Thinking about the Arctic Oscillation
Richard B. Rood
University of Michigan
for the National Park Service
August 8, 2013
Outline
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Why am I giving this talk?
Some aspects of climate variability
The Arctic Oscillation
A heuristic: vortices
The Arctic Oscillation and Climate Change
Synthesis
• Big Thanks to Jim Hurrell for consultation and
some slides.
• This talk and backup material at GLISAclimate.org
Why am I giving this talk?
• Worked on an adaptation planning activity with
Isle Royale Park
• The Arctic Oscillation emerged as an important
weather-climate driver
• The Arctic Oscillation has major impact on warmcold, dry-wet, especially in winter and spring in
the eastern half of North America
• The response of ecosystems to this variability can
amplify the weather-climate variability
• Will the behavior of the Arctic Oscillation change?
Some Aspects of Climate Variability
• One of the ways to think about climate variability
is to think about persistent patterns of weather
– Rainy periods
• Floods
– Dry periods
• Droughts
• During these times the weather for a region does
not appear random – it perhaps appears
relentless
Cold
Messy
Warm
Cold
Messy
Temperature
An example of variability: Seasons
Winter
Summer
Rain
comes in
fronts
Rain comes in
thunderstorms
Winter
Forced variability
responding to solar
heating
Internal Variability
(Rood Class Lecture 2010)
• Weather – single “events” – waves, vortices
• There are modes of internal variability in the climate
system which have global consequences.
– El Nino – La Nina
• What is El Nino
– North Atlantic Oscillation / Arctic Oscillation
• Climate Prediction Center: North Atlantic Oscillation
– Annular Mode
– Inter-decadal Tropical Atlantic
– Pacific Decadal Oscillation
Definition: CPC Climate Glossary
Arctic Oscillation (AO) - The Arctic Oscillation is a pattern in which
atmospheric pressure at polar and middle latitudes fluctuates
between negative and positive phases. The negative phase brings
higher-than-normal pressure over the polar region and lower-thannormal pressure at about 45 degrees north latitude. The negative
phase allows cold air to plunge into the Midwestern United States
and western Europe, and storms bring rain to the Mediterranean.
The positive phase brings the opposite conditions, steering ocean
storms farther north and bringing wetter weather to Alaska,
Scotland and Scandinavia and drier conditions to areas such as
California, Spain and the Middle East. The North Atlantic Oscillation
is often considered to be a regional manifestation of the AO.
Some Attributes of Arctic Oscillation
• For our discussion Arctic Oscillation, North Atlantic
Oscillation, and Northern Annular Mode are related –
essentially the same
• Largest mode of variability in northern middle and high
latitudes
• It is present all year, we notice it more in winter and spring
El Nino – La Nina
• Ocean – Atmosphere
• Global Influence
• Predictable
Arctic Oscillation
• Atmosphere
• Strong Regional Influence
• Difficult to predict
Year-to-Year Changes in Winter Temperatures
Differences Relative to 1961-1990 Average
Late 1970s
2006-2011
From Jim Hurrell
Winter (Dec-Feb) Surface Temperature
Differences Relative to 1961-1990 Average (32.6ºF)
United States (lower 48)
• Lots of variability including very large changes from one winter to the next
• Winter of 1979 was the coldest in the US record (5.3ºF below average)
• Most winters since 1985 have been warm; colder winters early in the record
•February 1985 was the last month below twentieth century average
• Contiguous US winter temperatures have warmed ~2ºF since 1895
• Winter of 2010 was 15th coldest since 1895 (1.4ºF below average),
while winter 2011 was the 39th coldest (0.35ºF below average).
From Jim Hurrell
Arctic Oscillation
1895 – 2011
Daily Index
Period used in
Previous Maps
2010
2011
Side by Side Comparison
Arctic Oscillation and North American Temperature
DJF Temperature: Anomaly 1961-91
From Jim Hurrell
Some basic references
• Hurrell, 1995: Decadal trends in the North Atlantic
Oscillation: Regional Temperature and Precipitation
• Hurrell and Deser, 2010: North Atlantic climate
variability: The role of the North Atlantic Oscillation
• Kuzmina et al. 2005: The North Atlantic Oscillation and
Greenhouse Gas Forcing
• Bai et al., 2012: Great Lakes ice and Arctic Oscillation and
El Nino
What’s going on? A heuristic
• A conceptual physics-based foundation
• A vortex is circulating air.
• If there is a low pressure system on Earth in
the northern hemisphere then air circulates
counterclockwise around the low.
Heuristic: A vortex
fast
Low
http://commons.wikimedia.org/wiki/File:Rotational_vortex.gif
Heuristic: A vortex and a ball
Try to roll the ball towards the vortex
fast
Low
http://commons.wikimedia.org/wiki/File:Rotational_vortex.gif
http://i206.photobucket.com/albums/bb194/Dantejfisher/RollingBall.gif
Heuristic: A vortex and a ball
Try to roll the ball towards the vortex
fast
Low
• Vortices are boundaries or separators.
• Air inside of vortices often takes on distinct
characteristics.
http://commons.wikimedia.org/wiki/File:Rotational_vortex.gif
http://i206.photobucket.com/albums/bb194/Dantejfisher/RollingBall.gif
Ball rolling experiment
Ball roller and friend
http://24.media.tumblr.com/tumblr_m3q2hkeyJV1r3a6jho1_500.gif
Cold vortex
Imagine air isolated over the pole in winter, with no sun.
Cold vortex surrounded by warm air
Cold at y
y
X
Warm at x
Strong vortex and weak vortex
STRONG
WEAK
Weak vortex surrounded by warm air
Warm at y
y
X
Cold at x
Concept of Blocking
Bring it back to the atmosphere
The Arctic Oscillation
“Positive” Phase
• Strong low (high) air pressure
at high (middle) latitudes
• Extremely cold air confined
to Arctic
• Warm middle latitudes
Strong vortex
“Negative” Phase
• Pressure systems weaker
• Cold Arctic air spills into
middle latitudes
• Warm middle latitude air
moves into Arctic
Weak vortex
From Jim Hurrell
Year-to-Year Changes in Winter Temperatures
Differences Relative to 1961-1990 Average
Late 1970s
2006-2011
From Jim Hurrell
Wave Motion and Climate
What about climate change?
What Climate Processes Govern NAO Variability?
EOF1 SLP
(Dec-Mar)
• 200 years of NCAR CAM without
variations in “external” forcings
• Basic structure & time scale arises
from internal nonlinear atmospheric
dynamics
Simulated NAO
Index
(Dec-Mar)
Random
Randomand
andUnpredictable
Unpredictable
Variations
Variations
r (1yr) = -0.07
Observed
r (1yr) = -0.03
Except for the latter half
of the 20th century
r (1yr) = 0.4
A role for external forcing?
What’s the future?
• The indication from model simulations prior to
2012 are that the positive phase of the Arctic
Oscillation will become more prominent …
• But … these models don’t have the loss of sea ice
and northern snow cover …
– Huge changes in the forcing of the atmosphere
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Radiative forcing due to change in color
Heat flux between ocean and atmosphere
Heat flux between land and atmosphere
Moisture flux between ocean-land-atmosphere
And in the end what might really matter –
how storms propagate
Edge of the vortex
• Strength of storms
• Direction of storms
• Speed of storms
Warm at y
y
X
Cold at x
North Atlantic Oscillation
(from Lamont-Doherty )
Positive Phase
U.S. East, Mild and Wet
Europe North, Warm and Wet
Canada North & Greenland, Cold and Dry
Negative Phase
U.S. East, Cold Air Outbreaks, Snow (dry)
Europe North, Cold; South, Wet
Greenland, Warm
Some recent research
• Liu et al., 2012: Impact of declining Arctic sea ice
on recent winter snow fall
“ some resemblance to the negative phase of the winter
Arctic oscillation. However, the atmospheric circulation
change linked to the reduction of sea ice shows much
broader meridional meanders in midlatitudes and clearly
different interannual variability than the classical Arctic
oscillation.”
Some recent research
• Francis and Vavrus, 2012: Evidence linking Arctic
amplification to extreme weather in mid-latitudes
“Slower progression of upper-level waves would cause
associated weather patterns in mid-latitudes to be more
persistent, which may lead to an increased probability of
extreme weather events that result from prolonged
conditions, such as drought, flooding, cold spells, and heat
waves.”
Some recent research
• Greene et al., 2013: Superstorm Sandy: A series
of unfortunate events?
“However, there is increasing evidence that the loss of
summertime Arctic sea ice due to greenhouse warming
stacks the deck in favor of (1) larger amplitude meanders in
the jet stream, (2) more frequent invasions of Arctic air
masses into the middle latitudes, and (3) more frequent
blocking events of the kind that steered Sandy to the west”
Some synthesis
• We are seeing, here, an instance of the “non-stationarity” of climate.
– Change in the surface, changes energy and moisture characteristics of weather
– The statistical distribution will change
– This is not a simple shift of the distribution function
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Evidence that the variability will increase
– But, remember, we are in warming climate
• Changes in regional and seasonal heat and moisture budget
– Heavy snow, fast melt, change of water supply and quality, winter and spring
flooding
• Propagation of storms is likely to change to cause the accumulation of
weather effects into more extreme events
– Slow moving storms are very good at, for instance, building up storm surges
– Sustained precipitation followed by sustained heat and dry
• If I were a planner, then I would be expecting more variability with
increasing extremes associated with storms surges, heat, air quality,
drought and flood
Some Ecological References
• Walther et al., 2002: Ecological responses to
climate change
• Post et al., 2009: Population dynamics and hot
spots of response to climate change
• Hurrell and Deser, 2010: North Atlantic
Climate Variability (reference to other
literature)
GLISAclimate.org
• Big Thanks to Jim Hurrell for consultation and
some slides.
• Material and more in project on Arctic Oscillation
at GLISAclimate.org . Please join project, write
comments, re-use material, correct mistakes, ask
questions, and add more.
• http://glisaclimate.org/project/arcticoscillation%3A-climate-variability-in-great-lakes