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In the final days of 2015, a North Atlantic storm swept across Iceland, the UK and Ireland, and plunged the Arctic into a heat wave that has eaten away at sea ice to a new record low.
OUT OF THIS WORLD | Earth, Space And The Stuff In Between - a daily journey through weather, space and science with meteorologist/science writer Scott Sutherland

Arctic 'heat wave' sets new record low for sea ice

Scott Sutherland
Meteorologist/Science Writer

Wednesday, January 6, 2016, 5:33 PM - In the final days of 2015, a North Atlantic storm swept across Iceland, the UK and Ireland, and plunged the Arctic into a heat wave that has eaten away at sea ice to a new record low.

Arctic Impacts

The UK Met Office has noted that this type of storm is not that unusual for this time of year.

As they wrote on their website:

This very unsettled and occasionally stormy spell was well signalled in our recent three month outlooks and is not unusual for this time of year, indeed this is when climatologically we would expect to have most of our storms.
We only need to go back to the winter of 2013-14 to see storms of similar strength to that of Frank. There are comparable or more severe storms in recent years, including 3 January 2012 and 8 December 2011, each of which caused widespread impacts.

What was unusual, however, was the impact that this storm has had on the Arctic.

Air temperature and air temperature anomaly maps for the North Atlantic and Arctic, from Dec 27, 2015 to Jan 5, 2016. Credit: Climate Reanalyzer

As the animation above shows, above freezing temperatures (shades of green in the left panel) pushed far to the north due to wind flow from the storm, and temperatures as high as 7 or 8 degrees Celsius were recorded on January 1-2. As the right panel reveals, these temperatures over a widespread region of the Arctic reached at least 30 degrees Celsius higher than they normally should be for this time of year.

The warmest temperatures were to the north of Europe and Russia, however the pattern also chased the coldest temperatures out of the Canadian Arctic, pushing them well to the south.

This intrusion of warm air into the Arctic had a very noticeable effect on sea ice.

Snow and Ice analysis for Dec 27, 2015 to Jan 5, 2016. Inset zooms in on the region affected by Storm Frank. Credit: Climate Reanalyzer

As the animation shows, Arctic sea ice extent was still growing as as of Dec 27-29, but once the storm pushed in on Dec 30, it began to eat away at the sea ice in the region of the Arctic north of Europe. 

According to the US National Snow and Ice Data Center, sea ice extent in the Arctic during the latter half of Dec 2015 grew at a rate just greater than was seen in the last two weeks of Dec 2014.

When Storm Frank arrived, however, that growth ground to a halt, as losses from that region of the Arctic almost completely offset gains in sea ice extent in other areas (such as the Bering Strait).

Data from NSIDC

Whereas total sea ice extent grew by around 73,000 square kilometres from Jan 1 to Jan 4, 2015, the same period in 2016 saw only 3,000 square kilometres of growth.

Arctic sea ice extent at the end of 2015 was already lagging behind end-of-year 2014, by 179,000 square kilometres. This did not necessarily lock-in 2016 as a new lowest maximum sea ice extent on record, since weather patterns can easily put a blast of extra cold air over the Arctic to freeze more ice, and this can happen well into March, thus surpassing the 2015 maximum.

With the heat from Storm Frank costing the Arctic about 70,000 square kilometres worth of sea ice growth in less than a week (or more, assuming the December growth rate had held), though, this leaves the region even further behind - by 273,000 square kilometres as of Jan 4, 2016. Also, according to NSIDC records, on January 4, 2016, Arctic sea ice was at its lowest extent ever recorded for that day of year - at 91,000 square km behind the previous record low, set on Jan 4, 2011.

While this is also no guarantee of a new record low extent in 2016, it does make that outcome more likely.

Update: Some encouraging news from the NSIDC on Jan 5:

While the event was remarkable and may account for the slow ice growth during the first few days of January 2016, it was short lived and is unlikely to have any long-term effects on the sea ice cover.

North Atlantic Weather Bomb

This North Atlantic storm, powered along by an initial pulse of heat from the Gulf Stream below and powerful winds from the Jet Stream above, developed overnight from Dec 29 to Dec 30 into a weather bomb - a meteorological term referring to a storm whose central pressure drops by at least 24 millibars in 24 hours.

According to the US National Weather Service Ocean Prediction Center, the storm had a central pressure of 958 millibars as of 12 UTC (7 a.m. EST) on Tuesday, Dec 29 and just 18 hours later, the pressure at the core of the storm dropped to 928 mb.

Credit: National Weather Service Ocean Prediction Center

With the pressure dipping by that much, not only was it a weather bomb, but it even exceeded the forecast expectations by 4 millibars. This made for a very intense weather system.

Surface wind speeds and patterns from 10 a.m. EST Monday through until 10 a.m. EST Wednesday. Credit: earth.nullschool.net with notations by S. Sutherland

The data recorded at the Höfn í Hornafirði weather station, in eastern Iceland, was even more impressive though, showing a roughly 65 millibar pressure drop in that 18 hour period, from near 990 mb down to around 935 mb as the storm passed by.

Wind speeds at Höfn í Hornafirði peaked Dec 30 at 104 km/h, while Sandbúðir, in the central part of the island, recorded speeds of 112 km/h - both equivalent to tropical storm force winds.

Other portions of the island, especially in the west and northwest, were spared these intense winds. The capital city of Reykjavík, in the southwest, experienced a much more moderate wind speed peak of 50 km/h.

Prior to that, however, as the storm swung past Ireland and northern regions of the UK on Tuesday night, the UK Met Office was expecting at least tropical storm-like conditions, if not worse.

According to the UK Met Office's Tuesday forecast:

On Tuesday night unsettled, stormy weather is predicted. Storm Frank will bring gales or severe gales to western parts of the UK from Tuesday evening into Wednesday. Gusts of 55-65 mph [88-104 kph] are likely quite widely, with gusts reaching 70-80 mph [112-128 kph] in the most exposed areas, particularly in northwest Scotland.
Rainfall associated with this system is also expected to cause some disruption with persistent, heavy rain over parts of Northern Ireland, west and southwest Scotland, spreading to northwest England and Wales early on Wednesday. Amber 'be prepared' rainfall warnings are in force. Rainfall totals of 20-40mm are expected widely across these areas but with 80mm possible over high ground and some exposed areas in central and southern Scotland and Cumbria have the potential to receive in excess of 100mm of rainfall.

The Met Office Twitter account shared an impressive satellite view of what they've named Storm Frank, along with various recorded wind peaks, from 120 km/h across the Isles of Scilly, off the southwest tip of Britain, up to 136 km/h in South Uist off the west coast of northern Scotland. On the Saffir-Simpson wind scale, these winds are the equivalent of a Category 1 Hurricane.

As reported on their website, the Met Office recorded 24 hour rainfall amounts of between 48 to 85 mm on Dec 30.

The fuel that drove this storm to such extremes was the combination of an initial pulse of heat it picked up passing over very warm Gulf Stream waters, along with extremely powerful winds flowing along the Jet Stream above.

These Jet Stream winds, reaching up to 370 km/h, both helped and hindered trans-Atlantic flights on Monday, as passengers from New York to London arrived up to 90 minutes earlier than expected, while those travelling along the opposite route had to endure longer flight times as jetliners fought against the current.

Check back for more updates soon, as these unusual Arctic weather conditions progress.

Sources: Icelandic Met Office | UK Met OfficeNational Snow and Ice Data Center | Climate Reanalyzer | NSIDC News

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