The Arctic Paradox Photo by Janes Glen Gerberg Weather and Climate Summit Breckenridge, CO -- 8-13 January 2012 or... Arctic Sea Ice: A Tragic Tale of.

The Arctic Paradox

Photo by Janes

Glen Gerberg Weather and Climate SummitBreckenridge, CO -- 8-13 January 2012

or...

Arctic Sea Ice: A Tragic Tale of Loss and

RevengeJennifer Francis, Rutgers University

In the good old days… The new normal.

The difference in ice area is ~1,300,000 miles2.

That’s an area covering about 42% of the lower 48.

generated by J. Masters

…it’s how can it not ?

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

The story goes like this…The fossil fuel era began with the industrial revolution…

CO2 Concentration

Rothrock and Kwok, 2009

Ice

thic

knes

s (m

)

Increasing GHGs and related feedbacks caused ice to gradually thin.

Good ol’ days1990s

Normal conditions

Positive AO Index

Ice extent in the good ol’ days was controlled mainly by wind variations...…but the recent thinner ice was defenseless against the attack of the AO+during the ‘90s

Arctic Oscillation Index

Ice-age MovieFrom NOAA’sClimateWatch

Ice Age is a Big Deal because…

by Maslanik and Fowler, NSIDC, Arctic Report Card 2011

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

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: THE ARCTIC DIPOLE (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

∆SST

AK

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.

…it’s how can it not ?

Which brings us back to the question:

It’s not whether sea-ice loss is affecting large-scale atmospheric circulation…

And what are the mechanisms ?

Budikova, Global Planet. Change, 2009 Honda et al, GRL, 2009Bhatt et al, Geophys. Mono., 2008 Overland and Wang, Tellus, 2010Deser et al, J. Climate, 2007, 2010 Petoukhov and Semenov, JGR, 2010Francis et al, GRL, 2009 Seierstad and Bader, Clim. Dyn., 2009Higgins and Cassano, JGR, 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

500 hPa

Hottest days in Atlanta

500 hPa

Wettest days in Chicago

500 hPa

OND

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

Temperature anomaly at 700 mbduring fall 2000 to 2010

1000-500 hPa thickness anomalyduring fall 2000 to 2010

… and winter

Temperature anomaly at 850 mbduring fall 2000 to 2010

Near-surface temperature anomalyduring fall 2000 to 2010

Pole

war

d 10

00-5

00 h

Pa

thic

knes

s gr

adie

ntNorth Atlantic

High ice

Low ice

9 10 11 12 1 2 3 month

North PacificHigh ice

Low ice

9 10 11 12 1 2 3 month

from Francis et al, GRL, 2009

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.

1000-500 hPa thickness difference between 80-60oN and 50-30oN

N. America and N. Atlantic

OND JFM JFMOND

JAS

AMJZonal mean wind at 500 hPa, 40-60oN

14

12

10

8

~ 20% less

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 trajectoryAnalyze 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?

Wave amplitude measured as seasonal-mean difference in latitude between ridges and troughs at each longitude Amplitude is increasing almost everywhere

Trends (OND)

How has the spatial and temporal distribution of 500 hPa heights changed during autumn?

Increased ridging north of 50oN Decreased troughs Has wave amplitude increased or has whole pattern shifted northward?

Maximum latitude of ridges increasing Bottoms of troughs steady since ~1980 Amplitude increasing steadily since ~1980 High correl’n with ice

r = -0.8

r = -0.1

r = -0.8

Where are northward elongations occurring?

Ridge peaks located mainly over western N. America and eastern N. Atlantic Number of ridge points north of 50oN increasing west of Greenland

Autumn (OND)

300

340260

Trends (OND)

Could this be contributing to increasing max and min fall temperatures in U.S. since mid-1990s??

1920 1940 1960 1980 2000

T-MIN

T-MAX

1920 1940 1960 1980 2000

from NCDC/NOAA Climate Extremes Index

Now let’s take a look at winter:

Increased ridging north of 40oN Decreased troughs Increased wave amplitude ?

Winter (JFM)

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

Sunspots

from NOAA/CPC

300

340260

Winter (JFM)

Ridge peaks located mainly over western N. America and eastern N. Atlantic Number of ridge points north of 40oN increasing, especially over N. America

Trends (JFM)

300

340

260

Winter (JFM) troughs

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

Trends (JFM)

What about summer?

from Rutgers Snow Lab

Snow is melting earlier over high-latitude land

Soil is exposed to sunlight earlier, so it dries and warms earlier

Further Arctic amplification

SummersurfaceT anoms

Summer (JAS)

Ridge peaks and troughs shifting northward Amplitude increasing High correlations with May snow area

May snow area

r = -0.9

r = -0.9

r = -0.7

300

340260

Summer (JAS)

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

Trends (JAS)

Could this be contributing to increasing max and min summer temperatures in U.S.?

1920 1940 1960 1980 2000

T-MIN

T-MAX

1920 1940 1960 1980 2000

from NCDC/NOAA Climate Extremes Index

SummaryArctic 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

J.A. Francis – Rutgers Univ.Weather and Climate Summit, 2012

Northern Hemisphere, OND

Northern Hemisphere, JFM (5400)