NSIDC, Report of July 6, 2011: Sea ice enters critical period of melt season

NSIDC, July 6, 2011

Sea ice enters critical period of melt season

Arctic sea ice extent for June 2011 was the second lowest in the satellite data record since 1979, continuing the trend of declining summer ice cover. Average ice extent fell below that for June 2007, which had the lowest minimum ice extent at the end of summer. However, ice extent this year was greater than in June 2010. The sea ice has entered a critical period of the melt season: weather over the next few weeks will determine whether the Arctic sea ice cover will again approach record lows.

Figure 1. Arctic sea ice extent for June 2011 was 11.01 million square kilometers (4.25 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data.  —Credit: National Snow and Ice Data Center. High-resolution image

Overview of conditions
Average ice extent for June 2011 was 11.01 million square kilometers (4.25 million square miles). This is 140,000 square kilometers (54,000 square miles) above the previous record low for the month, set in June 2010, and 2.15 million square kilometers (830,000 square miles) below the average for 1979-2000.

June ice extent was lower than normal in much of the Arctic, but the Kara Sea region had particularly low ice extent. Ice has also started to break up off the coast of Alaska in the Beaufort Sea. These open water areas absorb the sun's energy, which will help to further ice melt through the summer.

Figure 2. The graph above shows daily Arctic sea ice extent as of July 4, 2011, along with daily ice extents for previous low-ice-extent years in the month of May. Light blue indicates 2011, dashed green shows 2007, dark blue shows 2010, and dark gray shows the 1979 to 2000 average. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data. —Credit: National Snow and Ice Data Center. High-resolution image

Conditions in contextIce extent during June 2011 declined at an average rate of 80,800 square kilometers (31,200 square miles) per day, about 50% faster than the average decline rate for June 1979-2000. Ice extent declined more slowly than in June 2010, the year with the lowest average ice extent for the month. However, ice declined faster than in June 2007, the year when September sea ice extent reached the lowest in the satellite record. Ice loss in the Kara Sea was especially fast, more than double the average rate and close to double the rate of the past four years (2007 to 2010). Sea ice has largely disappeared in the southern Kara Sea, which normally still has considerable ice cover at this time of year.

At the end of June, Arctic sea ice extent was 9.54 million square kilometers (3.68 million square miles), 375,000 square kilometers (145,000 square miles) less than the ice extent on June 30, 2007, and 264,000 square kilometers (102,000 square miles) above the record low for June 30, set in 2010.

Figure 3. Monthly June ice extent for 1979 to 2011 shows a decline of 3.6% per decade. 
—Credit: National Snow and Ice Data Center. 
High-resolution image

June 2011 compared to past yearsArctic sea ice extent in June 2011 was the second lowest in the satellite record, consistent with the overall downward trend of the past thirty years. The lowest year for June was 2010. June average ice extent exceeded 12 million square kilometers (4.6 million square miles) 16 out of 21 years between 1979 and 1999, but has been below that value every year since.

Figure 4. This map of air temperature anomalies for June 2011 shows warmer than average temperatures over much of the Arctic Ocean, except in the Greenland and Beaufort seas, where temperatures were near and slightly below normal. —Credit: NSIDC courtesy NOAA ESRL PSD. High-resolution image

Warmer than average temperatures continueAir temperatures for June were 1-4 °C (2-7 °F) warmer than average over most of the Arctic Ocean, except in the Beaufort and Greenland seas, where temperatures were near normal or slightly below normal. High pressure dominated most of the central Arctic, with the highest pressures over the Beaufort Sea. The monthly averaged pressure field shows a circulation pattern somewhat similar to a pattern known as the dipole anomaly, with unusually high pressure over the Beaufort Sea and unusually low pressure over central Siberia. Similar patterns have become common in recent summers.

Figure 5. This MODIS image from June 28 shows ice in the Beaufort Sea region off the coast of Barrow, breaking up into smaller floes and open water. But while open water is apparent, a layer of ice still clings to the coastline. —Credit: NSIDC courtesy MODIS Rapid Response System Arctic Mosaic. High-resolution image

A detailed view from MODIS dataData from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) provide a detailed view of seasonal ice breakup. Along the Alaska coast, large ice floes are breaking away near the coast southwest of Barrow. However, in this image from June 28, a narrow strip of landfast ice remained anchored to the coast, bounded on the seaward side by grounded ridged ice. That last bit of ice broke up around July 3, according to the Geophysical Institute at the University of Alaska, Fairbanks

Sea ice breakup in Barrow is defined as the time when the landfast ice along the coast starts to move. The timing of this breakup is closely tied to the cumulative amount of solar energy input to the Barrow region—the amount of sunshine the area receives—after June 5. The Geophysical Institute uses this relationship to forecast the breakup: this year they predicted the breakup to occur on July 11.

Further Reading

Ocean heat
An article published recently in the journal Science showed that the flow of ocean heat into the Arctic Ocean from the Atlantic is now higher than any time in the past 2000 years. The warm, salty Atlantic water flows up from the mid-latitudes and then cools and sinks below the cold, fresh water from the Arctic. The higher salt content of the Atlantic water means that it is denser than fresher Arctic water, so it circulates through the Arctic Ocean at a depth of around 100 meters (328 feet). This Atlantic water is potentially important for sea ice because the temperature is 1-2 °C (1.5-3.0 °F) above freezing. If that water rose to the surface, it could add to sea ice melt.

Spielhagen, R.F., K. Werner, S. Sorensen, K. Zamelczyk, E. Kandiano, G. Budeus, K. Husum, T.M. Marchitto, M. Hald. Enhanced modern heat transfer to the Arctic by warm Atlantic Water, Science, 331 (2011) 450-453, 28.

New ice thickness data
The first preliminary map of sea ice thickness data from the European Space Agency's Cryosat-2 was released in June. This radar altimeter measures the height of features such as snow and sea ice on the Earth surface. This initial map is very preliminary and considerable work will be required before the thickness retrievals are validated and useful for scientific study. Researchers expect that Cryosat-2 will eventually provide additional information about changes in sea ice thickness and volume. http://www.esa.int/esaLP/SEMAAW0T1PG_LPcryosat_0.html

 http://nsidc.org/arcticseaicenews/

Sharp drop in oldest, thickest Arctic sea ice. 2010 melt season ends, likely setting the record for lowest volume

Sharp drop in oldest, thickest Arctic sea ice.

2010 melt season ends, likely setting the record for lowest volume

by Joseph Romm, Climate Progress, September 14, 2010
 

Last week, National Snow and Ice Data Center (NSIDC) director Mark Serreze said, “Every bit of evidence we have says the ice is thinning.”  Monday, NSIDC scientist Julienne Stroeve sent me this figure from a forthcoming article using data provided by J. Maslanik and C. Fowler (click to enlarge):


This is the end-of-winter sea ice extent in the Arctic Basin, broken down by age.  Stroeve explains:

This figure would support thinning of the icepack over the last couple of decades since older ice tends to be thicker than younger ice.  You can see in this figure how little of the really old, and thick ice there is left in the Arctic Basin.

In fact, the figure shows ice 5 years or older dropping from 800,000 sq-km in 2008 to 400,000 in 2009 to only 320,000 sq-km.

Spring 2010 also saw a record low in the amount of ice 4 years or older.

Now you can see that we just about hit the same Arctic sea ice area that we did in 2008:



Given that the ice is almost certainly thinner now than in 2008, we are very likely to have witnessed a lower total ice volume.

Remember, 2008 had substantially less ice volume than 2007, even though it had more area.  Last year, some of the leading cryoscientists at JPL, the Polar Science Center at the University of Washington, and NASA published a major peer-reviewed article, “Thinning and volume loss of the Arctic Ocean sea ice cover: 2003–2008” (subs. req’d).

You can find a basic discussion of their findings here on NASA’s website, which points out, “Arctic sea ice thinned dramatically between the winters of 2004 and 2008, with thin seasonal ice replacing thick older ice as the dominant type for the first time on record.”  That link has some excellent figures, like this one:



Today, PSC’s Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) has determined that “September Ice Volume was lowest in 2009 at 5,800 km³ or 67% below its 1979 maximum” and that “Total Arctic Ice Volume for March 2010 is 20,300 km³, the lowest over the 1979-2010 period.”

So although it may be a while before we have a definitive statement, the likelihood seems high that we just set the record low Arctic sea ice volume — possibly for several thousand years (see Major analysis finds “less ice covers the Arctic today than at any time in recent geologic history”).

Link:  http://climateprogress.org/2010/09/14/exclusive-scientists-track-sharp-drop-in-oldest-thickest-arctic-sea-ice/#more-33196

Chris Mooney: Arctic Ice -- Less Than Meets The Eye

Chris Mooney:  Arctic Ice -- Less Than Meets The Eye

NewScientist, August 25, 2010

The ice may not retreat as much as feared this year, but what remains may be more rotten than robust

LAST September, David Barber was on board the Canadian icebreaker CCGS Amundsen (pictured below), heading into the Beaufort Sea, north of Alaska. He was part of a team investigating ice conditions in autumn, the time when Arctic sea ice shrinks to its smallest extent before starting to grow again as winter sets in.

Barber, an environmental scientist at the University of Manitoba in Winnipeg, Canada, went to sleep one night at midnight, just before the ship was due to reach a region of very thick sea ice. The Amundsen is only capable of breaking solid ice about a metre thick, so according to the ice forecasts for ships, the region should have been impassable.

Yet when Barber woke up early the next morning, the ship was still cruising along almost as fast as usual. Either someone had made a mistake and the ship was headed for catastrophe, or there was something very wrong with the ice, he thought, as he rushed to the bridge in his pyjamas.

On the surface, the situation in the Arctic looks dramatic enough. In September 2007, the total extent of sea with surface ice shrank further than ever recorded before -- to nearly 40% below the long-term average. This low has yet to be surpassed. But the extent of sea ice is not all that matters, as Barber found. Look deeper and there are even more dramatic changes. This is something everyone should be concerned about because the transformation of the Arctic will affect us all.

The record low in 2007 cannot be blamed on global warming alone; weather played a big role too. That year saw a build-up of high pressure over the Beaufort Sea and a trough of low pressure over northern Siberia -- a weather pattern called the Arctic dipole anomaly. It brings warm, southerly winds that increase melting. The winds also drive sea ice away from the Siberian coast and out of the Arctic Ocean towards the Atlantic, where it melts.

In 2008 and 2009, the dipole anomaly did not dominate and the extent of ice did not shrink as much during summer. This rebound led to much talk of a recovery in Arctic ice.

This June, the dipole anomaly returned and the ice extent for the month was the lowest ever. In July, however, the dipole pattern broke up and the rate of ice loss slowed. "Whether or not we set a new record depends very much on the weather patterns," says Mark Serreze of the US National Snow and Ice Data Center based in Boulder, Colorado, which monitors the extent of sea ice -- a particular way of measuring its area.

While much attention is likely to be paid to whether or not a new record is reached in the next month, there is more to sea ice than area alone. New sea ice can grow up to 2 metres thick during the winter. If it survives the summer melt, it can grow even thicker over the three to six years it might last before being swept past Greenland and out into the Atlantic Ocean, or succumbing to the summer melt. In places, this multi-year ice can pile up forming "pressure ridges" as much as 50 metres deep. But its average thickness is now less than 3 metres according to ICESat, the only satellite capable of measuring ice height and thus thickness (Geophysical Research Letters, vol 36, L15501).

There is no long-term record of the total volume of ice because we have only patchy data; ICESat was launched in 2003 and failed earlier this year. The nearest thing we have are estimates from PIOMAS, developed by Jinlun Zhang and his colleagues at the University of Washington's Polar Science Center in Seattle. Actual satellite measurements of sea ice concentration since 1978 are fed into a computer model of the growth, melting and motion of sea ice to produce an estimate of ice volume. PIOMAS's results correspond well with independent measurements by submarines and by ICESat.

According to PIOMAS estimates supplied to New Scientist by Zhang, the average volume of Arctic ice between July and September has fallen from 21,000 cubic kilometres in 1979 to 8000 cubic kilometres in 2009. That is a 55% fall compared with the 1979-2000 average. "The loss of ice volume is faster than the loss of ice extent," says Zhang. His model suggests that not only has the total volume of Arctic ice continued to decline since 2007, but that the rate of loss is accelerating (see "Going, going...").

How can ice volume have kept falling when extent increased again after 2007? Because less and less ice is surviving to see its first birthday. "First-year ice is now the dominant ice type in the Arctic, whereas a few years ago multi-year ice was dominant," says Barber.

Young ice is thinner than multi-year ice, and thus more likely to break into smaller pieces that melt more quickly, and more likely to be swept out of the Arctic and into warmer seas. That is precisely what happened in 2007, when persistent winds blew a thinner ice pack through the Fram Strait between Greenland and the island of Spitsbergen, leading to the dramatic ice loss. "The same wind 30 years ago when the ice was thicker would not have done as much damage," says Bruno Tremblay, a climate researcher at McGill University in Montreal, Canada.

And while the area of young ice increased in 2008 and 2009, the amount of multi-year ice continued to fall. "There wasn't a recovery at all," Barber says.

Even the nature of the remaining sea ice might be changing. When Barber rushed up to the bridge that morning in September 2009, the first officer told him that while it looked like there was ice, it was no barrier to the ship at all. The reason: the ice was rotten.

It consisted of multi-year ice that had become riddled with surface thaw holes and had broken into pieces. Over winter, a 5-cm layer of new ice had formed over the dispersed floes. If a person tried standing on it they would fall right through, so it was no obstacle to the Amundsen. It is not clear how widespread these conditions are because satellites cannot distinguish between rotten and more solid ice (Geophysical Research Letters, vol 36, p L24501). The rotten ice is less of a barrier to waves as well as ships, meaning waves can penetrate further into ice packs and break up more ice.

What it all means is that, much like the Amundsen, we are now cruising effortlessly into a world that may soon feature an essentially ice-free Arctic during at least part of the year. "Thirty years from now, maybe even 20 years from now, if you were to look at the Arctic from space you would see a blue ocean [in summer]," says Serreze.

The implications of such changes for wildlife and the human inhabitants of the region, for the global climate and for geopolitics are profound. The Arctic would be traversable by ship. It would be far more open to oil and gas exploration, and mineral extraction. Its dark ocean waters, mostly devoid of ice, would absorb still more sunlight, further warming the overlying atmosphere during an increasingly lengthy ice-free season, reshaping weather throughout the region and well beyond it.

Worryingly, the melting of the Arctic sea ice is proceeding considerably more quickly than most climate models have predicted. Among the suite of models submitted for the 2007 report of the Intergovernmental Panel on Climate Change (IPCC), only two out of 23 yielded results for Arctic sea ice that were consistent with observations, says Cecilia Bitz of the University of Washington in Seattle.

According to the 2007 models, the Arctic will not become ice-free in summer until some time after 2050. However, researchers like Barber and Serreze think this landmark occurrence will come much earlier. Barber has predicted that it will occur sometime between 2013 and 2030.

If most models aren't capturing the full extent of changes in the Arctic, it is probably because the modelled feedbacks are too weak, says Bitz. In other words, they may not be sensitive enough to processes that, once they get going, self-amplify in a continuing loop.

Every model includes the "ice albedo feedback," in which the melting of ice that reflects most of the sun's heat exposes dark water that absorbs most heat. That leads to more melting and so on -- a positive feedback. But there could be many others.

Consider, for instance, the role of Arctic storms. They break up ice with their winds and waves, making it more prone to melting -- and the more open water there is, the more powerful waves can become. These larger waves -- which were not included in any models -- then penetrate further into the ice pack, breaking it up into smaller and smaller pieces, says Barber. From the bridge of the Amundsen as it sat moored in the ice last year, Barber himself watched as a large swell broke a chunk of ice the size of Manhattan into a number of pieces roughly 100 metres across.

Storms also bring snow, which in autumn and winter actually slows the growth of sea ice by insulating it from cold winds, as well as reducing heat loss from the sea below. So if climate change leads to more snow in autumn and winter, this will be yet another factor contributing to the loss of sea ice.

Bitz thinks the 2007 low was a wake-up call for climate modellers, compelling them to look more closely at how their programs handle sea ice. She expects that when the next set of models is submitted to the IPCC for its 2013 report, their outputs will be much more in line with observations. "The modelling centres are short of resources for giving focus to a particular part of the model," she says. "But when a big story comes out like 2007, they redirect, and that will pay off."

The implications of the loss of Arctic sea ice in the summer are hard to overstate. Most attention has focused on charismatic megafauna like polar bears and walruses, but they are just the icons of a broader ecosystem that is already being dramatically disrupted. The sea ice is as important as the trees to a rainforest, Barber says.

The loss of sea ice will also have many other impacts. For instance, the increase in the size of waves has already begun to cause serious coastal erosion in places like Alaska, with the effect magnified by warmer waters and rising sea level. The impact of the waves eventually melts the permafrost of which the coastline is composed. "Some of those coastlines are made of very fine silt," says Tremblay. "The land just washes away."

A warmer Arctic will also affect weather in the mid-latitudes -- indeed, it has already begun. Take the Great Plains of the US. According to Michael MacCracken of the Climate Institute in Washington, DC, this region's weather is very much determined by clashes between cold air masses coming down from the Arctic and warm air masses from the Gulf of Mexico. As the Arctic blasts are less cold than they used to be, the Gulf's warm air tends to push further northwards. The result is a northward shift of weather patterns, and more extreme storms and heavy precipitation events in regions not used to them.

Finally, there are the economic and industrial implications. "The engineering challenges get simpler," says Barber, "for drilling, for putting drill ships in place, for having icebreakers, to make tankers carry oil across the pole -- all those kinds of challenges associated with industrial development." Such challenges will diminish, or even vanish entirely. The Amundsen's surprisingly easy voyage through the Beaufort Sea in September 2009 could be a herald of things to come.

Chris Mooney is a host of the Point of Inquiry

Link:  http://www.newscientist.com/article/mg20727751.300-arctic-ice-less-than-meets-the-eye.html?full=true

Extraordinary September Arctic sea ice reductions and their relationships with storm behavior over 1979–2008

Geophysical Research Letters, 36 (2009) L19715; doi: 10.1029/2009GL039810.

Extraordinary September Arctic sea ice reductions and their relationships with storm behavior over 1979–2008

Extraordinary September Arctic sea ice reductions and their relationships with storm behavior over 1979–2008

Ian Simmonds and Kevin Keay (School of Earth Sciences, The University of Melbourne, Victoria, Australia)

Received 29 June 2009; accepted 1 September 2009; published 14 October 2009. 

Abstract

Dramatic changes have been observed in Arctic sea ice, cyclone behavior and atmospheric circulation in recent decades. Decreases in September ice extent have been remarkable over the last 30 years, and particularly so in very recent times. The analysis reveals that the trends and variability in September ice coverage and mean cyclone characteristics are related, and that the strength (rather than the number) of cyclones in the Arctic basin is playing a central role in the changes observed in that region, especially in the last few years. The findings reinforce suggestions that the decline in the extent and thickness of Arctic ice has started to render it particularly vulnerable to future anomalous cyclonic activity and atmospheric forcing.

Link to abstract:  http://www.agu.org/pubs/crossref/2009/2009GL039810.shtml

NSIDC Report of August 18, 2009: A change in ice motion slows seasonal decline

NSIDC Report of August 18, 2009: A change in ice motion slows seasonal decline

During the first half of August 2009, Arctic ice extent declined more slowly than during the same period in 2007 and 2008. The slower decline is primarily due to a recent atmospheric circulation pattern, which transported ice toward the Siberian coast and discouraged export of ice out of the Arctic Ocean. It is now unlikely that 2009 will see a record low extent, but the minimum summer ice extent will still be much lower than the 1979 to 2000 average.

Note: This mid-monthly analysis update shows a single-day extent value for Figure 1, rather than the usual monthly average. While monthly average extent images are more accurate in understanding long-term changes, the daily images are helpful in monitoring sea ice conditions in near-real time.

Figure 1. Daily Arctic sea ice extent on August 17, 2009, was 6.26 million km² (2.42 million sq. miles). The orange line shows the 1979-2000 median extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data. —Credit: National Snow and Ice Data Center. High-resolution image

Overview of conditions

On August 17, 2009, Arctic sea ice extent was 6.26 million km² (2.42 million sq. miles). This is 960,000 km² (370,000 sq. miles) more ice than for the same day in 2007, and 1.37 million km² (530,000 sq. miles) below the 1979-2000 average. On August 8, the 2009 extent decreased below the 1979-2000 average minimum annual extent, with a month of melt still remaining.

Figure 2. The graph above shows daily sea ice extent as of August 17, 2009. The solid light blue line indicates 2009; the solid dark blue line shows 2008; the dashed green line shows 2007; and the solid gray line indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data. —Credit: National Snow and Ice Data Center. High-resolution image

Conditions in context

From August 1 to 17, Arctic sea ice extent declined at an average rate of 54,000 km² (21,000 sq. miles) per day. This decline was slower than the same period in 2008, when it was 91,000 km² (35,000 sq. miles) per day, and for the same period in 2007, when ice extent declined at a rate of 84,000 km² (32,000 sq. miles) per day. The recent rate of ice loss has slowed considerably compared to most of July. Arctic sea ice extent is now greater than the same day in 2008.

Figure 3. Sea ice motion, derived from AMSR-E data and averaged for June, July, and the first week of August 2009 (the most recent data available), shows a recent change, with ice motion towards the eastern Siberian coast and little export of ice out of the Arctic Ocean via Fram Strait. —Credit: National Snow and Ice Data Center. High-resolution image

Ice motion changes in August

A recent atmospheric circulation pattern, which led to a change in ice motion, caused the ice loss rate to slow down significantly in the first two weeks of August. As discussed in the August 4 post, during much of June and July, a strong Beaufort Sea high-pressure pattern promoted winds that helped push ice out of the Siberian coastal seas, and also brought clear skies and warm temperatures that helped induce melt.

Toward the end of July, the atmospheric pattern changed. Averaged over the past two weeks, a high-pressure system has been centered over the Barents Sea, with low pressure centered over the Laptev Sea. In accordance with Buys Ballot's Law, this pattern led to winds that redirected the motion of the ice cover, pushing the ice edge outward toward the Siberian coast and discouraging ice from exiting the Arctic Ocean through Fram Strait.

Figure 4. The map of sea ice concentration from AMSR-E from August 16, 2009, shows ice clogging many of the channels of the Canadian Archipelago. The Northern Sea Route may be clear in the next few weeks. NASA AMSR-E data. —Credit: From National Snow and Ice Data Center, courtesy IUP, University of Bremen, Germany. High-resolution image

The Northwest Passage and Northern Sea Route

So far this year, neither the Northwest Passage nor the Northern Sea Route has opened. The Northern Sea Route appears likely to open soon, but ice still clogs many of the channels in the Northwest Passage.

Whether or not the navigational passages through the Arctic Ocean will open in a given summer depends on atmospheric circulation and ice thickness. For example, although 2007 was a record low extent in the Arctic and the Northwest Passage was nearly completely open, the Northern Sea Route was still choked with ice because of a circulation pattern that pushed a tongue of ice against the Siberian coast. Recent research by Stephen Howell at the University of Waterloo in Canada shows that whether the Northwest Passage clears depends less on how much melt occurs, and more on whether multi-year sea ice is pushed into the channels. Counterintuitively, as the ice cover thins, ice may flow more easily into the channels, preventing the Northwest Passage from regularly opening in coming decades.

Figure 4. The map of sea level pressure (in millibars) from June and July 2009 shows a strong high-pressure cell over the Beaufort Sea, similar to the pattern in 2007. In the past, such patterns were rare. —Credit: From National Snow and Ice Data Center, courtesy NOAA/ESRL Physical Sciences Division. High-resolution image

Comment on atmospheric circulation patterns

James Overland of the NOAA Pacific Marine Environmental Laboratory in Seattle, Washington, has taken a close look at patterns of atmospheric circulation in recent summers. Overland notes that the periods June through August 2007 and June and July 2009 both saw an unusual atmospheric pattern of sea level pressure, with higher pressure on the Alaskan side of the Arctic and lower pressure on the Eurasian side. This pressure difference brought warm air into the central Arctic and transported sea ice towards the Atlantic. Historically, such a pattern is a rare event—before 2007, it only occurred twice in 30 years. Normally, there is little difference in pressure across the Arctic during summer, and winds are slack.

This rare condition may result from the convergence of the three main patterns of climate variability: the Arctic Oscillation (AO) climate pattern, which features either high or low pressure over most of the Arctic; the positive phase of the Pacific North American (PNA) pattern, which is characterized by low pressure over the Bering Sea and high pressure over the Canadian Rockies; and the Arctic dipole pattern, which features high pressure on one side of the Arctic and low pressure on the other. In 2007 and 2009 all three patterns have been in play. A clue to the cause of these unusual conditions comes from the wind flow in the middle atmosphere. Normally winds flow in a counter-clockwise direction around the central Arctic Ocean, a flow known as the polar vortex. In the summers of 2007 and 2009 the polar vortex shifted to mostly to the Eurasian side of the Arctic, allowing higher pressures to develop on the Alaskan side. Scientists are now studying whether this dipole pattern will become more common in the future and whether the loss of summer sea ice itself is helping to make this pattern more frequent.

References

Howell, S. E. L., C. R. Duguay, & T. Markus. 2009. Sea ice conditions and melt season duration variability within the Canadian Arctic Archipelago: 1979–2008, Geophys. Res. Lett., 36, L10502; doi: 10.1029/2009GL037681.

Overland, J. E., & M. Wang. 2005. The third Arctic climate pattern: 1930s and early 2000s. Geophys. Res. Lett., 32(23), L23808; doi: 10.1029/2005GL024254.

Wang, M., N. A. Bond, & J. E. Overland. 2007. Comparison of atmospheric forcing in four sub-arctic seas. Deep-Sea Research II, 54, 2543-2559; doi: 10.1016/j.dsr2.2007.08.014

Wang et al., GRL, 36 (2009), Is the Dipole Anomaly a major driver to record lows in Arctic summer sea ice extent?

Geophysical Research Letters, 36 (2009) L05706; doi: 10.1029/2008GL036706.

Is the Dipole Anomaly a major driver to record lows in Arctic summer sea ice extent?

Is the Dipole Anomaly a major driver to record lows in Arctic summer sea ice extent?

Jia Wang (Great Lakes Environmental Research Laboratory, NOAA, Ann Arbor, MI, U.S.A.), Jinlun Zhang (Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, WA, U.S.A.), Eiji Watanabe (International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, AK, U.S.A.), Moto Ikeda (Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan), Kohei Mizobata (Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Tokyo, Japan), John E. Walsh (International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, AK, U.S.A.), Xuezhi Bai (Cooperative Institute for Limnology and Ecosystems Research, University of Michigan, Ann Arbor, MI, U.S.A.), and Bingyi Wu (Chinese Academy of Meteorological Sciences, Beijing, China)

Abstract

Recent record lows of Arctic summer sea ice extent are found to be triggered by the Arctic atmospheric Dipole Anomaly (DA) pattern. This local, second–leading mode of sea–level pressure (SLP) anomaly in the Arctic produced a strong meridional wind anomaly that drove more sea ice out of the Arctic Ocean from the western to the eastern Arctic into the northern Atlantic during the summers of 1995, 1999, 2002, 2005, and 2007. In the 2007 summer, the DA also enhanced anomalous oceanic heat flux into the Arctic Ocean via Bering Strait, which accelerated bottom and lateral melting of sea ice and amplified the ice–albedo feedback. A coupled ice–ocean model was used to confirm the historical record lows of summer sea ice extent.

Received 17 November 2008, accepted 28 January 2009, published 6 March 2009.

Citation: Wang, J., J. Zhang, E. Watanabe, M. Ikeda, K. Mizobata, J. E. Walsh, X. Bai, & B. Wu (2009), Is the Dipole Anomaly a major driver to record lows in Arctic summer sea ice extent?, Geophysical Researcg Letters, 36, L05706; doi: 10.1029/2008GL036706.

Link to abstract: http://www.agu.org/pubs/crossref/2009/2008GL036706.shtml