the arctic paradox
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Arctic Sea Ice: A Tragic Tale of Loss and Revenge. Jennifer Francis, Rutgers University. The Arctic Paradox. or. Glen Gerberg Weather and Climate Summit Breckenridge, CO -- 8-13 January 2012. Photo by Janes. In the good old days… . The new normal. - PowerPoint PPT PresentationTRANSCRIPT
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 gra
dien
tNorth 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)