Seemorerocks: The Arctic melt season

Central Arctic ‘Heat Dome’ to Replace ‘Warm Storm’ As Melt Season Shifts to New Extreme?

8 July, 2013

All the updates are in and with the major melt month of June now in the rear view mirror, it’s time take a fresh look at the volatile melt season of 2013.

In short, June melt proceeded rapidly, but not rapidly enough to break into new record territory after the slow melt month of May. Meanwhile, PAC 2013, which turned a large section of the central Arctic into a mush of broken ice faded as high pressure began to deepen and exert its own unique sets of influences over the region. As the clouds broke, air temperatures began to heat up in the Central Arctic even as anticyclonic pumping began to pull ice into the large hole formed by the storms of June. Above average temperatures ruled much of the Arctic edge as Scandinavia and North-Eastern Europe, Siberian Kamchatka, Eastern Alaska and Central Canada all showed hotter than normal conditions. The high, entrenching itself, began to pool warm air directly over the Arctic’s fractured heart…

Major Monitors Show 2013 Melted Rapidly in June through early July, But Not Rapidly Enough to Break into New Record Territory

A combination of a storm thinning the ice of the Central Arctic and hot air pulses rushing in from the ice edge resulted in a near record pace of melt for sea ice area, volume, and extent during June through early July. This furious pace of melt was fast enough to challenge previous record lows, if not to break them.

(Data Source: NSIDC, Image Source: Pogoda i Klimat)

Sea ice extent measures produced by NSIDC provide a good allegory for the overall melt trend seen in June through early July. In early to mid June, extent melt proceeded at a gradual pace at first. By late June and into early July, extent melt had drastically increased showing multiple days of 150,000 kilometer or greater loss. This extraordinarily steep pace of melt can be seen in the above graph. If such a rapid pace continues through mid July, a new record low extent level will be breached.

Currently, sea ice extent is 6th lowest on record and is only slightly above the 2007 melt line. This puts sea ice extent, according to NSIDC, about 1.4 million square kilometers below the 1979-2000 average.

To this point, it is important to consider that NSIDC has now included the extreme melt decade of 2000-2010 in its official records. So NSIDC ‘averages’ on site include these shifting goal-posts. The data set includes a declining curve and, therefore, cannot be seen entirely as ‘normal.’ Instead, it provides an anomaly base-line for a highly anomalous period and should be viewed as such. To the superficial observer, presenting the data in this fashion will somewhat serve to mask what can best be described as a sea ice death spiral. A plain example of this discrepancy is the fact that 1979 sea ice values for the same date (July 8) were about 2.1 million square kilometers higher than today. A severe decline by any measure. It is worth noting, though, that NSIDC does provide a very useful interactive tool in which all sea ice extent records are available here. (Hat-tip to Physicist-retired who provided this link in the comments section below).

(Data Source: Cryosphere Today, Image Source: Pogoda i Klimat)

Pace of sea ice area melt was also rapid during the month of June through early July with more than 4 million square kilometers lost during the five-week period. As a result, sea ice area measurements are now around 4th or 5th lowest in the record or about 1.8 million square kilometers below 1979 values. Though rapid, this melt rate still puts current measures about 800,000 square kilometers above record low totals seen for this date in 2012. So area melt will have to be steep, indeed, for new records to be reached by end of summer.

(Image Source: PIOMAS)

The critical measure of sea ice volume showed a quickening pace of decline from mid-May to mid-June. PIOMAS showed volume levels about tied with 2010 as third lowest in the measure by about June 15th. PIOMAS tends to lag a bit behind area and extent. So we don’t yet have an idea of where volume stands come early July.

That said, it is important to note that much of the region usually covered with thick ice — the Beaufort and the area north of Greenland and the CAA are substantially thinned compared to previous years. NASA’s Ice Bridge survey found this region about 8% thinner during March and April of 2013 than during the same period of 2012. Thinner ice in regions that are typically the bastion for thick ice during late summer may show much more rapid melt in July and August (especially at times when strong high pressure systems dominate the Central Arctic).

(Image provided by NSIDC as a compilation of NASA Ice Bridge Data)

Note the large region where ice thickness is 2 meters or less from the middle Canadian Archipelago and stretching on into the Beaufort. A large pulse of melt now advances from the Chukchi and along the coast of Canada and Alaska into this region. A persistent blocking pattern has also driven pulses of much warmer than normal air into this area consistently throughout June. Weather models forecast additional atmospheric warming through at least mid July. With a strong high pressure ridge now forming in the Central Arctic, this region will be one to watch for potentially rapid melt as July progresses into August.

High Pressure Forms in the Wake of PAC 2013

The dominant feature of the Central Arctic during June of 2013, a Persistent Arctic Cyclone that turned a large section of this region into an icy slurry, finally faded as of last week. The impact of this storm has now been widely accepted with NSIDC providing expert analysis on the subject:

High-resolution passive microwave concentration data from the Japan Aerospace Exploration Agency AMSR2 sensor, produced by the University of Bremen, indicate a highly unusual region of broken-up ice near the North Pole. Development of this low concentration ice may have been assisted by the cyclonic atmospheric pattern noted earlier.

…MODIS data do confirm that the ice is highly fractured with numerous small floes. Such small floes are more easily melted from the sides and the bottom by ocean waters that are exposed to the 24-hour sunlight. It remains to be seen how many of these small floes will ultimately melt completely (emphasis added).

(Image source: NSIDC)

I wrote extensively on the subject of PAC 2013 ice thinning during June. Now, NSIDC confirms a large region north of Svalbard featuring sea ice with concentrations of 50% or less that may be vulnerable to melt as July and August progress.

This condition may become particularly evident as the dipole switches from storm over the Central Arctic to clear air, warmer temperatures and higher pressure. A 1020 millibar high has already formed over the central Arctic and is expected to heighten into a 1030 millibar high by the middle of July. This thickening high will bring sunny conditions and much warmer air temperatures to the Central Arctic. It will also create an anti-cyclonic down-welling near its center. This pumping action will tend to have the effect of drawing edge ice into the hole created by PAC 2013. If the waters in the hole are substantially warmed, it is possible that enhanced melt will occur in this region even as edge ice is drawn back into the hole.

You can see some of this potential melt action predicted in the US Navy CICE model run for the 30 days from mid June through the end of next week:

(Image source: US Navy)

The effect a high like the one predicted has on sea ice is clearly demonstrated at the end of the above model run. The down-welling in the Central Arctic is seen to suck large portions of the ice in this region toward the hole formed by PAC 2013. At the edges, an upwelling action combines with counter-clockwise winds around the high to pull the ice edge inward even as the warmer upwelling waters eat away at the outliers. Note the rapid drawing in of all ice from the Beaufort, East Siberian Sea, Laptev and in a broad region north of Svalbard.

This action is the exact opposite of the effect seen during June via the impacts of PAC 2013. Then, a storm created an anomalous hole in the central sea ice even as it shoved ice toward warmer regions. Now, the rapid switch from storm conditions to strong high pressure conditions creates the potential for another unusual event: the collapse of thick ice and edge ice into the hole PAC created. Such an event would likely have an amplified effect on sea ice melt, especially in the extent measures. So we’ll will have to keep a close eye on both this building high pressure system and its interaction with the hole created by PAC 2013. Should these CICE model runs bear out, the next few weeks will be extraordinarily interesting.

It is also important to note that CICE only shows impacts through July 15th. Yet, according to ECMWF weather forecasts, a strong, 1030 millibar high is expected to last in the Central Arctic at least until July 18th.

Arctic Heat Dome Starting to Form?

To this point, it is worth noting that the weather models indicate a potential for yet another extreme Arctic weather event: the formation of an Arctic ‘heat dome.’

(Image source: ECMWF)

ECMWF forecasts show a powerful high pressure ridge developing over the Central Arctic through mid July. Associated with this high is a river of warmer air that is predicted to run directly over the North Pole. Indications are for 40 degree plus average temperatures at the 5,000 foot level by July 18th. This translates to average surface temperatures as high as the mid 50s over a broad section of the Beaufort, through the North Pole and on over to Svalbard. For the high Arctic, which averages just above freezing for this time of year, that’s a heatwave.

The establishment of this ‘dome’ high pressure system has already begun with a 1020 millibar high strengthening over the Laptev and Central Arctic. Should this ‘heat dome’ continue to strengthen and entrench as predicted, it is likely that edge melt will be greatly enhanced even as thicker ice is pulled into the melt hole created by PAC 2013 as July progresses.

The formation of such a strong high and associated warmer atmospheric temperatures during July is not conducive for ice preservation. In fact, the formation of this kind of weather system would have resulted in hastening melt even during times when the ice was thicker and more resilient. Instead, the ice suffered at the hands of a storm that, typically, would have helped preserve it. Now, the formation of a powerful high pressure system threatens a crowning blow.

So an interesting and volatile melt season continues. Anomalous storm melting of Central Basin sea ice appears to be transitioning to a powerful regime of high pressure that threatens to bring much warmer temperatures to the Central Arctic all while drawing edge ice into the deep melt hole formed by PAC 2013.

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