably get about two dozen of those kinds of
intensively-- rapidly intensifying storms around the
whole northern hemisphere each winter.
So they're not that unusual.
- And that's what's happening on the east coast?
- That's exactly what happened on the east coast.
This one was rather extreme in terms of how fast it developed.
It might be-- instead of one in two dozen,
it may be one in five type of storm per winter.
So it's really an exceptional event.
- And that is expected to be followed by a polar vortex?
- By very, very cold air.
Polar vortex is a word that a few years ago got into the
popular lexicon as a result of a cold winter.
It's a meteorological term that describes the tendency for
circulation around the pole at very high altitudes, 10,
20 miles above the ground.
So polar vortex now seems to mean cold air.
On the west side of such an intense cyclone,
where the circulation is counter-clockwise,
you can't help but drag colder air from higher latitudes down southward.
-That's what we're in right now?
- That's exactly what we're in. - And the trajectory of that?
Are we supposed to be in it for a while?
- Few more days, I think.
The extreme, waking up every morning to below zero temperatures,
a few more days of that.
And then we'll get back a little bit to normal.
There's no way to tell whether we'll see it again this winter,
but we may.
- Why is it happening?
- That is a great question.
It's the kind of question that gets answered in research that
one does after the event occurs.
So I'm currently beginning to think about answers
to that question.
One of the ingredients to get us really cold
is a high amplitude flow.
Very strong, north-south meanders of the atmospheric flow
at all levels, including the jet stream.
That's at about six miles above the ground.
That occurs every once in a while during the cold season,
but it isn't something that you can see coming
20 days in advance.
We did know this cold snap was coming around Christmastime or
even before that.
So 10 days or so in advance, the forecasts were really good for
prolonged cold snap in the eastern part of North America.
But longer than that is a difficult task.
- Does this have anything to do with climate change?
- My view on that is I'm rather skeptical that individual cold
snaps like this one are directly related to the broad background
warming that's going on around the planet.
And this is a difficult subject to sort of broach in some ways.
There's no doubt that such a thing is occurring.
The planet is warming up at a very slow but steady rate and
there are many ways to see that.
Whether or not it's cold in your backyard is not really
discern ably attributable to that change on a case-by-case basis.
I think that's safe to say for this one.
- What's hard to understand is that as the globe heats up,
we experience these kind of things like polar vortexes.
- Right. Right.
One of the interesting theories out there right now,
we're debating it, the community of scientists I'm involved in
is debating this rather haughtily.
There are sometimes some pretty strong opinions out there on
some of these issues.
But one thing that may occur when the planet warms up,
we know for sure the ice at high latitudes
gets weaker and thinner.
That might add some extra warming to the lower part of the
atmosphere in late fall, early winter that wasn't there 50 or
100 years ago.
That might have a tendency to increase the frequency of some
of these high amplitude flows, these strong north-south
variations.
If that's the case, because it still gets cold at the North Pole.
The sun is down for six months at the North Pole.
You're not going to change that.
You're still going to produce cold air up there.
If you can tap it with one of these excursions pole-ward of
the jet stream and drag it southward,
as is happening right now, with greater frequency,
then one might actually, somewhat paradoxically,
in a warmer planet, if the amplitude of the jet stream is
intensified because of that, I don't think the evidence is in
on that question but if that's true,
then we might have a higher frequency
of some of these cold snaps.
But there's no way to tell where they're going to hit.
Right now it's unusually warm in Russia.
Moscow's enjoying a really warm December and January.
Of course it's frigid over our part of the world.
- Jonathan Martin, thanks very much for your explanation.
- You bet. Thank you.