Jennifer Francis, Rutgers University or...
Glen Gerberg Weather and Climate Summit
Breckenridge, CO -- 8-13 January 2012
Photo by Janes

In the good old days… The new normal.
The difference in ice area is ~1,300,000 miles 2 .

That’s an area covering about 42% of the lower 48.
generated by J. Masters

So, the question is not whether sea-ice loss is affecting large-scale atmospheric circulation…
…but, let’s back up a bit.
How did we get into this mess?

from Bill Chapman’s The Cryosphere Today

with the industrial revolution…
CO
2
Concentration

Good ol’ days
Increasing GHGs and related feedbacks caused ice to gradually thin.
Rothrock and Kwok, 2009

attack of the AO+ during the ‘90s
Normal conditions
Arctic Oscillation Index
Positive AO Index
Ice-age Movie
From NOAA’s
ClimateWatch

Ice Age is a Big Deal because… it’s a proxy for ice thickness.
And THAT’s a big deal because a thinner ice cover is more easily melted, more easily moved by the wind, and more likely to follow a trajectory of loss as GHGs continue to increase.
Thick ice by Maslanik and Fowler, NSIDC, Arctic Report Card 2011

8
Ice age at the end of March
5+ years
6
4
4
2
3
Ice age at the end of summer
2
First year ice 8
0
5+ years
4
2
4
3
2
First year ice
0
1985 1990 1995 2000 2005 2010
From Stroeve et al. (2011) Climatic Change

The thinner ice cover is more mobile and more vulnerable to anomalous wind patterns, like those generated by a high-amplitude jet stream:
T HE A RCTIC D IPOLE (Overland and Wang, 2010)
2007 2008 2009 2010 2011
Thick ice of the good ol’ days was much less affected by these wind patterns
(Wang et al, 2009)

All that new open water absorbs additional solar radiation during spring and summer…
…that heats the sea surface and adds yet more fuel to the Arctic fire…
Sea surface temps
AK
∆SST

Summary so far…
 GHGs = > gradual thinning
 Natural variability: period of AO+ flushes thick ice out of Arctic in ‘90s
 Thinner ice cover more easily pushed by winds and melted by anomalous heat fluxes: it can’t recover
 Additional open water absorbs more sunlight, heats ocean surface, melts more ice

What’s up with all that heat??
Ice extent anomaly
1960 1970 1980 1990 2000

During autumn and winter, energy
- lots more than normal – is being transferred to the atmosphere as sensible heat, water vapor, and infrared radiation.

Which brings us back to the question:
It’s not whether sea-ice loss is affecting largescale atmospheric circulation…
not
And what are the mechanisms ?
Budikova, Global Planet. Change, 2009
Bhatt et al, Geophys. Mono., 2008
Deser et al, J. Climate, 2007, 2010
Francis et al, GRL, 2009
Higgins and Cassano, JGR, 2009
Honda et al, GRL, 2009
Overland and Wang, Tellus, 2010
Petoukhov and Semenov, JGR, 2010
Seierstad and Bader, Clim. Dyn., 2009
Sokolova et al, GRL, 2007

This study focuses on the connections between
Arctic Amplification and extreme weather in northern hemisphere mid-latitudes
Extreme weather = high-amplitude, slow-moving upper-level patterns that cause persistent weather conditions
Coldest days in Tampa Hottest days in Atlanta Wettest days in Chicago
500 hPa
500 hPa
500 hPa

North Atlantic
High ice
Low ice
9 10 11 12 1 2 3 month
North Pacific
High ice
Low ice from Francis et al, GRL, 2009
9 10 11 12 1 2 3 month
Data obtained from NCEP/NCAR Reanalysis, Kalnay et al.
(1996), NOAA/ESRL Physical Sciences Division, Boulder CO from their web site at http://www.esrl.noaa.gov/psd
1000-500 hPa thickness anomaly during fall 2000 to 2010
OND
… and winter

Connecting the dots (focus on fall and winter):
Thickness increases are larger in high latitudes than in mid-latitudes => expect 2 main effects:
First effect: Weaker poleward temperature gradient
=> weaker zonal wind speeds . Do we see that? Yep.
N. America and N. Atlantic
OND
JFM
OND
JFM
14
1000-500 hPa thickness difference between
80-60 o N and 50-30 o N
12
10
JAS
AMJ
Zonal mean wind at
500 hPa, 40-60 o N
~ 20% less
8

Weaker zonal wind speeds favor slower moving Rossby waves, which leads to more persistent “stuck” weather patterns.
Sound familiar?

Second effect:
Larger warming at high latitudes causes peaks of ridges to elongate
 Wave amplitude increases
 Higher-amplitude waves progress more slowly
 More persistent weather patterns
500 hPa isopleth

Is this really happening? Let’s dig deeper:
 Focus on 500 hPa heights – integrates effects of heating in lower troposphere.
 Select narrow height range that captures trajectory
 Analyze temporal and spatial behavior
All data for this work are from the NCEP/NCAR Reanalysis, Kalnay et al. (1996), obtained from the NOAA/ESRL
Physical Sciences Division, Boulder CO at http://www.esrl.noaa.gov/psd

Is wave amplitude really increasing?
Trends (OND)
 Wave amplitude measured as seasonalmean difference in latitude between ridges and troughs at each longitude
 Amplitude is increasing almost everywhere

How has the spatial and temporal distribution of 500 hPa heights changed during autumn ?
 Increased ridging north of 50 o N
 Decreased troughs
 Has wave amplitude increased or has whole pattern shifted northward?
Autumn (OND)
Fractional anomalies in number of gridpoints with selected 500 hPa height

 Maximum latitude of ridges increasing
 Bottoms of troughs steady since ~1980
 Amplitude increasing steadily since ~1980
 High correl’n with ice
Autumn (OND)
Sept ice area r = -0.8
r = -0.1
r = -0.8

Where are northward elongations occurring?
Autumn (OND)
Trends (OND)
 Ridge peaks located mainly over western N.
America and eastern N.
Atlantic
 Number of ridge points north of 50 o N increasing west of Greenland

Could this be contributing to increasing max and min fall temperatures in
U.S. since mid-1990s??
1920 1940 1960 1980 2000
TMAX
TMIN from NCDC/NOAA Climate Extremes Index
1920 1940 1960 1980 2000

Now let’s take a look at winter :
 Increased ridging north of 40 o N
 Decreased troughs
 Increased wave
amplitude ?
Winter (JFM)
Fractional anomalies in number of gridpoints with selected 500 hPa height

 Maximum latitude of ridges increasing
 Bottoms of troughs shifting northward
 Amplitude increasing steadily since late 1980s
 Weak correl’n with AO
Winter (JFM)
AO Index r = 0.3
r = 0.7
r = 0.1

from NOAA/CPC
Sunspots

 Ridge peaks located mainly over western N.
America and eastern N.
Atlantic
 Number of ridge points north of 40 o N increasing, especially over N. America
Trends (JFM)
Winter (JFM)

 Troughs consolidating along US east coast
 Fewer (weaker) troughs over west/central US and eastern N. Atlantic troughs

What about summer?
 Snow is melting earlier over highlatitude land
 Soil is exposed to sunlight earlier, so it dries and warms earlier
 Further Arctic amplification
Summer surface

 Ridge peaks and troughs shifting northward
 Amplitude increasing
 High correlations with
May snow area
Summer (JAS)
May snow area r = -0.9
r = -0.9
r = -0.7

 Preferential ridging over western N. America
 Ridging increasing generally, especially in recent years and in western
N. Atlantic (=> Greenland?)

Could this be contributing to increasing max and min summer temperatures in U.S.?
1920 1940 1960 1980 2000
TMAX
TMIN from NCDC/NOAA Climate Extremes Index
1920 1940 1960 1980 2000

J.A. Francis – Rutgers Univ.
Weather and Climate Summit, 2012
Arctic Amplification
High latitudes warming more than mid-latitudes, especially in fall and winter, but also in summer over land
=> Poleward thickness gradient weakening
Weaker upper-level, zonal-mean flow, reduced phase speed
Peaks of upper-level ridges elongate northward, wave amplitude increases
 Rossby waves progress more slowly
 Weather conditions more persistent
 Increased probability of extremes: cold spells, heat waves, flooding, prolonged snowfall, and drought

Northern Hemisphere, OND

Northern Hemisphere, JFM (5400)